Vol. 2 N. 3 Sep/Dec. 2010
ISSN 1984-9648 ISSN 2175-9146 (online) www.jatm.com.br
Journal of Aerospace Technology and Management V.2, n. 3, Sep/Dec. 2010
General Information
Correspondence
Journal of Aerospace Technology and Management (JATM) is a techno-scientific publication serialized, edited,
All correspondence should be sent to:
and published by the Institute of Aeronautics and Space (Instituto de Aeronáutica e Espaço-IAE). It contains
Journal of Aerospace Technology and Management
articles that have been selected by an Editorial Committee composed of researchers and technologists from
Instituto de Aeronáutica e Espaço (IAE)
the scientific community. The magazine is published every four months and its main objective is to show the
Praça Mal. Eduardo Gomes, 50- Vila das Acácias
scientific and technological research results related to the aerospace field, as well as promote an additional
CEP 12228-901
source of diffusion and interaction, providing public access to all of its contents, following the principle of
São José dos Campos/ São Paulo/Brazil
making free access to research and generate a greater global exchange of knowledge. JATM is added/ indexed in the following databases; CAS - Chemical Abstracts Service; DOAJ - Directory of
Contact
Open Access Journals; J-GATE - The e-journal gateway from global literature; LIVRE - Portal to Free Access
Phone: (55)12-3947-5115/6444
Journals; GOOGLE SCHOLAR; SUMÁRIOS.ORG - Summaries of Brazilian Journals; EZB- Electronic
E-mail: editor@jatm.com.br
Journals Library; ULRICHSWEB - Ulrich´s Periodicals Directory; SOCOL@AR - China Educational
Order your copy (for free): secretary@jatm.com.br
Publications; LATINDEX - Regional Cooperative Online Information System for Scholarly Journals and is
Web: http://www.jatm.com.br
under analysis in other major indexing databases. JATM is affiliated to ABEC - Brazilian Association of Scientific Editors and all published articles contain DOI numbers attributed by Crossref.
Journal of Aerospace Technology and Management
Published and distributed by: Institute of Aeronautics and Space
Vol. 2, n.3 (sep./dec. 2010) – São José dos Campos: Zeppelini Editorial, 2010
Desktop publishing and printing: Zeppelini Editorial
Four monthly issue
Edition: 750 São José dos Campos, SP, Brazil
1. Aerospace sciences
ISSN 1984-9648
2. Technologies
Note: This publication is sponsored by the Institute of Aeronautics and Space (IAE) to whom the copyright on
3. Aerospace engineering CDU:629.73
all published material belongs. Permission must be requested prior to use
General Information
Correspondence
Journal of Aerospace Technology and Management (JATM) is a techno-scientific publication serialized, edited,
All correspondence should be sent to:
and published by the Institute of Aeronautics and Space (Instituto de Aeronáutica e Espaço-IAE). It contains
Journal of Aerospace Technology and Management
articles that have been selected by an Editorial Committee composed of researchers and technologists from
Instituto de Aeronáutica e Espaço (IAE)
the scientific community. The magazine is published every four months and its main objective is to show the
Praça Mal. Eduardo Gomes, 50- Vila das Acácias
scientific and technological research results related to the aerospace field, as well as promote an additional
CEP 12228-901
source of diffusion and interaction, providing public access to all of its contents, following the principle of
São José dos Campos/ São Paulo/Brazil
making free access to research and generate a greater global exchange of knowledge. JATM is added/ indexed in the following databases; CAS - Chemical Abstracts Service; DOAJ - Directory of
Contact
Open Access Journals; J-GATE - The e-journal gateway from global literature; LIVRE - Portal to Free Access
Phone: (55)12-3947-5115/6444
Journals; GOOGLE SCHOLAR; SUMÁRIOS.ORG - Summaries of Brazilian Journals; EZB- Electronic
E-mail: editor@jatm.com.br
Journals Library; ULRICHSWEB - Ulrich´s Periodicals Directory; SOCOL@AR - China Educational
Order your copy (for free): secretary@jatm.com.br
Publications; LATINDEX - Regional Cooperative Online Information System for Scholarly Journals and is
Web: http://www.jatm.com.br
under analysis in other major indexing databases. JATM is affiliated to ABEC - Brazilian Association of Scientific Editors and all published articles contain DOI numbers attributed by Crossref.
Journal of Aerospace Technology and Management
Published and distributed by: Institute of Aeronautics and Space
Vol. 2, n.3 (sep./dec. 2010) – São José dos Campos: Zeppelini Editorial, 2010
Desktop publishing and printing: Zeppelini Editorial
Four monthly issue
Edition: 750 São José dos Campos, SP, Brazil
1. Aerospace sciences
ISSN 1984-9648
2. Technologies
Note: This publication is sponsored by the Institute of Aeronautics and Space (IAE) to whom the copyright on
3. Aerospace engineering CDU:629.73
all published material belongs. Permission must be requested prior to use
Journal of Aerospace Technology and Management J. Aerosp. Technol. Manag. Vol. 2, Nº. 3, Sep – Dec. 2010
Editor in Chief
Executive Editor
Francisco Cristovão Lourenço de Melo Institute of Aeronautics and Space São José dos Campos - Brazil editor@jatm.com.br
Ana Marlene Freitas de Morais Institute of Aeronautics and Space São José dos Campos- Brazil secretary@jatm.com.br
ASSOCIATE EDITORS Adriana Medeiros Gama - Institute of Aeronautics and Space - São José dos Campos - Brazil Ana Cristina Avelar - Institute of Aeronautics and Space - São José dos Campos - Brazil André Fenili - Universidade Federal do ABC- São Paulo - Brazil Angelo Pássaro - Institute for Advanced Studies - São José dos Campos - Brazil Antonio Fernando Bertachini - National Institute for Space Research - São José dos Campos - Brazil Antonio Pascoal Del’Arco Jr.- Institute of Aeronautics and Space - São José dos Campos - Brazil Carlos de Moura Neto - Technological Institute of Aeronautics - São José dos Campos - Brazil Cynthia C. Martins Junqueira - Institute of Aeronautics and Space - São José dos Campos - Brazil Eduardo Morgado Belo - University of São Paulo - São Carlos - Brazil Elizabeth da Costa Mattos - Institute of Aeronautics and Space - São José dos Campos - Brazil Flaminio Levy Neto - Federal University of Brasília - Brasília - Brazil Gilberto Fisch - Institute of Aeronautics and Space - São José dos Campos - Brazil João Luiz F. Azevedo - Institute of Aeronautics and Space - São José dos Campos - Brazil José Márcio Machado- Univ. Estadual Paulista - São José do Rio Preto - Brazil José Roberto de França Arruda - State Universiy of Campinas- Campinas - Brazil Marcos Pinotti Barbosa - Federal University of Minas Gerais- Belo Horizonte - Brazil Mischel Carmen N. Belderrain- Technological Institute of Aeronautics - São José dos Campos - Brazil Paulo Tadeu de Melo Lourenção - Embraer - São José dos Campos - Brazil Valder Steffen Junior - Federal University of Uberlândia - Uberlândia - Brazil Waldemar de Castro Leite - Institute of Aeronautics and Space - São José dos Campos - Brazil
Editorial Production Ana Cristina C. Sant’Anna Glauco da Silva Helena Prado A. Silva Márcia M. E. Robles Fracasso
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 257-122, Sep-Dec., 2010
257
Editorial Board
Editorial Board Acir Mércio Loredo Souza - Federal University of Rio Grande do Sul - Porto Alegre - Brazil Adam S. Cumming - Defence Science and Technology Laborator - Fort Halstead - UK Adrian R. Wittwer - National University of the Northeast - Resistencia - Argentine Alain Azoulay - Superior School of Eletricity - Paris - France Alexandre Queiroz Bracarense - Federal University of Minas Gerais- Belo Horizonte - Brazil Antonio Henriques de Araujo Jr - State University of Rio de Janeiro - Rio de Janeiro - Brazil Antonio Sérgio Bezerra Sombra - Federal University of Ceará - Fortaleza - Brazil Bert Pluymers - Catolic University of Leuven - Leuven - Belgium Carlos Eduardo S. Cesnik - University of Michigan - Ann Arbor - USA Carlos Henrique Marchi - Federal University of Paraná - Curitiba - Brazil Charles Casemiro Cavalcante - Federal University of Ceará - Fortaleza - Brazil Cosme Roberto Moreira da Silva - University of Brasília - Brasília - Brazil Edson Aparecida de A. Querido Oliveira - University of Taubaté - Taubaté - Brazil Edson Cocchieri Botelho - Univ. Estadual Paulista - Guaratinguetá - Brazil Fabrice Burel - National Institute of Applied Sciences - Lion - France Fernando Luiz Bastian - Federal University of Rio de Janeiro - Rio de Janeiro - Brazil Francisco Souza - Federal University of Uberlândia - Uberlândia - Brazil Frederic Plourde - Superior National School of Mechanics and Aerotechnics - Poitiers - France Gerson Marinucci - Institute for Nuclear and Energy Research São Paulo - Brazil Gilson da Silva - National Industrial Property Institute - Rio de Janeiro - Brazil Hazin Ali Al Quresh - Federal University of Santa Catarina - Florianópolis - Brazil Hugo P. Simão - Princeton University - Princeton - USA João Amato Neto - University of São Paulo - São Paulo - Brazil Joern Sesterhenn - University of Munich - Munich - Germany Johannes Quaas - Max Planck Institute for Meteorology - Hamburg - Germany John Cater - The University of Auckland - Auckland - New Zealand Jorge Carlos Narciso Dutra Institute of Aeronautics and Space - São José dos Campos - Brazil José Alberto Cuminato - São Carlos School of Engineering - São Carlos - Brazil José Ângelo Gregolin - Federal University of São Carlos - São Carlos - Brazil José Atílio Fritz Rocco - Technological Institute of Aeronautics - São José dos Campos - Brazil José Carlos Góis - University of Coimbra - Coimbra - Portugal José Leandro Andrade Campos - University of Coimbra - Coimbra - Portugal José Maria Fonte Ferreira - University of Aveiro - Aveiro - Portugal José Rubens G. Carneiro - Pontifícia Univers. Católica de Minas Gerais- Belo Horizonte- Brazil Juno Gallego - Univ. Estadual Paulista - Ilha Solteira - Brazil Ligia M. Souto Vieira - Technological Institute of Aeronautics - São José dos Campos - Brazil Luis Fernando Figueira da Silva - Pontifical Catholic University - Rio de Janeiro - Brazil Luiz Antonio Pessan - Federal University of São Carlos - São Carlos - Brazil Márcia Barbosa Henriques Mantelli - University of Santa Catarina - Florianópolis - Brazil Maurizio Ferrante - Federal University of São Carlos - São Carlos - Brazil Michael Gaster - University of London - London - UK Mirabel Cerqueira Resende - Institute of Aeronautics and Space - São José dos Campos - Brazil Nicolau A.S. Rodrigues - Institute for Advanced Studies - São José dos Campos - Brazil Paulo Celso Greco - São Carlos School of Engineering - São Carlos - Brazil Paulo Varoto - São Carlos School of Engineering - São Carlos - Brazil Rita de Cássia L. Dutra - Institute of Aeronautics and Space - São José dos Campos - Brazil Roberto Costa Lima - Naval Research Institute - Rio de Janeiro - Brazil Roberto Roma Vasconcelos - Institute of Aeronautics and Space - São José dos Campos - Brazil Samuel Machado Leal da Silva - Army Technological Center - Rio de Janeiro - Brazil Selma Shin Shimizu Melnikoff - University of São Paulo - São Paulo- Brazil Tessaleno Devezas - University of Beira Interior - Covilha - Portugal Ulrich Teipel - University of Nuremberg - Nuremberg - Germany Vassilis Theofilis - Polytechnic University of Madrid - Madrid - Spain Vinicius André R.Henriques -Institute of Aeronautics and Space - São José dos Campos - Brazil Wim P. C. de Klerk - TNO Defence - Rijswijk - The Netherlands 258
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 257-122, Sep-Dec., 2010
ISSN 1984-9648 ISSN 2175-9146 (online)
Journal of Aerospace Technology and Management Vol. 02, N. 03, Sep. - Dec. 2010
CONTENTS EDITORIAL 261 ITA: sixty years Reginaldo dos Santos TECHNICAL PAPERS 263 Technique applied in electrical power distribution for Satellite Launch Vehicle Bizarria, F. C. P., Bizarria, J. W. P., Spina, F. D., Rosário, J. M. 269 Liquid rocket combustion chamber acoustic characterization Pirk, R., Souto, C.A., Silveira, D. D., Souza, C. M., Góes, L. C. S. 279 Development of access-based metrics for site location of ground segment in LEO missions Khamseh, H. B., Navabi, M. 287 Identifying dependability requirements for space software systems Romani, M. A. S., Lahoz, C. H. N., Yano, E.T. 301
Welding of AA1050 aluminum with AISI 304 stainless steel by rotary friction welding process Alves, E. P., Piorino Neto, F., An, C.Y.
307
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants Kawamoto, A. M., Diniz M. F., Lourenço V. L., Takahashi, M. F. K., Keicher, T., Krause, H., Menke, K., Kempa, P. B.
323
Performance evaluation of commercial copper chromites as burning rate catalyst for solid propellants Campos, E. A., Dutra, R. C. L., Rezende, L. C., Diniz, M. F., Nawa, W. M. D., Ilha, K.
331
Polimorfismo: caracterização e estudo das propriedades de uma fase cristalina Polymorphism: characterization and study of the properties of a crystalline phase Silva, G., Iha, K.
339
Prioritization of R&D projects in the aerospace sector: AHP method with ratings Silva, A. C. S., Belderrain, M. C. N., Pantoja, F. C. M.
349 Open innovation as an alternative for strategic development in the aerospace industry in Brazil Dewes, M. F., Gonçalez, O. L., Pássaro, A., Padula, A. D.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 257-122, Sep-Dec., 2010
259
361
Communication skills: a mandatory competence for ground and airplane crew to reduce tension in extreme situations Vieira, A. M., Santos, I. C.
371
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas The native identification friend-foe of Brazil: questions and replies Wurts, E.J. THESIS ABSTRACTS
387
Environmental and energetic impacts from use of fuel cells instead internal combustion engine in automotive vehicles Lorenzi, C. E.
387
Application of AHP method with ratings and BOCR approaches: F-X2 Project Nascimento, L. P. A. S.
388
Study of thermoplastic composite processing of PPS/carbon fiber by consolidation in autoclave Marques, L. S.
388 Design and performance analysis of an axial turbine used in turbopump unit of a liquid propellant rocket engine of 55 kN of thrust Araujo Filho, J. S. 389
AD HOC REFEREES
391 Instructions to the author
260
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 257-122, Sep-Dec., 2010
Reginaldo dos Santos
Rector of Instituto Tecnológico de Aeronáutica São José dos Campos – Brazil reitor@ita.br
Editorial ITA: sixty years
To celebrate the 60th anniversary of the “Instituto Tecnológico de Aeronáutica” (ITA), it is mandatory to recall to some facts that had preceded and influenced Lieutenant Colonel Aviator and Aeronautical Engineer Casimiro Montenegro Filho decision on creating the “Centro Técnico de Aeronáutica” (CTA), having ITA as its first institute. Let´s start referring to the 1st National Congress of Aeronautics, sponsored by the Aeroclube de São Paulo in 1934. The idea of the Aeroclube with the congress was to discuss the technological and industrial possibilities of the country for the implementation of an aeronautical industry, and the main motivation and concern were the number of imported aircrafts flying in Brazil. From 1927 to 1934, the country had imported over 550 aircrafts. During the Congress, the Army Lieutenant Colonel and Aeronautical Engineer Antonio Guedes Muniz presented the paper “The Building of Engines and Airplanes in Brazil”, suggesting the ways of implementing an aeronautical industry in the country. After the presentation of the paper, the engineer Ary Torres, director of Instituto de Pesquisas Tecnológicas (IPT), suggested the creation of a graduation course in aeronautics in São Paulo. In other paper presented at the Congress, “Suggestions to Overcome the Problem of Building Aircrafts in Brazil”, Lieutenant-Commander and Navy pilot Raymundo Vasconcelos Aboim emphasized the need of preparing specialized human resources and creating a favorable environment for the development of research in aeronautics in the country, initially by means of technology licensing. At that time, Captain Casimiro Montenegro Filho, graduated in 1928 from the first class of the Army Aviation course, was commitioned in São Paulo as Commander of the 2nd Aviation Regiment, certainly participated in the debates and concerns with the status of the Brazilian aviation and became aware of the first tries of producing aircrafts in the country. As to recall, the first serial production aircrafts in the country were projects of Cel Antônio Guedes Muniz, the M-7 and M-9, and initiative of the “Indústria Brasileira de Aviação”, a subsidiary of the “Companhia Nacional de Navegação Aérea” (CNNA), in Campos dos Afonsos, Rio de Janeiro. The CNNA, founded by Henrique Lage in 1935, was in fact the first aircraft industry of Brazil. In 1935, during the government of President Getúlio Vargas, a commission with representatives from the Army, the Navy and the Civil Aviation was established to study the localization of an industry for production of military aircraft. The chosen place was Lagoa Santa Minas Gerais, and the company, Construções Aeronáuticas S.A., was founded in 1939, and started its activities based on an industrial model that could only permit it to fabricate under license North-American aircrafts. Concomitantly to the initiative in Lagoa Santa, an industrial installation was launched by the Navy in Ponta do Galeão, Ilha do Governador, Rio de Janeiro, in 1934. The “Oficinas Gerais da Aviação Naval” (OGAN) facilities were inaugurated in 1939, initially to assemble German aircrafts. The first aircrafts produced in OGAN were the Brazilian version of the Focker-Wulf 44, the Pintassilgo, and the Focker-Wulf 58. Casimiro Montenegro left the 2nd Aviation Regiment in 1936. Later on, in 1939, he decided to get enrolled in the first class of the recently created course of Aeronautical Engineering at the “Escola Técnica do Exército” (ETE), current Instituto Militar de Engenharia (IME), in Rio de Janeiro. With the creation of the Ministry of Aeronautics in January 20th 1941, Casimiro Montenegro left the Army and became part of the Brazilian Air Force. Despite the comfortable situation of the Brazilian initiatives of projecting and producing aircrafts, the Minister Salgado Filho, first minister of the newly created Ministry of Aeronautics, was convinced that to accomplish completely with his double attributions – civil and military – his ministry had to follow and get enrolled on the new improvements and development of the aeronautical technology. In order to do that, the Air Force implemented the Aeronautical Technology Division as the Sub-Direction of Material in December 26th 1941, and the Lieutenant-Colonel Casimiro Montenegro Filho, recently graduated Aeronautical Engineer by the “Escola Técnica do Exército”, was assigned the head of it. As predicting the collapse of the aeronautical industry of the country, Montenegro was considering the possibility of transforming the Sub-Direction of Material into an organization capable of accomplishing research that could sustain the development of
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 261-262, Sep-Dec., 2010
261
Reginaldo dos Santos
the aeronautical production and the airline industries. The existing private industries were producing small aircrafts with wood structure, with support of IPT. The industries established by the Government were enrolled in imported projects, like as was the case with OGAN and Construções Aeronáuticas S.A. However, Casimiro Montenegro wanted something bigger. At the time of the creation of the Ministry of Aeronautics, the Brazilian Air Force (FAB) had 428 airplanes received from the extinct Army and Navy aviations. However, the huge technological advances of the aeronautical industry in the second half of the 1930s had made the majority of the FAB airplanes obsolete for the war that was coming over the Europe. During the World War II, from 1942 to 1945, by means of a North American program called Lend-Lease, the FAB received over 400 training aircrafts and over 500 operational ones. It is a fact that, by the end of the World War II, the country had industrial facilities, machinery, tools and technicians, a patrimony built based on orders from the government, but it lacked technicians and engineers in a sufficient number to make the industries auto-sustainable and independent of government’s orders to supply the civil or military needs. After the war, the government politics changed, apparently due to a neo-liberal orientation, and the orders from it fell to almost zero. The United Stated of America, having a great deal of airplanes in stock, had donated or sold their airplanes at symbolic prices. Those facts might have been the reason that prevented the development of the aeronautical industry in the country back then. In few words, this was the environment in which Casimiro Montenegro and the pioneers that idealized CTA were living in the 1940s. Not satisfied, in 1945 Casimiro Montenegro went to the USA with the lieutenant colonel and engineer Telles Ribeiro, the colonel aviator Faria Lima and a group of Air Force Officers to visit some airbases and the US Air Force Maintenance Facilities in Wright Field, Ohio. The Brazilian Air Force Major Oswaldo Nascimento Leal, who was attending the course of Aeronautical Engineering at the Massachusetts Institute of Technology (MIT), went to Wright Field to speak with the group. Leal suggested to Montenegro that he should go to Boston to know MIT and to talk to the Professor Richard Smith, head of the Aeronautical Department of that Institute, before making any decision on the model and type of scientific and technological institution to be submitted to the Air Force General Staff and to the Minister of Aeronautics. Major Leal had the opinion that the necessity in Brazil was a higher level school to graduate aeronautical engineers, with emphasis in civil and military aviation, and not only to take care of the Air Force needs. It would also be necessary to train engineers to indirectly support the correlate industries, as is the case of quality control of product and aeronautical material, certification of projects and prototypes, optimization of the operation of airline companies, etc. The establishment of an institution with these patterns in South America had been a desire of Professor Smith for years, and a real necessity in Brazil in the vision of Colonel Montenegro. In August 1945, the general plan of the Technical Center of the Ministry of Aeronautics was finished, taking the MIT as a model. The plan was elaborated by Professor Smith under the orientation of Montenegro (Its is said that Professor Smith had prepared a similar plan for Argentine). The President of Brazil, Dr. José Linhares, approved the plan in November 16th, 1945. The Center would have two institutes – one directed to technical higher education, the ITA, and the other directed to research and cooperation with the industry, the “Instituto de Pesquisa e Desenvolvimento” (IPD). The Organization Committee of CTA (COCTA) was created on January 26th 1946. In 1950, the basic infrastructure of ITA, the priority of Montenegro, was finished, and from that year on the courses of ITA, which had started at the ETE, in Rio de Janeiro, were transferred to CTA. The CTA was considered organized in January 1st 1954, by the Decree nr 34,701 of November 26th 1953. ITA was finally formalized as a Higher Education Establishment under the jurisdiction of the Ministry of Aeronautics by the Law 2,165 of January 5th 1954. Nowadays, ITA holds approximately 600 undergraduated students, over 1500 graduate students, and 540 students enrolled in non-degree courses. The institution has already graduated 5,312 engineers, out of which 905 were militaries, 2,545 masters, being 187 militaries, 369 doctors, out of which 21 were militaries, and 703 specialists, being 355 militaries. ITA plans to double the number of undergraduate students in five years time and to enlarge even more its field of action, without losing its main objective that is the airspace. In these 60 years of existence, it is a fact that the contributions of ITA to aeronautical industry have made the dream of Montenegro and his followers come true, but they were also very important in fields such as telecommunications, automobile, space, air traffic, aeronautical infrastructure, banking automation, among others. The effort and the sacrifice of the pioneers were not in vain. Brazil, the State of São Paulo, the city of São José dos Campos and particularly the Aeronautics have gained a lot, and it is still gaining, with the teaching and research and development infrastructures implemented in São José dos Campos, São Paulo. 262
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 261-262, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02038410
Francisco Carlos P. Bizarria*
Institute of Aeronautics and Space São José dos Campos, Brazil bizarriafcpb@iae.cta.br
José Walter Parquet Bizarria
University of Taubaté Taubaté, Brazil jwpbiz@gmail.com
Fábio Duarte Spina
Institute of Aeronautics and Space São José dos Campos, Brazil spina@iae.cta.br
João Maurício Rosário
University of Campinas Campinas, Brazil rosario@fem.unicamp.br
* author for correspondence
Technique applied in electrical power distribution for Satellite Launch Vehicle Abstract: The Satellite Launch Vehicle electrical network, which is currently being developed in Brazil, is sub-divided for analysis in the following parts: Service Electrical Network, Controlling Electrical Network, Safety Electrical Network and Telemetry Electrical Network. During the prelaunching and launching phases, these electrical networks are associated electrically and mechanically to the structure of the vehicle. In order to succeed in the integration of these electrical networks it is necessary to employ techniques of electrical power distribution, which are proper to Launch Vehicle systems. This work presents the most important techniques to be considered in the characterization of the electrical power supply applied to Launch Vehicle systems. Such techniques are primarily designed to allow the electrical networks, when submitted to the single-phase fault to ground, to be able of keeping the power supply to the loads. Keywords: SLV, Electrical network, Power distribution.
LYST OF SYMBOLS SLV IEN SEN CEN SAEN TEN OBC L+ L- PE IPC If Vf Zcp+ Zc+ Zp ZICP Zcp-
Satellite Launcher Vehicle Integrated Electrical Networks Service Electrical Network Controlling Electrical Network Safety Electrical Network Telemetry Electrical Networks On Board Computer Positive line of direct current voltage source Negative line of direct current voltage source Protection cable Insulation Permanent Controller Current caused by the direct fault Voltage caused by the direct fault Resistance in the main cable segment, positive line Resistance in the load cable segment Resistance in the protection cable segment Internal resistance in the Insulation Permanent Controller Resistance in the main cable segment, negative line
INTRODUCTION The Satellite Launch Vehicle (SLV), shown in Fig. 1, is currently developed in Brazil by the Institute of Aeronautics and Space (IAE, acronym in Portuguese). The vehicle on board electrical network is sub-divided in Service Electrical Network (SEN), Controlling Electrical Received: 25/08/10 Accepted: 08/09/10
Figure 1: Main SLV subsystems (Palmério, 2002).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 263-268, Sep-Dec., 2010
263
Bizarria, F. C. P. et al.
Network (CEN), Safety Electrical Network (SAEN) and Telemetry Electrical Network (TEN) (Palmério, 2002). The requirements for SEN are: i) to store and provide electrical power; ii) to distribute electrical power; and iii) to perform the safety and the sequence of events during the flight of the vehicle. The main equipment used in CEN are: i) inertial sensors; ii) On Board Computer (OBC); and iii) electromechanical actuators, which allow the vehicle to follow a flight trajectory. SAEN performs the following functions: i) reception; ii) decoding; iii) command; iv) actuation of remote and auto destruction orders; and v) communication with the ground radar. TEN performs primarily the following functions: i) conditioning; ii) acquisition; iii) coding; and v) signal transmission to the ground station. During pre-launching and launching phases, these electrical networks are associated electrically and mechanically to the structure of the vehicle. When integrated into SLV, these electrical networks are called Integrated Electrical Networks (IEN). The techniques for Electrical Power Distribution (EPD), for launch vehicle, shall be applied to allow the conditions for a proper operation of IEN in normal condition as well in failure mode. GOALS OF THE WORK
Electrical power distribution The classification of the EDP is based on: i) Live Cables Scheme, and ii) Grounding Scheme (NBR 5410:2004). The Live Cables Scheme considers specially the nature of the equipment supplied by the electrical system; in other words, if there are three-phases, two-phases, single-phase etc. In the Grounding Scheme is given great importance to the connection of the power supply neutral conductor and the association between the metal case of the loads and the grounding reference of the system. Depending on how these connections are, three types of grounding scheme are obtained: TN, TT and IT. Based on electrical conductibility characteristics and the mechanical structure of the SLV, only the possibility of IT and/or TN schemes for IEN implementation are considered. IT grounding scheme The IT is the only scheme which does not require interruptions in the power supply for the load when submitted to the first single-phase fault to the ground (Hofheinz, 2000). In the IT grounding scheme, there is no point connecting the power supply (L+ or L-) to the ground, but the metal case of the load is directly connected to the ground reference. Figure 2 presents the electrical model of the IT grounding scheme.
The main goal of this work was to introduce the techniques of EPD for choosing the IEN architecture which will allow maintaining the power supply to the circuits submitted to a single-phase fault to ground and that the fault in one electrical network will not cause direct consequences in a different electrical network and vice-versa. PROPOSED TECHNIQUES The two main objectives shall be provided to maintain the power supply to the circuits submitted to first fault to ground and to avoid that the fault in an electrical network does not cause direct consequences in a different network. In order to achieve these objectives, the IEN shall: i) to use grounding scheme which will keep the power supply under condition of single-phase fault to ground, and ii) to use galvanic isolators in the circuits which transfer signals between different electrical networks.
264
Source: electrical power source in direct current; L+: positive line of direct current voltage source; L-: negative line of direct current voltage source; PE: protection cable; IPC: Insulation Permanent Controller; Grounding terminal: cable or a set of cables embedded to the earth. Figure 2: IT grounding scheme diagram.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 263-268, Sep-Dec., 2010
Technique applied in electrical power distribution for Satellite Launch Vehicle
The loads supplied by the IT grounding scheme must not have connection between their power supply conductors and their respective cases, structures etc.
The occurrence of a second fault in a system using IT grounding scheme must be avoided or have their effects minimized by overcurrent circuits protection.
The occurrence of one single-phase fault to ground, on the IT grounding scheme, will cause a low intensity current flow, because the electrical resistance path is high. Figure 3 shows the path of electric current in the occurrence of the fault on the IT grounding scheme.
All electronic components in circuits operating in IT grounding scheme must be designed considering the possibility of overvoltage caused by the faults or by the interferences in the electrical system.
Typically, the electrical resistance of the cables in the fault path is low. Nonetheless, the electrical resistance provided by the Insulation Permanent Controller (IPC) is high. These characteristics allow that the IT grounding scheme does not interrupt its power supply with the occurrence of the first single-phase fault to ground.
TN grounding scheme
In the IT grounding scheme, one single-phase fault to ground can be identified by an IPC. This equipment identifies the occurrence of a fault by measuring the electrical insulation of the system. However, this device does not identify the location of the fault in the system. The fault can be located through a manual equipment to search for short circuits.
In the TN grounding scheme the power supply is directly grounded and the metal cases of its loads are connected to this same point (Cotrim, 1985). This scheme can be implemented in three different versions: TN-C, TN-S and TN-C-S. The complementary letters define respectively: i) the neutral conductor is also used for interconnection of the metal cases, ii) the neutral and protection conductors are separated, and iii) the neutral and protection conductors are joined at the beginning of the circuit and are separated from a determined point of the conductors. Based on the requirement of establishing the electrical connection among all mechanical parts of the SLV structure, the implementation of TN-S grounding scheme was chosen only for the loads that require the connection of the power supply negative line and its load metal case. Figure 4 presents the TN-S grounding scheme electrical diagram. In the TN grounding scheme, the method to remove a single-phase fault to ground is overcurrent circuit protection.
If: current caused by the direct fault. Vf: voltage caused by the direct fault; Zcp+: resistance in the main cable segment, positive line; Zc+: resistance in the load cable segment; Zp: resistance in the protection cable segment; ZICP: internal resistance in the Insulation Permanent Controller (IPC); Zcp-: resistance in the main cable segment, negative line; L+: positive line of direct current voltage source; L-: negative line of direct current voltage source; PE: protection cable; Direct Fault: fault with negligible contact resistance; Source: electrical power source in direct current; Grounding terminal: cable or a set of cables embedded to the earth. Figure 3: Path of the fault current in the IT.
L+: positive line of direct current voltage source; L-: negative line of direct current voltage source; PE: protection cable; Source: electrical power source in direct current; Grounding terminal: cable or a set of cables embedded to the earth. Figure 4: TN-S grounding scheme diagram.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 263-268, Sep-Dec., 2010
265
Bizarria, F. C. P. et al.
The advantage of TN grounding scheme is the easy identification of the circuit under fault, which can be determined by its work stoppage due to the overcurrent protection trip. The great disadvantage is the loss of a circuit, which can create a negative effect on the system. Figure 5 shows an example of path of the fault current, in steady state, for the TN-S grounding scheme.
On board IT grounding scheme Statistically, the single-phase fault to ground is the most common failure in electrical systems, regardless of the grounding scheme adopted (Kindermann, 1992), across all the line from the power supply to the load circuit. Between conventional grounding schemes, IT is the only one which does not interrupt the power supply in case of the occurrence of a single-phase fault to ground. The immunity to the single-phase fault to ground is a great advantage of the IT grounding scheme over the TN grounding scheme. The IT grounding scheme disadvantage is the difficulty to identify the circuit where the fault occurred, which is usually performed by IPC associated to successive measurements made by the electrical system operator, aided by differential current pincers.
If: current caused by the direct fault; Zcp+: resistance in the main cable segment, positive line; Zc+: resistance in the load cable segment. Zp-: resistance in the protection cable segment. L+: positive line of direct current voltage source; L-: negative line of direct current voltage source; PE: protection cable; Direct fault: fault with negligible contact resistance; Source: electrical power source in direct current; Grounding terminal: cable or a set of cables embedded to the earth. Figure 5: Fault current path in TN.
Figure 6 presents an example of IT grounding scheme for unmanned vehicles. In the system presented in Fig. 6, the use of IPC only on the ground is foreseen. This will not allow the acquisition of electrical isolation data during the flight of the vehicle. The behavior of the electrical isolation, during the flight of the vehicle, shall be determined in ground tests using IPC, and simulating the flight conditions.
L+: positive line of direct current voltage source; L-: negative line of direct current voltage source; IPC: Insulation Permanent Controller. Figure 6: Example of IT grounding scheme. 266
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 263-268, Sep-Dec., 2010
Technique applied in electrical power distribution for Satellite Launch Vehicle
Galvanic separation The goal of galvanic separation is to create galvanic isolation among independent electric circuits that can be associated at the same electrical network, with different voltages which could damage equipment or cause undesirable interferences for the system operation. Normally, in a launch vehicle, can be identified electrical networks with different grounding schemes exchange signal each other. Figure 7 shows an example of circuit (Cts) which has no galvanic separation; however, it has the function of transferring signals between two electrical networks with IT and TN grounding scheme, respectively. In Figure 7, R1 resistor, in the IT grounding scheme network, provides analogical signal which is proportional to the level of voltage reached by the F2 power supply to the TR transmitter in the TN-S grounding scheme network, by means of Cts circuit. On normal operation, the absence of galvanic separation in the Cts circuit causes limited interference between
L+: positive line of direct current voltage source; L-: negative line of direct current voltage source; PE: protection cable; In1, In2 and Its: nominal currents. Figure 7: Signals transference without galvanic separation.
the two electrical networks, prevailing the nominal currents (In1, In2 and Its). Assuming that a single-phase fault to the metal case of the Load 1 occurs in the IT grounding scheme, it will cause short-circuit current (If) between the components of the electrical networks showed in Fig. 8. In the electrical network configuration showed in Fig. 8, the occurrence of one fault may cause undesirable consequences. In order to minimize the consequences of this fault, is proposed the installation of galvanic separators in the circuits of different networks which exchange signals with each other, as shown in Fig. 9. In the electrical diagram shown in Fig. 9, it can be observed the galvanic separator in the circuit of transference of signals (Cts), restraining the consequences of the fault and allowing the normal operation of both electrical networks. Figure 10 presents four examples of galvanic isolation circuits which can perform the transference of signals among different electrical networks (Mulville, 1998).
L+: positive line of direct current voltage source; L-: negative line of direct current voltage source; PE: protection cable; If: current caused by the direct fault. Figure 8: Fault path between the electrical networks.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 263-268, Sep-Dec., 2010
267
Bizarria, F. C. P. et al.
The optical coupler in Fig. 10 (c) can isolate digital signals. In most of applications, the weight and dimensions are proper; however, the optical coupler has low robustness when compared to relay. When the isolation of analogical circuits is necessary, with both direct and alternate current signals, insulation amplifier, as shown in Fig. 10 (d), can be employed. These amplifiers present significant complexity to be implemented in signals transference circuits. CONCLUSIONS The application of these techniques in the electrical networks of SLV will cause mainly the following positive impacts: i) it will allow that vital electrical equipment continues to operate under first-phase fault to ground, for instance, OBC and others which do not have redundancies, and ii) the path of fault current will be restricted to the electrical network in which that fault was created, avoiding the involvement of another electrical network. L+: positive line of direct current voltage source; L-: negative line of direct current voltage source; PE: protection cable; In1, In2: nominal currents. Figure 9: Transference of signals with galvanic separation.
The complexity to implement the IT grounding scheme in electrical networks is higher compared to the TN grounding scheme. On that context, IT grounding scheme requires specialized staff, galvanic separation systems and usage of IPC. REFERENCES Cotrim, A.A.M.B., 1985, “Manual de instalações elétricas”, 2nd ed. McGraw-Hill, São Paulo. Hofheinz, W., 2000, “Protective measures with insulation monitoring”, 2nd ed., VDE Verlag, Berlin-Offenbach, Germany.
Figure 10: Galvanic isolation circuits.
The transformer, presented in Fig. 10 (a), can be used to isolate the circuits that work with alternate current signals. Their dimensions and weight are characteristics which limit several launcher vehicle applications. In order to isolate both digital and analogical signals, the relay in Fig. 10 (b) can be employed. The relays have similar limitation compared to the transformer; however, they are robust and simple to implement in the electrical circuits.
268
Kindermann, G., 1992, “Curto-circuito”, Sagra/DC Luzzatto, Porto Alegre. Mulville, D.R., 1998, “Electrical grounding architecture for unmanned spacecraft: Nasa technical handbook”, Nasa, Washington. Palmério, A.F., 2002, “Introdução à Engenharia de Foguetes. Booklet course held at the Institute of Aeronautics and Space”, Brazil.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 263-268, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02038810
Rogério Pirk*
Liquid rocket combustion chamber acoustic characterization
Carlos d’Andrade Souto
Abstract: Over the last 40 years, many solid and liquid rocket motors have experienced combustion instabilities. Among other causes, there is the interaction of acoustic modes with the combustion and/or fluid dynamic processes inside the combustion chamber. Studies have been showing that, even if less than 1% of the available energy is diverted to an acoustic mode, combustion instability can be generated. On one hand, this instability can lead to ballistic pressure changes, couple with other propulsion systems such as guidance or thrust vector control, and in the worst case, cause motor structural failure. In this case, measures, applying acoustic techniques, must be taken to correct/minimize these influences on the combustion. The combustion chamber acoustic behavior in operating conditions can be estimated by considering its behavior in room conditions. In this way, acoustic tests can be easily performed, thus identifying the cavity modes. This paper describes the procedures to characterize the acoustic behavior in the inner cavity of four different configurations of a combustion chamber. Simple analytical models are used to calculate the acoustic resonance frequencies and these results are compared with acoustic natural frequencies measured at room conditions. Some comments about the measurement procedures are done, as well as the next steps for the continuity of this research. The analytical and experimental procedures results showed good agreement. However, limitations on high frequency band as well as in the identification of specific kinds of modes indicate that numerical methods able to model the real cavity geometry and an acoustic experimental modal analysis may be necessary for a more complete analysis. Future works shall also consider the presence of passive acoustic devices such as baffles and resonators capable of introducing damping and avoiding or limiting acoustic instabilities. Keywords: Combustion chamber, Combustion instability, Acoustic resonance, Liquid rocket engine (LRE).
Institute of Aeronautics and Space São José dos Campos – Brazil rogeriorp@iae.cta.br
Institute of Aeronautics and Space São José dos Campos – Brazil carloscdas@iae.cta.br
Dimas Donizeti da Silveira
Institute of Aeronautics and Space São José dos Campos – Brazil dimasdds@iae.cta.br
Cândido Magno de Souza
Institute of Aeronautics and Space São José dos Campos – Brazil candidocms@iae.cta.br
Luiz Carlos Sandoval Góes
Technological Institute of Aeronautics São José dos Campos – Brazil goes@ita.br *author for correspondence
INTRODUCTION Combustion instabilities have been present in the development of liquid rocket engines (LRE) over the last decades. There are basically three types of combustion instabilities in LRE: low frequency, medium frequency and high frequency. Low frequency instabilities, also called chugging, are caused by pressure interactions between the propellant feed system and the combustion chamber. Medium frequency instabilities, also called buzzing, are due to coupling between the combustion process and the propellant feed system flow. The high frequency instabilities are the most potentially dangerous and not well-understood ones. It occurs due to coupling of the combustion process and the chamber acoustics (Sutton and Biblarz, 2001). The presence of acoustic (high frequency) combustion instabilities shall be considered still in development Received: 14/09/10 Accepted: 20/10/10
phase, although only after real firing tests combustion instabilities can be clearly identified. Combustion chambers environments present high levels of acoustic noise. Bunrley and Culick (1997) described that this can be verified when the power spectrum of the acoustic pressure levels, measured during burning tests of the chambers, is analyzed. When an oscillation is observed, i.e., combustion instability, sound pressure peaks with well-defined magnitudes summed to the background noise are present. These peaks are correlated with the resonance frequencies of the combustion chambers cavities, where the sound pressure on each position of the acoustic fluid space represent the environment oscillation, attributed to the acoustic modes of these cavities. Such a way occurs the coupling of the acoustic natural frequencies and the burning oscillations of the combustion chamber, which can cause instabilities and consequent unexpected behavior such as efficiency loss or even explosion of the engine. A LRE combustion chamber has longitudinal, tangential and radial acoustic modes. Coupled modes combining
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
269
Pirk, R. et al.
these types are also possible to occur. The tangential and radial modes are the most dangerous to high frequency instabilities (Yang, Wicker and Yoon, 1994). The three basic types of acoustic modes of a cylinder representing a LRE combustion chamber are shown in Fig. 1.
Figure 1: Longitudinal (a), tangential (b) and radial modes (c).
Some works showed that the acoustic behavior of a combustion chamber is weakly affected by the combustion process. Comparing to room pressure and temperature conditions, the chamber cavity mode shapes remain basically the same, but its eigenfrequencies are shifted, actually multiplied by a number defined by the ratio of sound speed velocity at real operation temperature and at room temperature (Laudien et al., 1994). In the development of a liquid rocket engine of 75 KN thrust by the Institute of Aeronautics and Space (IAE), the acoustic behavior of the combustion chamber is being considered. An investigation of some different combustion chambers is proposed. These studies may be done in two steps, using theoretical calculation and experimental measurements. As such, theoretical and experimental natural frequencies of the acoustic cavity are obtained, and a comparison/validation of the mathematical model can be done. First, considering the geometry of the combustion chamber and the physical parameters of air, natural frequencies of this cavity are calculated theoretically. The acoustic frequencies can also be obtained by using a test setup to measure the sound pressure levels of this acoustic domain. A third possible method to obtain the acoustic behavior of combustion chambers is by modeling the cavity using numerical methods such as the Finite Element Method (FEM) or the Boundary Element Method (BEM). As such, by applying virtual prototypes’ techniques, besides calculating the resonance, the associated acoustic mode shapes are obtained. With these three methods, theoretical versus experimental comparisons can be carried out for the validation of the existing models. Since a combustion acoustic instability (and the acoustic mode to which it is related) is identified, some measures can be taken to avoid or minimize it. Some design parameters in the combustion chamber and injector play an important role in high frequency combustion instabilities. By
270
changing these parameters, one can obtain a design less susceptible to this kind of instabilities (Huzel and Huang, 1992). Also, passive acoustic devices for the attenuation of acoustic noise, as Helmholtz resonators, liners, baffles and ¼ wave filters can be introduced in the combustion chamber (Santana Junior et al., 2009). It is important to mention that, in the latter stages of this survey, numerical methods for modeling acoustics of chambers as well as insulation treatments for attenuating acoustic noises will be presented. Currently, only comparisons between theoretical versus experimental results, using simple mathematical models and measured frequency response functions, respectively, are carried out for different configurations of a combustion chamber. OBJETIVE The objective of this work was to present the adopted procedures for the dynamic characterization of different configurations of combustion chamber models for a liquid rocket engine capable of generating 75 kN thrust. The models were built on aluminum, in 1:1 scale. In order to assess the influence of the chamber geometry on the chamber acoustic behavior, the referred combustion chamber models were segmented. This segmentation allowed us analyzing the influence of the different lengths on the dynamic behavior of the acoustic environment. It is worth mentioning that the tests were performed under room environmental conditions, without simulating the pressure and temperature conditions during the combustion of a rocket engine. Hereinafter, the measurement procedures to obtain the acoustic parameters of different configurations of the 75 kN combustion chamber, as well as the method applied for the calculation of the theoretical natural frequencies were presented. Measuring setup, collected data and the applied criteria for the choice of FRF were described, as well as the results obtained. Theoretical versus experimental comparisons, for the different configurations, are done and the reliability of the formulation applied to calculate the analytical resonances is verified. PROCEDURES AND METHODOLOGIES As it was mentioned before, the experimental determination of the acoustic characteristics of combustion chambers was performed in room conditions, i. e., without considering the burning conditions inside the combustion chamber cavity as mixing of gasses, temperature, pressure, mass density etc. A mock up of the 75 kN LRE was built on aluminum, with the possibility of assembling different parts, thus creating many configurations of the referred engine. Figure 2 shows
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
Liquid rocket combustion chamber acoustic characterization
the 75 kN LRE, which was segmented in order to assess the inner combustion chamber dynamic behavior considering different configurations, including the different sizes of the nozzle. In other words, such segmentation allows verifying the influence of the different geometries on the acoustic behavior of the chamber cavity, which is an important source of combustion instability. The measured acoustic parameters of each configuration may be compared with the respective parameters, calculated by a mathematical model.
Table 1 describes, for each configuration, the connected segments to build up the different geometries of the combustion chamber. The numbers presented on the referred table represent the segments denoted in Fig. 2. THEORETICAL CALCULATIONS Equation 1 describes the considered mathematical model for the acoustic natural frequencies calculation of the set of configurations. The inner acoustic environment is treated as an acoustically closed system, even though the nozzle is in contact with the external fluid or external acoustic environment. Such approximation has showed good theoretical versus experimental agreement (Laudien et al., 1994).
Figure 2: Dimensions of the segmented combustion chamber in millimeters.
Note in Fig. 2 that it is possible to built 16 configurations for the 75 kN LRE. Even though it is possible to assemble such different configurations, this paper describes the analysis performed only for the configurations B1, B2, C1 and D1. As such, the influences of the internal volume and length of the combustion chamber as well as the size of the nozzle are assessed. Figure 3 presents all the possible configurations, with and without nozzle, including variations of the volume of the combustion chamber and the size of the nozzle.
Figure 3: Different configurations of the 75 kN LRE.
(1)
where: c: speed of sound; λ: transversal eigenvalue, for m,n = 0,1,2... (Laudien et al., 1994); k, m, n = 0,1,2... longitudinal, tangential and radial mode number directions; Rc: combustion chamber radius; Lc: effective acoustic length (distance between injectors faceplate and nozzle throat, less approximately one-half of the converging nozzle length). Note that in Eq. 1 the modes and its associated natural frequencies are function of the chamber geometry and the three orthogonal directions k, m and n. Table 2 gives the calculated values, assuming the temperature of the air 20ºC, universal gas constant at pressure and volume constants ( ), which yields speed of sound c = 343 m/s.
Table 1: Sequence of segments to be connected for each configuration
CFG* Segments CFG* A1 1-4 B1 A2 1-4-5 B2 A3 1-4-5-6 B3 A4 1-4-5-6-7 B4 * Segments are shown in Figure 2.
Segments 1-2-4 1-2-4-5 1-2-4-5-6 1-2-4-5-6-7
CFG* C1 C2 C3 C4
Segments 1-2-3-4 1-2-3-4-5 1-2-3-4-5-6 1-2-3-4-5-6-7
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
CFG* D1 D2 D3 D4
Segments 1-2-2-4 1-2-2-4-5 1-2-2-4-5-6 1-2-2-4-5-6-7
271
Pirk, R. et al.
Table 2: Calculated acoustic natural frequencies
Acoustic mode 1st long 2nd long 3rd long 1st tang 2nd tang 1st radial 2nd radial 1st rad/1st tang 1st rad/2nd tang 2nd rad/1st tang
Orthogonal directions λ transversal k m n 1 0 0 0 2 0 0 0 3 0 0 0 0 1 0 1.8412 0 2 0 3.0542 0 0 1 3.8317 0 0 2 7.0156 0 1 1 5.3314 0 2 1 6.7061 0 1 2 8.5363
EXPERIMENTAL MEASUREMENTS For the experimental procedure, a noise source was positioned inside the combustion chamber close to the injectors face plate. A microphone was placed in many different positions into the combustion chamber cavity. The microphone measured the acoustic pressure response due to the noise in some points. For each microphone position, Frequency Response Functions (FRF) measurements were taken, performing azimuthal swept at each 45º, positioning the microphone in the radial direction at distances 10 mm, 40 mm and 70 mm from the structure wall, and also performing an axial swept at each 50 mm. Figure 4 shows the position points to obtain the complete set of measurement data.
Figure 4: Microphones positioning.
Note that this measurement procedure generates a large amount of experimental data, since transversal data were measured at each 45º, positioned at 10 mm, 40 mm and 70 mm from the structure wall, taking as reference, the geometric center of the combustion chamber. Besides, axial measurements were performed at each 50 mm, up to 450 mm, depending on the chamber length. After a first analysis, the results indicated that an optimized measuring procedure could be adopted, since the FRF presented similar behavior when they were acquired on the same plane, perpendicular to the direction of the wave 272
CFG B1 717.812 1435.625 2153.437 1105.493 1833.803 2300.63 4212.307 3201.079 4026.477 5125.366
Configurations CFG B2 CFG C1 717.812 546.3603 1435.625 1092.721 2153.437 1639.081 1105.493 1105.493 1833.803 1833.803 2300.63 2300.63 4212.307 4212.307 3201.079 3201.079 4026.477 4026.477 5125.366 5125.366
CFG D1 471.3108 942.6216 1413.932 1105.493 1833.803 2300.63 4212.307 3201.079 4026.477 5125.366
propagation. For such optimization, one considered that the structural part of the combustion chamber is rigid and that the propagating acoustic waves in the inner acoustic environment of the combustion chamber assume a nearly acoustic plane wave or one-dimensional wave behavior. Such a way, the amount of measurements and data analysis for the next configurations can be decreased. Acoustic plane waves are the simplest type of propagating waves through the fluid medium. The characteristic property of such waves is that parameters such as acoustic pressure, particle displacements etc., have the same amplitude on all points of any plane, perpendicular to the direction of propagation. As an example, the propagating waves in a confined fluid, through a rigid tube, generated by a vibrating piston, positioned at one of the edges of the tube. Any divergent type of wave, in a homogeneous medium, also assumes the characteristics of a plane wave, when it propagates at long distances from its source (Gerges, 1994). An important remark about the acoustic plane waves is that they have characteristics similar to those presented by the longitudinal waves propagating in a bar. Consequently, it is possible to deduce the wave equation through a fluid media, in which it is admitted being confined in a rigid tube, with constant transversal section (Burnley and Culick, 1997). As such, the survey of the configurations B1, B2, C1 and D1 can define the optimization procedure for the next experiments, since some transversal measurement positions can be eliminated, assuming the plane wave behavior. MEASUREMENT OF THE ACOUSTIC PARAMETERS On these experimental assessments, the combustion chamber cavities were equipped with an external acoustic
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
Liquid rocket combustion chamber acoustic characterization
source, installed at the injection faceplate of the engine, which injected an excitation noise inside the acoustic cavity. This noise was generated by a signal generator, which provided the white noise (0 to 20 kHz) to be injected by the noise source. However, due to practical manufacturing characteristics of the referred acoustic source, the spectral content of the injected noise inside the chamber cavity was from 400 Hz to 20 kHz. The acquired FRF, describe the acoustic response of the fluid media (acoustic cavity) due to the external acoustic excitation. These FRF were captured by a ¼” capacitive pressure microphone, which was mounted on a thin rod, and with which it was possible to reach all the measurement positions, axial, azimuth and radial, in the chamber inner environment. This microphone was conditioned by power supply and preamplifier to measure the sound pressure level inside the combustion chamber, when it is subjected to an external acoustic excitation. The measured acoustic pressure levels were registered by using a digital analyzer, for posterior analysis. Figure 5 shows the measurement setup.
Figure 5: Measurement set up.
It is important to mention that this technique assumes linear behavior of the acoustic cavity. As such, the inherent dynamic characteristics of the combustion chamber are independent of the excitation type and its spectral components. Therefore, the dynamic behavior of an acoustic environment is the same for different excitations.
all points of a same plane, perpendicular to the direction of the wave propagation, may not present significant differences. As such, with the test results, this behavior could be verified and the experimental data points could be decreased, thus reducing the data to be analyzed. RESULTS Resonant frequencies of the combustion chamber were identified by analyzing the registered FRF (from 0 to 5,000 Hz), which were measured along the cavity of the chamber. Once identified, these frequencies were compared with the respective values, calculated theoretically (Table 2). As for each configuration, the theoretical frequencies were known, an experimental procedure of frequencies separation was performed by observing its value proximity (close to those calculated) and the higher amplitude (also considering the transversal/axial position of the microphone). Then, for each configuration, the acquired FRF were analyzed and the average of the frequencies and magnitudes was evaluated, by using the transversal and axial measurements, in order to obtain the set of resonant frequencies of the referred cavity. Such a way, with the theoretical versus experimental comparison, one can have an idea of the inherent acoustic mode shapes in the cavity, associated with the resonance frequencies. Nevertheless, it is important to highlight that this frequency separation method can still be improved, once the simple theoretical versus experimental frequency comparison is not sufficiently accurate, considering that the mathematical model is a simple model of the acoustic cavity of the combustion chamber, with some approximations. As such, a manner of confirming the calculated mode shapes is performing acoustic modal analysis of the cavity to have all the acoustic modal parameters of the cavities. This technique will be applied in further studies. Figures 6, 7, 8 and 9 show the configurations during test for FRF measurements.
As described on Table 2, longitudinal, radial, axial, as well as coupled modes frequencies must be measured, to obtain a complete experimental data set, which contains all the acoustic FRF, to be compared with the referred theoretical frequencies. Then, it is important to measure the required acoustic traveling waves, by positioning the microphone in the correct direction, according to the transverse or axial measurement axe. As a pressure type microphone was used, it was important to place the sensor diaphragm perpendicularly to the direction of the propagating wave. It is expected that the propagating waves inside the combustion chamber have a plane wave behavior, as described by Gerges (1994). This behavior can be verified when acoustic FRF in
Figure 6: Configuration B1.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
273
Pirk, R. et al.
are compared and an estimate of the error is described. The average magnitudes are also described. The natural frequencies described on the referred tables were obtained by calculating averages of all measured values, as well as the identified resonances, visualized on FRF. As mentioned before, the value proximity criterion is an inaccurate procedure. This can be confirmed, mainly in the higher frequency bands, where the FRF present large quantity of peaks (high modal density) and the frequency separation becomes a difficult task. One still may consider that higher orders mathematical models are inaccurate, which present inherent acceptable errors, only for a few modes in the low frequency band. Observe the Tables 3, 4, 5 and 6 and verify that the error increases as a function of frequency. It is important to mention that the adopted measurement setup (number of points) for an acquisition up to 5,000 Hz introduces a bias error in the frequency domain of 6 Hz, approximately. This is another indication that a stochastic treatment is a method more appropriated to identify natural frequencies, since different measurement points and significant bias error may be considered.
Figure 7: Configuration C1.
DISCUSSION Although the natural frequency determination procedure, using a simple mathematical model and considering the fluid room environmental conditions of temperature and pressure, gives a reasonable indication of its dynamic characteristics, it can still be improved to yield more accurate results. These first studies were useful, mainly for establishing an optimized measurement procedure, since the propagating plane wave behavior can be assumed for such experiment. As such, for other configurations, some transversal measurement points can be suppressed.
Figure 8: Configuration D1.
Figure 9: Configuration B2.
As the mathematical model assumes an acoustically closed environment, the influence of the nozzle was also verified. Tables 3, 4, 5 and 6 describe the identified experimental and calculated natural acoustic frequencies. These data 274
Note on Table 2 that the adopted mathematical model (Equation 1) calculated the same values of radial, tangential and coupled natural frequencies for all the configurations of the combustion chamber. This is due to the fact that these calculations take into account parameters as radial and transversal eigenvalues (Îťm,n) and radius of the combustion chamber (Rc), which have the same values for the referred configurations. Then, it means that there are no differences in the input data of the Equation 1. Therefore, the calculated axial or longitudinal natural frequencies for the configurations B1, C1 e D1 present different results, since these calculations are done by considering the mode number in the longitudinal direction (k), as well as the effective length of the chamber (Lc), which is function of the
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
Liquid rocket combustion chamber acoustic characterization
Table 3: Experimental results and theoretical versus experimental comparison (B1)
Acoustic mode 1 longitudinal 2nd longitudinal 3rd longitudinal 1st tangential 2nd tangential 1st radial 2nd radial 1st radial/1st tangential 1st radial/2nd tangential 2nd radial/1st tangential st
Experimental natural Theoretical natural frequency (Hz) frequency (Hz) 719.0 717.812 1272.3 1435.625 2380.6 2153.437 1137.5 1105.493 1793.2 1833.803 2583.6 2300.63 4351.6 4212.307 3237.2 3201.079 4456.7 4026.477 4744.3 5125.366
Error (%)
Mean value (dB)
0.1 12.8 9.5 2.8 2.2 11.0 3.2 1.1 9.6 8.0
110.0 95.0 105.0 86.0 85.0 107.0 90.0 98.0 83.0 93.0
Error (%)
Mean value (dB)
0.01 9.00 8.60 2.90 2.20 9.60 5.30 2.00 7.10 13.50
106.40 92.34 105.68 88.30 92.73 101.59 98.50 101.98 96.43 97.87
Error (%)
Mean value (dB)
3.9 5.2 12.8 5.3 18.6 6.5 2.7 3.1 1.4 8.7
110.8 100.0 90.0 100.9 102.2 100.7 95.6 100.2 91.6 94.9
Error (%)
Mean value (dB)
4.6 2.9 11.7 ----21.7 5.2 4.5 4.1 0.7 6.4
107.64 102.35 92.74 ----103.54 103.82 98.86 99.96 95.78 96.97
Table 4: Experimental results and theoretical versus experimental comparison (B2)
Acoustic mode 1st longitudinal 2nd longitudinal 3rd longitudinal 1st tangential 2nd tangential 1st radial 2nd radial 1st radial/1st tangential 1st radial/2nd tangential 2nd radial/1st tangential
Experimental natural Theoretical natural frequency (Hz) frequency (Hz) 718.231 717.8123 1311.623 1435.625 2357.355 2153.437 1138.944 1105.493 1875.003 1833.803 2545.043 2300.63 4446.734 4212.307 3267.713 3201.079 4333.683 4026.477 4515.181 5125.366
Table 5: Experimental results and theoretical versus experimental comparison (C1)
Acoustic mode 1 longitudinal 2nd longitudinal 3rd longitudinal 1st tangential 2nd tangential 1st radial 2nd radial 1st radial/1st tangential 1st radial/2nd tangential 2nd radial/1st tangential st
Experimental natural Theoretical natural frequency (Hz) frequency (Hz) 568.5 546.3603 1039.3 1092.721 1452.2 1639.081 1050.0 1105.493 2253.8 1833.803 2461.4 2300.63 4331.1 4212.307 2964.6 3201.079 4086.3 4026.477 4715.2 5125.366
Table 6: Experimental results and theoretical versus experimental comparison (D1)
Acoustic mode 1st longitudinal 2nd longitudinal 3rd longitudinal 1st tangential 2nd tangential 1st radial 2nd radial 1st radial/1st tangential 1st radial/2nd tangential 2nd radial/1st tangential
Experimental natural Theoretical natural frequency (Hz) frequency (Hz) 494.27 471.3108 915.72 942.6216 1265.07 1413.932 ----1105.493 2341.19 1833.803 2426.16 2300.63 4409.29 4212.307 3075.17 3201.079 4058.48 4026.477 4816.07 5125.366
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
275
Pirk, R. et al.
studied geometries. It is important to consider that configurations B1 and B2 present the same natural frequencies, since the considered acoustic effective length is the same for both configurations. Note in Fig. 1 and Fig. 2 that these configurations are different only by the nozzle segmentation in B2, which may have investigated its influence on the dynamic behavior of the acoustic cavity. Table 3, regarding B1, shows that the comparison of the natural frequencies does not present significant errors for the longitudinal modes. It can be noted that the approximation of the first longitudinal frequency, calculated by the theoretical model, presents good correlation with the measured value (0.1% error). The second and third longitudinal eigenvalues present 12.8 and 9.5%, respectively. Figure 10 shows a FRF, measured in axial direction, with the microphone positioned at 100 mm. Observe the curve below and verify that the first frequency of 719 Hz and the third of 2,380 Hz, are easily identified, since they present magnitudes higher than 100 dB, while the second frequency of 1,272 Hz presents a 95 dB magnitude, approximately. Comparison of the tangential frequencies, despite the low acoustic pressure levels obtained on the calculations of the averaged magnitude (around 85 dB), also presented excellent agreement between the calculated values and those measured. Concerning the two radial frequencies, the percent errors were 11 and 3%, respectively. These are significant errors, since the mathematical approximations usually present higher errors for the higher orders’ modes, what is not the case. Still on Table 3, the coupled modes present errors of 1.1%, 9.6% and 8%, respectively.
On Table 4, corresponding to configuration B2, it is verified that the experimental values also present good correlation with the values obtained by mathematical approximation. The calculated error for the first longitudinal natural frequency is very small (<0.05%). The other longitudinal frequencies presented 9.0 and 8.6% error, respectively. Tangential comparisons also presented excellent correlation, with 2.9 and 2.2 %. It can also be seen that first, second and third coupled modes presented 2.0%, 7.1% and 13.5% errors, respectively. For the radial frequencies, the calculated differences were 9.6 and 5.3%. Figure 11 shows the measured FRF, with microphone positioned in transversal direction, at 10 mm from the structure wall, 0º azimuth and 100 mm distance from the sound source. For the configuration C1, the comparisons are described on Table 5. Considering the longitudinal frequencies, it is verified that the results present a good correlation for the first and second resonances, since the calculated errors are 3.9 and 5.2%, respectively, with the measured magnitudes of 110 and 100 dB. The resonance of the inner environment due to the third longitudinal acoustic mode presented 12.8% error, with magnitude of 90 dB. Tangential frequencies also present an excellent agreement. Note the errors of 2.8 and 2.2%, respectively, for the two tangential natural frequencies of the configuration C1. Concerning the radial resonances, the errors were 11%, at the frequency of 2,583 Hz (first radial mode) and 3%, for the frequency of 4,351 Hz (second radial mode). The coupled frequencies presented 10.4%, 9.6% and 8%, respectively. Table 6 presents the comparisons concerning the configuration D1. Observe this table and note that, as
Figure 10: Axial measurement – Configuration CFGB1. 276
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
Liquid rocket combustion chamber acoustic characterization
Figure 11: Transversal measurement â&#x20AC;&#x201C; Configuration CFGB2
the other configurations, the resonances related to the longitudinal modes are easily identified. The theoretical versus experimental comparison presents 4.6% error for the first longitudinal mode and 2.9 and 11.7% for the second and third, respectively. Considering the averaged magnitudes, the measured longitudinal acoustic frequencies have 107, 102 and 92 dB. Table 6 depicts the results regarding the radial measurements. Considering the tangential modes, it is verified that the first acoustic frequency (1,105 Hz), calculated by Eq. 1, was not excited during the experimental tests. The second measured tangential frequency, when compared with the corresponding theoretical frequency, presented 21% error and its average magnitude was 103 dB. The radial modes presented 5.2 and 4.5% error, with average magnitudes of 103 and 98 dB, respectively. Finally, the coupled modes comparisons showed 4.1%, 0.7% and 6.4% errors. Observe the FRF (Fig. 9 and Fig. 10) and note that these curves present noise below 500 Hz. This is due the low signal/noise ratio, since the generated acoustic noise (white noise) does not excite spectral components below the referred frequency, due to the manufacture characteristics of the acoustic source. As such, the measurement noises, inherent to the measurement chain, are also captured in low frequency. Comparing Tables 3 and 4, we can verify the nozzle influence on the acoustic behavior of the combustion chamber cavity. Note the configurations B1 (without divergent) and B2 (long divergent) and verify that the obtained values of the first acoustic natural frequency do not change significantly. The second longitudinal frequency is approximately 40 Hz higher for the configuration
B2, with long divergent. The third longitudinal mode of the configuration B2 is 25 Hz lower than the respective frequency of the configuration B1, without divergent. Other frequencies as tangential, radial and coupled can also be compared on these tables. Therefore, significant changes in the inner cavity acoustic behavior are not verified, when the nozzle length is increased. CONCLUSIONS AND RECOMMENDATIONS The procedures for evaluation of the acoustic resonances present a reasonable indication to identify these frequencies and their associated modes. Therefore, it may be considered that the mathematical model described in Eq. 1, with the inherent approximations and assumptions can be inaccurate, mainly for the higher orders modes. As such, it is important that theoretical calculations consider geometry variations for the determination of the acoustic natural frequencies of combustion chambers. In view of better establishing the acoustic responses of the acoustic cavities, it is recommended that virtual prototypes be built up, using deterministic techniques as Finite Element Method (FEM) and Boundary Element Method (BEM), and acoustic analysis may be done to calculate the acoustic resonance frequency as well as to obtain their associated mode shapes, with more accurate models. Nevertheless, care must be taken with the limitations of these methods, since higher frequency analysis may consider a rule based on element discretization, which may be verified. Such rule states that an accurate model may present six to ten elements by wavelength, due to the relation between the wavelength and analysis frequency (Desmet and Vandepite, 2001).
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
277
Pirk, R. et al.
Concerning the FRF measurements, the adopted procedure can be optimized for other configurations. As mentioned in this paper, transversal measures can be performed only for a few azimuth points as well as for only one radial point, because traveling acoustic waves assume plane wave behavior in the combustion chamber. The identification and choice of the natural frequencies, for consequent association to the acoustic modes, despite presenting a reasonable indication by theoretical versus experimental comparisons, does not assure that these frequencies are the correct natural frequencies. Mainly for the tangential, radial and coupled modes, this identification and choice is a hard task, since it is done by visual analysis of the measured FRF as well as the average values of the magnitudes and frequencies. It is still important to consider the modal density of the FRF, which increases significantly when frequency increases, becoming the choice of the resonance peaks a difficult job. The assessment of the influence of the nozzle length on the acoustic behavior of the acoustic cavity shows that such geometry alteration does not influence significantly the natural frequencies of the configurations B1 and B2. A procedure indicated for experimental identification of the eigen-values and eigen-vectors of combustion chamber is the execution of the experimental modal analysis of the referred cavities. As such, transfer functions between input/output acoustic signals, measured by two microphones, can be obtained for the determination of the acoustic modal parameters (natural frequencies and mode shapes). Experimental acoustic modal analysis and theoretical acoustic modal analysis, calculated by deterministic tools, can be compared with the theoretical model validation and determination of the dynamic parameters of the combustion chamber cavity. As described before, some modes in transversal (tangential and radial) directions were not acoustically excited or did not have enough energy generated to excite them satisfactorily. Such modes may be verified by exciting the cavity using pure tone signals. As such, all the energy of the signal is designated to excite the cavity in the required frequency. The continuity of this combustion chamber instability survey may preview another research phase, in which acoustic noise passive insulation techniques should be applied. Such a way, baffles, filters and Helmholtz resonators may designed and with these devices attenuating or eliminating the sound pressure levels inside
278
the chamber cavity, consequently eliminating possible combustion instabilities due to the coupling between acoustic modes and the combustion process. Once again, it is suggested that virtual prototypes may be used for design simulations and sensitivity analysis, with the different applicable apparatus. REFERENCES Burnley, V. S., Culick, F. E. C., 1997, “The influence of Combustion Noise on Acoustic Instabilities”, Air Force Research Laboratory, OMB Nº 0704-0188. Culick, F. E. C., 2000, “Combustion Instabilities: Mating Dance of Chemical, Combustion and Combustor Dynamics, American Institute of Aeronautics & Astronautics, A0036437 in 36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Alabama, USA. Desmet, W., Vandepite, D., 2000, “Finite Element Method in Acoustic”, Grasmech Course, Katholieke Universiteit Leuven. Huzel, D. K., Huang, D.H., 1992, “Modern Engineering for design of liquid - propellant rocket engines”, American Institute of Aeronautics and Astronautics. Laudien, E., Pongratz, R., Piero, R., Preclik, D., 1995, “Experimental Procedures Aiding the Design of Acoustic Cavities”, in: V. Yang, W. E. Anderson (Eds.), Liquid Rocket Engine Combustion Instability, Vol. 169, chap. 14, Progress in Astronautics and Aeronautics, AIAA, Washington, DC, pp. 377-399. NASA, 1974, “Rocket Engine Combustion Stabilization Devices”, NASA Space Vehicle Design Criteria (Chemical Propulsion), NASA SP8113. Gerges, S. N. Y., 2000, “Ruído, Teoria e Fundamentos”, NR Editora, ISBN 85-87550-02-0. Santana Jr., A., et al., 2009, “Acoustic Cavities Design Procedures” Engenharia Térmica, Vol. 6, pp. 27-33. Sutton, G. P., Biblarz, O., 2001, “Rocket Propulsion Elements”, New York, John Wiley & Sons. Yang, V., Wicker, J. M., Yoon, M. W., 1994, “Acoustic Waves in Combustion Chambers”, Liquid Rocket Engine Combustion Instability, Progress in Astronautics and Aeronautics, Chapter 13, Vol. 169.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 269-278, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02038210
Hossein Bonyan Khamseh
Shahid Beheshti University Tehran - Iran h.bonyan@gmail.com
M. Navabi*
Shahid Beheshti University Tehran - Iran navabi.edu@gmail.com *author for correspondence
Development of access-based metrics for site location of ground segment in LEO missions Abstract: The classical metrics of ground segment site location do not take account of the pattern of ground segment access to the satellite. In this paper, based on the pattern of access between the ground segment and the satellite, two metrics for site location of ground segments in Low Earth Orbits (LEO) missions were developed. The two developed access-based metrics are total accessibility duration and longest accessibility gap in a given period of time. It is shown that repeatability cycle is the minimum necessary time interval to study the steady behavior of the two proposed metrics. System and subsystem characteristics of the satellite represented by each of the metrics are discussed. Incorporation of the two proposed metrics, along with the classical ones, in the ground segment site location process results in financial saving in satellite development phase and reduces the minimum required level of in-orbit autonomy of the satellite. To show the effectiveness of the proposed metrics, simulation results are included for illustration. Key words: Site location of ground segment, LEO satellite, Total accessibility duration, Longest accessibility gap, In-orbit autonomy.
INTRODUCTION In recent years, limited financial resources of space activities and the new paradigm of more responsive satellite systems have brought significant attraction toward management of various aspects of ground segment (Peter, 2006; Chester, 2009; Sandau, 2010). One of the most important aspects regarding effectiveness of the ground segment is its site location (Elbert, 2001). Classical metrics of ground segment site location in satellite missions are mainly derived from terrestrial or geostationary communication experiences. These metrics are based on topographical, atmospheric and electromagnetic aspects of ground segment location and its surroundings. Various atmospheric-attenuation phenomena were discussed by Roddy (2006) which may impose constraints on ground segment site location process. Elbert (2001) proposed proximity to the required resources, compatibility with international/national frequency allocations, operational costs and environmental conditions as the metrics for ground segment site location. As stated by Elbert (2001), International Telecommunication Union (ITU), founded in 1865, is the oldest and most prominent of international organizations in the field of telecommunication regulations. The same reference stated that clearance and interference in communication frequencies imposes constraints on ground segment site location. Soil condition for building establishment and horizon profile (i.e. neighboring Received: 27/07/10 Accepted: 03/09/10
obstacle height) were added by Ley, Wittmann and Hallmann (2009). Griffin and French (2004) stated that at high frequencies, e.g. X-Band and Ka/Ku, annual rain profile must be considered in ground segment site location, especially if communication with ground segment must be guaranteed. Continuous access between the transmitting source and receiver segment is an inherent characteristic of most terrestrial and high-altitude (35,780 km) geostationary applications (Griffin and French, 2004). Due to high cost of geostationary satellite missions, 500-1,500 km Low Earth Orbits (LEO) mission have begun to gain considerable attention during the last two decades. Regarding nearfuture activities, Petersen (1994), in his book “The road to 2015” says: “most of the new growth in commercial space appears to be in LEO missions”. In this paper, the pattern of ground segment access to LEO satellites is studied. For LEO satellite missions, pattern of ground segment access to the satellite is made up by short and infrequent access events (Wertz and Larson, 1999). The drawback of classical metrics of ground segment site location is that they do not take account of the mentioned pattern of ground segment access to the satellite in LEO missions. The contribution of this paper is to develop two accessbased metrics so that ground segment site location process takes account of the peculiar pattern of a ground segment access to LEO satellites. The incorporation of the two proposed metrics in ground segment site location process reduces the satellite development cost and lessens minimum required level of in-orbit autonomous operation of LEO satellites.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 279-286, Sep-Dec., 2010
279
Khamseh, H.B.; Navabi, M.
This paper is organized as follows: in the next section, the minimum time interval to achieve time-independent access-based metrics is studied. Then, numerical method of access pattern determination is presented. Afterward, the two access-based metrics are introduced. System/ subsystems characteristics of the satellite represented by each metric are discussed. Finally, based on simulation results of our case study, access pattern of two ground segments to a given LEO satellite are presented and the two access-based metrics are derived and compared.
Pattern of ground segment access to a LEO satellite is defined as the chronological order of accessibility events and the consecutive accessibility gaps. Pattern of ground segment access to a LEO satellite varies as the simulation time is increased. This imposes an immediate drawback since access-based metrics will be time-dependent. In order to obtain the access-based metrics in a time-independent manner, minimum time interval after which access patterns are identicallyrepetitive must be identified. This time interval is called repeatability cycle and is determined by the following method. If a satellite completes R full revolutions after D days, the longitude difference between each two consecutive ground tracks at the equator will be: D R
(1)
It is noted that, in Eq. 1, D and R are dimensionless values of number of days and number of full revolutions in a given repeatability cycle, respectively. Thus, Î&#x201D;L in Eq. 1 is in radians. On the other hand Î&#x201D;L is the accumulated variation in Right Ascension of Ascending Node (RAAN) in a period. Thus: ) T L " (\ e < n
(2) rad
In which \ e " 7.2925 10 sec is Earthâ&#x20AC;&#x2122;s rotation rate,< is variation rate of RAAN due to J2 effect and Tn is the orbital nodal (draconitic) period, in seconds; < is given by Capderou (2005): 5
2
" <
Š Re š 3 nJ º cos i 2 2 0 2ª 2(1 e )  a 
Where: 280
J2: 0.00108263; Re: Earth equatorial radius; a : orbit semi-major axis; i : inclination. Also, the nodal orbital period is determined by Capderou (2005):
ACCESS PATTERN â&#x20AC;&#x201C; MINIMUM TIME INTERVAL TO STUDY?
)L " 2U *
e: eccentricity;
(3)
Tn "
2U n0 n \
(4)
Âľ Where n0 " 3 is the keplerian mean motion, Âľ is Earth a gravitational parameter, Î&#x201D;n is correction term applied to keplerian mean motion due to variation of mean anomaly and \ is the variation of argument of perigee due to J2 effect. From Capderou (2005):
)n"
2
3 3
4(1 e2 ) 2
ŠR š n0 J 2 ª e º (3cos 2 i 1)  a 
(5)
2
\ "
Š Re š 3 2 nJ º (5 cos i 1) 2 2 0 2ª 4(1 e )  a 
(6)
Substituting Eq. 4 into Eq. 2, and equating right-hand sides of Eq. 1 and Eq. 2, the number of revolutions in the repeatability cycle is obtained: R"
( n0 ) n \ ) D \e <
(7)
In Eq. 7, only integer values of R give admissible repeatability scenarios. After R revolutions in an integer number of days namely D, the satellite ground tracks will be identical to those obtained in the first repeatability cycle. Also, assuming inertial Cartesian geocentric reference frame, the position of the ground segment varies periodically, with a period of an integer day. Thus, after D days, the relative geometry between the ground segment and the satellite will be identical, and time-independent access-based metrics are obtained. As it can be seen from Eq. 3, < is a function of orbit eccentricity, semi-major axis and inclination. Yet, variation of RAAN in sunsynchronous orbits, denoted by , is constant and given by Capderou (2005): < SS
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 279-286, Sep-Dec., 2010
Development of access-based metrics for site location of ground segment in LEO missions
" < SS
2U rad " 1.9965 10 7 sec 365.26 24 3600
rS: acceleration vector of the satellite;
By substituting < = < SS in Eq. 7, for the altitude range of 600-1,000 km, the repeatability cycle of sunsynchronous orbits is obtained and shown in Fig. 1, in which the number of revolutions is depicted beside the corresponding point in each scenario.
I rS: position vector of the satellite;
rs: magnitude of position vector of the satellite; Âľ: gravitational parameter of earth; ap: acceleration due to perturbation. In general:
Repeatability cycle (days)
a p " aNSE aNUMD aTBG aD aSRP
(9)
Where: aNSE
: non-spherical Earth effects including aJ (acceleration due to J2) and higher terms; 2
aNUMD: acceleration force due to non-uniform mass
distribution of earth; Orbit altitude (km)
aTBG: acceleration force due to third body gravity;
Figure 1: Repeatability cycle of sunsynchronous orbits as a function of altitude.
As an example, for a repeatability cycle of 10 days (vertical axis), from Fig. 1 it can be seen that there are 5 distinct sunsynchronous scenarios with 147, 143, 141, 139 and 137 revolutions. These scenarios correspond to orbital altitude of 655, 786, 854, 923 and 994 km (horizontal axis), respectively. The ground tracks repeat after each repeatability cycle. Identical ground tracks, in turn, result in time-independent accessbased metrics. Thus, repeatability cycle is taken as the minimum required time interval to study access-based metrics.
rS
Where:
a p
For LEO orbits higher than 500 km, Fortescue, Stark and Swinerd (2003) stated that acceleration due to J2
effect, i.e. aJ , exceeds all other perturbation forces by 2-3 orders of magnitude. Thus, perturbation forces other 2
than the dominant aJ are not taken into account in this 2
paper. To derive an expression for aJ , the following form of Earth gravity potential is adopted from Schaub and Junkins (2003): 2
Where:
To obtain the pattern of ground segment access to a given satellite, the position of the satellite in its orbit must be determined. In accordance with Cowellâ&#x20AC;&#x2122;s propagation formula, the translational equation of motion of the satellite in the geocentric equatorial frame is given by Schaub and Junkins (2003):
rS3
aSRP: acceleration force due to solar radiation pressure.
V ( r ,O) "
NUMERICAL METHOD OF ACCESS PATTERN DETERMINATION
rS " Âľ
aD: acceleration force due to atmospheric drag;
(8)
k Ÿ Š Re š ¾  h 1 8 k " 2 ª º J k Pk (sin O) ½ r  ½  r  Ž ž
(10)
Ď&#x2020; : latitude; Jk: Earth zonal harmonics; Pk: legendre polynomials. Legendre polynomials are given by Rodriguesâ&#x20AC;&#x2122; formula from Battin (1999): Pk (/ ) "
1 dk ( /2 1) k 2k k ! d / k
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 279-286, Sep-Dec., 2010
(11)
281
Khamseh, H.B.; Navabi, M.
For J2, the gravitational perturbation function RJ ( rI ) is obtained:
Where:
2
2
I J ƍŠ R š RJ ( r ) " 2 ª e º (3sin 2 O 1) 2 2 r r 
(12)
I Taking the gradient of RJ 2 ( r ) , the perturbing acceleration aJ due to J is given in terms of inertial Cartesian geocentric 2 2
reference frame as:
Š ª ª ª 2ª Š š R Š š ¨ ¾ I I 3 e ª aJ " RJ ( r ) " J 2 2 2 2 ª r 2 º ª r º ª ª ª ª ª 
š 2 Š Š Zš š X º ª 1 5ª º º ª  r  º r º º 2 º Š Š Zš š Y º ª 1 5ª º º ª  r  º r º º 2 º Š š Š Zš Z º ª 3 5ª º º ª  r  º r º 
rGS =R e +Alt GS : ground segment distance from earth center; Alt GS: ground segment altitude relative to mean sea level;
δ: latitude of ground segment; Î&#x203A;: longitude of ground segment. At any given time, position vector of the satellite relative to the ground segment is: I I I rS_rel_GS (t ) " rS (t ) rGS (t )
(17)
At any given time, the satellite is accessible from the ground segment if:
(13)
I I Šr (t ) Â&#x161; rGS (t ) š J (t ) " 90 cos 1 ÂŞ S_rel_GS Âş v J min ÂŤ rS_rel GS (t ) rGS Âť
(18)
To solve Eq. 8, an adaptive, single-step fourth- and fifthorder Runge-Kutta method with Dormand-Prince pair was employed. Time span of integration is [0 tf], where the final time t f " R Tn .
Where J min accounts for minimum-elevation constraint, typically 5 degrees for commercial communication hardware recommended by Roddy (2006).
With satellite position vector available at any given time, ground segment position vector must be determined. Relative Ito an inertial reference frame, derivative of a I I movingdA vector " \ w A with constant magnitude is given by dt Schaub and Junkins (2003):
METRIC DEVELOPMENT AND CASE STUDY
I dA I I "\ w A dt
(14)
I
Where \ is the angular velocity vector along the instantaneous rotation axis. Thus, position vector of the ground segment is given by: I I I I rGS (ti 1 ) " rGS (ti ) (\ e w rGS (ti )) ) t
(15) CASE STUDY â&#x20AC;&#x201C; SATELLITE ORBIT
Where: I \e "
2U 2U Ë&#x2020; Ë&#x2020; K= K 1 sidereal day 86160 sec
2U 2U Ë&#x2020; Where KË&#x2020; is the unit vector of equatorial geocentric frame K= 1 sidereal day 86160 sec in Z direction. In most applications, it is desirable to give I initial position of the ground segment (rGS t0 ) in terms
of longitude, latitude and relative altitude on the terrestrial surface. Position vector of the ground segment is given by:
I Ë&#x2020; Ë&#x2020; Ë&#x2020; I sin 1I+sin I K) rGS (t0 ) " rGS (cos I cos1I+cos 282
In this section, two metrics are developed to take spaceborne characteristics of LEO satellites into account. Peculiar characteristics of LEO satellites come from the fact that these satellites pass over large areas at high speed, e.g. 7.5 km/s. Consequently, short and infrequent events of ground segment access to the satellite are inherent characteristics of LEO missions. Two access-based metrics, namely total accessibility duration and longest accessibility gap are proposed to capture these peculiar access pattern considerations in the ground segment site location process. To quantitatively study the proposed metrics, a case study will be defined in the next section.
(16)
A hypothetical remote sensing satellite, called RS-Sat hereafter in this paper, in a 147-revolution 10-day orbit is adopted, with a local time of ascending node of 10:00 am. From Fig. 1, the altitude of such an orbit is 655 km which, for a sunsynchronous orbit, indicates orbital inclination of 98.01 degrees. Such orbital altitude has been selected to reflect the popularity of the 600-1,000 km range for spaceborne remote sensing applications given by Stephens (2002) and Sandau (2010). Similarly, local time of ascending node of 10:00 am has been purposefully adopted to reflect the popularity of such architecture for
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 279-286, Sep-Dec., 2010
Development of access-based metrics for site location of ground segment in LEO missions
imagery purposes suggested by Stephens (2002). The simulation was carried out for a 10-day period from Jan 1, 2010 00:00:00 to Jan 10, 2010 24:00:00. Just as in the case of preceding parameters, a 10-day period reflects the upper-bound of revisit-time requirements for various remote sensing applications as stated by Stephens (2002).
metrics discussed in this paper, exclusively due to site location of the ground segments. As suggested by Roddy (2006), a 5-degree minimum-elevation constraint has been applied in the simulation to take account of the elevation constraint in commercial communications systems. METRIC OF TOTAL ACCESSIBILITY DURATION
CASE STUDY – GROUND SEGMENT SCENARIOS Throughout the paper, two distinct scenarios for the ground segment in charge of RS-Sat will be discussed. The first scenario employs a ground segment at 15°E 45°N, i.e. somewhere in Europe. The second scenario employs a ground segment located at 120°W 60°N, i.e. somewhere in northern Canada. To avoid prohibitivelylong nomenclature for the two ground segments, they are hereafter called EU-GS and CA-GS, respectively. The location of the two ground segments have been chosen in a manner to best illustrate the variation of access-based
Accessibility to a given satellite is the primary reason to establish the corresponding ground segment. LEO satellites, due to their inherent orbital characteristics, are accessible from a ground segment only in limited portions of their orbits. As an example, simulation results of EU-GS and CA-GS access to RS-Sat in the first day of simulation are given in Tables 1 and 2, respectively. As it can be seen from Tables 1 and 2, total duration of EU-GS and CA-GS access to RS-Sat in the first day of simulation is 2,753 seconds (approximately 46 minutes) and 4,053 (approximately 68 minutes), respectively. Even
Table 1: EU-GS access to RS-Sat in the first day of simulation
Access # number
Start day
Start time (UTCG)
1 2 3 4 5 6
January 1, 2010 January 1, 2010 January 1, 2010 January 1, 2010 January 1, 2010 January 1, 2010
6:54:16 8:28:49 10:09:23 20:20:13 21:56:32 23:36:37
Stop day
Stop time (UTCG)
January 1, 2010 7:01:56 January 1, 2010 8:39:54 January 1, 2010 10:14:31 January 1, 2010 20:29:25 January 1, 2010 22:07:16 January 1, 2010 23:38:41 Proposed metrics
Total accessibility duration (seconds) Longest accessibility gap (seconds)
Accessibility duration (seconds) 460 665 308 552 644 124
Consecutive accessibility gap (seconds) 5,213 5,369 36,342 5,227 5,361 Not applicable
2,753 36,342
Table 2: CA-GS access to RS-Sat in the first day of simulation
Access # number
Start day
Start time (UTCG)
1 2 3 4 5 6 7 8
January 1, 2010 January 1, 2010 January 1, 2010 January 1, 2010 January 1, 2010 January 1, 2010 January 1, 2010 January 1, 2010
5:33:57 7:10:43 8:48:01 10:25:51 13:35:03 15:07:52 16:43:03 18:21:01
Total accessibility duration (seconds) Longest accessibility gap (seconds)
Stop day
Stop time (UTCG)
January 1, 2010 5:43:58 January 1, 2010 7:21:46 January 1, 2010 8:56:51 January 1, 2010 10:29:31 January 1, 2010 13:39:05 January 1, 2010 15:16:52 January 1, 2010 16:54:09 January 1, 2010 18:30:52 Proposed metrics
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 279-286, Sep-Dec., 2010
Accessibility duration (seconds) 601 663 530 220 242 540 666 591
Consecutive accessibility gap (seconds) 5,205 5,175 5,340 11,132 5,327 5,171 5,212 N/A
4,053 11,132 283
Khamseh, H.B.; Navabi, M.
for medium data volume of 500 MB per day, these very short accessibility durations imply downlink data rate requirements as high as 126-186 KB/sec. At this point, it is worthwhile to note that in satellite communication subsystem, data rate is a key factor in the required bandwidth for data transfer purposes. According to Shannon–Hartley channel capacity theorem given in Ley, Wittmann and Hallmann (2009): B"
R © S¹ log 2 ª 1 º N» «
(19)
Where B is bandwidth in Hz, R is bit rate in bit per second, S and N are signal and noise power in Watts, respectively. However, Maini and Agrawal (2007) state that larger bandwidths are viable at higher frequencies. Compared to low-frequency devices, Pelton (2006) states that highfrequency communication hardware is more complex and Dowla (2004) states that it is more expensive. Thus, if data rates are bounded to some moderate values, less complicated and less expensive hardware can be employed for communications purposes, both onboard the satellite and in ground segment facility. This is a key reason why total accessibility duration is introduced and employed as an access-based metric for technical evaluation of site location of ground segments in LEO applications. Also, according to Eq. 19, another benefit provided by reduced data rate requirement is that required signal transmission power is reduced. Statistical analysis of several spacecraft with various mission types given by Brown (2002) indicated that communication subsystem is one of the main onboard power consumers of satellites. Therefore, if communications tasks are less power-hungry and distributed over longer total accessibility duration, peak power requirements of the satellite are likely to lessen. Thus, lighter and more compact onboard battery units may be employed. In satellite technology, lighter and more compact units with less peakpower requirement simply mean less expense. It is concluded that, from a management and systems engineering point of view, enhancement of the metric of total accessibility duration is translated into improvement of the cost metrics of satellite projects. METRIC OF LONGEST ACCESSIBILITY GAP The longest accessibility gap is the second access-based metric proposed for comprehensive evaluation of site location of ground segment in LEO applications. The longest accessibility gap is defined as the longest duration between two consecutive accessibility events, in a given period of time. In previous research (Elfving, Stagnaro, 284
Winton, 2003; Rui, Pingyuan and Xiaofei, 2005; Ley, Wittmann, Hallmann, 2009; Chester, 2009; Bonyan Khamseh, 2010; Bonyan Khamseh and Navabi, 2010), the longest accessibility gap is the metric for minimum required level of in-orbit autonomous operation of the satellites. Long accessibility gaps are inherent characteristics of LEO missions. As an example, based on simulation results given in Tables 1 and 2, the longest gap in EU-GS and CA-GS access to RS-Sat in the first day of simulation was shown to be 36,342 seconds (approximately 10 hours) and 11,132 seconds (approximately 3 hours). From an engineering point of view, long accessibility gap is translated to the requirement of high levels of in-orbit autonomy of RS-Sat. It is recalled that high level of in-orbit autonomy is met by employing sophisticated onboard software packages. These software packages must accommodate decision-making frameworks onboard RS-Sat to handle planned/unplanned events. Also, such complicated software packages are accommodated within heavier and bulkier processing units with more onboard power consumption. Furthermore, since these software packages vary considerably from a mission to another they are developed exclusively for each mission. Consecutively, for long accessibility gaps and the corresponding requirement of high level of in-orbit autonomy, provision of software packages and the hardware to accommodate them can be translated into man-intensive activities and increased development cost. COMPARISON OF RESULTS AND DISCUSSION In two previous subsections, results of EU-GS and CA-GS access to RS-Sat were obtained for the first day of simulation. In this section, simulations were carried out for the 10-day repeatability cycle, i.e. from Jan 1, 2010 00:00:00 to Jan 10, 2010 24:00:00. Based on the obtained results, the number of EU-GS and CA-GS access events to RS-Sat is 52 and 84 times, respectively. To avoid prohibitive-long tables, only the concluding results of simulations are given in Tables 3 and 4. Table 3:
EU-GS CA-GS Table 4:
EU-GS CA-GS
Metric of total duration of EU-GS and CA-GS access to RS-Sat for the 10-day repeatability cycle
Metric of total accessibility duration (seconds) 26,337 41,832
Ratio of total accessibility duration (CA-GS/EU-GS) 1.59
Metric of the longest gap in EU-GS and CA-GS access to RS-Sat for the 10-day repeatability cycle
Metric of longest accessibility gap (seconds) 42,001 35,815
Ratio of longest accessibility gap (CA-GS/EU-GS) 0.85
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 279-286, Sep-Dec., 2010
Development of access-based metrics for site location of ground segment in LEO missions
As it can be seen from Table 3, RS-Sat will be accessible from EU-GS for a total period of 26337 seconds, i.e. 7 hours and 19 minutes, in the 10-day period of simulation. On the other hand, total duration of CA-GS access to RSSat is 41,832 seconds, i.e. 11 hours and 37 minutes. In other words, total duration of RS-Sat access from CA-GS is 1.59 times longer than that of EU-GS.
FUTURE WORK In the present paper, we introduced and developed two supplementary access-based metrics for ground segment site location in LEO applications. In our future work we will address semi-analytical optimization of ground segment site location subjected to the prescribed accessbased metrics, for various popular LEO orbits.
Based on the results of simulations, the longest gap in EUGS and CA-GS access events to RS-Sat were obtained and presented in Table 4.
REFERENCES
According to Table 4, the longest accessibility gap in EU-GS access to RS-Sat is 42,001 seconds, i.e. 11 hours and 40 minutes. For CA-GS, the metric of the longest accessibility gap is 35,815 seconds, i.e. 9 hours and 57 minutes. Thus, the longest gap in CA-GS access to RS-Sat is 0.85 shorter than that of EU-GS.
Brown, C.D., 2002, “Elements of Spacecraft Design”, AIAA, Reston, VA, 610 p.
It is noted that the mentioned improvement in the proposed metrics could have been qualitatively deduced since the latitude of CA-GS, in comparison with latitude of EU-GS, is closer to RS-Sat inclination. As a final point, the mentioned improvements in the metrics of total accessibility duration and the longest accessibility gap are achieved only as a result of modified ground segment location and, therefore, are gained with essentially no extra cost. CONCLUSIONS Two access-based metrics were developed to capture the peculiar pattern of ground segment access to LEO satellites. The first metric, namely total accessibility duration, represents the required communication data rate, complexity of onboard communications subsystem, peak-power requirement and size of battery units. The second metric, namely the longest accessibility gap, indicates the minimum required level of in-orbit autonomous operation of the satellite. High level of inorbit autonomy is achievable by man-intensive activities and increased development cost. Thus, reduction in the longest accessibility gap is translated to relaxed schedule and cost saving. A case study including a LEO satellite and two ground segments scenarios was defined. According to our simulation results, the ground segment location with longer total accessibility duration and shorter accessibility gap was identified and quantitative improvement in the proposed metrics was presented. By using our proposed approach, along with the classical metrics, one may evaluate various possible ground segment locations and select the position of ground segment in a more effective manner.
Battin, R.H., 1999, “An Introduction to the Mathematics and Methods of Astrodynamics, Revised Edition”, AIAA, Reston, VA, 799 p.
Bonyan Khamseh, H., 2010, “Looking into Future Systems Engineering of Microsatellites”, In: Arif, T.T. (ed.), “Aerospace Technologies Advancements”, Intech, Croatia Bonyan Khamseh, H., Navabi, M., 2010, “Development of Metrics for Ground Segment Site Location Based on Satellite Accessibility Pattern from Ground Segment”, The International Council on Systems Engineering (INCOSE), APCOSE 2010 - Aerospace Systems Session, Accepted for publication. Capderou, M., 2005, “Satellites Orbits and Missions”, Springer-Verlag Berlin, 364 p. Chester, E., 2009, “Down to Earth systems engineering: The forgotten ground segment,” Acta Astronautica Vol. 65, No 1-2 pp. 206–213. Dowla, F., 2004, “Handbook of RF and Wireless Technologies”, Newnes, Burlington, MA, 720 p. Elbert, B., 2001, “The Satellite Communication; Ground Segment and Earth Station Handbook” Artech House, Norwood, MA. Elfving, A., Stagnaro, L. and Winton, A., 2003, “SMART-1: Key Technologies and Autonomy Implementations,” Acta Astronautica Vol. 52, No 2-6 pp. 475-486. Fortescue, P., Stark, J. and Swinerd, G., 2003, “Spacecraft Systems Engineering”, John Wiley & Sons, London, 704 p. Griffin, M.D., French, J.R., 2004, “Space Vehicle Design”, AIA, Reston, VA, 660 p. Ley, W., Wittmann, K. and Hallmann, W., 2009 “Handbook of Space Technology” Wiley and Sons, London, 908 p.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 279-286, Sep-Dec., 2010
285
Khamseh, H.B.; Navabi, M.
Maini, A.K., Agrawal, V., 2007, “Satellite Technology Principles and Applications”, Wiley and Sons, London, 576 p. Pelton, J.N., 2006, “The Basics of Satellite Communications”, 2nd Edition, International Engineering Consortium, Chicagi ,IL, 372 p. Peter, N., 2006, “The changing geopolitics of space activities”, Space Policy, Vol. 22, No 2, pp. 100-109.
Spacecraft” Advances in Engineering Software, Vol. 36, No 4, pp. 266-272. Sandau, R., 2010, “Status and Trends of Small Satellite Missions for Earth Observation” Acta Astronautica, Vol. 66, N. 1-2, pp. 1-12. Schaub, H., Junkins, J.L., 2003, “Analytical Mechanics of Space Systems”, AIAA, Reston, VA, 716 p.
Roddy, D., 2006, “Satellite Communications,” 4th, McGraw-Hill, 636 p,
Stephens, J.P., 2002, “A Novel International Partnership: The Disaster Monitoring Constellation of Small Low Cost Satellites” Proceeding of the United Nations Regional Workshop on the use of Space Technology for Disaster Management in Asia and the Pacific, Bangkok, Thailand.
Rui, X., Pingyuan, C. and Xiaofei, X., 2005, “Realization of Multi-agent Planning System for Autonomous
Wertz, J.R., Larson, W.J., 1999, “Space Mission Analysis and Design”, 3rd Ed. Microcosm, Bloomington, IN, 969 p.
Petersen, J.L., 1994, “The Road to 2015: Profiles of the Future”, Waite Group Press, Corte Madera, CA, pp. 189-207.
286
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 279-286, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02037810
Marcos Alécio dos Santos Romani*
Instituto de Aeronáutica e Espaço São José dos Campos − Brazil marcosaleciomasr@iae.cta.br
Carlos Henrique Netto Lahoz
Instituto de Aeronáutica e Espaço São José dos Campos − Brazil lahozchnl@iae.cta.br
Edgar Toshiro Yano
Instituto Tecnológico de Aeronáutica São José dos Campos − Brazil yano@comp.ita.br *author for correspondence
Identifying dependability requirements for space software systems Abstract: Computer systems are increasingly used in space, whether in launch vehicles, satellites, ground support and payload systems. Software applications used in these systems have become more complex, mainly due to the high number of features to be met, thus contributing to a greater probability of hazards related to software faults. Therefore, it is fundamental that the specification activity of requirements have a decisive role in the effort of obtaining systems with high quality and safety standards. In critical systems like the embedded software of the Brazilian Satellite Launcher, ambiguity, non-completeness, and lack of good requirements can cause serious accidents with economic, material and human losses. One way to assure quality with safety, reliability and other dependability attributes may be the use of safety analysis techniques during the initial phases of the project in order to identify the most adequate dependability requirements to minimize possible fault or failure occurrences during the subsequent phases. This paper presents a structured software dependability requirements analysis process that uses system software requirement specifications and traditional safety analysis techniques. The main goal of the process is to help to identify a set of essential software dependability requirements which can be added to the software requirement previously specified for the system. The final results are more complete, consistent, and reliable specifications. Keywords: dependability, software systems, requirements, space computer systems, criticality analysis.
INTRODUCTION The aerospace systems, which involve critical software, are increasingly complex due to the great number of requirements to be satisfied, which contributes to a higher probability of hazards and risks in a project. Taking the reports of international space accidents as experience, most problems caused by software were related to requirements and to the misunderstanding of what it should do (Leveson, 2004). Lutz (1992), having examined 387 software errors during integration and system tests of the Voyager and Galileo spacecraft, found that most errors were caused by discrepancies between the documented requirements and the implementation of the functioning system. Another identified problem was the misunderstanding about the interface of the software with the rest of the system. All the reports of accidents are related to improper specification practices. Regarding the Brazilian scenario, there is no official reporting of space accidents involving software problems. However, as the complexity of space computer systems increases with an equivalent raise of presence of functions Received: 17/06/10 Accepted: 01/10/10
implemented by software, there is an increased risk of accidents that can be caused by problems in computer system development. According to the recommendations of the Brazilian Satellite Launcher VLS-1 V03 accident investigation (DEPED, 2004), the technical commission proposes that the safety and quality issues should be improved as a necessary condition for the continuation of the project. Problems related to requirements such as ambiguity, non-completeness and even the lack of non-functional requirements should be minimized during the development of space computer systems. Thus, a set of dependability attributes could be used as a start point to define most adequate non-functional requirements to minimize the possible fault or failure occurrences in the engineering phase of the requirements. For this work, dependability is the property of a computer system to provide its services with confidence, and dependability attributes are the parameters by which the dependability of a system is evaluated (Barbacci et al., 1995). During the development of space computer systems, it is necessary to give relevant importance to security, safety, reliability, performance, quality and other dependability attributes. It is believed that the
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
287
Romani, M.A.S., Lahoz, C.H.N., Yano, E.T.
use of these attributes helps the identification of nonfunctional requirements to be incorporated into the system, improving its quality assurance and helping to minimize the risk levels both in hardware and software parts.
Software System Requirements (Requirement 1…n) DEPROCESS
This paper presents the dependability requirements analysis process for space software systems (called in this work as DEPROCESS) (Romani, 2007), which is based on a dependability attribute set and software safety analysis techniques, selected according to space standards such as the European Space Agency (ESA), the National Aeronautics and Space Administration (NASA), the UK Ministry of Defence (MOD), the Brazilian Space Agency (AEB), and other approaches of well known researchers in this area.
No
Assign a criticality rate for the requirement
Step 1
Meet the project criticality rate?
Step 2
Yes Apply the safety analysis techniques
Identify the dependability attributes
No
Step 3
Step 4
Requirement n? Yes Software Dependability Requirements
First, the DEPROCESS is presented, emphasizing the project phase where it is applied and its steps with the activities to be executed. Also in this section, safety analysis techniques and dependability attributes used in the process are mentioned. Then, a case study applied in embedded software used in a hypothetical space vehicle is presented. The idea is to show the application of the process in a functional requirement related to the vehicle inertial system, which has an important role in its mission. Finally, there are some considerations about the application of the process the software requirement that was analyzed, and conclusions with recommendations for improving the process are reported. THE DEPROCESS APPROACH The DEPROCESS purpose is to identify dependability requirements at the beginning of software projects using safety analysis techniques (PHA, SFTA and SFMECA) and a dependability attributes classification (such as availability, reliability, safety, and others) specifically applied to the space area. According to the lifecycle project phases proposed by ESA (2009a), the DEPROCESS is applied after the “system engineering related to software” and before the “software requirements” and “architecture engineering” processes. As the input, it uses the system requirements specified for software, and the output is a set of software dependability requirements which must be discussed during the Preliminary Design Review (PDR), for the analysis of their viability and effective incorporation to the software in the software requirement specification document. The DEPROCESS is composed by four steps, whose activities are applied to each requirement as described in Fig. 1. 288
Figure 1: Dependability requirements analysis process for space software systems (DEPROCESS).
A project criticality rate must be specified for the whole project as a way to define the extension of the application of the process. This extension can vary according to the strategic conditions of the project, like the available resources, the execution schedule, and other information that should be evaluated. This case study was based on NASA criticality scale (NASA, 2005a) (Table 1). Table 1:
Criticality scale and its effects
Criticality 1 2 3 4 5 6
Effect Minor or negligible Significant degradation Subsystem loss Significant loss or degradation of mission Major loss or degradation of mission Complete loss of mission
The sequence of the DEPROCESS four-step execution for each studied requirement is as follows: 1. assign a criticality rate for each requirement: in this step, a criticality rate is attributed for each software system requirement, based on the results of the interviews with the project specialists, in order to compare the requirement criticality rate to the project criticality rate. 2. select if the requirement will be analyzed: in this step, it is decided if the requirement will be submitted to the application of the safety analysis techniques. It is carried out by comparing the requirement criticality rate with the project criticality rate before the start of
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
Identifying dependability requirements for space software systems
the application of the process. In case the requirement is not selected (requirement criticality rate < project criticality rate), it does not need a dependability analysis. 3. apply the safety analysis techniques: in this step, the requirement is submitted to the safety analysis techniques PHA, SFTA and SFMECA, considering the software interface requirements, functional requirements, performance requirements, safety requirements, and so on. As a support to this activity, keywords (NASA, 2005b) can be useful to find potential fault events and failure modes due to not meeting the requirement. 4. identify the dependability attributes: in this step, the dependability attributes are identified. They are obtained through the comparison of the results of SFTA and SFMECA techniques as to the potential system fault events/failure modes. These dependability attributes will be recommended as dependability requirements to minimize the occurrence of fault/ failure related to each analyzed requirement. The dependability requirements shall be evaluated during the PDR and those considered more relevant must be incorporated into software requirement specification document. DEPENDABILITY EVALUATING TECHNIQUES FOR THE DEPROCESS In the third step of DEPROCESS, the safety analysis techniques are applied to identify the potential fault events and failure modes, which will be used to help the identification of the attributes and the dependability requirements. These techniques were selected according to two criteria: 1. comparative survey of the safety analysis techniques according to international and Brazilian standard institutions (NASA, 2005a; NBR 14857-2), shown in Table 2, and consideration of well proved techniques used in accident investigations and also their predictive analysis (DEPED, 2004; Leveson, 1995; Camargo Junior, Almeida Junior, Melnikof, 1997). Table 2:
2. selection of the specific techniques for software, like SFTA and SFMECA, considering also the studies previously carried out in the software for the Brazilian space vehicles (IAE, 1994; Reis Filho, 1995). Then, the following safety analysis techniques have been chosen: Preliminary Hazard Analysis (PHA), Software Fault Tree Analysis (SFTA) and Software Failure Modes, Effects and Criticality Analysis (SFMECA). According to NASA (2005a), PHA identifies and classifies regarding to severity that potential hazards associate to the mission due to not meeting the analyzed requirement. SFTA is a “top-down” analysis, working from hazard (top event) to possible causes (basic events), using AND and OR logic gates to connect the events; while SFMECA is a “bottomup” analysis searching the failure modes of each function, their effects while they propagate through the system, and the hazard criticality rate at the upper level. When used together, SFTA and SFMECA allow finding possible failure modes and areas of interest, which cannot be found by applying only one technique. This bi-directional analysis can provide limited assurances. Nevertheless, they are essential to assure that the software has been systematically examined, and that it satisfies the safety requirement for software. However, during the beginning stages of software development, like the requirement phase, only a preliminary safety analysis can be executed. DEPENDABILITY ATTRIBUTES IDENTIFICATION FOR THE DEPROCESS In this work, in order to achieve an appropriate set of dependability attributes for space computer systems as a whole, all attributes related to the components that interact with the hardware, the software, or that have some kind of dependency relation were considered. As proposed by Firesmith (2006) it was defined an attribute hierarchy composed by quality factors with common concepts and related processes. These dependability attributes were classified in three groups: defensibility, soundness and quality. These attributes are also results of researches (Romani, 2007; Lahoz, 2009), and based on Brazilian and
Safety analysis techniques used by aerospace and defense institutions
Techniques/ Institutions ESA NASA MOD AEB
FMEA/ FMECA X X X X
FTA
SFMECA
SFTA
HSIA
PHA
SCCFA
X X X
X X -
X X X X
X -
X X X
X -
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
289
Romani, M.A.S., Lahoz, C.H.N., Yano, E.T.
international standard institutions (NBR 14959; MOD, 2003; ESA, 2004; NASA, 2005a), as well as studies related to the dependability of some authors in the area (Kitchenham and Pfleeger, 1996; Camargo Junior, Almeida Junior and Melnikof, 1997; Firesmith, 2003 and 2006; Rus, Komi-Sirvio and Costa, 2003; Sommerville, 2004). The definitions of dependability attributes selected in this work are presented in section Glossary, at the end of this paper. Figure 2 shows the hierarchy created for the dependability attributes selected for space computer systems. Dependability
Soundness
Defensibility
Quality
Failure tolerance
Availability
Safety
Completeness
Efficiency
Security
Consistency
Maintainability Modularity
Accuracy
Simplicity
Correctness
Survivability
Recoverability
Portability
Robustness
Reliability
Testability
Self-description Stability Traceability
Figure 2: Attributes and Dependability hierarchy, based on Firesmith (2006).
In the “defensibility” branch, attributes are related to the way the system or its component can defend itself from accidents and attacks. In this group, failure tolerance, safety, security, simplicity, survivability and robustness attributes were included. In the “soundness” branch, attributes are related to the way the system or its component is suitable for use. In this group, availability, completeness, consistency, correctness, recoverability, reliability, self-description, stability and traceability attributes were included. In the “quality” branch, other attributes considered as quality factors relevant to the system or its component were classified. In this group, accuracy, efficiency, maintainability, modularity, portability and testability attributes were included. Following, based on its definitions, the relevance of each dependability attribute selected for space computer systems is discussed. Accuracy An inaccurate value resulting from the calculation of the logic of a spacecraft control may lead to insertion of 290
errors, accumulated during its flight, leading it to follow an unexpected trajectory, and the insertion of the satellite out of the desired orbit. An inaccurate value was one of the causes of the accident with Ariane 5 launcher in 1996 (Leveson, 2009). The precision of the navigation software in the flight control computer (on-board computer) depends on the precision of the inertial reference system measurements, but in the Ariane system test facility this precision could not be achieved by the electronics creating the test signals. The precision of the simulation may be further reduced because the base period of the inertial reference system is 1 versus 6 miliseconds in the simulation at the system test facility. Availability Availability may be calculated as a function of mean time to failure (MTTF) and mean time to repair (MTTR). One example cited by Fortescue, Stark and Swinerd (2003) is that for a “service” type spacecraft, such as the telephony/television communications satellite, down time or “unavailability” constitutes loss of revenue, and hence the cost benefits of design improvements to increase reliability can be optimized against their impact on revenue return. As another example, the lack of navigation data during a certain period of time of the vehicle control cycle can destabilize it, in such a way to cause the loss of the mission. Therefore, subsystems or components of the vehicle as the on-board computer, the inertial system and the data bus should be available to perform their functions in the moment they are requested. Completeness The report of the fault that caused the destruction of the Mars Polar Lander during entry and landing stage in 2000 says that the document of requirements at the system level did not specify the modes of failure related to possible transient effects to prematurely identify the touch of the ship on the ground. It is speculated that the designers of the software, or one of the auditors could have discovered the missing requirement if they were aware of its rationale (Leveson, 2004). This demonstrates that the non-consideration of the completeness attribute in the requirements may lead to occurrence of a system failure. Consistency During investigation of the American launcher Titan IV Centaur space accident, occurred in 1999, one of the causes found arose from the installation procedure of the inertial navigation system software, where the rolling rate
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
Identifying dependability requirements for space software systems
-0.1992476 was placed instead of -1.992476. The fault could have been identified during the pre-launch, but the consequences were not properly understood and the necessary corrections were not made because there was not a verification activity of critical data entry (Leveson, 2009). Correctness Leveson (2009) stated that in the Titan/Centaur accident, there was apparently no checking of the correctness of the software after the standard testing performed during development. For example, on the day of the launch, the attitude rates for the vehicle on the launch pad were not properly sensing the Earth’s rotation rate (the software was consistently reporting a zero roll rate) but no one had the responsibility to specifically monitor that rate data or to perform a check to see if the software attitude filters were operating correctly. In fact, there were no formal processes to check the validity of the filter constants or to monitor attitude rates once the flight tape was actually loaded into the Inertial Navigation Unit at the launch site. Potential hardware failures are usually checked up to launch time, but it may have been assumed that testing removed all software errors and no further checks were needed. Efficiency Control actions will, in general, lag in their effects on the process because of delays in signal propagation around the control loop: an actuator may not immediately respond to an external command signal (called dead time); the process may have delays in responding to manipulated variables (time constants) and the sensors may obtain values only at certain sampling intervals (feedback delays). Time lags restrict the speed and extent, with which the effects of disturbances, both within the process itself and externally derived, can be reduced. They also impose extra requirements on the controller, for example, the need to infer delays that are not directly observable (Leveson, 2009). Considering a real-time software system, efficiency is a relevant attribute in the care of their temporal constraints, and is related to performance, as the checks from time response, CPU and memory usage. For example, a function that performs the acquisition and processing of inertial data to the space vehicle control system must strictly comply with their execution time, to ensure proper steering of the spacecraft during its flight. Failure tolerance There are many ways in which data processing may fail – through software and hardware, and whenever
possible, spacecraft systems must be capable of tolerating failures (Pisacane, 2005). Failure tolerance is achieved primarily via hardware, but inappropriate software can compromise the system failure tolerance. During the realtime software project, it is necessary to define a strategy to meet the system required level of failure tolerance. If it is well designed, the software can detect and correct errors in an intelligent way. NASA has established levels of failure tolerance based on two levels of acceptable risk severity: catastrophic hazards must be able to tolerate two control failures and critical hazards must be able to tolerate a single control failure (NASA, 2000). Examples of software failure are the input and output errors of sensors and actuators. This failure could be tolerated by checking the data range and forcing the software to assume an acceptable value. An example of hardware failure in electronic components is the single-event upset (SEU), an annoying kind of radiation-induced failure. SEUs and their effects can be detected or corrected using some mitigation methods like error detection and correction (EDAC) codes, watchdog timers, fault rollback and watchdog processors. Maintainability It must be easy for space computer systems to maintain their subsystems, modules or components during any phase of the mission, whether on the ground or in space. The purpose of maintenance can be repair a discovered error, or allow a system upgrade to include new features of improvements. As an example, one can cite the maintenance remotely performed by NASA on Mars Exploration Rovers Spirit and Opportunity, launched toward Mars in 2003. According to Jet Propulsion Laboratory site information (JPL, 2007), the communications with the Earth is maintained through the Deep Space Network (DSN), an international network of antennas that provide communication links between the scientists and engineers on Earth and the Mars Exploration Rovers in space and on Mars. Through the DNS, it was possible to detect a problem in the first weeks of the mission that affected the Spirit rover software, causing it to remain in silence for some time, until the engineers could fix the error. The failure was related to flash memory and it was necessary a software update to fix it. It was also noted that if the Opportunity rover had landed first, it would have the same problem. Modularity The partitioning of critical systems in modules provides advantages, such as easy maintainability and traceability of the design to code, and allows the distributed software
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
291
Romani, M.A.S., Lahoz, C.H.N., Yano, E.T.
development. Modularity contributes to the verification and validation process and errors detection during the unit, component and integration tests as well as maintenance activities. The modularity facilitates the failure isolation, preventing their spread to other modules. The independent development assists implementation and integration. As an example, a space software configuration item (ICSW) can be divided into software components (CSW), which can be divided into units or modules (USW), which correspond to the tasks to be performed during pre-flight and flight phases, in the interaction with the communication interfaces, sensors and actuators, and the transmission of data to the telemetry system. Portability The space software projects can be long-term and, during its development, there may be situations that require technological changes to improve the application, and to overcome problems such as the exchange of equipment due to the high dependence on product suppliers. For example, it is desirable that the code can be compiled into an ANSI standard in the space software systems. This will enable the code to be run on different hardware platforms and in any compatible computer system, making only specific adaptations to be transferred from one environment to another. Reliability The reliability of Space computer systems reliability depends on other factors like correct selection of components, correct derating, correct definition of the environmental stresses, restriction of vibration and thermal transfer effects from other subsystems, representative testing, proper manufacturing and so on (Fortescue, Stark and Swinerd, 2003). Reliability is calculated using failure rates, and hence the accuracy of the calculations depends on the accuracy and realism of our knowledge of failure mechanisms and modes. For most established electronic parts, failure rates are well known, but the same cannot be said for mechanical, electromechanical, and electrochemical parts or man. The author states that, in modern applications in which computers and their embedded software are often integrated into the system, the reliability of the software must also be considered. One way to define acceptable reliability levels for space systems is by regulatory authorities and, in the case of components, by the manufacture industries. An example of a space system reliability case history was cited by Pisacane (2005). The Asteroid Rendezvous (NEAR) spacecraft had a twenty-seven month development time, a four-year Cruise to the asteroid, and spent one year
292
in orbit about the asteroid EROS. The spacecraft was successfully landed on EROS in February 2001 after one year in orbit. Reliability was maximized by limiting the number of movable and deployable mechanical and electromechanical systems. Recoverability In the autonomous embedded systems, i.e., that do not require human operators and interact with sensors and actuators, failures with severe consequences are clearly more damaging than those in which repair and recovery are simple (Sommerville, 2004). Therefore, the embedded computer systems must be able to recover themselves during the space mission situations where it is not possible to perform the maintenance. As an example, in the execution of a embedded software during the unmanned rocket flight, it is recommended that the function responsible for acquiring the data have a mechanism for recovery. In case of a failure, that does not allow the Inertial System data reading; it is necessary a recovery mechanism to provide this information to the control system so that the vehicle is not driven to a wrong trajectory. Robustness In addition to physically withstand the environment to which they will be submitted, computer systems must also be able to deal with circumstances outside the nominal values, without causing the loss of critical data that undermine the success or safety of the mission. In case of hardware failure or software errors at run time, the system critical functions should continue to be executed. As an example of software robustness assessment, NASA (2000) mention fault injection, which is a dynamic-type testing because it must be used in the context of running software following a particular input sequence and internal state profile. In fault forecasting, software fault injection is used to assess the fault tolerance robustness of a piece of software (e.g., an off-the-shelf operating system). Safety According to Fortescue, Stark and Swinerd, (2003), the overall objective of the safety program is to ensure that accidents be prevented and all hazards or threats to people, the system and the mission be identified and controlled. Safety attribute is applied to all program phases and embrace ground and flight hardware, software and documentation. They also endeavor to protect people from man-induced hazards. In the case of manned spacecraft, safety is a severe design requirement, and compliance
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
Identifying dependability requirements for space software systems
must be demonstrated prior to launch. Hazards can be classified as “catastrophic”, “critical” or “marginal” depending on their consequences (loss of life, spacecraft loss, injury, damage etc.). Also, the most intensive and complete analysis can be carried out by constructing a safety fault tree. The software safety requirements should be derived from the system safety requirements and should not be analyzed separately (ESA, 2009a). In the software space systems, an indicator of criticality for each module defining the level of associated risk, called safety integrity level, should be specified. The most critical modules involve greater strictness in their development process (NASA, 2004a). Security Space systems have as a feature to protect information, due to the strategic interest of obtaining the technology of satellite launch vehicles, currently still dominated by few countries in the world. There should be a strict control in the access to information in these systems, because if a change occurs accidentally or maliciously, this can compromise the success of a mission. Barbacci et al. (1995) emphasizes that in government and military applications the disclosure of information was the primary risk that was to be averted at all costs. As an example of the influence of this attribute, a remote destruction command of a spacecraft launch system must be able to block another command maliciously sent from an unknown source, which seeks to prevent the vehicle from being destroyed, when it violates the flight safety plan. Self-description Re-use of technology is common in the course of space programs, that is, many systems or subsystems are reused in subsequent missions, and so require maintenance or adjustments. To minimize the possibility of introducing errors in the project, it is desirable that the computer system to be reused have a description that allows an easy understanding. For example, it is recommended that the code of a software application have comments that explain the operation of its functions, thus facilitating developers to carry out future required changes. Simplicity Simplicity is an essential aspect for the software used in critical systems, since the more complex the software, the greater the difficulty in assessing its safety (Camargo Junior, Almeida Junior and Melnikof, 1997). This is a desirable feature in a space software application because
functions with simple code have expected operation and are therefore safer than others with difficulties in their understanding, which can produce indeterminate results. Software simplicity is also related to the ease of maintaining its code. For example, IV & V lessons learned from Mars Exploration Rover project (NASA, 2004b) provided evidence of the importance of this attribute. According to NASA report, portions of the file system using the system memory were very complex and modules have poor testability and maintainability. This factor contributed to a system level fault that put the Rover in a degraded communication state and allowed some unexpected commands. The file system was not the cause of the problem, but brought the lack of memory to light and created the task deadlock. Stability Space computer systems require high reliability, and their subsystems and components must continue to perform their functions within the specified operational level without causing the interruption of service provision during the mission, even if the system is operated for an extended period of time. Examples are the satellites that depend upon the performance of solar cell arrays for the production of primary power to support on-board housekeeping systems and payloads throughout their 7 to 15 years operational lifetime in orbit. The positioning systems of solar panels must have stable operation during the long-term missions, so that the satellite keeps the solar cell arrays towards the sun when going through its trajectory. Survivability The space systems are designed to operate in an environment with different features from those on Earth, such as extreme gravity, temperature, pressure, vibration, radiation, EMI variations etc. Fortescue, Stark and Swinerd (2003) noted that the different phases in the life of a space system, namely, manufacture, pre-launch, launch and finally space operation, have their own distinctive features. Although the space systems spend the majority of their lives in space, it is evident that it must survive on other environments for complete success. Critical systems should continue to provide their essential services even if they suffer accidental or malicious damage. This includes the system being able to resist to risks and threats, eliminating them or minimizing their negative effects, besides recognize accidents or attacks to allow a system reaction in case of their occurrence and recovery after the loss or degradation due to an accident or attack (Firesmith, 2003).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
293
Romani, M.A.S., Lahoz, C.H.N., Yano, E.T.
Testability
Table 3:
A comprehensive spacecraft test program requires the use of several different types of facilities. These are required to fulfill the system testing requirements and may include some facilities like clean room, vibration, acoustic, EMC, magnetic and RF compatibility (Pisacane, 2005). In the case of a critical software system, this feature is crucial, especially during the unit test, integration, system and acceptance and validation phases (Camargo Junior, Almeida Junior and Melnikof, 1997). The real-time software application should be tested as much as its functionality and its performance, ensuring the fulfillment of its functions during the mission within the specified time. Traceability This attribute is particularly important for computer system requirements. In a software application, the code should be linked to the requirement that originated it, thus enabling the verification through the test cases if its specified functionalities were correctly implemented. This also represents the possibility of mapping the safety requirements in all system development phases. Based on the definitions of these factors, a table was elaborated. It generically describes the potential fault events or failure modes that can result from the application of the SFTA and SFMECA techniques and the corresponding dependability attributes recommended to minimize the occurrence of fault/failure. This table is used as a reference to execute the last DEPROCESS step, helping the analyst to identify the dependability attributes according to each fault/failure obtained. Part of this reference table is presented in Table 3. CASE STUDY The chosen example for DEPROCESS application was the requirement of “process inertial information necessary to the control algorithms of the vehicle system”. This requirement was extracted from the Software System Specification document (SSS) and it is related to the control system of a space vehicle. This system has an inertial system (IS) that communicates, through a data bus (DB), with the on board computer (OBC), to periodically provide the vehicle position and instantaneous acceleration data. In order to acquire the IS data and their validation to be used by control algorithms, a software function called ISDA (Inertial System Data Acquisition) should be used and executed in less than 10 miliseconds.
294
Correspondence between the fault events/failure modes and the dependability attributes
SFTA and SFMECA results Dependability attributes Function omits some aspect in its implementation, which leads to the occurrence of a failure in its functioning.
Completeness
Function contains unverified errors, which leads to the occurrence of a failure in its functioning or performance.
Consistency
Function does not maintain a certain performance level specified in case of software failures or violation of the specified interfaces.
Failure tolerance
Function operates without of its designated temporal constraints.
Performance
Function faults generating incorrect/unexpected results or effects.
Precision
Function fails in the reestablishment of its performance level and in the recovery of the data directly affected.
Recoverability
Function whose source code does not allow easy understanding of its functioning.
Self-description
Function does not continue to satisfy certain critical requirements due to adverse conditions.
Survivability
Function was not correctly validated.
Testability
Function with its general safety requirements not mapped in the specification or in its respective implementation.
Traceability
In this case study example, the DEPROCESS was applied in the ISDA function. The lack of this function does not make possible the inertial data acquisition from the IS, not allowing the OBC to process the vehicle position and angular velocity calculations.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
Identifying dependability requirements for space software systems
Applying the DEPROCESS steps, the following results were obtained: 1. assign a criticality rate for the requirement: for this case study, it was defined a criticality rate 6 (complete loss of mission). The lack of information from the IS does not allow that the data related to position be correctly processed, which can leave the vehicle out of control and/or head it into an offnominal trajectory. 2. select if the requirement will be analyzed: as this requirement has a maximum criticality rate, the next step was automatically executed. This means that the project criticality rate did not need to be considered.
Table 4: Hazard severity definitions according to NASA
Hazard severity category Definitions I – Catastrophic
Loss of human life or permanent disability; loss of entire system; loss of ground facility; severe environmental damage.
II – Critical
Severe injury or temporary disability; major system or environmental damage.
III – Moderate
Minor injury; minor system damage.
IV – Negligible
No injury or minor injury; some system stress, but no system damage.
3. apply the safety analysis techniques: 3.1. PHA – the PHA identified the potential hazard to the vehicle system, due to not meeting this requirement: “vehicle out of control during the flight”. Having the classification of NASA severity categories (ref. 8) as a reference, shown in Table 4, it was classified as category I (catastrophic).
1
Logic error in the ISDA function
1.2
1.1 Logic error in the ISDA function
Performance error in the ISDA function
ISDA function logic test did not detect the error
1.1.1
1.1.2
Implementation error in the ISDA function
1.1.2
3.2. SFTA – as shown below, the fault trees for the ISDA function are presented in Fig. 3, from the root (top event) and expanding until the leaf levels (pre-conditions to the top event occurrence). 3.3. SFMECA – as shown below, a SFMECA built for the ISDA function is presented in Table 5, according to a model proposed by ESA (2009b).
1.1
Failure in the ISDA function
1.2
Implementation error in the ISDA function
1.1.2.1 Code error in the ISDA function
Performance error in the ISDA function
1.1.2.2
Requirement design error in the ISDA function
ISDA function performance test did not detect the error
1.2.1
Timing error in the ISDA function
1.2.2
Figure 3: FTA of the ISDA function.
Table 5: SFMECA worksheet for the ISDA function
Failure mode
Failure cause
Failure effect
Criticality
Failure detection method/ Compensation Observable symptoms provisions
ISDA-1: no ISDA function inertial data is not responding acquired by the OBC (omission)
No inertial data is acquired by the OBC to process the vehicle control algorithms
I
Monitoring the function Create logic status/Data not received by recovery the OBC mechanisms for the function
ISDA-2: error in the inertial data (null, corrupted, spurious, or incorrect value) acquired by the OBC
Incorrect results in the calculations of the inertial information processed by the OBC
I
Comparison of the previous inertial data with the current trajectory data at each instant/Trajectory data out of the specified limit
Create function logic test and create fault tolerance mechanisms for incorrect values
II
Verify the data input time in the OBC/Control actuators being activated out of the specified time
Create function performance test
Failure during the execution of the ISDA function
ISDA-3: ISDA ISDA function Inertial data function with responding after acquired by the incorrect timing the specified OBC out of time time
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
295
Romani, M.A.S., Lahoz, C.H.N., Yano, E.T.
4. Identify the dependability attributes: the dependability attributes for the ISDA function were identified by comparing the basic events obtained in SFTA (step 3.2) and the failure causes obtained in SFMECA (step 3.3) with the list of potential fault events/failure modes (Table 3). The recommended dependability requirements for this case study (Table 6) were based on the recommendations of NASA (2005b) and from some authors in the critical system area (Storey, 1996; Laplante, 2004). The set of non-functional requirements extracted by the DEPROCESS must be discussed during the Preliminary Design Review (PDR), for the analysis of their viability and effective incorporation to the software project in the software requirement specification document.
As the SFTA and the SFMECA are bidirectional techniques, in this case study it was possible to map the possible hazards in a detailed and complementary way. The compensation provisions presented through the SFMECA provided some information that helped to define the recommended dependability requirements. CONCLUSIONS It is important to point out that each project that will apply the DEPROCESS can be tailored to obtain the most effective result. For example, criticality scale, safety analysis techniques and dependability attributes set can be adjusted according to the technical features of the project. Besides, the previous knowledge about different safety techniques used by the organization should be
Table 6: Attributes and dependability requirements for the ISDA function
Basic event (SFTA)/ Identified attributes Failure causes (SFMECA)
Recommended dependability requirements
Function logic test did not - Consistency detect error/Failure during - Testability the execution of the ISDA - Failure tolerance function
- Verify critical commands before the transmission and after the reception of the data - The function should be able to consist, in each time cycle, the IS acquired values - Create “black box” test cases, exercising the different possible sets of inputs and testing the limit values - Create “white box” test cases to verify the coverage of the commands, branches, and decisions in the function source code - The function should be able to tolerate, within a predetermined time interval, incorrect values acquired by the IS
Code error in the function - Self-description - Precision
- Create a complete, simple, concise, and direct documentation, and keep this information always updated - Make available to the implementers a good program practice “check list”
Requirement design error in the function
- Specify the input and output data for the module and the data that are shared internally or with other modules - List all possible failures inside the module or in the associated I/O devices. For each failure module, indicate how the failure can occur and how it can be detected and treated
- Completeness - Traceability
Timing error in the - Consistency function AND - Performance Function performance test - Testability did not detect the error / ISDA function responding out of the specified time
- Verify the function responding time, the CPU and memory use during the execution of the function - Estimate function execution time counting its macroinstructions or measuring it using a logic analyzer to capture data or events
ISDA function not responding
- The function should be executed “n” times in case of failure in inertial data acquisition - For extreme situations, return the program to the previous state considered safe (soft reset capacity or a watchdog timer)
296
- Survivability - Recoverability - Failure tolerance
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
Identifying dependability requirements for space software systems
considered with DEPROCESS in order to facilitate the application of the process and the acquisition of more significant results. The set of dependability attributes can and should be discussed and adapted according to the mission or project profile. Other relevant factor to be considered during the DEPROCESS application is the prioritization of the requirements to be analyzed. If the project criticality rate is very low, a huge set of requirements were selected, and it could lead to the impracticable DEPROCESS application. As the DEPROCESS dependability attributes identification is a qualitative approach, its interpretation is subjective. A dependability attribute can have different meanings depending on by whom it is being evaluated, or even on its importance in the project or in the organization. For instance, diverse interpretations for the “simplicity” attribute can induce different recommendations. One view of simplicity, in computer program issues, recommended breaking up complex instructions. Another view of simplicity argues that segmented code instructions can lead to an increase of the code length, and consequently impact other quality attributes. One way to deal with this subjectiveness interpretation would be mitigate it through more than one person applying the DEPROCESS and then compare the results to find out what dependability attributes have been identified in common. Dependability attributes can be used to help identification and analysis of dependability requirements. The use of selected dependability attributes is an effective way to guide a requirement development team to discover and refine requirements. A dependability attribute persuades an analyst to focus on a dependability issue related to a functional requirement. As result, the analyst can discover new issues and identify requirements to deal with these new demands. In conclusion, this paper presented a structured and systematic process that addresses the dependability, focused on software systems for Brazilian space vehicles. Through pre-established criteria, such as the criticality rating scale, proper safety analysis techniques, and a set of dependability attributes, it was possible to generate some important information, such as the dependability requirements. The purpose of these recommendations is to guarantee the software functioning, and also the preliminary survey of possible vulnerable points that should be investigated in the project as whole in order to improve its quality.
Glossary Accuracy Software attributes that demonstrate the generation of results or correct effects or according to what has been agreed upon (Camargo Junior, Almeida Junior and Melnikof, 1997). Availability The ability of an item to be in a state to perform a required function under given conditions at a given instant of time or over a given time interval, assuming that the required external resources are provided (ESA, 2004). Completeness Software feature in which there is an omission on some aspect of its application which can cause the system to reach an unsafe state (Camargo Junior, Almeida Junior and Melnikof, 1997). Consistency Software feature to contain errors that are not checked, which can lead the system to an unsafe situation (Camargo Junior, Almeida Junior and Melnikof, 1997). Correctness The degree to which a work product and its outputs are free from defects since the work product is delivered (Firesmith, 2003). Efficiency It refers to timing aspects that are key factors in a critical system (Camargo Junior, Almeida Junior and Melnikof, 1997). Failure tolerance Software attributes that demonstrate its ability to maintain a specified performance level in cases of software failures or violation in the specified interfaces (Camargo Junior, Almeida Junior and Melnikof, 1997). Maintainability The ability of an item, under given conditions of use, to be retained in, or restored to, a state in which it can perform a required function, when maintenance is performed under given conditions and using stated procedures and resources (ESA, 2004). Modularity Software attributes that demonstrate the coupling degree, i.e., interdependence between its modules and low cohesion, that is, the module includes two or more independent functions (Camargo Junior, Almeida Junior and Melnikof, 1997).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
297
Romani, M.A.S., Lahoz, C.H.N., Yano, E.T.
Portability A set of attributes that bear on the ability of software to be transferred from one environment to another, including the organizational, hardware or software environment (Kitchenham, Pfleeger, 1996). Reliability The probability with which a spacecraft will successfully complete the specified mission performance for the required mission time (Fortescue, Stark, Swinerd, 2003). The ability of an item to perform a required function under stated conditions for a specified period of time (MOD, 2003). Recoverability Software attributes that demonstrate its ability to restore its performance level and recover the data directly affected in case of failure and the time and effort necessary for it (ABNT, 2003). Robustness The degree to which a system or component can correctly function in the presence of invalid inputs or stressful environmental conditions (Rus, Komi-Sirvio and Costa, 2003). Safety The possibility of catastrophic failure of systems in such a way as to compromise the safety of people or property, or result in mission failure (NASA, 2005a). Security Ability of the System to protect itself against accidental or deliberate intrusion (Sommerville, 2004). Self-description Software attributes that allow greater facility of its understanding and, in future maintenance, reduce the possibility of introducing new errors (Camargo Junior, Almeida Junior and Melnikof, 1997). Simplicity Critical system software feature to facilitate its safety evaluation (Camargo Junior, Almeida Junior and Melnikof, 1997). Stability The degree to which mission-critical services continue to be delivered during a given time period under a given operational profile regardless of any failures whereby the failures limiting the delivery of mission-critical services occur at unpredictable times and root causes of such failures are difficult to identify efficiently (Firesmith, 2003).
298
Survivability The ability of a computer-communication systembased application to continue satisfying certain critical requirements (e.g., requirements for security, reliability, real-time responsiveness, and correctness) in face of adverse conditions (Rus, Komi-Sirvio, Costa, 2003). Testability Software attributes that demonstrate the effort needed to validate the modified software (NBR 14959). Traceability It represents the possibility that all the general safety requirements are perfectly mappable in the software specification and in its implementation (Camargo Junior, Almeida Junior and Melnikof, 1997). REFERENCES Barbacci, M. et al., 1995, “Quality Attributes, Technical Report CMU/SEI-95-TR-021”, Pittsburgh, USA: Software Engineering Institute/Carnegie Mellon University, 56 p. Camargo Junior, J.B., Almeida Junior, J.R. and Melnikof, S.S.S., 1997, “O uso de fatores de qualidade na avaliação da segurança de software em sistemas críticos”. Proceedings of Conferência internacional de tecnologia de software: qualidade de software, 8, Curitiba : CTIS, pp. 181-185. Departamento de Pesquisas e Desenvolvimento (DEPED), Ministério da Defesa, Comando da Aeronáutica, 2004, “Relatório da investigação do acidente ocorrido com o VLS-1 V03, em 22 de agosto de 2003, em Alcântara, Maranhão”, [cited November 06, 2006], Available at: http://www.iae.cta.br/VLS-1_ V03_Relatorio_Final.pdf European Space Agency (ESA), 2004, European Cooperation for Space Standardization “ECSS-P-001-B, Glossary of Terms”, The Netherlands: ESA. European Space Agency (ESA), 2009a, European Cooperation for Space Standardization “ECSS-E-ST-40C, Space Engineering – Software”, The Netherlands: ESA. European Space Agency (ESA), 2009b, European Cooperation for Space Standardization “ECSS-Q-ST-80C, Space Product Assurance – Software Product Assurance”, The Netherlands: ESA. Firesmith, D.G., 2003, “Common Concepts Underlying Safety, Security, and Survivability Engineering,
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
Identifying dependability requirements for space software systems
Technical Note CMU/SEI-2003- 033”, Pittsburgh, USA: Software Engineering Institute/Carnegie Mellon University, 70 p.
Report 92-27”. Ames, Iowa, USA: Department of Computer Science, Iowa State University of Science and Technology.
Firesmith, D.G., 2006, “Engineering Safety-Related Requirements for Software-Intensive Systems”, Proceedings of the 28th International Conference on Software Engineering, ACM SIGSOFT/IEEE, Shangai, China, pp. 1047-1048, 2006.
NASA, 2000, “Software fault tolerance: a tutorial, technical memorandum NASA/TM-2000-210616”, Hampton, USA: Langley Research Center.
Fortescue, P., Stark, J. and Swinerd, G., 2003, “Spacecraft systems engineering”, 3rd Ed., London: John Wiley & Sons, 678 p. Instituto de Aeronáutica e Espaço (IAE), 1994, “Plano de Confiabilidade do Software Aplicativo de Bordo (SOAB) para o Veículo Lançador de Satélites VLS PT-01 – Preliminar – (PCS-P)”. Jet Propulsion Laboratory (JPL), 2007, “Mars Exploration Rover Mission – Communications with Earth”, [cited May 15, 2009], Available at: http://marsrovers.nasa.gov/ mission/communications.html Kitchenham, B., Pfleeger, S.L., 1996, “Software Quality: the elusive target”, IEEE Software, Vol. 13, N° 1, pp.12-21. Lahoz, C.H.N., 2009, “Elicere: o processo de elicitação de metas de dependabilidade para sistemas computacionais críticos: estudo de caso aplicado a Área Espacial.” PhD thesis, Universidade de São Paulo, São Paulo. Laplante, P.A., 2004, “Real-Time Systems Design and Analysis”. 3rd Ed. New York: John Wiley & Sons. Leveson, N.G., 2009, “Engineering a safer world. System safety for the 21st century (or Systems thinking applied to safety)”, Aeronautics and Astronautics Engineering Systems Division. Massachusetts Institute of Technology, [cited May 13, 2009], Available at: http://sunnyday.mit. edu/book2.pdf Leveson, N.G., 1995, “Safeware: system safety and computers”. New York: Addison-Wesley. Leveson, N.G., 2004, “The role of software in spacecraft accidents”. AIAA Journal of Spacecraft and Rockets, Vol. 41, N° 4, pp. 564-575. Lutz, R.R., 1992, “Analyzing software requirements errors in safety-critical, embedded systems. Technical
NASA, 2004a, “Software Safety Guidebook, NASA-GB8719.13”, [cited October 19, 2006], Available at: http:// www.hq.nasa.gov/office/codeq/doctree/871913.pdf NASA, 2004b, “IV&V Lessons Learned – Mars Exploration Rovers and the Spirit SOL-18 Anomaly: NASA IV&V Involvement”, [cited May 14, 2009], Available at: http://www.klabs.org/mapld04/presentations/ session_s/2_s111_costello_s.ppt NASA, 2005a, “Software Assurance Guidebook, NASAGB-A201”, [cited August 25, 2006], Available at: http:// satc.gsfc.nasa.gov/assure/agb.txt NASA, 2005b, “Software Fault Analysis Handbook: Software Fault Tree Analysis (SFTA) & Software Failure Modes, Effects and Criticality Analysis (SFMECA)”, [cited May 07, 2007], Available at: http://sato.gsfc.nasa. gov/guidebook/assets/SQI_SFA_Handbook_05022005. doc Pisacane, V.L., 2005, “Fundamentals of Space Systems”, 2nd Reis Filho, J.V.B., 1995, “Uma abordagem de Qualidade e Confiabilidade para Software Crítico”. Masters dissertation, Instituto Tecnológico de Aeronáutica. Romani, M.A.S., 2007, “Processo de Análise de Requisitos de Dependabilidade para Software Espacial”. Masters dissertation, Instituto Tecnológico de Aeronáutica. Rus, I., Komi-Sirvio, S., Costa, P., 2003, “Software dependability properties: a survey of definitions, measures and techniques. Technical Report 03-110. High Dependability Computing Program (HDCP)”, Maryland: Fraunhofer Center for Experimental Software Engineering. Sommerville, I. “Software Engineering”, 2004, 7th Ed. Glasgow, UK: Addison-Wesley. Storey, N., 1996, “Safety-Critical Computer Systems”. Boston: Addison-Wesley Longman.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
299
Romani, M.A.S., Lahoz, C.H.N., Yano, E.T.
UK Ministry of Defence (MOD), 2003, “Reliability and Maintainability (R&M) – Part 7 (ARMP -7), NATO R&M Terminology Applicable to ARMP’s, Defence Standard 00-40 Part 7”.
300
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 287-300, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02037110
Eder Paduan Alves*
Institute of Aeronautics and Space São José dos Campos - Brazil ederep@yahoo.com.br
Francisco Piorino Neto
Institute of Aeronautics and Space São José dos Campos - Brazil piorinofpn@iae.cta.br
Chen Ying An
National Institute for Space Research São José dos Campos - Brazil chen@las.inpe.br *author for correspondence
Welding of AA1050 aluminum with AISI 304 stainless steel by rotary friction welding process Abstract: The purpose of this work was to assess the development of solid state joints of dissimilar material AA1050 aluminum and AISI 304 stainless steel, which can be used in pipes of tanks of liquid propellants and other components of the Satellite Launch Vehicle. The joints were obtained by rotary friction welding process (RFW), which combines the heat generated from friction between two surfaces and plastic deformation. Tests were conducted with different welding process parameters. The results were analyzed by means of tensile tests, Vickers microhardness, metallographic tests and SEM-EDX. The strength of the joints varied with increasing friction time and the use of different pressure values. Joints were obtained with superior mechanical properties of the AA1050 aluminum, with fracture occurring in the aluminum away from the bonding interface. The analysis by EDX at the interface of the junction showed that interdiffusion occurs between the main chemical components of the materials involved. The RFW proves to be a great method for obtaining joints between dissimilar materials, which is not possible by fusion welding processes. Keywords: Friction welding, Aluminum, Stainless steel, Dissimilar materials.
INTRODUCTION During recent years, the use of joints between dissimilar materials has considerably increased. Conventional structures made of steel have been replaced by lighter materials, capable of providing high mechanical strength, lower volume of material and good corrosion resistance. In the developing of new technologies for the aerospace industry, these junctions are of great importance, because they allow the systems, subsystems and components manufactured in stainless steel and aluminum to be structurally united. Even the fusion welding processes by presenting a heat affected zone (HAZ) well reduced (as laser and electron beam welding processes) generate junctions with inferior properties of the base metal. The difficulties in the welding of aluminum alloy with stainless steel by fusion welding processes have been a great challenge for engineering, because they result from hard and brittle intermetallic phases that are formed between aluminum and steel at elevated temperatures (Fe3Al, FeAl, FeAl2, Fe2Al5, FeAl3). The Fe-Al phases diagram shows the well defined intermetallic phases (Banker and Nobili, 2002).
Received: 26/06/10 Accepted: 06/10/10
In order to obtain junctions between the AA1050 aluminum (commercially pure aluminum, 99.5% Al) and AISI 304 stainless steel for structural applications that can be used in the aerospace sector, several studies and analysis of welding processes were carried out. Among them, rotary friction welding process (RFW) showed the best result. In this study, these materials have been joined by RFW and the results were analyzed and presented. Tensile tests were performed to define welding parameters and analyze the resistance of the weld. After obtaining the best results (the fracture occurred away from the bonding interface) in the AA1050 aluminum (lower resistance), the process was optimized and analyzed in the bonding interface by optical microscopy, electron microscopy of EDX and Vickers microhardness test. ROTARY FRICTION WELDING PROCESS Friction welding process is classified by the American Welding Society (AWS) as a solid state joining process in which bonding is produced at temperatures lower than the melting point of the base materials (MaldonadoZepeda, 2001). All heating responsible by the union is mechanically generated by friction between the parts to be welded. This heating occurs due one part that is fixed, be pressed on the other that is in high rotation (Wainer, Brandi and Homem
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 301-306, Sep-Dec., 2010
301
Alves, E.P. et al.
de Mello, 2002). The friction between the surfaces makes possible a rapid temperature rise in the bonding interface, causing the mass to deform plastically and flows depending on the application of pressure and centrifugal force, creating a flash. With this flash, impurities and oxides are removed from the surface, promoting the creation of a surface with excellent physical and chemical adhesion. The increase of temperature in the bonding interface and the application of pressure on that surface originate the diffusion between the two materials, and hence their union.
Figure 2 shows the basic layout of RFW equipment. Usually the structure is fairly rigid to provide stability to the equipment working at high speeds and is driven by high pressure forging. Modern equipment is automatic and allows all the parameters be adjusted, controlled and monitored directly on the control panel.
The main parameters used to perform the set up are: Pressure P1 and time t1 – heating phase; Pressure P2 and time t2– forging phase; and rotation per minute (RPM). Figure 1 shows the phases of the process. Figure 2: Equipment of rotary friction welding.
EXPERIMENTAL PROCEDURE Materials and surfaces preparation The materials used in this study were AA1050 aluminum (commercially pure aluminum, 99.5% Al) and AISI 304 austenitic stainless steel. Both materials were machined with a diameter of 14.8 mm and lengths of 100 and 110 mm, respectively. After machining, they were subjected to a cleaning with acetone to remove organic contaminants such as oils, greases etc. Tables 1 and 2 present chemical compositions and mechanical properties of materials. Friction welding equipment Figure 1: Phases of conventional friction welding process. (A) Period of approximation; (B) P1, t1 application; (C) end of P1, t1 application, and braking of the machine (RPM = 0); (D) P2, t2 application and finish welding. Table 1:
A rotary friction welding machine of brand GATWIK was used with fixed speed of 3,200 RPM, P1 = 2.1 MPa, t1 = 32 seconds, P2 = 1.4 MPa and t2 = 2 seconds. The materials were placed as shown in Fig. 3.
Nominal chemical compositions of materials
AA1050 aluminum AISI 304 stainless steel
Si 0.07 Si 0.38
Fe 0.26 S 0.024
Cu <0.001 P 0.036
Elements (wt %) Mn Mg <0.001 Mn C 1.67 0.054
Cr Cr 18.2
Zn <0.002 Ni 8.0
Ti <0.007 -
Table 2: Mechanical properties of materials used in present study
Material AA1050 aluminum AISI 304 stainless steel
302
Strenght σ (MPa) Yield Maximum 44.70 78.48 354.69 643.79
Mechanical properties Elongation ε (%) Maximum Fracture 21 43 48 63
Modulus of elasticity E (GPa) 59.12 177.10
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 301-306, Sep-Dec., 2010
Welding of AA1050 aluminum with AISI 304 stainless steel by rotary friction welding process
region and ends of the sample. It was used an electron microscope (JSM 5310, Jeol Ltd., Japan), allocated in the Associate Laboratory of Sensors and Materials of the National Institute of Space Research (Inpe, acronym in Portuguese). RESULTS Macrostructure Figure 3: Schematic view of the positioning of the materials before welding.
Tensile tests After welding was performed, tensile tests were carried out to evaluate the mechanical properties of joints, besides parameter settings, optimization and qualification of welding procedures and processes. The welded specimens were machined according to ASTM E 8M (2004), and subjected to tensile tests on a machine brand ZWICK 1474 with a load cell of 100 kN at room temperature of 25°C, and a test speed of 3 mm/minute.
In macrostructure level, it was observed the formation of flashes with circular symmetry, different formats, and also significant reductions in length of the cylindrical pin AA1050 aluminum in accordance with the adopted parameters. The AISI 304 stainless steel side was not deformed because this material has higher strength than the aluminum alloy, and it thus provide more resistance to deformation. Hence, the formation of flashes was restricted to AA1050 aluminum only. Figure 4 shows the interfaces that were bonded (A), the flash generated by RFW (B), and the specimen used for tensile test after machining (C).
Vickers microhardness tests A sample with the same parameters of the junction which showed 100% of efficiency was analyzed by Vickers microhardness using a digital microhardness tester (Future-Tech Corporation, Japan) with a 300 gF load (stainless steel) and 100 gF (aluminum) for 10 seconds. Microhardness was conducted at the interface of the weld and in the regions near both the aluminum and the AISI 304 stainless steel sides. Metallographic analysis The joints were cut in the transverse weld, embedded in an array of bakelite, polished and examined in the region of the interface on the aluminum and AISI 304 stainless steel sides, according to ASTM E3 (2007). Aluminum was attacked with Keller reagent and stainless steel with electrolytic acid oxalic 10% and examined under a microscope (Leica DMRXP, Spectronic Analytical Instruments, United Kingdom). Analysis of the bonding interface In order to verify the main bonding mechanism by friction − the diffusion − analyses were carried out by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) at the bonding interface on the central
Figure 4: Interfaces of pins that were joined (A); flash generated by the process (B); specimen for tensile test (C); samples on graph paper.
Mechanical strength of the joint welded by friction The results of tensile tests for different welding parameters used (t1, t2 and P2) are shown in Table 3. The junction with the best mechanical strength (σt max.) refers to the specimen number 8, with higher mechanical strength to the material with lower mechanical strength − aluminum AA1050. Time t1 and friction welding pressure P2 were the parameters that most influenced in joint strength. In the welding of dissimilar materials such as AA1050 aluminum and AISI 304 stainless steel, the friction time t1 = 32 seconds allowed the increase of temperature, at the bonding interface, to values sufficient for a perfect union between the materials.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 301-306, Sep-Dec., 2010
303
Alves, E.P. et al.
Table 3:
Nº 1 2 3 4 5 6 7 8 9 10
Tensile tests
P1 (MPa/psi) 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1
t1 (s) 7 17 17 27 32 32 32 32 32 32
P2 (MPa/psi) 2.1 1.4 2.1 1.4 0.7 0.7 1.4 1.4 2.1 2.8
t2 (s) 2 1 1 1 1 2 1 2 1 1
σt máx (MPa) 72.0 64.12 69.63 62.94 47.45 53.37 70.63 80.08 74.23 76.54
The welding pressure P2 = 1.4 MPa, applied at time t2 = 2 seconds on heated interface, completed the welding with desired strength. The results also showed that when there is an increase in the P2 pressure values, the joint strength also increases until it reaches its limit and then decreases again. Everything indicates that this occurs due to increased plastic deformation resulting from the application of excessive pressure P2 when RPM = 0. The relative speed (RPM), the pressure P1 and the time t1 are essential for the occurrence of temperature elevation at the bonding interface and diffusion of the materials involved, while P2 and t2 are responsible for the completion of welding. When there is no interaction between these various parameters involved in the process, the joint loses its quality, because unbonded regions or the formation of undesirable intermetallic layers may occur at the bonding interface, resulting in lower joint strenght than that of the base aluminum alloy. Figure 5 shows the specimens number 5 and 8 after they were tested and removed from the tensile test machine.
Figure 5: Specimen number 5: (A) − rupture on the bonding interface; specimen number 8: (B) − rupture away from the bonding interface.
The specimen number 8, that showed the best results, had its parameters repeated in the welding of new specimens. The tensile tests confirmed previous results, with the rupture occurring away from the bonding interface. Figure 6 shows the specimens after tension tests. 304
Figure 6: Specimens number 1, 2 and 3 − AA1050 aluminum/ AISI 304 stainless steel after completion of tensile tests.
Vickers microhardness tests Vickers microhardness tests were performed from bonding interface to AA1050 aluminum, and also from bonding interface to stainless steel AISI 304, central region. In the AA1050 aluminum, a slight increase of Vickers microhardness has occurred as the interface was approached (points 1, 2, 3 and 4); from point 5 to 20, the average value of measurements (30.9 HV) represents the typical value of AA1050 aluminum microhardness (30.0 HV) (AALCO, n/d). On the side of AISI 304 stainless steel, the results also showed an increase of microhardness values as the points were close to the bonding interface. This variation in microhardness values occurred from point 1 (highest) to point 12. From the point 13 to 20, the average value of measurements (198.8 HV) refers to the typical value of microhardness of AISI 304 stainless steel used in this work. On the side of AA1050 aluminum, the increase of Vickers microhardness values near the bonding interface occurs due to the large plastic deformation underwent by this material and temperature raises in this region. By the side of AISI 304 stainless steel, everything indicates that the increase of microhardness values near the bonding interface is derived from the increase of temperature and displacement of the heat flow in these regions, since the material does not undergo considerable plastic deformation during welding, as occurs with AA1050 aluminum. Figure 7 shows the variation of Vickers microhardness values through the graphs microhardness (HV) x distance bonding interface, for AA1050 aluminum (a) and AISI 304 stainless steel (b). The dotted lines express the microhardness values (HV) of the materials used in this work. Figure 8 shows that, on the alloy AA1050, the region with the variation of Vickers microhardness as a function of plastic strain (1, 2 and 3) reaches a maximum distance of the bonding interface of about 0.7 mm. Metallographic analysis of the bonding interface Figure 9 shows a photomicrograph of the junction between AA1050 aluminum and AISI 304 stainless steel, taken in
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 301-306, Sep-Dec., 2010
Welding of AA1050 aluminum with AISI 304 stainless steel by rotary friction welding process
Figure 7: HV microhardness x distance bonding interface. (A) AA1050 aluminum; (B) AISI 304 stainless steel.
Figure 8: Photomicrograph of the bonding interface between the AA1050 aluminum and AISI 304 stainless steel, showing the measuring points and the approximate distance in scale of the regions that presented a variation of the Vickers microhardness values.
the central region of the sample with an increase of 100 X. The interface region is characterized by a straight line with some imperfections under the friction welding process. Both in the aluminum and stainless steel sides, microstructural changes are not observed near the interface region, as it occurs in fusion welding processes. All plastic deformation resulting from the parameters used in the process occurred in the AA1050 aluminum, due to the fact that this material has lower strength and lower hot forging temperature. Analysis of the bonding interface by energy dispersive X-ray spectroscopy Semiquantitative analysis by scanning linescan - EDX was performed at the central region of bonding interface and also at the ends. The results were very similar, with little variation in the diffusion layer between the main chemical elements that make up the AA1050 aluminum and AISI 304 stainless
Figure 9: Photomicrograph of the interface bonding between the AA1050 aluminum and AISI 304 stainless steel with an increase of 100 X.
steel, like Al and Fe. Figure 10 shows the interdiffusion between Fe and Al, characterizing the diffusion as the main bonding mechanism in the rotary friction welding process, according to Fukumoto et al. (1997; 1999), Fuji et al. (1997), Kimura et al. (2003), and Ylbas et al. (1995). The Al diffused less in Fe than Fe in Al, and a reason for this is the smallest diameter of Fe atom in relation to Al. Another reason for the different distances from the diffusion zone is the different concentrations of Fe and Al contained in each material. Junctions obtained through the rotary friction welding process The great finish in the welded regions and the absence of surface defects (Fig. 11), so common to fusion welded joints, show the efficiency of this process in welding
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 301-306, Sep-Dec., 2010
305
Alves, E.P. et al.
Vickers microhardness values measured in the side of AA1050 aluminum and in the side of AISI 304 stainless steel, near the bonding interface, central region, were higher than in the metal bases. As the measurement points move away from the interface, they decrease until they reach the reference values of microhardness for each material.
Figure 10: Analysis by semiquantitative EDX showing the interdiffusion of the main elements of alloy AA1050 (Al) and AISI 304 stainless steel (Fe).
The results of this study have fundamental importance for the understanding and comprehension of the main characteristics of friction welding process, the bonding mechanisms between dissimilar materials, and the feasibility of applying this process in the production of structural joints that will be used in aeronautic and aerospace industry. REFERENCES AALCO, n/d, “Aluminium alloys − Aluminium 1050 proprierties, fabrication and applications, supplier data by Aalco. Typical mechanical properties for aluminum alloy 1050” Available at: www.azom.com/details. asp?ArticleID=2798#_Alloy_Designations Banker, J., Nobili, A., 2002, “Aluminum-Steel Electric Transition Joints, Effects of Temperature and Time upon Mechanical Properties. Draft of paper for presentation at 2002 TMS 131st Annual Meeting”, Seatle, WA, USA. Fukumoto, S. et al., 1997, “Evaluation of friction weld interface of aluminum to austenitic stainless steel joint”, Materials Science and Technology, Vol. 13, Nº. 8, pp. 679-686.
Figure 11: Joints produced by the rotary friction welding process (RFW) (dark part: AISI 304 stainless steel; clear part: AA1050 aluminum).
materials that are highly dissimilar, as AA1050 aluminum and AISI 304 stainless steel. The efficiency of this welding process (analyzed by tensile tests), its repeatability and high productivity open new possibilities of alternative processes for obtaining joints between dissimilar materials with applications in aerospace field. CONCLUSIONS The friction welding process was very efficient in the welding of dissimilar materials such as AA1050 aluminum and AISI 304 stainless steel. It is showed by the results of tension mechanical tests that presented mechanical properties which are not possible to achieve by means of fusion welding processes. Among the parameters used for testing the welding, the one that showed the best results in tensile tests − with superior values of mechanical strength of the AA1050 aluminum − was number 8 (Table 3), in which P1 = 2.1 MPa; t1 = 32 seconds, P2 = 1.4 MPa; t2 = 2 seconds. 306
Fukumoto, S. et al., 1999, “Friction welding process of 5052 aluminum alloy to 304 stainless steel”. Materials Science and Technology, Vol. 15, Nº. 9, pp.1080. Fuji, A. et al., 1997, “Mechanical properties of titanium - 5083 aluminum alloy friction joints”, Materials Science and Technology, Vol. 13, Nº. 8, pp. 673-678. Kimura, M. et al., 2003, “Observation of joining phenomena in friction stage and improving friction welding method”, JSME International Journal, Series A, Vol. 46, Nº. 3, pp. 384-390. Maldonado-Zepeda, C., 2001, “The effect of interlayers on dissimilar friction weld properties”, PhD thesis, University of Toronto, Canada. Wainer, E., Brandi, S.D. and Homem de Mello, F.D., 2002, “Soldagem: processos e metalurgia”, 3. ed. São Paulo: Edgard Blücher. Ylbas, B.S. et al., 1995, “Friction welding of St-Al and Al-Cu materials”, Journal of Materials Processing Technology, Vol. 49, Nº. 3-4, pp. 431-443. doi: 10.1016/0924-0136(94)01349-6
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 301-306, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02037910
Aparecida Minhoco Kawamoto*
Institute of Aeronautics and Space São José dos Campos – Brazil aparecidamkawamoto@hotmail.com
Milton Faria Diniz
Institute of Aeronautics and Space São José dos Campos – Brazil miltonmfd@iae.cta.br
Vera Lúcia Lourenço
Institute of Aeronautics and Space São José dos Campos – Brazil veravll@iae.cta.br
Marta Ferreira K. Takahashi
Institute of Aeronautics and Space São José dos Campos – Brazil martamfkt@iae.cta.br
Thomas Keicher
Institut Chemische Technologie Pfinztal – Germany thomas.keicher@ict.fhg.de
Horst Krause
Institut Chemische Technologie Pfinztal – Germany kr@ict.fhg.de
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants Abstract: The main objective of these studies was the synthesis and characterization of new energetic binders and their use in some propellant formulations. Following the working plan elaborated, the synthesis and characterization of the following compounds has been done successfully: • GAP; • energetic Monomer BAMO; • energetic Binders; • copolymer GAP/PolyBAMO. The scale up for the synthesis of copolymer GAP/PolyBAMO and PolyBAMO using GAP as initiator has been done and they were fully characterized by IR, (1H, 13C) NMR-spectroscopy, GPC, elemental analysis, OH-functionality, differential scanning calorimetry (DSC) and sensitivity tests (friction, impact). For this two scale up synthesis some propellant formulations were carried out and the results of mechanical and burning properties have been compared with GAP propellants. Keywords: Energetic binders, PolyBAMO, Copolymer GAP/PolyBAMO, Propellants.
Klaus Menke
Institut Chemische Technologie Pfinztal – Germany kr@ict.fhg.de
Paul Bernt Kempa.
Institut Chemische Technologie Pfinztal – Germany kempa@ict.fhg.de *author for correspondence
LIST OF SYMBOLS ACE Al AM AMMO AP ARC BAM
BAMO BDNPF/A Received: 28/06/10 Accepted: 02/08/10
Activated chain end Aluminium Activated monomer 3-Azidomethyl-3-methyl oxetane Ammonium perchlorate Accelerated rate calorimetry Federal Institute for Materials Research and Testing in Germany (Bundesanstalt fuer Materialforschung und -pruefung) 3,3-Bis-azidomethyl oxetane Bisdinitropropylformal/acetal
BDO BF3O Et2O BF3THF BBrMO BrMMO BBrdiol
Butanediol Boron trifluoride etherate Boron trifuoride tetrahydrofuran bisbromomethyl oxetane 3-Bromomethyl-3-methyl oxetane 2,2-Bis(bromomethyl)-1,3propanediol BTTN 1,2,4-Butanetrioletrinitrate CHN Elemental analysis CcGAP/PolyBAMO Energetic copolymer from GAP and PolyBAMO D Polydispersity (dispersion broadness): Mw/Mn DCM Dichloromethane DMA Dimethylacetamide DMF Dimethylformamide DMSO Dimethylsulfoxide DOA Dioctyl adipate
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
307
Kawamoto, A.M. et al.
DSC D22 ECH GAP GPC HDI HMX HTPB IR Mw Mn MP NaN3 NCO NMR N100 PECH PolyAMMO PolyBAMO PPG PS RDX SnCl4 TA TEOFF TFBE Tc THF Tg TG TLC TMA TMETN UV
Differential scanning calorimetry Dibutyltin dilaurate Epichlorohydrin Glycidylazidopolymer Gel permeation chromatography hexamethylene diisocyanate ciclotetrametilene-tetranitramine Hydroxylterminated polybutadiene Infrared spectroscopy Molecular weight (average weight) Molecular weight (average number) Molecular weight at peak maximum Sodium azide Isocyanate group Nuclear magnetic resonance Isocyanate from Bayer Material Science – Desmodur® N-100 Polyepichlorohydrin Polymer of 3-azidomethyl-3methyl oxetane Polymer of 3,3-bis-azidomethyl oxetane Polypropyleneglycol Polystyrene Cyclotrimetylenetrinitramine Tin tetrachloride Themal analysis Triethyl oxonium hexafluoro phosphate Trifluoride boron etherate Critical temperature Tetrahydrofuran Glass transition temperature Thermogravimetry Tin layer chromatography Thermomechanical analyzer Trimethylolethanetrinitrate Ultraviolet spectroscopy
INTRODUCTION The use of energetic binders in formulation of cast-cured composite solid propellants has been presenting growing interest in the recent years. They are hydroxyl-terminated polyethers with azido or nitric groups polymers of low molecular weight that hold fuel and oxidizer compounds from the propellant. The OH groups from the propellant mixture react with the isocyanate groups forming a polyurethanic matrix that binds the solid propellant ingredients in a tough elastomeric three dimensional network structure capable of absorbing and dissipating energy. In these new class of energetic binder, the polymer GAP showed to be very useful for high energetic rocket propellants (Provatas, 2000; Helmy, 1984). Together with energetic plasticizers, like nitrate esters, aliphatic nitro- and 308
nitramine compounds, it offers high thermodynamic energy and performance with traditional oxidizers like ammonium perchlorate (Eisele, Zimdahl and Menke, 2002; Yoshio et al., 1994; Eishu and Yoshio, 1996), with nitramines (Menke and Eisele, 1997; Menke et al., 2002) and even with low energetic oxidizers, like ammonium nitrate (Menke, Böhnlein-Mauß and Schubert, 1996). Due to its positive heat of formation, good oxygen balance and high density, GAP opens the gate to high energetic composite propellants with much lower amount of solids and yet higher specific impulse and overall performance than traditional composite propellants based on AP/HTPB ingredients. With GAP, it is possible to formulate composite rocket propellants with higher energy, higher density and higher burning rates in connection to a significant reduced content of hydrogen chloride and chlorine in the exhaust. Consequently, it is pointing directly to high energetic chlorine reduced low pollution propellants for an eco-friendly environment. Due to its higher content of azido groups, PolyBAMO offers an enhanced kinetic and thermodynamic advantage for propellant application in comparison to GAP (Yoshio et al., 1994; Eishu and Yoshio, 1996). However, the high melting and glass transition point plus poor processability in comparison to GAP bring some disadvantages. Therefore, to overcome these drawbacks the copolymer GAP/ PolyBAMO has been developed to produce a binder with similar properties, but higher energy content, which will be the binder of choice for the formulation of high energetic rocket propellants that will keep the advantages of AP/GAP formulations, and even improve their processability, glass transition points and mechanical properties. The objective of this study was to investigate the behavior of GAP/BAMO copolymers in propellant formulation with AP, AP/RDX 82 – 10, and a convenient energetic plasticizer, BDNPF/A, was chosen due to experiences with the AP/GAP propellants (Eisele, Zimdahl and Menke, 2002) and to keep a low mechanical and applicable sensitivity of the system. The synthesis of the GAP/Poly BAMO binders was carried out by cationic copolymerization of epichlorohydrin and 3,3-bis(bromomethyl)oxetane (BBrMO), using butane-1,4-diol (BDO) as initiator and boron trifluoride etherate (BF3OEt2) as catalyst, followed by azidation with sodium azide and dimethylsulfoxide as solvent (DMSO). The polymerization can proceed by two different mechanisms: the activated monomer (AM) and the activated chain end (ACE). AM mechanism involves successive additions of the protonated (activated) monomer to terminal hydroxyl groups of the initiator and after on the growing macromolecules (Elie, 1990). Macromolecules growing by AM mechanism should have the structure shown in Fig. 1
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants
EXPERIMENTAL H-NMR, 13C-NMR analysis were conducted on a 300 MHz Bruker MSL-300 spectrometer. The proton and carbon chemical shifts were recorded in ppm and calibrated on the solvents as internal standard. Infrared analyses were conducted on a Nicolet SX 5 spectrometer. Gel permeation chromatography was conducted on a water’s gel permeation chromatography equipped with four ultrastyragel columns (100 Å, 500 Å, 1000 Å and 10000 Å), a refractive index detector and a Datamodule 730. THF was used as the mobile phase. The GPC was calibrated with a set of well characterized (i.e., Mn, Mw are well known) polystyrene and polypropylene standards (narrow standards), and thus the number average molecular weight (Mn) and weight average molecular weight (Mw) are reported relative to polystyrene and polypropylene. Differential scanning calorimetry (DSC) was carried out by a TA instrument Q 1000 using aluminium pans. Scans were carried out on each sample, at scan rates of 5°C/min, under argon flux, in the 40-450°C range. Thermogravimetric analysis (TGA) was performed by a TA Q500 apparatus, with a scan rate of 10°C/min, under nitrogen flux, in the 30-530°C range. OH group titration was carried out by standard ASTM procedure (Biedron, Kubisa and Penczek, 1991). 1
Figure 1: AM mechanism for polymerization of oxetane ring.
In the polymerization reactions that involve an ACE mechanism, a cationic oxonium ion is formed at the end of the chain and reacts with the incoming monomer molecules. The incoming molecules then acquire this cationic reactivity as they bond to the chain end to promote further chain growth (propagation). The polymerization proceeds in the presence of an initiator, present in a small quantity which is part of the propagation polymer chain (Kubisa et al., 2000). Macromolecules growing by ACE mechanism should have the structure shown in Fig. 2.
Solvents were purchased from Aldrich®, Fluka® or Merck & Co., Inc., according to the required purity, price and availability. DCM (Dichloromethane) was dried on P2O5 and distilled at atmospheric pressure (39°C); ECH (Epichlorohydrin) was dried on MgSO4 and distilled at atmospheric pressure (116°C); BBrMO (3,3-bis (bromomethyl) oxetane) was distilled at 10 mmHg, 98°C; BDO (1,4 butanediol) was distilled at 7 mmHg, 103°C. CoPolymerization ECH/BBrMO
Figure 2: ACE mechanism for polymerization of oxetane ring.
The HO- groups are formed by reaction of the first protonated monomer molecule with an oxygen atom of another oxetane ring (a), while the tail groups are formed by deactivation of the cyclic tertiary oxonium ion. When the deactivating agent is water, the OH group is the end group of the final product.
A solution of butane-1,4-diol (1.8 g, 19.97 mmol) and BF3.Et2O (5.76 g, 39.94 mmol) in anhydrous methylene chloride (300 mL) was stirred at 25°C for 2 hours under argon in a reaction calorimeter (RC1, Mettler–Toledo, Inc.). During this period of time, the first calibration of the heating measuring system was executed and the complex BF3.Et2O-BDO was formed. The reaction mixture was kept at 25°C and a solution of 3,3-bis-(bromomethyl) oxetane (60.55 g, 257.7 mmol) and epichlorohydrin (69.34 g, 749.4 mmol) in methylene chloride (300 mL) was added within a period of 2 hours with a controlled flow of 2.5 mL/min, and during this operation the heat of the reaction was measured. When the addition was complete, the reaction was left stirring for an additional hour for the second calibration of the reaction calorimeter system and then the reaction mixture was left standing overnight at room temperature. Solvent was evaporated
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
309
Kawamoto, A.M. et al.
(vacuum/room temperature) and two times 150 mL of water were added and intensively mixed for quenching. Then the polymer was washed two times with 125 mL of a water/methanol 50/50 %vol mixture. Then it was dissolved in DCM, dried with magnesium sulphate, and the solvent was evaporated on a rotary evaporator; finally, it was dried under high vacuum at 70°C. The aspect of the material is a clear high viscous substance.
Synthesis of monomer 3,3-bis (bromomethyl) oxetane (BBrMO) 3,3-bis(bromomethyl)oxetane (BBrMO) was synthesized as shown in Fig. 3.
Analysis GPC: number average molecular weight (Mn) 1134; weight average molecular weight (Mw) 1356; Polydispersity (Disp) 1.20; 1H NMR (CDCl3) δ 1.58-1.63 (m, 4H, BDO), 3.35-3.95 (m, overlapping protons from BBrMO and PECH); 13C NMR (CDCl3) δ 37.05 (Poly BBrMO, CH2Br), 44.17 (PECH, CH2Cl), 45.47 (Poly BBrMO), 68.85 (BDO), 69.64 (PECH), 70.06-73.42 (signals for CH and CH2 of PECH and Poly BBrMO), 77.88 (Poly BBrMO), 79.44 (PECH). The heat of reaction was 78 kJ/mol. Azidation of CoPolymer ECH/BBrMO CoPolymer ECH/BBrMO (126.7 g) was added to a round bottom flask with 500 mL of DMSO and heated to 120°C. To this mixture, sodium azide (119.1 g) was added and left stirring for 18 hours. Then it was cooled to room temperature and slowly added to 1.25 L of water with stirring and ice-water bath. The polymer was recovered, dissolved in about 100 mL of DCM and filtered to a clear solution free from sodium salts. The final purification was carried out by reprecipitation in pentane (450 mL). The recovered polymer was finally dried under high vacuum at 70°C to give a high viscous yellow and clear compound. Analysis
Figure 3: Synthesis of BBrMO.
The synthetic process started from the available tribromoneopentyl alcohol supplied as free sample from the American Brom, Inc. of New York Company. However, we should emphasize that the compound is not easily ready available. Tribromo-neopentyl alcohol was then converted into the corresponding BBrMO in a reaction with toluene and potassium hydroxide in an improved method from one described in literature (US Patent 5,663,289, 1997; Bednarek, Kubisa and Penczek, 2001). The process previously described by other authors has always used tetrabutylammonium bromide as phase transfer catalyst for the synthesis. However, we could prove in our studies that the product can be obtained at a high purity (99%) and higher yield without the use of the catalyst. Since catalyst normally dictates the high cost of a chemical process, a significant reduction on the cost will be achieved with more environmentally friendly conditions. Synthesis of copolymer GAP/Poly BAMO As stated above, the synthesis of the GAP/Poly BAMO copolymer was performed by cationic polymerization of halogenated monomers using butane-1,4-diol as initiator and boron trifluoride etherate (BF3OEt2) as catalyst, followed by azidation with sodium azide in dimethylsulfoxide (DMSO) medium. The reaction steps are outlined in Fig. 4.
GPC: number average molecular weight (Mn) 1383; weight average molecular weight (Mw) 1646; Polydispersity (Disp) 1.19; Equivalent Weight (titration) 1087, Hydroxyl functionality 1.27; 1H NMR (CDCl3) δ 1.59-1.63 (m, 4H, BDO), 3.15-3.90 (m, overlapping protons from BAMO and GAP); 13C NMR (CDCl3) δ 45.26 (BAMO), 50.76 (BDO), 51.71, 51.38 (BAMO and GAP), 68.91 (BDO), 69.79 (GAP), 70.65 (BAMO), 78.23 (GAP); IR(neat) 2873, 2089, 1445, 1277, 1103, 902; CHN. C, 36.96; H, 5.54; N, 43.32; Calc. C, 36.4; H, 5.04; N, 44.47. DSC (on Peak): exothermic decomposition at 244.70°C (+2570 J/g). 310
Figure 4: Synthesis of copolymer GAP/PolyBAMO. Butanediol has been used as initiator and therefore the copolymers should be difunctional.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants
RESULTS AND DISCUSSION Under the conditions described in the experimental part, the polymerization reaction is expected to proceed mainly by an activated monomer mechanism (AMM), involving successive additions of the protonated (activated) monomer to the terminal hydroxyl groups of the growing macromolecules (Kubisa et al., 2000; US Patent 5,663,289, 1997; Bednarek, Kubisa and Penczek, 2001 ). This polymerization produces polymers of narrow polydispersity since all the chains at the reaction mixture are expected to grow at approximately the same rate. However, in practice, the presence of cyclic oligomers during the polymerization process is unavoidable. These cyclic oligomers are undesirable compounds as they contain no functionality and therefore do not participate in the cross-linking step, and their low molecular weight may interfere in the desirable mechanical properties of the final product.
The IR spectra gave a first confirmation of the copolymer structure. In Figure 6, the spectra of the unreacted monomers mixture, of the halogenated copolymer and of the azido copolymers are reported. The comparison between the first two spectra shows that the C-O-C symmetrical stretching is shifted from 987 cm-1 to 1125 cm-1, due to the opening of the heterocyclic rings of the monomers. The two peaks at 1277 and 2108 cm-1, corresponding to the symmetrical and the asymmetrical stretching of N3 groups, respectively, show the presence of the azido group in the third spectrum. The substitution of chlorine groups is confirmed by the complete disappearance of the CH2Cl peak at 746 cm-1, while the same cannot be done for bromine groups because the band at 605 cm-1, corresponding to the C-Br bond, is not detectable even in the spectrum before azidation (Oliveira et al., 2006; 2007).
In order to favor the AMM mechanism and thus limit the appearance of these cyclic oligomers, it is very important to keep the monomer concentration as low as possible during the polymerization (USPatent 5,313,000; Kubisa and Penczek, 1999; Biedron, Kubisa and Penczek, 1991; Penczek, 1988). Therefore, all synthesis were performed by slowly dropping the ECH and BBrMO monomers mixture (two hours dropping time was the minimum that guaranteed very precise isothermal conditions during all the reaction time). The ratio of the monomers was selected considering that the binder must be completely non-crystalline in order to be used in casting propellant formulations. Based on preliminary investigations, using different molar ratios of the halogenated monomers, all polymerizations were carried out with the following molar ratios: ECH/BBrMO = 75/25 (corresponding to a theoretical nitrogen content equal to 45.2% by weight); (ECH+BBrMO)/BF3OEt2 = 25/1 and BF3OEt2/BDO = 2/1. However, the exact composition of the copolymer was determined by 13C-NMR. The structure of the compound is shown in Fig. 5.
Figure 5: Structure of copolymer GAP/PolyBAMO.
Figure 6: Infrared spectra of ECH/BBrMO=75/25, molar ratio, mixture of un-reacted monomers, and of the corresponding copolymer before and after azidation.
However, the presence of bromine groups and their complete displacement after azidation has been confirmed by 13C-NMR analysis (disappearance of the peak at 36 ppm from the spectra of the halogenated copolymers). The NMR analysis was used to determine the real composition of the synthesized copolymers. The 13C NMR spectrum is shown in Fig. 7. The signal at 44.3 is attributed to C quaternary (a) of polyBAMO unity. The signals that appear at 49.5-51.8 and 52.5-53.2 are attributed to CH2N3 of polyBAMO and GAP units (b). The intensities and integration of these carbon signals that are giving in Fig. 6 were a:b = 5.7:29.80. The ratio of CH2N3 is 2:1 PolyBAMO:GAP. According to this ratio, 5.7 of signal a was multiplied by 2 for PolyBAMO units and the difference to signal b was attributed to GAP units. Therefore, the molar ratio observed in 13C NMR for GAP/
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
311
Kawamoto, A.M. et al.
PolyBAMO was 62.4% GAP/29.8%PolyBAMO. This composition gives approximately 16% of PolyBAMO, higher than the initial planned one. Since PECH is more likely to form oligomers during polymerization reactions, this difference can be explained due to the partial consumption of ECH monomers to cyclic oligomers, which were partially removed during purification. An attempt to use NMR technique to do end-group analysis has also been done. For this purpose, the hydroxyl end
Figure 7:
13
C NMR for CcGAP.
Figure 8:
13
C spectra for Acetylated CcGAP.
312
groups were converted into ester ones by reaction with acetyl chloride. Spectra of acetylated and non acetylated polymers are shown in Fig. 8. The signals at 53.2-52.5 that correspond to CH2N3 were shifted upper field and overlapped with the other signals at 51.8-49.5. This shifting indicates that these CH2N3 groups are next to the –(C=O)CH3 group introduced by the acetylation of the hydroxyl end groups. Because in GAP the CH2N3 groups at the end of the chains are in
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants
β-position to the secondary hydroxyl groups, unlike BAMO, in which the CH2N3 groups are separated by one more CH2-group, it is more likely that the shifted CH2N3 groups belong to GAP end units (Lieber et al.,1963). The signals at 72.5-70.6 that correspond to CH2O are also shifted upper field overlapping with the other signals at 70.6-67.4. This indicates that this terminal unit belongs to Poly-BAMO. The signals at 26.4-25.1 are due to the CH2 group in the OCH2CH2CH2CH2O units, coming from butane-1,4-diol (BDO), used as initiator. Considering that each sequence of macromolecule has one BDO and at least one or two OH terminal group, the intensity of the signals should be in the same proportion. However, the integration of the signals BDO: CH2O: CH2N3 are: 0.66:3.17:3.30, which differs from the value expected from the AMM mechanism, which should lead to one BDO molecule per chain. Therefore, the presence of a mechanism of propagation alternative and contemporary to AMM must be hypothesized. This is reasonable, also considering that the chosen starting ratio BF3OEt2/BDO is 2:1 and a chain transfer reaction with unreacted ether groups of BF3OEt2, leading to O-CH2CH3 end-groups, may occur. This is compatible with the weak signals at 65.5-64.6 ppm and 14.4-13.9 ppm, assigned to O-CH2CH3 and O-CH2CH3, respectively. From the spectrum of the acetylated copolymer, the amount of hydroxyl end groups and OCH2CH3 end groups is calculated from the integrals of the signals at 19.51 ppm O(C=O)CH3 and signals at 14.40, 13.84 ppm OCH2CH3. Assuming that OH and OCH2CH3 are the only existing end groups in the copolymer, there are 74% of OH and 26% of OCH2CH3 end groups. The integral values of CH2 from the initiator BDO at 25.63, 25.14 ppm give only 9.5% mol of BDO when it is compared with the integral values of the end groups (OH and OCH2CH3). This value for BDO is too small, which confirms again that some alternative mechanism can operate in this polymerisation. The molecular weights of the copolymers were evaluated by GPC analysis and the hydroxyl terminal functionalities, responsible for the peak around 3400 cm-1 (Fig. 2), were measured by titration. The GPC is shown in Fig. 9. The curve is bimodal and the left peak, corresponding to lower molecular weights, should belong to cyclic oligomers, while the right one should belong to the linear chains. A deconvolution analysis of the curves leads to an estimated content of cyclic oligomers varying in the range of 6-11% by weight. Combining the GPC analysis and the OH group titration, the degree of functionality relative to the
Figure 9: GPC analysis of copolymer.
linear chains could be estimated. However, it should be emphasized that the GPC was calibrated with polystyrene standards (since a copolymer standard was not available) and this can lead to significant errors in the absolute values. The low value of the polydispersity confirms that AMM, even if it is not the only mechanism involved, should be the prevailing one. Since thermal decomposition of the propellant binders is a very important and crucial parameter for the combustion of the composite solid propellant, DSC and TGA analysis were performed for all the copolymers. At DSC, all the curves presented a main single exothermic peak between 244-245°C that can be associated to the decomposition of the azide groups to give nitrogen molecules. Considering that the same peak for GAP homopolymer corresponds to an energy release of 2240 J/g, the values obtained for the copolymers can be compared with those expected, based on the composition estimated with NMR. In fact, the experimental values are a little bit higher but quite close to the expected ones. This small difference can be explained by the TGA (Fig. 10) that, in correspondence with the same phenomena, shows a sharp weight loss of around 40-45%, with respect to the total. Again, this value is higher than that corresponding to nitrogen release alone, but at those temperatures, the phenomenon is superposed to an incipient degradation of the polymer chains, as it can be seen from the TGA curve that after the sharp step does not level, but, instead, shows a gradual weight loss. In any case, both DSC and TGA confirm that the copolymers start to decompose/ degrade at high temperatures, thus showing a satisfactory thermal stability. The C, H, N analysis is in Table 1, which showed the nitrogen content of the copolymers in comparison with GAP.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
313
Kawamoto, A.M. et al.
Figure 10: Thermogravimetric curve and its derivative vs temperature for the copolymer. Table 1:
C, H, N content of the copolymers
Product GAP Cc GAP/PolyBAMO
C % 34.72 36.96
H % 4.93 5.54
N % 38.51 43.92
As it was wished and expected, the copolymers have higher energy content compared to GAP alone. Test of the binder in propellant formulation Several studies have been done over the past years to develop high energy binders to provide better performance than the common binder HTPB in the propellant formulations. It is well known that GAP has been employed as an energetic binder as well as energetic plasticizer to increase the burn rate, specific impulse etc., in ammonium nitrate, nitramide, nitramine and perchlorate propellant systems due to its positive heat of formation and high density (ASTM E222-94). Another good advantage to be pointed is the eco-friendly environment, that leads to chlorine reduced low pollution propellants. However, the use of GAP as an energetic binder or as plasticizer with HTPB has not been so successful, as it results in propellants with poor mechanical properties. The literature (Provatas, 2000) has reported that the critical temperature (Tc), at which the binder begins to loose its elastomeric properties under motor operations, is around -30°C, which is considered very high. This temperature is lowered down by adding plasticizer, but this technique has some limitations as the mechanical 314
properties required for rocket motor operations limit the maximum ratio of GAP:Plasticizer to 1:1. Therefore, to overcome these problems energetic binders of copolymers of GAP and PolyBAMO has been suggested in this study. The higher energy content of GAP/PolyBAMO may contribute also to an enhanced performance of the resulting propellant. The copolymer GAP/PolyBAMO has been initially synthesized, at Fraunhofer-Institut fur Chemische Technologie (ICT), in Germany, as part of the cooperation program between ICT and the Chemistry Division (AQI) of IAE (Space Aeronautical Institute). At ICT, this copolymer was tested in propellant formulation. The synthesis of the copolymer was repeated at the synthesis laboratory of Chemistry Division of IAE, and it was tested in a typical composite propellant formulation. Test of the copolymer at the Fraunhofer-Institut fur Chemische Technologie (ICT) The copolymer GAP/PolyBAMO -AK 264 was used for the propellant formulation at ICT and compared with the results obtained from the traditional HTPB composite propellant. In principle, this new energetic binder will allow formulations of smokeless propellants with high specific impulse and comparatively low solid loading. Rocket propellant formulations with a specific impulse Isp ≥ 2450 Ns/kg at 1000 psi are possible with RDX/GAP/TMETN/ BTTN ingredients. Table 2 shows a standard AP/HTPB propellant formulation and also the properties of this propellant that can be used
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants
Table 2:
AP/HTPB Composite Propellant AP 1092 for comparison with AP/GAP/BAMO propellant
Ingredients Solid loading AP 192 um mps AP 45 um mps AP 4,9 um with 0,7% Petro® Burning modifiers Iron-III-oxide 6 m²/g Zircon carbide 2 um Plasticizer Diisooctyladipat DOA Antioxidant Irganox 565 HTPB Prepolymer R 45 M eq = 1288 Bonding agent HX 878 eq = 200 Isocyanate IPDI eq = 111 Curing Catalyst Triphenylbismut TPB Properties Theoretical Density (ρ) Energetic solids Total solids volumetric Total Binder Plasticizer p. o. B. R=NCO/OH Specific Impulse (Isp) Specific Impulse (Isp) Volumetric Specific Impulse (Isp*ρ) Characteristic Velocity C* Temperatur of Combustion Tc Kappa (Cp/Cv) Casting viscosity EOM Friction sensitivity Impact sensitivity Flash temperature 20°/min Dutch test 8-72 hours, 105°C Vacuum stability 40 hours/100°C Max. tensile strength Elongation at break E-Modulus Burning rate (2MPa) Burning rate (4MPa) Burning rate (7MPa) Burning rate (10MPa) Burning rate (13MPa) Burning rate (18MPa) Burning rate (25MPa) Calculated pressure exponent (2 to 25MPa)
Density AP 1092 (g/cm³) 86% 1.95 48% 1.95 24% 1.94 13% 5.24 6.73
0.7% 0.3
0.925
3.5
1.09
0.2
0.9
9.36
1.1
0.16
1.05
0.78 200ppm
1.693g/cm³ 85ma% 74.17% vol% 14ma% 25.00ma% 0.87eq 2410Ns/kg 245.7s 4080Ns/dm³ 1498m/s 2916K 1.216 136Pas 48N 10Nm 256°C 0% 0.05mL/g 1.02N/mm² 25% 8.97N/mm² 8.8mm/s 11.6mm/s 14.5mm/s 16.6mm/s 18.7mm/s 21.8mm/s 26.6mm/s 0.43
for comparison with the new energetic binder ones that are proposed in this study. Thermodynamic properties were calculated for the expansion ratio of 70:1, the mechanical properties were experimentally obtained at 20°C and rate of 50 mm/min and the burning rates values were obtained at different pressure as indicated (p in MPa) Mechanical properties 20°C/50 mm/min. With the energetic binder synthesized at ICT, three propellant formulations (GAP 03, 05b and 07) have been performed, and the composition, physical and mechanical properties were compared to equal formulations with GAP alone (GAP 02, 04a, 09 and 10), as shown in Table 3. All three formulations with the new binder and GAP diol is endowed with a higher specific impulse than the AP/ HTPB propellant. The propellants have been targeted to a maximum of specific impulse, usually accompanied by an oxygen balance between -5% ≤ O2 ≤ 0%. The maximum between 2450 Ns/kg ≤ Isp ≤ 2500 Ns/kg is reached for AP/GAP/BDNPF/A formulations between 70-75% energetic solids depending on the amount of plasticizer and the incorporation of nitramines like RDX and HMX. The addition of 10 - 15% of RDX gives a 1% higher Isp compared to the formulations without nitramine. Processing and mechanical properties Contrary to AP/HTPB propellants with 85% of energetic solids, the AP/GAP/PolyBAMO formulations are easier for casting and process. With about 50% of BDNPF/A plasticizer, the propellants GAP 03 and 05b with the new binder present excellent casting viscosity; even propellant GAP 07 with 76.6% of energetic solids and without plasticizer reflects good processing. The higher softness of the GAP/PolyBAMO propellants compared to those with pure GAP diol may have its reason from plasticizing parts within the new product. Further optimization on the ratio of curing agent and the amount of plasticizer will be necessary if the polymer binder is produced in a larger scale. Similar results are obtained for the mechanical properties of AP/GAP and AP/GAP/PolyBAMO propellants. Further optimization and the addition of a suitable bonding agent appear to be necessary for both types of propellant formulations. The AP/GAP propellants should be equipped with a higher tensile strength, a better elongation and a reduced modulus. Glass transition points The glass transition points have been determined by DSC and TMA. Both values are outlined in Table 3. For
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
315
316
AP 200 µm SNPE AP 45 µm SNPE AP 6,6 µm with 0,6%TCP RDX 5 µm Dyno GAP Diole (SNPE) Gap/PolyBamo copolymer N100 BDNPF/A iron-III-oxide 240m²/g iron-III-oxide 6m²/g Zirconcarbide Carbon D22 Total Theoretical Density O2 balance propellant Total solids R=NCO/OH value Plasticizer in binder Properties Specific Impulse Specific Impulse Volumetric Specific Impulse Characteristic Velocity C* Tc Combustion viscosity before curing viscosity EOM Surface Hardness Max. tensile strength elongation at max. tensile strength elongation at break E-modulus Tg (DSC) Tg (TMA) Impact sensitivity Friction sensitivity Chemical stability Ignition temperature 20°C/min Dutch test 8-72hours/105°C Vacuum Stability 40hours/100°C 213 0,14 0,29
212 0,17 0,3
°C % weight loss mL/g
g/cm³ % mass (%)
2478 252.6 4266 1498 3067.5 48 44 20 0,26 24,4 26,8 1,61 -50,4 -50,7 5 30
11.83 2.67 14 0.5
2482 253.1 4280 1496 3068 72 64 60 0,41 7,8 10,3 7,42 -48,3 -49,85 6 30
1.75 14 0.5
12.75
Mass (%) 40 20 11
GAP-03
% Units Ns/kg s Ns/dm³ m/s K Pas Pas Shore A N/mm² % % N/mm² °C °C Nm Nm
1470 1021 192
Mass (%) 40 20 11
GAP-02
5 100 1.721 -3.41 71.5 1.20 49.12%
% 34.04 34.04 33.84 -21.61 -118.26 -119.9 -200.58 -57.64 10.02 10.02 -61.99 -266.41
g/cm³ 1.95 1.95 1.95 1.816 1.29 1.29 1.14 1.39 5.24 5.24 6.73 1.85 drops
Equivalent weight g
5 100 1.724 -2.46 71.5 1.05 49.12%
O2 balance
Density
AP/GAP/BAMO propellants in comparison to AP/GAP propellants
Ingredients
Table 3:
208 0,16 0,34
5 20
2503 255,1 4348 1512 3112 96 76 53 0,36 13,1 18,3 5,44
5 100 1.737 -4.22 75 1.05 50.00%
1.51 12.5 0.5
11.5
11.5 10.99
209 0,15 0,31
2499 254.7 4334 1514 3108.8 72 56 20-25 0,21 37,4 44,4 0,9 -50,5 -51 5 30
5 100 1.734 -5.12 75 1.26 50.00%
10.1 2.4 12.5 0.5
Mass (%) 42 21
GAP-05b
Mass (%) 42 21
GAP-04a
200 0.14 0.36
2469 251.7 4293 1503 3059 408 248 65 0.68 12.8 15.4 8.17 -40.9 -40.7 5 32
5 100 1.739 -4.73 77.2 1.25 0.00%
0.6
18.46 4.34
Mass (%) 43.2 21.6 11.8
GAP-07
207 0.14 0.3
2504 255.2 4380 1511 3110.5 224 152 70 0.56 7.6 12.2 14.57 -44.4 -43.8 5 32
5 100 1.749 -3.49 77.8 1.05 33.33%
1.78 7.4 0.5
11.9 13.02
Mass (%) 43.6 21.8
GAP-09
206 0.22 0.3
5 48
2479 252.7 4325 1490 3055.5 186 160 78 0.73 4.8 6.6 23.39 -43.3
5 100 1.744 -1.12 75.8 1.05 25.00%
2.19 6.05 0.6
15.96
Mass (%) 42.4 21.2 11.6
GAP-10
Kawamoto, A.M. et al.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants
formulations with equal amounts of plasticizer like GAP 03 and GAP 05b, the AP/GAP/PolyBAMO propellants with GAP/PolyBAMO copolymer (Tg = -50°C) show a clear advantage over those of AP/GAP formulations like GAP 02 (Tg = -48°C). As shown in Figs. 11 and 12, the copolymer GAP/PolyBAMO with -54.3°C already shows a lower glass transition point than GAP diol – here it is GAP OP 2A 653 from SNPE with -49.3°C. Chemical stability and sensitivity Although the values of Dutch test, vacuum stability and deflagration point represent only the results of short term tests; the chemical stability of both AP/GAP and
AP/GAP/PolyBAMO propellants appear convenient and quite sufficient for practical purpose. The limits for the Dutch test are 2% of mass loss within 8 - 72 h heating at 105°C and the limits for vacuum stability are 1.2 mL/g gas evolution within 40 hours heating at 100°C. Both terms have been fulfilled within a good margin. Sensitivity values have been determined only by impact and friction sensitivity, as it was outlined above for the monomers and copolymers. The determined reaction limits of Friction Test (BAM) hammer and friction apparatus are within a convenient scope for application if they are compared to those of AP/HTPB rocket propellants, which were determined by the same operator.
Figure 11: Glass transition of GAP/PolyBAMO copolymer.
Figure 12: Glass transition of GAP diol OP2A 653. J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
317
Kawamoto, A.M. et al.
Burning behaviour The burning behaviour was determined by Crawford Bomb tests. Burning rates were determined on coated propellant strands with 5 mm x 5 mm cross section and 50 mm measuring distance. The burning rate was calculated using the expression (Eq.1): r = Apn
or
ln r = nln p + ln A
(1)
Where p is the pressure, n is the pressure exponent and A is the burn rate constant (for propellants with n ≤ 1 and explosives with n ≤ 1). Practicable values for rocket propellants are n ≤ 0.6, and the more convenient values for TMP propellants are n ≤ 0.5. The values for AP/HTPB composite propellants are usually in the range between 0.3 ≤ n ≤ 0.5.
Figure 14: Burning behaviour of the AP/GAP propellant GAPCom-02 and the AP/GAP/PolyBAMO propellant GAP-Com-03.
The burning behaviour of the reference AP/HTPB propellant formulation AP 1092 is presented in Fig. 13.
Figure 15: Burning behaviour of the AP/GAP and AP/GAP/ PolyBAMO propellant 02 and 03 in comparison to the AP/RDX/GAP and AP/RDX/GAP/BAMO propellants 04a and 05b.
Figure 13: Burn rate versus pressure diagram for AP 1092.
The burning behaviour of the propellant formulations for GAP/PolyBAMO copolymer, comparatively with GAP, accordingly with the formulations from Table 3, is graphically presented in Figs. 14 to 18. Burn rates and pressure exponents are outlined in Table 4. Propellants with 11 - 12% RDX 5µ like GAP 04a, 05b and 09 clearly differ in burn rates with 16 - 19 mm/s at 10 MPa compared to propellants with AP 6 µ like GAP 02, 03, 07 and 10 with 23 to 31 mm/s at 10 MPa. An increase of burn rates at lower pressures is also observed for propellants with reduced amount of plasticizer BDNPF/A. The azido polymer GAP and GAP/PolyBAMO favour burn rate increase and overall performance of the formulation compared to traditional AP/HTPB propellants. Propellants with GAP/ PolyBAMO copolymer, GAP 03 and 07 are endowed 318
Figure 16: Burning behaviour of the AP/RDX/GAP propellant GAP 04a and the AP/RDX/GAP/BAMO propellant with Gap/PolyBamo copolymer: GAP 05b.
with a beneficial reduction of pressure exponents. A slight advantage in pressure exponents can be observed for the AP 6 µ in comparison to those with RDX 5 µ. Nevertheless, all propellant formulations exhibit quite
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants
convenient burning behaviour, which may be brought to good use in rocket motor applications. Figures 14 to 18 refer to the burning behaviour of composite propellants using AP and GAP/PolyBAMO copolymer (mixtures of AP/GAP/BDNPFA and AP/GAP/PolyBAMO/ BDNPF/A), determined by Crawford measurements at 23 - 24°C. Test of the copolymer at the Chemistry Division of IAE
Figure 17: Burning behaviour of the AP/GAP propellant GAP 02 in comparison to the AP/RDX/GAP propellant GAP 04a.
The synthesis of the copolymer GAP/PolyBAMO was reproduced at the Synthesis Laboratory and then tested in a typical formulation of composite propellant at the Propellant Research Laboratory of Chemistry Division. Curing test of the copolymer Before the use in propellant formulation, the copolymer was submitted to a curing test, using a tri-functional isocyanate (Desmodur® N 100, Bayer Material Science), the same one that has been used at ICT. For comparison reasons, curing tests with N100 were also done with the pre-polymers HTPB and GAP. Dibutyltin dilaurate (DBTDL - D22) was used as catalyst for all three curing reactions, the same catalyst used in the tests at ICT (as it can be seen at Table 4). Two drops of the catalyst were used for each 5 g of the pre-polymer.
Figure 18: Burning behaviour of the AP/GAP/BAMO propellant GAP 03 in comparison with AP/RDX/ GAP/PolyBAMO propellant GAP 05b.
Table 4:
Initially, in the tests, a NCO/OH ratio of 1:1 for all the three pre-polymers was used, and the curing agent was
Burning rates and pressure exponents of propellant formulations for Gap/PolyBAMO copolymer comparatively with GAP
Burning rate
Units
Burning rate (2MPa) mm/s
GAP-02
GAP-03
GAP-04a
GAP-05b
GAP-07
GAP-09
GAP-10
18.13
11.95
12.15
23.9
13.9
23
15.2
Burning rate (4MPa) mm/s Burning rate (7MPa) mm/s
22.8
21.5
14.75
14.62
27
16.8
27.8
Burning rate (10MPa) mm/s
24.75
23.4
16.9
16.81
29
19
31.5
Burning rate (13MPa) mm/s
26.2
24.95
19.05
19.22
30.5
21.7
32.5
26.1
22.47
22.18
34
26
33.8
Burning rate (18MPa) mm/s Pressure exponents n1
0.32 (2-7)
0.31 (4-7)
0.38 (4-10)
0.35 (4-7)
0.22 (4-7)
0.34 (4-7)
0.34 (4-10)
n2
0.24 (7-10)
0.24 (7-13)
0.49 (10-18)
0.37 (7-10)
0.20 (7-13)
0.53 (7-18)
0.12 (10-18)
n3
0.21 (10-13) 0.14 (13-18)
0.41 (4-18)
0.26 (4-18)
n average
0.30 (2-13)
0.25 (4-18)
0.47 (10-18) 0.33 (13-18) 0.42 (4-18)
0.40 (4-18)
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
0.23 (4-18)
319
Kawamoto, A.M. et al.
adjusted according to the OH equivalent of each prepolymer. After heating at 60°C for 24 hours, it was observed the curing of HTPB and the GAP pre-polymers with a hardness of 42 Shore A. However, the mixture containing the copolymers GAP/PolyBAMO resulted in a softer stick polymer. Therefore, as an attempted to solve the problem, a value of 1.55 for the ratio of NCO/OH was used, which is the same used at the formulations tests at ICT (Table 4). As a result, it was possible to increase the hardness of the polymer; however, still with lower value than the ones for HTPB and GAP. Nevertheless, it was the value used for testing GAP/PolyBAMO copolymer in propellant formulation. Test of GAP/PolyBAMO copolymer in propellant formulation The propellant formulation at the Chemistry Division of IAE using GAP/PolyBAMO copolymer was carried out based on the results obtained in ICT (Table 4). Due to the small amount of copolymer available for the test, only 1 kg of propellant was processed, which is presented in Table 5. Since some components like RDX and AP 6 µm were not available in internal market, they were excluded from the formulation. The energetic plasticizer, BDNPF/A, was replaced by DOA, and AP 200 µm was replaced by AP 400 µm. However, the percentage of solids (77.5%) for the propellant formulation was the same as the one used in ICT. Table 5:
Composite propellant formulation containing GAP/ Poly BAMO tested at AQI/IAE
Component GAP/Poly BAMO
% 14.56
Mass (g) 145.6
DOA Fe2O3 AP 400 µm AP 30 µm N 100 DBTDL
4.5 0.5 54.0 23.0 3.44 -----
45.0 5.0 540.0 230.0 34.4 40 drops
For safety reasons, the propellant formulation was processed using a helicone mixer (one gallon) located at the explosive pilot plant of Defense System Division – Explosive department (ASC-XPQ) at IAE. Then, the mixture was loaded in 2 moulds measuring 125 x 125 x 10 mm, and left curing at 60°C for 192 hours. During the processing, the mixture had an aspect of low viscosity before the addition of the curing agent, but it was not possible to measure precisely the value of it, due to the small amount of available propellant. After the addition of the curing agent, the substances were mixed for 10
320
minutes and loaded into the moulds. During the loading, the viscosity rapidly increased, which brought difficulty to finish the operation. This behavior was attributed to the excess of DBTDL (curing catalyst) that was used. Therefore, for future formulations, it is recommended the use of lower quantity of catalyst in order to extend the pot life of the mixture. The propellant was cured at 60°C for 192 hours. The measured hardness was 45 Shore A and it is an intermediate value between the ones obtained at ICT: 20 Shore A for formulations containing BDNPF/A, and 65 Shore A for formulations without plasticizer. The mechanical properties of the propellant samples were measured at the Mechanical Properties Laboratory (PPM) of the Chemistry Division. Stress and strength properties were measured and gave a value of 0.2 MPa and 10% of elongation. Despite being low values, they are similar to the results obtained in some formulations that were carried out at ICT, especially the ones containing BDNPF/A (Table 4). The fragility of the propellant observed in the test performed at AQI can be attributed mainly due to the presence of bubbles in the propellant. This bubbles appeared for technical reason since it was not possible to cast the propellant under vacuum. Nevertheless, both values – one from AQI and other from ICT – are low, which shows a propellant with fragile mechanical properties for being used in rockets, especially the big sized ones. Klaus Menke, phD, from ICT (Eisele, Zimdahl and Menke, 2002), has already mentioned that the low values can also be due to the mono functional molecules which might be present at the copolymer that can disturb the cross linking process of the polymeric matrix, which is in agreement with the results obtained in the curing tests of the copolymer (item Curing test of the copolymer). Klaus Menke also suggested that the mechanical properties of the propellant can be improved by a previous reaction of the copolymer with an excess of diisocyanate (for example, HDI), which leads to a new copolymer with isocyanate terminal groups. Another alternative to improve the mechanical properties of the propellant could be executed with the use of a bonding agent that is regularly used in HTPB propellant formulation. The propellant processed at AQI was also tested in burning rate at Crawford Bomb and have presented values around 20 mm/s, which are similar to the ones obtained at ICT. However, under the narrow range of pressure in which the samples were tested (4 to 6 MPa), the value of the exponent of the pressure (n) is very low (close to zero). Some formulations tested at ICT also presented low values of n (0.12 to 0.20), with an increase on the
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
Synthesis and characterization of GAP/BAMO copolymers applied at high energetic composite propellants
values of pressure. The low values of n can be considered an advantage in some specific propellant formulation. However, this burning behavior with low value of n should be better evaluated in future work, especially using a wider range of pressure. CONCLUSIONS Random copolymers of GAP/PolyBAMO with nominal composition 75/25 were synthesized to produce a material which has been tested as energetic binder in some formulations of solid rocket propellant. The synthetic route started with the synthesis of the halogenated polymeric precursor and then by its azidation. The introduction of PolyBAMO units in the GAP chain has the advantage of an increase in the azide groups and, consequently, in the energetic content of the material, but with a limited value that preserves the amorphous morphology of the polymer. The operating conditions and the catalytic system were chosen in order to favour a living character of the polymerization and the formation of hydroxyl-terminated chains. However, the characterization of the final product showed that the addition of monomeric units followed also some alternative ways which led to the formation of cyclic oligomers, of non-hydroxylic end groups and to a not very small polydispersity index. Although the measurements of GPC has been done without an appropriate standard, the calculated average number of OH groups for each chain resulted coherent with the value estimated from NMR analysis. The preliminary curing tests showed a promising elastomeric rubber with very good mechanical properties. Samples of the copolymer have been tested at ICT (Germany) and at the Chemistry Division of IAE, and a comparative analysis has been carried out. The first results showed that the copolymer has good potential to be used as binder in propellant formulations, which will lead to a propellant with high specific impulse. However, lots of work still need to be done till a specific propellant formulation containing the new energetic copolymer be ready for use in reality at a flying rocket motor. REFERENCES Bednarek, M., Kubisa, P. and Penczek, S., 2001, Macromolecules, Vol. 34, pp.5112.
Formulations”, Proceedings of the 33rd Intern. Annual Conference of ICT in Karlsruhe - Germany, June 25-28, pp. 145. Eishu, K., Yoshio, O., 1996, “Insensitive munitions and combustion characteristics of BAMO/NMMO propellants”. J. Energ. Mater. Vol. 14, N. 3-4, pp. 201-215. Elie, A., 1990, “European Patent Application, A2 0 350 226”. Helmy, A.M., 1984, “Investigation of new energetic ingredients for minimum signature propellants”. AIAA84-1434, Proceedings of the 20th Joint Propulsion Conference, Cincinnati, Ohio, USA. Kubisa, P., Penczek, S., 1999, Prog. Polym. Sci., Vol. 24, pp. 1409-1437. Kubisa, P. et al., 2000, Macromolecules Symposia, pp. 153-217. Lieber, E. et al., 1963, “Infrared spectra of acid azides, carbamyl azides and other azido derivatives. Anomalous splittings of the N3 stretching bands”, Vol. 19, pp. 1135-1144. Menke, K. et al., 2002, “Minimum Smoke Propellants with High Burning Rates and Thermodynamic Performance””, AVT Conference 089, RTO-MP-091, Aalborg. Menke, K., Böhnlein-Mauß, J. and Schubert, H., 1996, “Characteristic Properties of AN/GAP Propellants”, Propellants, Explosives, Pyrotechnics, Vol. 21, pp. 1-7. Menke, K., Böhnlein-Mauß, J. and Schubert, H., 1996, “Characteristic Properties of AN/GAP Propellants”, Propellants, Explosives, Pyrotechnics, Vol. 21, pp. 1-7. Oliveira, J.I.S. et al., 2007, “Determination of CHN Content in Energetic Binder by MIR Analysis”. Polímeros, Vol. 17, pp. 42-46. Oliveira, J.I.S. et al., 2006, “MIR/NIR/FIR Characterization of Poly-AMMO and Poly-BAMO and their Precursors as Energetic Binder to be used in Solid Propellants”, Propellants, Explosives, Pyrotechnics, Vol. 31, p. 395-400.
Biedron, T., Kubisa, P. and Penczek, S., 1991, Journal of Polymer Science Part A: Polymer Chemistry., Vol. 29, pp. 619-628.
Penczek, S., 1988, ACS Polymer Preprints, Vol. 29, No 2, p. 38.
Eisele, S., Zimdahl, L. and Menke, K., 2002, “Burning Propellants Based on Silicone and GAP Binder
Provatas, A., 2000, “Energetic polymers and plasticisers for explosive formulations – a review of recent advances”.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
321
Kawamoto, A.M. et al.
Melbourne: Defense Science & Technology Organisation (DSTO). Yoshio, O. et al., 1994, “Burning rate augmentation of BAMO based propellants”. Propellants, Explosives, Pyrotechnichs, Vol. 19, No 4, pp. 180-186.
322
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 307-322, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02038010
Eunice Aparecida Campos*
Institute of Aeronautics and Space São José dos Campos – Brazil euniceeac@iae.cta.br
Rita de Cássia L. Dutra
Institute of Aeronautics and Space São José dos Campos – Brazil ritarcld@iae.cta.br
Luis Cláudio Rezende
Institute of Aeronautics and Space São José dos Campos – Brazil lluisclaudiolcr@iae.cta.br
Milton Faria Diniz
Institute of Aeronautics and Space São José dos Campos – Brazil miltonmfd@iae.cta.br
Wilma Massae Dio Nawa
Institute of Aeronautics and Space São José dos Campos – Brazil wilmawmdn@iae.cta.br
Koshun Iha
Technological Institute of Aeronautics São José dos Campos – Brazil koshun@ita.br *author for correspondence
Performance evaluation of commercial copper chromites as burning rate catalyst for solid propellants Abstract: Copper chromites are well known as burning rate catalysts for the combustion of composite solid propellants, used as a source of energy for rocket propulsion. The propellant burning rate depends upon the catalyst characteristics such as chemical composition and specific surface area. In this work, copper chromite samples from different suppliers were characterized by chemical analysis, FT-IR spectroscopy and by surface area measurement (BET). The samples were then evaluated as burning rate catalyst in a typical composite propellant formulation based on HTPB binder, ammonium perchlorate and aluminum. The obtained surface area values are very close to those informed by the catalyst suppliers. The propellant processing as well as its mechanical properties were not substantially affected by the type of catalyst. Some copper chromite catalysts caused an increase in the propellant burning rate in comparison to the iron oxide catalyst. The results show that in addition to the surface area, other parameters like chemical composition, crystalline structure and the presence of impurities might be affecting the catalyst performance. All evaluated copper chromite samples may be used as burning rate catalyst in composite solid propellant formulations, with slight advantages for the SX14, Cu-0202P and Cu-1800P samples, which led to the highest burning rate propellants. Keywords: Copper chromite, Composite propellant, BET, Burning rate catalyst.
INTRODUCTION Composite solid propellants are used as the energy source for the propulsion of solid rocket motors. This kind of propellant is considered a heterogeneous mixture in which solid particles are embedded in a polymeric matrix (binder) (Kubota, 2007; Davenas, 2003; Rezende et al., 2002). Nowadays, the most commonly used polymer is hydroxyl polybutadiene, which acts as a binder for the solid particles and also as a fuel during the combustion of the propellant. The solid particles are mainly composed of an oxidizer, usually ammonium perchlorate (AP), and a metallic fuel, usually aluminum powder, used to increase the temperature of the combustion products (Prajakta et al., 2006; Ma and Li, 2006; Sciamareli, Takahashi and Teixeira, 2002). In addition to the basic components, the propellant formulation contains other ingredients like plasticizers, bonding agents and combustion catalysts. The latter have Received: 30/06/10 Accepted: 26/07/10
the function of increasing the burning rate of the propellant (Prajakta et al., 2006; Kubota, 2007; Li, Cheng, 2007). This happens when one can no longer increase the burning rate through decreasing the particle size of the solid components, for example, the ammonium perchlorate used as oxidizer (Kubota 2007; Prajakta et al., 2006). The first catalysts evaluated as accelerators for the thermal decomposition of AP based propellants were the transition metal oxides, like ferric oxide (III) (Fe2O3), cobalt oxide (III) (Co2O3), manganese oxide (MnO2), chromium oxide (III) (Cr2O3) and copper chromite (II) (CuCr2O4). The efficiency of these catalysts was also evaluated in the thermal decomposition of AP only (Ma, Li, 2006). The characteristics of the metal oxides, such as particle size, surface area and defects in the crystalline structure may affect the burning behavior of ammonium perchlorate based propellants (Engen and Johannesen, 1990; Ma and Li, 2006). Different mechanisms have been suggested to explain the thermal decomposition, but no model is completely satisfactory (Kishore and Sunitha, 1979; Carvalheira, Gadiot and Klerk, 1995).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 323-330, Sep-Dec., 2010
323
Campos, E.A. et al.
Among the metal oxides, the most widely used as burning rate catalysts for composite propellants have been iron oxide and copper chromite (Prasad, 2005). The latter has been considered the most effective, due to the spinel shape of its crystalline structure and the arrangement of copper in its structure (Boldyreva et al., 1975). Pekel et al. (1990) studied the effect of two iron oxides with different specific surface area on the burning rate of composite propellant. They observed that the greater the specific surface area the higher the propellant burning rate. A similar conclusion was reached by Burnside (1975) and Engen and Johannessen (1990), on evaluating the effect of the specific surface area and particle size of different types of iron oxide on the burning rate of composite propellants. Considering the performance of a rocket motor, it is known that the propellant burning rate varies according to the internal pressure of the combustion chamber (Kubota, 2007; Li and Cheng, 2007) usually expressed by the equation of Saint Robert and Vieille (Eq. 1): Vb=a.Pn
(1)
Where Vb is the burning rate (mm/s), a is the constant rate, P is the combustion chamber pressure (MPa) and n is the pressure exponent. The latter, with typical values between 0.2 and 0.7, indicates the sensitivity of the burning rate with pressure variation (Davenas, 2003; Benmahamed et al., 2002). Practically, it is desirable that the value of n be as low as possible in order to increase the stability of combustion of the propellant. The value of n depends on the composition of the propellant and, mainly, on the characteristics of the burning rate catalysts (Davenas, 2003). Copper chromite can be synthesized by ceramic method (oxide method), co-precipitation method and also via citric acid synthesis (Li, Cheng, 2007). The ceramic method consists of calcination of copper oxide (II) (CuO) and chromium oxide (III) (Cr2O3) mixtures at 500 to 800°C, usually containing stoichiometric amounts of both reactants (Reaction 1). If the calcination is carried out at a higher temperature (900°C), copper chromite (I) (Cu2Cr2O4) will be formed (Reaction 2): sC CuO s Cr2O3 s  500-800    q CuCrO 2 4 s
(Reaction 4), which is first obtained from the reaction between potassium dichromate and pentahydrated copper sulfate in the presence of ammonia (Reaction 3). By increasing the calcination temperature to 600°C or higher, copper chromite (I) can be formed (Reaction 5).
Reaction 3
sC 2Cu OH NH 4 CrO 4 Â 100-500 Â Â Â q CuO(S) CuCr2 O 4(S)
Reaction 4
1 600 s C CuCr2 O 4 CuO(S) Â #Â Â q Cu 2 Cr2 O 4(S) O 2(g) 2
Reaction 5
Previously, copper chromite was synthesized in our laboratories by the two methods presented above (Kawamoto et al., 2004). Different techniques based on infrared analysis (IR), like transmission, diffuse reflection (DRIFT) and photoacoustic, were used aiming the characterization of the catalysts prepared by the two methods (Campos et al., 2003). It was observed that through the appropriate use of different IR techniques, it is possible to identify the copper chromite synthesis method. Based on these results, copper chromite samples from different suppliers and synthesis methods were analysed in our laboratories by different IR techniques. With copper chromite samples from the same supplier, it have been observed IR bands related to the reagents used in the synthesis, and the better results have been obtained with the surface analysis techniques (DRIFT and PAS) (Campos et al., 2003). In this work, copper chromite samples from different suppliers were evaluated as burning rate catalysts in a typical composite propellant formulation. Firstly, the catalysts were analyzed by chemical (Furman, 1996), FT-IR and BET techniques (Campos, 2004). Afterwards, the catalysts were individually incorporated into the propellant formulation for hardness, tensile strength, density and mainly burning rate evaluation. There is an attempt to correlate the characteristics of the catalysts with the propellant properties (Campos, 2004).
Reaction 1
1 sC CuO s CuCrO Â 900 Â Â q CuCr O O 2 4 2 2 4 s 2 2(g)
EXPERIMENTAL
Copper chromite samples
Reaction 2
In the co-precipitation method, the catalyst is obtained by calcinations at 100 to 500°C of basic copper chromate 324
2CuSO 4(aq) K 2 Cr2 O7(aq) 4NH 3(aq) 3H 2 O(1) q 2Cu OH NH 4 CrO 4(S) K 2SO 4(aq) NH 4 2 SO 4(aq)
The following copper chromite samples were evaluated in this work: Cu-0202P, Cu-1950P and Cu-1800P from
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 323-330, Sep-Dec., 2010
Performance evaluation of commercial copper chromites as burning rate catalyst for solid propellants
Engelhard; HOX 80:20 and HOX 50:50 from Oxiteno; a sample from IPM (Instituto de Pesquisa da Marinha); and SX 14 from AEQ (Aliança Eletroquímica). A sample of iron oxide catalyst (23 FF from Globo) was used for comparison. Chemical analysis The copper content of each sample was determined by electrogravimetric analysis and the chromium content was determined by volumetric analysis (Furman, 1962).
viscosity during the mixing process was measured at 48 50°C by a Brookfield viscometer, using a type A spindle at 1 rpm. The propellant cure was followed by shore A hardness measured by a Zwick durometer (NBR 7456). Tensile tests of the propellant samples were carried out in an Instron 1130 machine at room temperature and at 50 mm/s (NBR 9717). The burning rate of the propellant samples was obtained in a Crawford bomb. RESULTS AND DISCUSSION IR analysis
Instrumental neutron activation analysis The copper and chromium contents of each sample were also measured by instrumental neutron activation analysis (INAA), at Instituto de Pesquisas Energéticas e Nucleares (IPEN) and Laboratório de Radioisótopos (Centro de Energia Nuclear na Agricultura of Universidade de São Paulo). The INAA consists in irradiating the samples (50 - 300 mg) with a neutron flux of about 1013 n cm-2s-1 for 1 hour and then measuring the induced radioactivity after 4, 8 and 17 days of radioactive decay, using germanium semiconductor detectors. The neutron flux was estimated by using nickel-chromium wires irradiated together with the samples. The copper/chromium contents were calculated by a specific software (Tagliaferro et al., 2006). IR analysis A FT-IR Spectrum 2000 Perkinelmer was used for IR analyses of the catalysts. The spectra were obtained by KBr transmission technique (0.8:400 mg) in the range of 4000-300 cm-1, with 4 cm-1 resolution and gain 1. Surface area analysis The values of surface area of the catalysts were obtained by adsorption of N2 at 77 K, using Accusorb 2100E Micromeritics equipment (Campos, 2004; D-4222-83, 1983). Evaluation of the catalysts in the propellant formulation After characterization, 2% (w/w) of each catalyst was incorporated into a typical composite propellant formulation (named PC18) based on HTPB binder (14%), ammonium perchlorate (72%) and aluminum (12%). The propellant formulation was processed in a vertical mixer, under vacuum and at 48 50°C. The propellant
According to a previous work (Campos et al., 2003), the KBr transmission IR technique can be used to identify chromite anion bands and also the bands of the raw materials (reagents) used to synthesize the copper chromite by the ceramic or co-precipitation method. The bands at 614 and 524 cm-1, attributed to the Cr2O4= anion, are related to the copper chromite prepared by ceramic method. The bands related to the copper chromite prepared by co-precipitation method are those between 500 - 620 cm-1 (Cr2O4= anion), in addition to those in the range of 1 100 - 1 200 cm-1 (SO4= anion) and those in the range of 800 - 900 cm-1 (CrO4= anion) (Miller, Wilkins, 1952). Figure 1 presents the IR spectra of copper chromite samples evaluated in this work. The spectra A to E indicate that catalysts Cu-0202P, Cu-1950P, Cu-1800P, HOX 80:20 and HOX 50:50, were synthesized by ceramic method. Based on the characteristics bands of the chromite anion, it can be concluded that the IPM and the SX14 copper chromites (spectra F and G) were synthesized by coprecipitation method. In addition, the band at 800 cm-1, which is the main difference between spectra F and G, can be attributed to the reagents used in the synthesis of each copper chromite. According to the literature, solutions of chromium and copper nitrate can also be used as reagents in the co-precipitation method (Carvalho, Feitosa and Rangel, 2000; (Li, Cheng and 2007). As the band close to 800 cm-1 is in the region of chromate and nitrate absorptions (Miller, Wilkins, 1952), it can be concluded that the IPM and SX14 copper chromites were synthesized by co-precipitation method. In the case of SX14 copper chromite, this conclusion was confirmed by the supplier. Chemical analysis Table 1 presents the Cu/Cr contents of the copper chromite samples measured by electrogravimetric, volumetric and INAA analyses. Except for the lower Cu content of Cu1800P sample determined by analysis, all other Cu and
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 323-330, Sep-Dec., 2010
325
Campos, E.A. et al.
*sulfate anion ; **chromate anion; ***chromite anion; +nitrate. Figure 1: FT-IR spectra - ceramic method: (A) Cu-0202P; (B) Cu-1950P; (C) Cu-1800P; (D) HOX 80:20; (E) HOX 50:50 and coprecipitation: (F) IPM; (G) AEQ SX 14. Table 1:
Cu/Cr contents (w/w) of copper chromite samples measured by electrogravimetric, volumetric and instrumental neutron activation analysis (INAA)
Copper chromite SX14 Cu 0202P Cu 1800P Cu 1950P HOX 80:20 IPM
Eletrogravimetric (%Cu) 38.4 66 41.5 36.4 56.8 32.7
INAA (%Cu) 35.6 63.5 38.3 35.7 58.6 33.6
Cr values determined by the two techniques present good similarity among them. Surface area The specific surface area values of the copper chromites evaluated are shown in Table 2, with the properties of the propellant compositions. The catalysts supplied by Oxiteno (HOX 80:20), Engelhard (Cu-1950P and Cu1800P), AEQ (SX 14), as well as the 23 FF ferric oxide present the highest values of surface area, and the copper chromite from IPM presents the smallest value (3m2/g). Effect of the catalysts in composite propellant formulation Table 2 presents the properties of a typical composite propellant formulation containing the different copper 326
Reference (%Cu) ---------67 43 36 ----------------
Volumetric (%Cr) 25.3 10 30.9 30 12.1 28.9
INAA (%Cr) 25.5 10 31.3 32.2 12.3 27.8
Reference (%Cr) ---------12 31 33 --------
chromite catalysts. The iron oxide containing composition is considered a reference with a burning rate of about 13 mm/s at 6 MPa, measured in a Crawford bomb. The end of mix viscosity (EOM) of each composition is the viscosity value measured just after the incorporation of the curing agent (last component). “Pot life’’ is the time after the addition of the curing agent, within which the viscosity of the propellant is still suitable (low enough) for casting the rocket motor with the propellant. The values corresponding to “pot life 30 min” and “pot life 60 min” refer to the viscosity of the propellant measured after 30 and 60 minutes, respectively, from the addition of the curing agent. Concerning the propellant processing, it was observed that the viscosity behavior followed a similar pattern for all compositions, which means requiring three hours of mixing before the addition of the curing agent (data not presented). The lowest EOM viscosity is related to the HOX 80:20 catalyst and the highest values are associated with
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 323-330, Sep-Dec., 2010
Performance evaluation of commercial copper chromites as burning rate catalyst for solid propellants
Table 2:
Properties of a typical composite propellant formulation containing copper chromites from different suppliers
23FF
Cu-0202P
HOX 80:20
HOX 50:50
IPM
SX 14
Surface area (m2/g)
46
19
52
28
3
44
32
34
EOM (Pa.s)
320
312
240
344
376
328
320
400
Pot life 30 min (Pa.s)
408
320
264
360
568
344
344
496
Pot life 60 min (Pa.s)
-----
336
280
384
696
360
360
528
1.74±0.01
1.75±0.01
1.75±0.01
1.75±0.01
1.75±0.01
1.75±0.01
1.75±0.01
1.75±0.01
72±1
76±1
76±1
77±1
76±1
75±1
74±1
73±1
0.95±0.02
0.90±0.02
0.93±0.02
0.94±0.02
1 ±0.03
1.04±0.01
0.85±0.01
0.85±0.01
46±1
38±1
46±2
23±2
36±1
41±2
36±1
49±2
6.50.Pc0,41
7.59.Pc0,36
5.80.Pc0,45
6.39.Pc0,42
5.19.Pc0,46
6.55.Pc0,47
6.90.Pc0,43
5.76.Pc0,40
13.4
14.3
13.1
13.5
11.8
15.2
15
11.9
Density (g/cm3) Hardness (Shore A) Tensile strength (MPa) Elongation (%) Burning rate equation Burning rate at 6 MPa (mm/s)
IPM and Cu-1950P catalysts. All other EOM values are not much different from one another, taking into account a typical dispersion of 16 Pa.s for the measures. For most of the compositions, the increase of the pot life viscosity is within the normal range for this kind of propellant formulation. The exception is the highest increase of the pot life viscosity for the composition containing the IPM copper chromite. Even in this case, the viscosity value is still adequate for a good propellant casting. The density values of the cured propellant compositions are nearly the same, regardless of the copper chromite sample used, and also very similar to the composition with iron oxide. This is an expected result, since the catalyst content (2% w/w) is low compared to the total amount of solids (86%) of the propellant formulation. Similarly, no remarkable variation was observed in the hardness of the propellant as function of the type of evaluated copper chromite. In principle, the mechanical properties of the propellant should not be affected by the type of catalyst. In general, the differences observed among the evaluated compositions can be considered normal, taking into account that composite propellants are heterogeneous materials. It can be observed that most of the copper chromite containing compositions present tensile strength (TS) and elongation (ε) very close to the composition
Cu-1800P Cu-1950P
with iron oxide. Without any defined reason, the lowest values of TS are presented by the compositions containing the Cu-1800P and Cu-1950P catalysts. Despite this, all TS values can be considered normal, allowing the propellant to be used in a real application. Similarly, the elongation values between 36 and 49% are also considered appropriate for a real application of the propellant. The only value outside this range is the one related to the composition containing the HOX 50:50 catalyst. However, if necessary, this elongation can be increased by adjusting the ratio between the curing agent and the polymeric binder. Regarding burning behavior, some copper chromites caused an increase in the propellant burning rate in comparison to the iron oxide catalyst. It is observed that the highest burning rate values were obtained with Cu -1800P, Cu -0202P and SX 14 catalysts. In general, the highest burning rate could be associated to the catalysts with the highest specific surface area (Pekel et al., 1990). This assumption is confirmed by the catalyst from IPM, which has the smallest surface area and leads to the lowest burning rate. However, this general rule is not followed by the Cu-0202P catalyst, because despite presenting the lowest surface area it leads to a high burning rate. This behavior could be due to the higher copper content of this catalyst, since it has been suggested that this metal can play an important role in the catalytic activity of copper chromites (Boldyreva et
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 323-330, Sep-Dec., 2010
327
Campos, E.A. et al.
al., 1975). Generally, it was observed in this work that copper chromites with a copper content higher than 41% lead to burning rates higher than that obtained with the iron oxide catalyst. However, the HOX 80:20 catalyst contradicts the general rules of surface area and copper content. Despite possessing a high surface area and a high copper content, it does not lead, as expected, to the highest burning rate propellant. This has been attributed to any unpredictable experimental mistake. As previously mentioned, an important parameter related to the combustion of propellants is the pressure exponent (n) of the burning rate equation (Vb=a.Pn). Analyzing the data of Table 2, it is observed that for most copper chromites the pressure exponents are close or slightly higher than that related to the iron oxide, with the lowest value being presented by the Cu-0202P catalyst. Despite the small differences, all pressure exponent values enable the propellant to be used in rocket motors for a real application (Kubota, 2007). With relation to the catalysts evaluated in this work, except SX14, there is no information from the suppliers about the method used to synthesize the catalysts, whether by ceramic or co-precipitation method. For both methods it is known that the formation of the copper chromite takes place when the samples are treated at higher temperatures, being higher in the ceramic method. Carvalho, Feitosa and Rangel (2000) observed that treatments at lower temperatures can increase the specific surface area of the copper chromite. It is believed that different temperatures can lead to the formation of crystals of different shapes and sizes, and this could affect the catalytic activity of the copper chromite (Rajeev et al., 1995; Prasad, 2005). Some authors evaluated the effect of copper chromite catalysts on the burning behavior of a propellant formulation similar to that used in this work. They observed that the highest burning rates were obtained with the copper chromite obtained by co-precipitation (Faillace, 2001). Using scanning electron microscopy analysis, the increase in the burning rate was attributed to the fact that the copper chromite synthesized by co-precipitation presents larger and better defined crystals than the catalyst obtained by ceramic method. Analyzing the results obtained in this work, it is not possible to identify any effect of the method used to synthesize the catalyst (ceramic or co-precipitation) on the propellant burning rate. The highest burning rate values were obtained with SX 14 and Cu-1800P catalysts, obtained by co-precipitation and ceramic method, respectively.
328
In conclusion, the results obtained in this work suggest that, in addition to the specific surface area, other characteristics, such as copper and chromium contents, crystalline structure, active surface area (Prasad, 2005) and the presence of impurities, may affect the performance of copper chromites as burning rate catalyst in composite propellants. The possible effect of the active surface area is planned to be evaluated in a future work, by using chemisorption analysis (Webb, 2003). Despite the inconclusive results, all copper chromites evaluated in this work could be used as a burning catalyst in composite propellant formulations, with slight advantage for the SX 14 sample from AEQ and Cu- 0202P and Cu1800P samples from Engelhard, which led to the highest burning rates. CONCLUSION Copper chromites from different suppliers were characterized and evaluated as burning rate catalysts in a typical composite propellant formulation. Based on a previous work, the IR analysis allowed identifying the preparation method of each catalyst. The processing and mechanical properties of the propellant were not significantly affected by the type of copper chromite evaluated, and most of the results are similar to those related to the iron oxide containing composition. Most of the copper chromites evaluated caused an increase in the propellant burning rate when compared to iron oxide. All copper chromites could be used for a real application of the propellant. Besides the surface area, other parameters like copper and chromium contents, crystalline structure, active surface area, and the presence of impurities might affect the performance of the catalysts. REFERENCES Benmahamed, M.A et al., 2002, “Effect of Copper Chromite Particle Size on the Combustion process of a Plastisol Propellant. Part II: Combustion laws by Crawford”, Proceeding of the 33rd International Annual Conference of ICT, Karlsruhe, Germany, pp. 124-1_124-9 Boldyreva, A.V. et al., 1975, “Effects of spinels on the pyrolysis and combustion rates for ammonium perchlorate mixtures”, Combustion Explosives and Shock Waves,Vol.11, No 5, pp.611-613. doi:10.1007/BF00751084
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 323-330, Sep-Dec., 2010
Performance evaluation of commercial copper chromites as burning rate catalyst for solid propellants
Burnside, C. H., 1975, “Correlation of ferric oxide surface area and propellant burning rate”. Technical Report – AIAA Paper 75-234”, AIAA, Pasadena, CA, USA. Campos, E.A. et al., 2003, “Aplicação de Técnicas FT-IR na caracterização de catalisador cromito de cobre utilizado na indústria aeroespacial” Anais da Associação Brasileira de Química, Vol. 52, No 1, pp.22-25. Campos, E.A., 2004, “Caracterização e avaliação de propriedades de cromito de cobre como catalisador de queima para propelentes sólidos”. Thesis. Instituto Tecnológico da Aeronáutica, São José dos Campos, SP, Brazil,170 p. Carvalheira, P., Gadiot, G.M.H.J.L. and Klerk, W.P.C., 1995, “Thermal decomposition of phase-stabilised ammonium nitrate (PSAN), hydroxyl-terminated polybutadiene (HTPB) based propellants. The effect of iron (III) oxide burning-rate catalyst” Thermochimica Acta, Vol. 269-270, pp. 273-293. Carvalho, M.F.A., Feitosa, S. and Rangel, M.C., 2000, “Influência da temperatura de calcinação sobre as propriedades catalíticas de cromitos de cobre”, 23a Reunião Anual da Sociedade Brasileira de Química, Poços de Caldas, MG, Brazil. Davenas, A., 2003, “Development of modern solid propellant”. Journal of Propulsion and Power, Vol.19, No 6, pp. 1108-1128. Engen, T. K., Johannessen, T.C., 1990, “The effects of two types of iron oxide on the burning rate of a composite propellant”, Proceeding of the 21st International Annual Conference of Technology of Polymer Compounds and Energetic Materials”, Karlsruhe, Germany, pp. 81.1-81.12. Faillace, J.G., 2001, “Cromito de cobre II: Síntese, Caracterização e Propriedades”, Thesis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil, 60 p. Furman, N.H., 1996, “Standard Methods of Chemical Analysis”, Van Nostrand Company Inc., Princeton, New Jersey, USA, Sixth Edition, Vol. 1, pp. 402-403. Jones, H.E., Strahle,W.C., 1973, “Effects of copper chromite and iron oxides catalysts on AP/CTPB sandwiches”, Proceedings of the 14th International Symposium on Combustion. Kawamoto, A.M. et al., 2004, “Copper Chromite as catalyst for composite solid propellant” Proceedings of the 35th International Annual Conference of Technology of Polymer Compounds and Energetic Materials, Karlsruhe, Germany, pp. 56.1-56.13.
Kishore, K., Sunitha, M.R., 1979, “Effect of transition metal oxides on decomposition and deflagration of composite solid propellant systems: a survey”, AIAA Journal, Vol.17, No10, pp.1118-1125. Kishore, K., Verneker, P. and Sunitha, M.R., 1980, “Action of Transition Metal Oxides on Composite Solid Propellants”, AIAA Journal, Vol. 18, No11,pp. 1404-1405. Kubota, N., 2007, “Propellants and explosives: thermochemical aspects of combustion, “ Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim, Germany. Li, W., Cheng, H., 2007, “Cu-Cr-O nanocomposites: Synthesis and characterization as catalysts for solid state propellants”, Solid State Sciences, Vol. 9, No 8, pp. 750-755. Ma, Z., Li, F., 2006, “Preparation and thermal decomposition behavior of TMOS/AP composite nanoparticles”, Nanocience, Vol. 11, No 2, pp. 142-145. Miller, F.A., Wilkins, C.H., 1952, “Infrared Spectra and Characteristic frequencies of inorganic ions” Anal. Chem, Washington, Vol. 24, pp. 1253-1294. Pekel, F.E. et al., 1990, “An investigation of the Catalytic Effect of Iron (III) Oxide on the Burning rate of Aluminized HTPB/AP Composite Propellant”, Proceedings of the 21st International Annual Conference of Technology of Polymer Compounds and Energetic Materials, Karlsruhe, Germany, pp.1-8. Prasad, R., 2005, “Highly active copper chromite catalyst produced by thermal decomposition of ammoniac copper oxalate chromate” Materials Letters, Vol. 59, No 29-30, pp. 3945-3949. Prajakta, R.P., Krishnamurthy, V.N., Satyawati, S.J., 2006, “Differential Scanning Calorimetric Study of HTPB based Composite Propellants in Presence of Nano Ferric Oxide”, Propellants Explosives, Pyrotechnics Vol. 31, No 6, pp. 442-446. Rajeev, R. et al., 1995, “Thermal decomposition studies. Part 19. Kinetics and mechanism of thermal decomposition of copper ammonium chromate precursor to copper chromite catalyst and correlation of surface parameters of the catalyst with propellant burning rate”, Thermochimica Acta, Vol. 254, pp. 235-247. Rastogi, R.P. et al., 1980, “Solid state chemistry of copper chromite used as a catalyst for the burning of ammonium perchlorate/polystyrene propellants”, Journal of Catalysis, Vol. 65, No 1, pp. 25-30.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 323-330, Sep-Dec., 2010
329
Campos, E.A. et al.
Rezende, M.C. et al., 2002, “Efeito da concentração do catalisador acetilacetonato férrico na cura de poliuretano à base de polibutadieno líquido hidroxilado (pblh) e diisocianato de isoforona (IPDI)”, Química Nova, Vol. 25. No 2, pp. 221-225. doi: 10.1590/S0100-40422002000200009
Singh, G., 1978, “Burnning rate modifiers for composite solid propellants”, Journal of Scientific Industrial Research, Vol. 37, No 2, pp. 79-85.
Sciamareli, J., Takahashi, M.F.K. and Teixeira, J.M., 2002, “Propelente sólido compósito polibutadiênico: I-influência do agente de ligação”, Química Nova, Vol. 25, No 1, pp. 107-110.
Tagliaferro, F.S. et al., 2006, “INAA for the validation of chromium and copper determination in copper chromite by infrared spectrometry”, Journal of Radioanalytical and Nuclear Chemistry, Vol. 269, No 2, pp. 403-406.
Shadman-Yazdi, F., Petersen, E.E., 1972, “The effect of catalysts on the deflagration limits of ammonium perchlorate”, Combustion Science and Technology, Vol. 5, No 1, pp. 61-67. doi: 10.1080/00102207208952504
Webb, P.A., 2003, “Introdution to chemical adsorption analytical techniques and their applications to catalysis”, Micromeritics Instrument Corp., Norcross, Georgia 30093.
330
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 323-330, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02038310
Gilson da Silva*
Instituto Nacional da Propriedade Industrial Rio de Janeiro – Brazil gilsondasilva@uol.com.br
Koshun Iha
Instituto Tecnológico de Aeronáutica São José dos Campos – Brazil koshun@ita.br *author for correspondence
Polimorfismo: caracterização e estudo das propriedades de uma fase cristalina Resumo: Embora a composição química seja a mesma, as propriedades físico-químicas dos polimorfos podem ser totalmente distintas, como, por exemplo, a condução ou não de eletricidade. Discute-se até mesmo a legalidade de reconhecê-los como produtos totalmente novos, dadas as características próprias que um polimorfo pode ter em detrimento de outro. Fato é que os diferenciais de solubilidade, estabilidade e formação de sítios ativos de fases distintas de uma substância despertam interesse dos variados setores economicamente ativos. Não são poucos os materiais energéticos polimórficos, ou precursores deles, que também apresentam aplicações terapêuticas. Portanto, algumas das técnicas desenvolvidas pela lucrativa indústria farmacêutica para o estudo do polimorfismo podem ser adaptadas às necessidades da indústria de material de defesa. Este trabalho visou apresentar materiais energéticos e farmacológicos reconhecidos por seu polimorfismo, bem como discorrer sobre propriedades, técnicas de caracterização e estudo de transição de fase nesses materiais. Palavras-chave: Polimorfismo, CL-20, HMX, FT-IR, DSC, DRXP.
Polymorphism: characterization and study of the properties of a crystalline phase Abstract: Despite the same chemical composition, the physicochemical properties of polymorphs can be totally different, such as leading or not electricity. The legality of recognize them as completely new products is discussed, in front of the characteristics that a polymorph may have over another. The fact is that the differential solubility and stability and formation of active sites in different phases of a substance engage the interest of many active sectors of the economy. There are no few polymorphic energetic materials, or their precursors, which also have therapeutic applications. Therefore, some of the techniques developed by the lucrative pharmaceutical industry to study the polymorphism can be tailored to the needs of the war industry. This paper presents energetic and pharmacological materials recognized for their polymorphism and discuss properties, characterization techniques and the study of phase transition in these materials. Keywords: Polymorphism, CL-20, HMX, FT-IR, DSC, DRXP.
Introdução Polimorfo (do grego “muitas formas”) é o termo atribuído a uma das formas cristalinas em que uma mesma substância pode ser encontrada. As diferenças entre as formas envolvem igualmente a estrutura cristalina, número de átomos numa molécula de gás ou estrutura molecular de um líquido (Hawley, 1987). As chamadas “formas polimórficas” são muito mais comuns do que se pode imaginar e cotidianamente se interage com elas sem que se note. O exemplo clássico Received: 29/07/10 Accepted: 22/08/10
de polimorfismo é o carbono nas suas formas grafite e diamante. Todavia, substâncias ainda mais abundantes apresentam polimorfismo, tal como a água, que pode cristalizar-se exibindo, no mínimo, oito diferentes formas sólidas, cada qual com estrutura cristalina única. O pseudopolimorfismo se dá pela ocorrência de moléculas do solvente na estrutura cristalina que, não menos importante, é reportado com frequência em argilas de diversos fins (Cavani, Trifirò e Vaccari, 1991). A literatura não descreve apenas diferenças simples nos arranjos cristalinos de polimorfos, mas também mudanças significativas de solubilidade, processabilidade e estabilidades física e química entre diferentes polimorfos
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 331-338, Sep-Dec., 2010
331
Silva, G., Iha, K.
de uma substância (Aguiar, Gemal, Gil e 1999). As propriedades físico-químicas distintas dos polimorfos os tornam atrativos, em especial, para as indústrias farmacêuticas, uma vez que elas podem interferir diretamente no mecanismo de absorção do fármaco pelos organismos vivos, atuando diretamente na eficácia terapêutica do fármaco. Assim, é importante o controle e a identificação de todas as formas polimórficas de um medicamento (Damas et al., 2009). Não distante disso, a indústria de material de defesa não poderia deixar de considerar o polimorfismo de um material energético no estudo de sua estabilidade e segurança. Esses materiais podem ser enquadrados em dois principais grupos: os explosivos deflagradores, ou de baixa potência, e os explosivos detonadores, ou de alta potência (Urbanski, 1984). Os explosivos de baixa potência consistem numa mistura de substâncias que reagem umas com as outras para liberar uma quantidade considerável de energia (como, por exemplo, pólvora) ou de compostos químicos que liberam energia ao serem decompostos (como a nitrocelulose). Já os explosivos de alta potência são aqueles que se decompõem mais rapidamente do que os explosivos de baixa potência e geram pressões muito maiores, resultando em elevado poder de destruição. Alguns explosivos de alta potência exigem detonação e não ignição antes de explodir; isso diminui o perigo na sua manipulação (Urbanski, 1984). Existe ainda uma classe de explosivo denominada explosivo de iniciação, utilizada na produção de cápsulas de detonação, detonadores e iniciadores. Esses explosivos apresentam alta sensibilidade à chama, calor, impacto ou atrito (Hawley, 1987), sendo empregados como “trens explosivos” na iniciação de explosivos mais estáveis. São exemplos dessa classe: azoteto de chumbo, fulminato de mercúrio, diazodinitrofenol, nitroguanidina, estifinato de chumbo e pentanitroeretritol-tetranitrado (PETN). Podem ser destacados o octogênio e o azoteto de chumbo como exemplos de materiais energéticos da classe dos explosivos de alta potência e dos iniciadores, respectivamente, que apresentam diversos polimorfos. Materiais Energéticos Azoteto de chumbo O azoteto de chumbo, ou azida de chumbo, é uma substância que pode ser encontrada em quatro diferentes formas polimórficas: α, β, γ e δ. A α, ortorrômbica, é a única forma aceitável para aplicações técnicas (Urbanski, 1984). A forma β, monoclínica, é estável quando seca, mas recristaliza-se na forma α. As formas γ e δ são menos 332
estáveis do que as formas α e β, sendo produzidas por precipitação simultânea do material em álcool vinílico em faixas de pH entre 3,5 e 7,0. A massa específica do azoteto de chumbo nas formas ortorrômbica e monoclínica é 4,68 e 4,87 g/cm3, respectivamente (Department of the Army, 1990). Material mais comumente empregado na confecção de detonadores, o azoteto de chumbo foi desenvolvido após a Primeira Guerra Mundial, sendo preparado por reação entre o nitrato ou acetato de chumbo com azoteto de sódio em meio básico, para evitar a formação do instável ácido hidrazóico (Mathieu e Stucki, 2004). Reporta-se na literatura (Urbanski, 1984) que explosões espontâneas podem ocorrer em soluções saturadas de azoteto durante a recristalização. A dextrina é empregada como agente coloidal na produção de cristais de azoteto de chumbo (Destrined Lead Azide − DLA) e previne a formação de cristais grandes e sensíveis, controlando também a forma cristalina durante a produção do azoteto (Department of the Army, 1990). Ainda na forma coloidal, porém sem dextrina, o azoteto de chumbo CLA (colloidal lead azide) é constituído por partículas pequenas, entre 3 e 4 µm, sendo ideais para emprego como cargas pontuais e impressas de iniciadores elétricos de baixa energia (Department of the Army, 1990). O azoteto de chumbo é um excelente iniciador para altos explosivos, notadamente superior na iniciação de explosivos como Tetril, Hexogênio e Pentanitroeretritol. Sua estabilidade é excepcional, não apresentando alterações quanto ao teor de pureza ou teste de brisância, mesmo após 25 meses de estocagem a 50°C ou misturado à água/etanol (Department of the Army, 1990). Leslie (1964) descreveu o uso e processo de produção do azoteto de chumbo como explosivo primário de iniciação. O processo de produção consiste na reação, em meio aquoso, entre o azoteto de sódio e um sal solúvel de chumbo, sendo separado em seguida o precipitado formado de azoteto de chumbo. Para modificar a estrutura cristalina do azoteto de chumbo e impedir a formação de cristais sensíveis, a precipitação é efetuada em presença de um coloide. O coloide pode estar contido dentro da solução aquosa dos dois reagentes, mas sua adição é preferencialmente efetuada a partir de uma solução aquosa contendo-o entre 0,5 a 1,0% em peso, em que se adiciona simultaneamente, sob agitação, as soluções aquosas concentradas dos dois reagentes, numa relação sensivelmente estequiométrica. O coloide compreende uma mistura de gelatina e de dextrina; a gelatina não constitui mais do que 60%, em peso, da totalidade do coloide e a concentração da dextrina dentro da solução coloidal é de, ao menos, 0,3%, em peso. O azoteto de
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 331-338, Sep-Dec., 2010
Polimorfismo: caracterização e estudo das propriedades de uma fase cristalina
chumbo produzido apresenta maior resistência ao impacto e sensibilidade à descarga eletrostática menos intensa. Vernon et al. (2008) observaram mudança de fase cristalina do azoteto de chumbo sob longos períodos de estocagem e a identificaram como causadora de mudanças potencialmente perigosas na performance e sensibilidade do produto. A solução encontrada foi o desenvolvimento de um processo de produção em pequena escala e sob demanda. O processo foi desenvolvido em um misturador do tipo “T” ou “Y”, em que as soluções de azoteto de sódio e o sal de chumbo são colocados em reação para a produção do azoteto de chumbo, de onde os cristais de azoteto de chumbo são posteriormente separados do meio aquoso. A escala reduzida na qual o processo é conduzido dispensa estruturas complexas do reator e equipamentos usados no controle de temperatura durante a reação. Octogênio O HMX, também conhecido como 1,3,5,7- tetranitro-1,3,5,7tetra-azaciclo-octano, ciclotetrametileno tetranitroamina (C4H8N8O8), ou octogênio, é um dos mais importantes entre os modernos componentes energéticos para propelentes sólidos, devido às suas atraentes propriedades de ausência de fumaça, alto impulso específico e estabilidade térmica (Tang et al., 1999). Cady e Smith (1961) verificaram que as fases cristalinas do HMX podem desempenhar importante papel na sua decomposição química. O HMX existe em quatro fases polimórficas, de acordo com as condições de cristalização, conhecidas como: formas α, β, γ e δ. A forma β, que apresenta estrutura cristalina monoclínica, é a mais estável à temperatura ambiente e de tradicional interesse, sendo usada para aplicações gerais. Além da menor sensibilidade do HMX na forma β, a maior massa específica é obtida na configuração desse polimorfo, despertando grande interesse para a produção de artefatos bélicos, pois permite obtenção de cargas de mesmo volume com maior conteúdo energético. O γHMX, monoclínico, é o mais sensível na temperatura ambiente, e o polimorfo δ, hexagonal, só existe em temperaturas acima de 160°C. Tanto o polimorfo α, ortorrômbico, quanto o β, monoclínico, podem ser diretamente sintetizados (Cady e Smith, 1961). Todavia, o processo mais utilizado − processo Bachmann (Robbins and Boswell, 1973) − obtém o explosivo na forma α, sendo o polimorfo β posteriormente obtido por meio de recristalização em acetona.
O processo Bachmann produz concomitantemente RDX (hexahidro-1,3,5-trinitro-1,3,5-triazina) e HMX. O RDX é utilizado normalmente com adição de mais de 8% de HMX, enquanto o HMX é empregado puro. Diferentemente do HMX, o RDX não apresenta polimorfismo. O polimorfo β do HMX tem massa específica de 1,90 g/cm3. O hexogênio tem massa específica de 1,82 g/cm3. Todavia, a densidade de 1,76 g/cm 3 pode ser observada para o HMX quando na fase de transição γ, não utilizada na produção de artefatos bélicos e obtida durante a cristalização do HMX. As nitroaminas explosivas (HMX e RDX) são de particular interesse em cristais muito finos, isto é, de 2 a 10µm de diâmetro, para uso em formulações de propelentes e ogivas. Apesar disso, os cristais muito finos de HMX e de RDX são menos sensíveis à fricção e apresentam maior uniformidade do que cristais maiores. Esses cristais muito finos apresentam grande atividade superficial na forma de uma carga negativa. A essa carga eletrostática são atribuídos sérios problemas de segurança quando as nitroaminas são manipuladas em estado seco. Voigt e Strauss (1992) propuseram uma leve modificação nos finos cristais de HMX e RDX para aumentar a resistência ao impacto deles e, consequentemente, a segurança na manipulação. Tal modificação é efetuada durante a transição de fase cristalina entre o polimorfo γ para o β, em que uma pequena quantidade de polivinilpirrolidona (PVP) é adicionada. O polímero adere à superfície dos cristais finos e também é adsorvido por eles, modificando internamente os cristais muito finos em função da formação de complexo entre o grupo pirrolidona e o HMX. Dessa forma, pode-se observar que o mecanismo de transição de fase cristalina não é estimado apenas para a obtenção de cristais com massa específica que permite a produção de artefatos com maior carga material e, consequentemente, explosiva, mas também é um mecanismo para interferir diretamente nas propriedades dos cristais obtidos. Muravyev et al. (2010) relataram estudos conduzidos com partículas convencionais e ultrafinas de HMX, em que a velocidade de detonação das partículas ultrafinas é maior do que a obtida com partículas convencionais de mesma densidade, permanecendo a sensibilidade ao impacto inalterada. As partículas ultrafinas de HMX compreendem polimorfos de diferentes tipos. Especificamente, no estudo conduzido por Muravyev et al., as partículas ultrafinas de HMX eram inicialmente constituídas por 40%, em peso, do polimorfo α e 60% do polimorfo β. Todavia, após o processo de prensagem (350 MPa durante 3 minutos)
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 331-338, Sep-Dec., 2010
333
Silva, G., Iha, K.
ao qual o material foi submetido, os autores observaram aumento de 10% no teor da fase β. A literatura por eles consultada indicava que a conversão completa do polimorfo α em β dar-se-ia sobre pressão de 207 MPa por 5 minutos. Esse estudo revelou ainda que as partículas de ultrafinas de HMX não alteraram a velocidade de combustão da formulação de propelente testado.
é a mais corrente diante da possibilidade de obtenção de maior quantidade de explosivo por volume. A distribuição granulométrica ampla dos cristais também possibilita maior empacotamento deles em ogivas.
O emprego conjunto de HMX de partículas convencionais e ultrafinas com alumínio ultrafino, “Alex” (Cliff, Tepper e Lisetsky, 2001; Rocco et al., 2010), também foi avaliado por Muravyev et al. (2010). Os sistemas investigados por eles demonstraram que Alex é mais eficiente quando usado com HMX com tamanho de partícula convencional, podendo resultar em velocidades de combustão até 30% superiores.
O 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetraciclo [5.5.005,903,11]-dodecano, conhecido como CL-20, é um importante constituinte de formulações propelentes e sistemas de defesa. Sua performance também depende da estrutura polimórfica selecionada.
O estudo conduzido por Muravyev et al. (2010) demonstra que a transição de fase cristalina do HMX não é intrínseca aos processos de recristalização em solventes, mas também pode ser causada, mesmo indiretamente, durante etapas de prensagem de formulações propelentes. Imamura (2002) estudou as transições cristalinas α→δ HMX e β→δ HMX por meio da calorimetria exploratória diferencial (DSC), com análises em atmosfera de nitrogênio, sem confinamento do material energético (cápsulas DSC perfuradas) e com razão de aquecimento de 15°C/min. Segundo Imamura, o pico da transição β→δ HMX ocorre a 199,5 ± 0,8°C, enquanto que para a transição α→δ HMX o pico foi em 219,5 ± 0,7°C. Uma vez que os resultados obtidos estavam em acordo com a literatura pesquisada, porém apresentando picos de temperatura de transição em valores mais elevados do que os reportados, outras condições foram consideradas para análise da transição de fase, tais como o efeito da razão de aquecimento e a granulometria dos cristais. Imamura (2002) verificou então que o aumento da temperatura de transição de fase cristalina é diretamente relacionado à razão de aquecimento utilizada, sendo que a temperatura do pico de transição aumenta em função do aumento da razão de aquecimento empregada em ambas as transições cristalinas estudadas (α→δ HMX e β→δ HMX). Quanto à granulometria, Imamura (2002) verificou que a redução dos cristais resulta em aumento da temperatura de transição de fase cristalina. Contudo, partículas mais grosseiras resultam em picos múltiplos de transição pouco repetitivos. Por conseguinte, pôde-se verificar que as transições polimórficas do HMX podem ser induzidas através de cristalização ou ação da pressão e temperatura sobre seus cristais já formados. Contudo, a escolha do polimorfo β
334
Hexanitrohexaazaisowurtzitano
O CL-20 é utilizado como carga energética ou componente propulsor nos sistemas de armas, podendo ampliar a penetração em antiblindagem, bem como aumentar a velocidade e eficiência de voo de mísseis e torpedos. O polimorfismo do CL-20 consiste na existência de diversos cristais como o α, β, ε e γ. O polimorfo ε é conhecido na técnica e apresenta uma performance energética e massa específica elevadas, além de baixa sensibilidade comparativamente aos outros polimorfos, o que justifica sua procura e emprego em sistemas de armas e propulsores. Como também é comum para o octogênio, o polimorfo do CL-20 obtido diretamente por vários processos de síntese é o α, e a massa específica do cristal é consideravelmente inferior à do polimorfo ε. Consequentemente, o CL-20 obtido na forma α é submetido a processo de recristalização para aumentar a proporção do polimorfo ε. No modo clássico para cristalização do ε-CL-20 é utilizando um não solvente − clorofórmio − para precipitar o material a partir de solução em acetato de etila, sendo que o clorofórmio como não solvente permite boa reprodutibilidade. Não obstante, o uso do clorofórmio tem como inconveniente a existência de múltiplas formas cristalinas, como aglomerados, dentre a estrutura cristalina ε. Scott et al. (2005) propuseram um processo de cristalização para a obtenção do polimorfo ε do CL-20, que consiste na combinação do CL-20 com ao menos um solvente orgânico e um não solvente, na qual o solvente orgânico pode ser o acetato de etila e o não solvente, o formiato ou acetato de benzila. Um co-não solvente pode também ser usado, sendo indicados o óleo naftalênico ou parafínico. Cristais do polimorfo ε podem ainda ser adicionados à solução saturada de cristalização, agindo como “sementes”. O solvente orgânico é evaporado da solução saturada por vácuo ou expulso por insuflação de gás anidro sobre a solução de cristalização.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 331-338, Sep-Dec., 2010
Polimorfismo: caracterização e estudo das propriedades de uma fase cristalina
Além dos polimorfos do CL-20 citados, existe ainda em alta pressão a estrutura ζ, que é uma fase reversível obtida a partir da fase γ. Quanto à estabilidade dos polimorfos CL-20, quando isolados apresentam estabilidade decrescente na ordem ε > γ > α > β, sendo o polimorfo ζ instável sob condições normais (Kholod et al., 2007). Técnicas de caracterização de polimorfos Diversas técnicas analíticas são empregadas na caracterização e estudo das transições de fase cristalina. Entre as várias técnicas utilizadas, será dada ênfase à análise térmica, DSC e termogravimetria (TG), espectroscopia de infravermelho com Transformada de Fourier (FT-IR) e a difração de raios X. A difração de raios X é um dos métodos mais conhecidos e empregados para a caracterização de materiais, sendo rotineiramente utilizada na identificação de fases cristalinas. Na indústria farmacêutica, grande quantidade de fármacos policristalinos são simultaneamente identificados e quantificados. Ferreira et al. (2009) verificaram que o emprego de fontes de luz síncroton para experimentos de difração de raios X por policristais (DRXP) aumenta de modo significativo a quantidade de informações estruturais obtidas, quando comparadas a fontes convencionais, em face da alta intensidade e colimação dos feixes de raios X, além da resolução angular instrumental. Ainda na área farmacêutica, Damas et al. (2009) identificaram novas formas polimórficas do fluconazol (C13H12F2N6O) e da nimesulida (C13H12N2O5S), respectivamente um fungicida e um fármaco com propriedades analgésicas, anti-inflamatórias e antipiréticas, por meio da difração de raios X. Segundo o estudo realizado, as estruturas reportadas na base de dados Cambridge Struture Database não justificaram todos os picos dos difratogramas observados nos fármacos. Imamura (2002) estudou o octogênio por difração de raios X, visto que cristais únicos do β-HMX apresentavam comportamento térmico distinto do observado em aglomerados cristalinos, clusters, do polimorfo com mesma faixa de distribuição granulométrica. Imamura observou que a posição dos picos de reflexão não sofre alteração entre cristais e aglomerados. No entanto, a intensidade desses picos nos aglomerados é irregular, sendo ora mais ora menos intensos do que os picos obtidos dos cristais. Estudos da transição α→δHMX (Silva et al., 2004) foram conduzidos por DSC para determinação da energia de
ativação da transição, sendo relatada entre 487 e 495 kJ/mol. Também a transição β→δHMX foi estudada por Weese, Maienschein e Perrino (2003), e a energia de ativação a ela associada foi calculada em, aproximadamente, 500 kJ/mol. Esses trabalhos revelaram valores para a energia de ativação das transições α→δHMX e β→δHMX muito acima do até então descrito na literatura (204 kJ/mol) e atribuíram as possíveis causas aos mecanismos complexos de nucleação e/ou possibilidade da transição não serem uma simples reação de primeira ordem. A transição β→δHMX foi revelada por DSC em razões de aquecimento de 10 e 0,5ºC/min, segundo Weese e Burnham (2005). No entanto, a reconversão − δ→βHMX − não foi observada no resfriamento da mesma amostra. Numa segunda rampa de aquecimento, Weese e Burnham também não observaram a ocorrência da transição β→δHMX na amostra. Após sucessivos aquecimentos de uma mesma amostra, em que intervalos crescentes de tempo foram feitos, observaram que a reconversão δ→βHMX ocorre de modo mais lento. A FT-IR também foi apresentada no estudo conduzido por Silva et al. (2004). Essa técnica foi empregada para confirmar a forma polimórfica do HMX estudado, uma vez que, segundo Mattos (2001), a identificação do polimorfo α-HMX é feita facilmente pela ausência da banda de absorção em 1145 cm-1. Kholod et al. (2007) descreveram que a identificação dos polimorfos do CL-20 também poderia ser conduzida com FT-IR ou Raman. Foltz et al. (1994) estudaram transições de fase cristalina em polimorfos α, β, γ e ε do CL-20 em função da temperatura, descrevendo os resultados do estudo do equilíbrio de soluções em alta temperatura em ligação com FT-IR, permitindo a identificação da transição polimórfica. O estudo do crescimento de cristal e solvatação foi conduzido em amostras de CL-20 imersas em bis(2-flúor-2,2-dinitroetil)formol (FEFO) aquecido, sendo que o aumento da temperatura entre 35 e 80ºC resulta na dissolução dos polimorfos na sequência β, α, γ e ε. O estudo revelou que solventes com grupos hidroxila (i.e., alcoóis, água) estabilizam preferencialmente a fase polimórfica α, retardando sua conversão para a fase mais estável ε. Todavia, a ordem de solubilidade dos polimorfos não estava em concordância com a ordem de estabilidade de α-hidrato > ε > α-seco > β > γ. Nedelko et al. (2000) investigaram a decomposição térmica do CL-20 por meio de TG. As reações procedem com autoaceleração e podem ser descritas por uma lei cinética de primeira ordem com autocatálise. Verificou-se que a cinética de decomposição depende do estado polimórfico inicial, logo que a decomposição térmica aumenta na série α < γ < ε. Em experimentos conduzidos com diferentes
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 331-338, Sep-Dec., 2010
335
Silva, G., Iha, K.
amostras de α-CL-20, Nedelko et al. observaram ainda diferentes razões de decomposição, verificando que, para um mesmo polimorfo, a decomposição depende do tamanho e distribuição granulométrica dos cristais. Considerações Finais Como observado na breve revisão apresentada, não são exíguas as diferenças quando as propriedades ou mesmo a resposta a um mesmo estímulo externo são avaliadas em polimorfos. Para a indústria de material de defesa, as qualidades de um polimorfo podem ser consideradas de suma importância na performance balística por ele provida, bem como na segurança e condições de manuseio requeridas para emprego e estocagem do produto. A transição de fase cristalina durante períodos de estocagem é um risco iminente em alguns compostos energéticos, sendo que o polimorfo resultante pode não ser o mais estável quando observado relativamente à possibilidade de iniciação por impacto ou atrito. Não obstante, a necessidade de quantidades maiores de materiais energéticos, para uso no carregamento de ogivas e composições propelentes, impede que muitos deles sejam produzidos em escala reduzida para pronto uso, devendo ainda ser considerada a possibilidade de a transição cristalina ocorrer em materiais energéticos já compreendidos em formulações, por exemplo, em combinação com polímeros (Plastic-bonded Explosive − PBX). A solubilidade em diferentes solventes ou influenciada pelo pH do meio, intrínseca ao polimorfo, deve ser cuidadosamente considerada, principalmente quando o polimorfo estudado tem uso farmacológico, uma vez que sua absorção e eficiência nos organismos vivos dependem também da concentração do produto. Referências Aguiar, M.R.M.P., Gemal, A.L. e Gil, R.A.S.S., 1999, “Caracterização de polimorfismo em fármacos por ressonância magnética nuclear no estado sólido”, Química Nova, Vol. 22, No 4, pp. 553-564. Cady, H.H., Smith, L.C., 1961, “Studies on the polymorphs of HMX”, LAMS 2652, Los Alamos Scientific Laboratory, Los Alamos, NM, USA. Cavani, F., Trifirò, F., Vaccari e A., 1991, “Hydrotalcitetype anionic clays: preparation, properties and applications”, Catalysis Today, Vol. 11, pp. 173-301. Cliff, M., Tepper, F. e Lisetsky, V., 2001, “Ageing characteristics of Alex* nanosized aluminium”,
336
Proceedings of the 37th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Salt Lake City, USA. Damas, G.B. et al., 2009, “Estudo de novas formas polimórficas de fármacos por difração de raios X”, Proceedings of the 19th Reunião da Associação Brasileira de Cristalografia, Belo Horizonte, MG, Brazil. Department of the Army, 1990, “TM 9-1300-214. Military Explosives”, Headquarters, Department of the Army, Washington, D.C., USA. Ferreira, F.F. et al., 2009, “Caracterização de fármacos policristalinos com o uso da difração de raios X”, Proceedings of the 19th Reunião da Associação Brasileira de Cristalografia, Belo Horizonte, MG, Brazil. Foltz, M.F. et al., 1994, “The thermal stability of the polymorphs of hexanitrohexaazaisowurtzitane, Part I”, Propellants, Explosives, Pyrotechnics, Vol. 19, No 1, pp. 19-25. Hawley, G.G., 1987, “Condensed chemical dictionary”, 11st ed., Van Nostrand Reinhold, New York, USA, 1288 p. Imamura, Y.Y., 2002, “Avaliação do efeito da granulometria sobre a transição cristalina de β−HMX por calorimetria exploratória diferencial e microscopia eletrônica de varredura”, Thesis, Instituto Tecnológico de Aeronáutica, São José dos Campos, SP, Brazil, 141f. Kholod, Y. et al., 2007, “An analysis of stable forms of CL20: a DFT study of conformational transitions, infrared and Raman spectra”, Journal of Molecular Structure, Vol. 843, No 1-3, pp. 14-25. Leslie, J.P.M., 1964, “Procédé pour la préparation d’azoture de plomb convenant pur être utilisé comme explosif d’allumage primaire dans des détonateurs”, Institut National de la Propriété Industrielle FR1367761. Mathieu, J., Stucki, H., 2004, “Military high explosives”, Chimia, Vol. 58, No 6, pp. 383-389. Mattos, E.C., 2001, “Síntese de HMX e avaliação da aplicabilidade de técnicas FTIR na sua caracterização e quantificação”, Thesis, Instituto Tecnológico de Aeronáutica, São José dos Campos, SP, Brazil, 120f. Muravyev, N. et al., 2010, “Influence of particle size and mixing technology on combustion of HMX/Al compositions”, Propellants, Explosives, Pyrotechnics, Vol. 35, No 3, pp. 226-232.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 331-338, Sep-Dec., 2010
Polimorfismo: caracterização e estudo das propriedades de uma fase cristalina
Nedelko, V. V., et al., 2000, “Comparative Investigation of thermal decomposition of various modifications of hexanitrohexaazaisowurtzitane (CL-20)”, Propellants, Explosives, Pyrotechnics, Vol. 25, N o 5, pp. 255-259. Robbins, R., Boswell, B.C., 1973, “Direct production of beta-HMX”, U.S. Patents 3,770,721. Rocco, J.A.F.F. et al., 2010, “Evaluation of nanoparticles in the performance of energetic materials”, Journal of Aerospace Technology and Management, Vol. 2, No 1, pp. 47-52. doi 10.5028/jatm.2010.02014752 Scott, H. et al., 2005, “Cristallisation a haute temperature du 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12hexaazatetracyclo[5.5.005,903,11]-dodecane”, Institut National de la Propriété Industrielle FR2858620. Silva, G., 2004, “Avaliação da energia de ativação e sensibilidade de materiais altamente energéticos”, Thesis, Instituto Tecnológico de Aeronáutica, São José dos Campos, SP, Brazil, 96f. Silva, G. et al., 2004, “Aplicação da Calorimetria Exploratória Diferencial no estudo da cinética de transição
alfa - delta HMX”, Química Nova, Vol. 27, No 6, pp. 889891. doi: 10.1590/S0100-40422004000600009 Tang, C.J. et al., 1999, “A study of the gas-phase chemical structure during CO2 laser assisted combustion of HMX”, Combustion and Flame, Vol. 117, No 1-2, pp. 170-188. Urbanski, T., 1984, “Chemistry and tecnology of explosives”, Vol. 4, Pergamon Press, New York, 678 p. Vernon, A.P. et al., 2008, “On-demand lead azide production”, U.S. Patent 7,407,638. Voigt Jr, W.H., Strauss, B., 1992, “Process of reducing shock sensitivity of explosive nitramine compounds by crystal modification”, U.S. Patent 5,099,008. Weese, R.K., Burnham, A.K., 2005, “Coefficient of thermal expansion of the beta and delta polymorphs of HMX”, Propellants, Explosives, Pyrotechnics, Vol. 30, No 5, pp. 344-350. Weese, R.K., Maienschein, J.L. e Perrino, C.T., 2003, “Kinetics of the β-δsolid-solid phase transition of HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine”, Thermochimica Acta, Vol. 401, No 1, pp. 1-7.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 331-338, Sep-Dec., 2010
337
doi: 10.5028/jatm.2010.02039110
Amanda C. Simões da Silva*
Technologycal Institute of Aeronautics São José dos Campos – Brazil amanda@ita.br
Mischel Carmen N. Belderrain
Technologycal Institute of Aeronautics São José dos Campos – Brazil carmen@ita.br
Francisco Carlos M. Pantoja
Institute of Aeronautics and Space São José dos Campos – Brazil diretor@iae.cta.br * author for correspondence
Prioritization of R&D projects in the aerospace sector: AHP method with ratings Abstract: The prioritization of R&D projects in the Aerospace Sector is considered a complex problem because it involves qualitative and quantitative issues that are frequently conflicting. This paper aimed to apply the AHP (Analytic Hierarchy Process) method with ratings to select projects of R&D in a Brazilian aerospace institution, Department of Science and Aerospace Technology (DCTA). The results showed that using ratings is appropriate when there is a great quantity of projects, since it reduces the judgments required to the decision maker. Keywords: Prioritization of Research and Development Projects (R&D), AHP, Ratings.
INTRODUCTION Nowadays, most of organizations have been facing difficulties regarding the evaluation of projects prioritization. These difficulties are due to the complexity of the problems analyzed before a decision making. In literature, the selection of R&D projects is considered a complex problem because it involves qualitative and quantitative issues that are frequently conflicting. It also presents risks and uncertainties, as well as the necessity of balancing important factors, interdependence between projects and a great number of feasible portfolios (Ghasemzadeh and Archer, 2000). In order to deal with the complexity of decision making problems with many criteria, some methods to support it can be used. These methods aim to clarify the decisionmaking process, assisting and guiding the decision maker (or makers) regarding structure, evaluation and alternatives of the problem (Gomes, Gomes and Almeida, 2006). This work aimed to apply the Analytic Hierarchy Process (AHP) method with ratings to select aerospace R&D projects of a sector in a Brazilian aerospace organization. Using ratings means categorizing previously defined criteria and/or subcriteria in order to classify alternatives. This procedure is suitable when there are many projects, since this procedure reduces the number of judgment required to the decision maker.
Received: 08/10/10 Accepted: 26/10/10
As an example, we describe the application exercise of the Department of Science and Aerospace Technology (DCTA), São José dos Campos, São Paulo, Brazil. This work is presented as follows: first, we describe the prioritization of R&D projects and the Analytic Hierarchy Process (AHP) method with ratings; next, we explain the application of the proposed method to select projects of R&D aerospace; finally, we present the final considerations. THEORETICAL REFERENCE Prioritization of R&D projects According to Weisz (2006), R&D projects are risky and require long-term investments. Selecting the best R&D projects means to choose projects whose responsible organization will support them financially. According to Meade and Presley (2002), the selection of R&D projects is frequently based on financial criteria such as Net Present Value (NPV) and Internal Rate of Return (IRR). Despite the importance of such criteria, the authors claim that once the decisions must be strategically considered, other criteria must be taken into account, even though it is difficult to quantify. The R&D selection and prioritization is performed in a decision-making environment depicted by multicriteria that allow the use of Multiple-Criteria Decision-Making methods (MCDM), including the Analytic Hierarchy Process (AHP) method using ratings.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
339
Silva, A. C. S. et al.
Analytic Hierarchy Process using ratings Developed by Thomas L. Saaty in 1980, the AHP is one of the first methods developed in an environment of discrete multicriteria decision. The AHP method divides the problem into hierarchic levels, which makes its comprehension and evaluation easier and clearly determines a global action for each alternative by the value synthesis of the decision makers, prioritizing or classifying them after finalizing the method. According to Saaty (2008), to make a decision in an structured way and generate priorities, we need to decompose the decision into the following steps: 1) define the problem and determine the kind of knowledge sought, 2) structure the decision hierarchy starting from the top with the goal of the decision, and of the objectives from a broad perspective, through the intermediate levels (criteria on which subsequent elements depend) to the lowest level (which usually is a set of the alternatives), 3) construct a set of pairwise comparison matrices. Each element in upper levels is used to compare the elements of the immediately lower level with respect to it and, 4) use of priorities obtained from the comparisons to weigh the priorities in the immediately lower level. This must be performed for each element. Then for each element in the lower level, the weighed values are added and the overall or global priority is obtained. Continue this process of weighing and adding until the final priorities of the alternatives in the bottom levels are obtained. The AHP method will not be detailed. For further details see Saaty (1980). Step 1: Define the problem and determine the kind of knowledge sought In this step the goal of the decision process is decided, the criteria and subcriteria are identified based on the decision maker’s values and beliefs, as well as the alternatives of decision to solve the problem. Step 2: Structure the decision hierarchy The hierarchy structure is build aiming at the top decision, followed by intermediate levels (the criteria on which the posterior elements depend) to the inferior level (which is usually a set of alternatives). Based on a representation of a decision problem in a hierarchic structure, the decision maker builds the pairwise matrix of the elements. Step 3: Construct a set of pairwise comparison matrices Pairwise comparison matrices are built from results between elements, considering the Saaty Fundamental
340
Scale (Saaty, 1980). Each element in the upper level is used to compare the elements of an immediate inferior level with respect to the former. That is, the alternatives are compared with respect to the subcriteria, the subcriteria are compared with respect to the criteria and these criteria are compared with respect to the global objective. In this step, the verification of the pair comparison judgments consistency is also made. Step 4: Use the priorities obtained from the comparisons to weigh the priorities in the immediately lower level The last step refers to the obtainment of elements priorities (called eigenvector or priority vectors) to generate the final values of the alternative priorities. The local priorities obtained from the comparisons are used to ponder the priorities of the immediately lower level for each element. Thus, pondered values are added for each element in lower levels, and the total or global priority is obtained. The total priorities of the alternatives are found by multiplying their local priorities by the global alternatives of all criteria and respective subcriteria, resulting in the addition of the results to all alternatives. Therefore, we obtain the priority ranking of alternatives and also of the criteria and subcriteria. Ratings (absolute measurement) Duarte Júnior (2005) defines ratings as a set of intensity levels (or categories) that serves as a base to evaluate the performance of the alternatives in terms of each criterion and/or subcriterion. The categories that form the ratings must be clearly defined, in the less ambiguous way as possible, to adequately describe the criterion/subcriteria. The rating is considered suitable as the decision makers consider it an appropriate tool to evaluate alternatives. Figure 1 shows the hierarchy structure from the rating mode. The hierarchy begins with the global objective. The criteria are at the second level. The categories associated to the subcriteria are at the last level. The structure with ratings differs from the traditional AHP (relative measurement), because in the last level the alternatives are not found. The evaluation is performed by intensity levels (categories) attributed to each subcriteria related to each alternative, instead of evaluating the alternatives by pairwise comparisons.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
Prioritization of R&D projects in the aerospace sector: AHP method with ratings
Figure 1: Hierarchy structure – ratings model.
To establish the relative importance of these categories (obtaining priority vectors), the specialist’s (or specialists’) values/opinions are incorporated to the rating system. Duarte Júnior (2005) presents proposals to obtain numerical values of ratings (priority vectors) such as pairwise comparison process of AHP method. In this proposal, the rating pairwise comparisons are performed to define the priorities of each criterion (or subcriterion). Saaty (1987, 2006, 2008) suggests that when working with ratings the priority vectors obtained are idealised, that is, the best category receives the value 1 and the others must be proportionally smaller. The synthesis of results, that is, the alternatives of final priorities are found by adding the values referring to the multiplication between the properties of each category and the global priorities of the criteria/subcriteria in these categories. The main advantage of using ratings is to decrease the number of comparisons necessary when there are a large number of alternatives. Besides, when using absolute measurement (ratings), it does not matter how many new alternatives are introduced, or old ones are excluded because there is no inversion of the alternatives ranking. The software Expert Choice and SuperDecisions include, besides the traditional AHP, the AHP with ratings (absolute measurement). In this paper, a brief description of AHP with ratings is presented and the application exercise used the software SuperDecisions, developed by Creative Decisions Foundation. AHP APPLICATION WITH RATINGS: SELECT PROJECTS OF R&D AEROSPACE (DCTA) The application of the AHP method in this paper is based on the study case of Lima and Damiani, 2010.
Step 1: Define the problem and determine the kind of knowledge sought Lima and Damiani (2010) present a proposal of problem structuring to prioritize the aerospace R&D projects. The authors reported that the goal of this proposal was to suggest an analytical structure that could enable a R&D institution acting in the aerospace sector to identify and structure their own decision criteria in relation to the selection process of R&D processes, with a wide range of possibilities. The study case of Lima and Damiani (2010) has been performed in the Department of Science and Aerospace Technology (DCTA). This organization, founded in 1953, focus the progress of technical-scientific activities related to the aerospace education, research and development that are interesting to the Ministry of Defense. As R&D projects prioritization is a complex decisionmaking problem, the authors preferred structuring the problem through a tool of cognitive maps, employing the constructivist paradigm of decision support. Therefore, the purpose of this work was to select aerospace R&D projects, in association with the organization strategies. This paper is based on the problem structuring of Lima and Damiani (2010). The MCDM method chosen for this evaluation is the AHP using ratings. The decision maker is the same as Lima and Damiani (2010). The criteria are: Potential to generate Innovation (PI), Technological Maturity (TM), Duality (D), Operational Alignment (OA), Means Availability (MA), Risk Response (RR), and Opportune Attendance (OpA). The MA criterion presents the subcriteria: Finance Resources (FR), Human Capacitation (HC), and Infrastructure (IS). More details and further explanation of the criteria and subcriteria are found in Lima and Damiani (2010).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
341
Silva, A. C. S. et al.
All criteria and subcriteria were considered independent, as the AHP method indicates. The definition of the ratings for problem criteria and subcriteria follows Table 1. The alternatives selected by the organization are five big R&D projects named: Project A, Project B, Project C, Project D and Project E. Three of these projects are real projects of the institution.
level is the global objective: “prioritize projects”. On the second level, the main aspects that the decision maker has to consider when performing the prioritization of R&D projects are Strategic Alignment (SA) and Realization Potential (RP). On the third level, the criteria and, on the fourth level, the subcriteria. In the last level, the categories (Table 1) that describe the associated criteria and subcriteria are found.
Step 2: Structure the decision hierarchy
According to the decision maker, this hierarchy is used to evaluate small and big projects. The AS aspects are more important when bigger projects are evaluated.
Figure 2 presents the hierarchy structure for the problem of aerospace R&D projects selection. The first hierarchic
After the problem is formulated, and the hierarchy is built and validated, the judgment process is started when the
Table 1:
Definition of the ratings for the criteria and subcriteria
Criteria and subcriteria
Ratings
Potential to generate Innovation (PI) PI1- is involved in the industry since its inception. PI2- has the potential to involve industry. PI3- there is no industrial interest with regard to the project. Technological Maturity (TM)
TM1- the project attempts an elevation of the current level of technological maturity. TM2- the project strengthens the current level of technological maturity. TM3- the project has no effect on the current level of technological maturity.
Duality (D)
D1- it has the potential to generate civilian and military application. D2- it has the potential to generate for civilian use only. D3- it has the potential to generate only a military application.
Operational Alignment (OA)
OA1- responds to a formalized operational need. OA2- it serves an operational need not formalized. OA3- there is a possibility of operational implementation. OA4- has not operational application.
Means Availability (MA) MA1. Finance Resources (FR) FR1- has resources available (officially announced). FR2- has potential for features (has promises) FR3- it is necessary to obtain resources management (persuasion). FR4- there are reasons to believe that resources are not available. MA2. Human Capacitation (HC)
HC1- there is availability of trained human resources for the project. HC2- there is trained human resources, but availability must be shared with other projects. HC3- there is availability of staff, but requiring training. HC4- there is no available and qualified human resources for the project.
MA3.Infrastructure (IS)
IS1- OM (military organization) already has the infrastructure to serve the project. IS2- OM has partial infrastructure to support the project. IS3- there is no infrastructure in the OM, but availability is feasible. IS4- there is a great difficulty in providing OM infrastructure that meets the project.
Risk Response (RR)
RR1- the risk analysis shows that the project presents no significant risk. RR2- the risk analysis shows that they can be avoided by mitigation measures. RR3- the risk analysis provides risk mitigation difficult
Opportune Attendance (OpA)
OpA1- the period planned to exceed customer’s expectations. OpA2- the period planned to meet customer’s expectations. OpA3- the term planned partially meets the customer’s expectations. OpA4- the planned period is not satisfying for the customer’s expectations.
342
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
Figure 2: Hierarchy structure for the problem.
decision makers express their preferences through the pairwise comparison matrices of the criteria/subcriteria and ratings. Step 3: Construct a set of pairwise comparison matrices In this step, the decision matrix is formed in order to obtain the values of importance of the criteria, subcriteria and ratings. These values attribution is based on Saaty’s Fundamental Scale (Saaty, 1980). For each decision, the Consistency Ratio (CR) is calculated. The priorities of each category are determined by using the pairwise comparison process of AHP method. The decision matrices are shown as follows. Table 2 presents decision matrices of judgments of the main aspects that the decision maker considers when prioritizing the R&D projects in relation to the objective.
Table 2:
Decision matrix of judgments of the main aspects with respect to the objective
Objective
SA
RP
Priorities
SA
1
3/2
0.6
RP
2/3
1
0.4
Table 3:
Decision matrix of judgments of the criteria with respect to the SA aspect
SA
PI
TM
D
PI
1
1
3
3
0.367
1
4
3
0.396
1
1
0.114
1
0.122
TM D OA Table 4:
OA Priorities
MA
RR
Table 3 presents the decision matrix of judgments between the criteria with respect to and SA aspect.
MA
1
4
3/2
0.532
1
1/2
0.146
Table 4 presents the decision matrix of judgments between the criteria with respect to RP aspect.
OpA
1
0.322
In order to obtain the numerical values of ratings, a comparison matrix between the rating intensity levels was built. Through this matrix, the relative importance among levels of intensity was found, calculating the
RR
Table 5:
CR=0.0039
Decision matrix of judgments for criteria with respect to the RP aspect.
RP
Table 5 presents the decision matrix of judgments between the subcriteria with respect to and Means Availability (MA).
CR=0.0
OpA Priorities CR=0.0089
Decision matrix of judgments for the subcriteria with respect to Means Availability (MA).
MA
FR
HC
IS
Priorities
FR
1
1
1
0.337
1
3
0.457
1
0.207
HC IS
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
CR=0.0904
343
self-vector that represents the “performance” for each intensity level. The rating numerical values for the criteria and subcriteria are presented in tables. These ratings must be idealised before the alternative final priorities calculation. Table 6 presents a decision matrix of comparisons for the rating levels of intensity with respect to the Potential of Generating Innovation (PI). Table 7 presents a decision matrix of comparisons for the ratings levels of intensity with respect to the criteria of Technological Maturity (TM). Table 8 presents a decision matrix of comparisons for the rating levels of intensity with respect to the criteria of Duality (D). Table 9 presents a decision matrix of comparisons for the rating levels of intensity with respect to the criteria of Operational Alignment (OA).
Table 10 presents a decision matrix of comparisons for the rating levels of intensity with respect to the subcriteria of Finance Resources (FR). Table 11 presents a decision matrix of comparisons for the ratings levels of intensity with respect to the subcriteria of Human Capacitation (HC). Table 12 presents a decision matrix of comparisons for the rating levels of intensity with respect to the subcriteria of Infrastructure (IS). Table 13 presents a decision matrix of comparisons for the rating levels of intensity with respect to the criteria of Risk Response (RR). Table 9:
OA OA1
Table 6:
PI
Decision matrix of comparisons for the rating levels of intensity with respect to the Potential of generating Innovation (PI) (CR=0.0311)
PI1 PI2
PI1
1
PI2
PI3 Priorities Idealised priorities
3
7
0.659
1.000
1
4
0.263
0.399
1
0.079
0.119
PI3 Table 7:
TM
Decision matrix of comparisons for the rating levels of intensity with respect to the criteria of Technological Maturity (TM) (CR=0.0824)
TM1 TM2 TM3
TM1
1
TM2
1
4
0.280
0.446
1
0.094
0.149
TM3
Table 8:
Decision matrix of comparisons for the rating levels of intensity with respect to the criteria of Duality (D) (CR=0.0516)
FR FR1
HC
D2
D1
1
1
2
0.413
1.000
HC2
1
1
0.327
0.794
HC3
1
0.260
0.630
HC4
344
0.412
1.000
1
1
3
0.282
0.684
1
3
0.231
0.562
1
0.075
0.181
FR1 FR2 FR3 FR4 Priorities 1
Idealised priorities
2
4
7
0.536
1.000
1
1
3
0.215
0.401
1
3
0.181
0.339
1
0.068
0.128
Table 11: Decision matrix of comparisons for the rating levels of intensity with respect to the subcriteria of Human Capacitation (HC) (CR=0.0638)
D1
D3
7
FR3
D D2
D3 Priorities Idealised priorities
2
Table 10: Decision matrix of comparisons for the ratings levels of intensity with respect to the subcriteria of Finance Resources (FR) (CR=0.0188)
FR4
1.000
Idealised priorities
1
OA4
FR2
0.627
1
OA3
Idealised priorities
5
OA1 OA2 OA3 OA4 Priorities
OA2
Priorities
3
Decision matrix of comparisons for the rating levels of intensity with respect to the criteria of Operational Alignment (OA) (CR=0.0290)
HC1
HC1 HC2 HC3 HC4 Priorities 1
Idealised priorities
3
4
7
0.542
1.000
1
3
5
0.269
0.496
1
4
0.137
0.252
1
0.052
0.096
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
Table 12: Decision matrix of comparisons for the rating levels of intensity with respect to the subcriteria of Infrastructure (IS) (CR=0.0030)
IE1
IE2
IE3
IE1
1
2
3
9
0.507
1.000
1
2
4
0.280
0.552
1
3
0.157
0.310
1
0.055
0.108
IE2 IE3 IE4
IE4 Priorities
Idealised priorities
IE
RR1 RR2
RR1 RR2 RR3 Priorities Idealised priorities 1
2
7
0.592
1.000
1
5
0.333
0.563
1
0.075
0.127
RR3
The judgment consistency was made through pairwise matrices. All the presented CR (Consistency Ratio) less than 10% (or 0,1) indicate the judgment coherence of the decision makers. Step 4: Use the priorities obtained from the comparisons to weigh the priorities in the level immediately below
Table 13: Decision matrix of comparisons for the rating levels of intensity with respect to the criteria of Risk Response (RR) (CR=0.0136)
RR
Table 14 presents a decision matrix of comparisons for the rating levels of intensity with respect to the criteria of Opportune Attendance (OpA).
Based on the vectors generated by the method, the local priorities of the criteria and subcriteria were obtained. Figure 3 presents the global priorities of the criteria and subcriteria (in parentheses) and the numerical values of the ratings (idealised) for criteria and subcriteria. Table 15 presents the classification of alternatives (projects) in the criteria and subcriteria ratings corresponding to the categories (Fig. 3).
Table 14: Decision matrix of comparisons for the ratings levels of intensity with respect to the criteria of Opportune Attendance (OpA) (CR=0.0354)
OpA
OpA1
OpA2
OpA3
OpA4
Priorities
Idealised priorities
OpA1
1
1
4
7
0.444
1.000
1
2
3
0.338
0.761
1
4
0.162
0.365
1
0.055
0.125
OpA2 OpA3 OpA4
Figure 3: Global priorities and idealised ratings of criteria/subcriteria.
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
345
Table 16 presents a final punctuation for each Project. It is calculated by adding the products between the global priorities of the criteria and subcriteria and the ratings values for each alternative, thus obtaining the “Totals” column which normalized presents the final punctuation (“Final priorities”). For example, for Project A, we have: Totals_Project_A = (0.220 x 1.000) + (0.238 x 1.000) + (0.069 x 1.000) + (0.073 x 0.684) + (0.072 x 0.401) + (0.097x 0.252) + (0.044 x 0.310) + (0.058 x 1.000) + (0.129 x 0.365) = 0.749
Table 17 presents the final priorities (in graphics) for the alternatives. The columns “Total” and “Normal” are equivalent to the total and final priorities of Table 16, respectively. The column “Ideal” is obtained by dividing all elements of “Total” by its highest value. In this case, the best evaluated project is Project D, followed by Project B, Project E, Project A and Project C. A sensitivity analysis would be required to study how to choose the project D over project B, since
Table 15: Classification of the alternatives in ratings
Criteria/Subcriteria
Ratings Project A
Project B
Project C
Project D
Project E
PI
PI1
PI1
PI2
PI1
PI1
TM
TM1
TM1
TM1
TM1
TM1
D
D1
D1
D1
D1
D1
OA
OA2
OA2
OA3
OA1
OA1
FR
FR2
FR1
FR1
FR1
FR1
HC
HC3
HC1
HC2
HC2
HC2
IS
IS3
IS1
IS2
IS2
IS3
RR
RR1
RR2
RR2
RR2
RR3
OpA
OpA3
OpA3
OpA3
OpA2
OpA4
Table 16: Final priorities of the alternatives
Alternatives
PI TM D OA FR HC IS RR OpA (0.220) (0.238) (0.069) (0.073) (0.072) (0.097) (0.044) (0.058) (0.129)
Total
Final Priorities
Project A
1.000
1.000
1.000
0.684
0.401
0.252
0.310
1.000
0.365
0.749
0.192
Project B
1.000
1.000
1.000
0.684
1.000
1.000
1.000
0.563
0.365
0.869
0.222
Project C
0.399
1.000
1.000
0.562
1.000
0.496
0.552
0.563
0.365
0.659
0.169
Project D
1.000
1.000
1.000
1.000
1.000
0.496
0.552
0.563
0.761
0.875
0.224
Project E
1.000
1.000
1.000
1.000
1.000
0.496
0.310
0.127
0.125
0.757
0.194
Table 17: Ranking of the alternatives
Graphic
346
Ratings alternatives
Total
Ideal
Normal
Ranking
Project A
0.7492
0.8562
0.1916
4
Project B
0.8694
0.9937
0.2224
2
Project C
0.6593
0.7535
0.1686
5
Project D
0.8749
1.0000
0.2238
1
Project E
0.7569
0.8651
0.1936
3
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
they have similar evaluations. Moreover, it is worth noting that the use of AHP method does not allow analyzing the portfolio projects with respect to resource constraints. In this case, one would have to use a hybrid methodology, such as AHP method and integer programming. For this problem, 55 comparisons were performed, as shown in Table 18. Table 18: Comparative study between AHP relative model and AHP rating model
Number of comparisons Number of alternatives AHP relative model AHP rating model 3
40
55
5
103
55
9
337
55
20
1723
55
However, in comparison with the AHP relative model, as the alternative number increases, the number of comparisons increases considerably, while in AHP rating model, it remains the same. It is known that, depending on the complexity of the problem, the use of AHP ratings model is advantageous, because it can significantly reduce time and effort in the decision-making process. FINAL CONSIDERATIONS The aim of this paper was to present a proposal of project selection and prioritization, through Multiple-Criteria Decision-Making methods (MCDM), AHP with ratings. The use of this procedure enables the reduction of judgment numbers required to decision maker when the alternatives are numerous. Besides, it enables the insertion and removal of alternatives without inverting the ranking during the decision-making process. The problem hierarchy in this paper considers “aspects” in the first level rather than criteria as we see in most applications. The reason for using “aspects” is a better perception and evaluation by the decision maker. These characteristics are advantageous once they allow the representation of a complex problem of projects selection and prioritization. The application of the method was possible in this project because the problem had
been structured before, with ratings defined by Lima and Damiani (2010). However, there are many ways to evaluate and select projects for the problem. Thus, the parts involved must decide and adapt the best method to the problem decision, in agreement with its specific requirements. For further studies, the implementation of procedures, ratings and BOCR (benefits, opportunities, cost and risks) in the AHP method is suggested. ACKNOWLEDGMENTS The authors thank Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the financial support. REFERENCES Duarte Júnior, A.M., 2005, “Gestão de riscos para fundos de investimentos”, Prentice Hall, São Paulo, pp. 141155. Ghasemzadeh, F., Archer, N.P., 2000, “Project portfolio selection through decision support”, Decision Support Systems, Vol. 29, pp. 73-88. doi: 10.1016/S01679236(00)00065-8. Gomes, L.F.A.M, Gomes, C.F.S. and Almeida, A.T., 2006, “Tomada de decisão gerencial: enfoque multicritério”, São Paulo, Atlas. Lima, A.S., Damiani, J.H.S., 2010, “Proposta de método para modelagem de critérios de priorização de projetos de pesquisa e desenvolvimento aeroespaciais”, In: Marins, F.A.S.; Pereira, M.S.; Belderrain, M.C.N.; Urbina, L.M.S. (Org.), Métodos de tomada de decisão com múltiplos critérios: aplicações na indústria aeroespacial. 1 ed. São Paulo: Edgard Blucher Ltda., Vol. 1, pp. 77-107. Meade L.M., Presley, A. 2002, “R&D project selection using the analytic network process. IEEE Transactions on Engineering Management”, Vol. 49, No 1, pp. 55-66. doi: 10.1109/17.985748. Saaty, R.W., 2003, “Decision making in complex. The analytic hierarchy process for decision making and the analytic network process for decision making with dependence and feedback” [Superdecisions Tutorial]. Saaty, T.L., 2008, “Decision making with the analytic hierarchy process”, International Journal of Services Sciences, Vol. 1, No 1, pp. 83-97.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
347
Saaty, T.L., 2006, “Rank from comparisons and from ratings in the analytic hierarchy/netwok processes”, European Journal of Operational Research, Vol. 168, No 2, pp. 557-570. doi: 10.1016/j.ejor.2004.04.032. Saaty, T.L., 1987, “Concepts, theory and techniques: Rank generation, preservation and reversal in the analytic hierarchy process”, Vol. 18, Decision Sciences.
348
Saaty, T.L., 1980, “The analytic hierarchy process”, McGraw-Hill, New York. Weisz, J., 2006, “Mecanismos de apoio à inovação tecnológica”, SENAI/DN, Brasília.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 339-348, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02038910
Mariana de Freitas Dewes*
Univ. Federal do Rio Grande do Sul Porto Alegre – Brazil mfdewes@ea.ufrgs.br
Odair Lelis Gonçalez
Instituto de Estudos Avançados São José dos Campos – Brazil odairl@ieav.cta.br
Angelo Pássaro
Instituto de Estudos Avançados São José dos Campos – Brazil angelopassaro@gmail.com
Antonio Domingos Padula
Univ. Federal do Rio Grande do Sul Porto Alegre – Brazil adpadula@ea.ufrgs.br * author for correspondence
Open innovation as an alternative for strategic development in the aerospace industry in Brazil Abstract: We present in this paper a case of technological competence development in the aerospace sector in Brazil, by addressing the complete cycle of integrated circuits for satellite applications, an area of high technology which is strategic to the country. The development of technological and business competences is linked to an understanding of the existing relations between different participating institutions, both public and private. There is an effort to establish a network for the development of radiation-hard integrated circuits in Brazil, comprising universities, research centers, private companies, design houses, funding and governmental agencies. These institutions have been working to define their roles, through participation in federally funded projects to develop robust component technology for the aerospace industry in Brazil. As a means to maintain and improve this network, it is suggested that long term planning tools such as technology roadmaps be adopted, as well as measures to increase awareness of and help clarify intellectual property issues, which is considered a significant bottleneck to advance technology development in this area. In this sense, open innovation may be considered an alternative for competitively enhancing the outcomes of the sector. Keywords: Open innovation, Aerospace applications, Interorganizational network, Intellectual property, Technology roadmap.
INTRODUCTION This paper presents a case of technological competence development in the aerospace sector in Brazil, by addressing the complete cycle of integrated circuits for satellite applications, an area of high technology which is strategic to the country. The development of technological and business competences is closely linked to an understanding of the existing relations between different participating institutions, both public and private. To enhance the space program and to develop critical products, a focused development of resources is necessary. The open innovation management perspective is increasingly useful to analyze strategic technology development such as this one. The objective of this paper was to present to the aerospace community open innovation as an alternative for competitively enhancing the outcomes of the sector, focusing on the development of radiation-hardened systems and components for spatial application. It can also be an adequate approach to join actors of the Brazilian aerospace network around a common plan, developing the space industry as a whole in the country. The main motivation to study this problem is that critical components may be subject to international commercial
Received: 16/09/10 Accepted: 18/10/10
restrictions. There are some alternatives to overcome this, such as joint development with companies in other countries, upscreening of less qualified components, changes in engineering project, bilateral agreements for mission development, and the development of a set of radiation-hardened integrated circuits. Considering the effort of the Brazilian government in developing endogenous expertise in microelectronics, internal development of radiation-hardened integrated circuits is a viable alternative. Research context The aerospace industry, in the context of the present study, draws its high technology components from the electronics sector. In Brazil, this sector has a historical trade balance deficit, which in 2008 reached US$ 3.426,7 million only in integrated circuits (semiconductors). However, this number does not reflect the entire deficit of the electronic industry, because imported electronic goods and the whole or parts of equipment with embedded semiconductors are not computed (Gutierrez and Mendes, 2009). From a strategic perspective, the Brazilian aerospace program may act as a mechanism to foster networking among participating companies, establishing links between universities and research institutions to solve technological problems. The aerospace program may
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
349
Dewes, M. F. et al.
also provide scientific, engineering, and societal benefits, leading to accomplishments in space which may have inspirational value for young people, such as cited by Norman Augustine (IEEE Spectrum Aerospace, 2009). In this context, our proposition is that the open innovation framework shall prove useful for analyzing the development of the network, in which many complementary competences, available in different institutions throughout the country, need to be coordinated, with the objective of building competences in the complete development cycle of integrated circuits for aerospace applications in Brazil. The cycle includes specification, design, simulation, layout, manufacturing, encapsulation, test, and qualification. By analyzing this specific development program as a case study, we hope to identify links between institutions. Specific issues concerning the institutional environment, business aspects, funding, intellectual property, technological trends, in which each institution or company contributes with a significant part of the development, and coordination of the group at the interorganizational level are discussed and alternatives for the network are proposed. Method and data analysis The method employed in this research was a case study of an interorganizational network. This network constitutes the level of analysis (Vanhaverbeke, 2006). Case studies are recommended as a research method when knowledge in a certain field is comparably limited and new, and when there is need to retain richness of the studied incident in its context (Eisenhardt, 1989; Yin, 2003). The presented case, the aerospace industry cluster concentrated in and around São José dos Campos, in the State of São Paulo, Brazil, is a network of companies, universities, and research institutions. It has the special characteristic of combining various types of both public and private organizations around a specific high technology industrial segment. This makes it a unique setting to conduct research in open innovation practices, because of the need to focus on development of complementary resources to manufacture critical components locally, which may suffer commercial restrictions from foreign countries. Data was collected during a three-day workshop held in October 2009 in São José dos Campos, São Paulo, Brazil, to discuss the effects of ionizing radiation on electronic components, in which companies, universities, research and government institutions participated. Data collection consisted of direct observation of the presentations and also interviews with a key representative from each of the following organizations: the Brazilian Space Agency (AEB), the Association of Aerospace Industries of Brazil
350
(AIAB), two federal research institutions, brazilian design houses, two universities, the Ministry of Science and Technology, and Brazil’s development bank (PEICE II, 2009). Questions were related to business aspects, funding, intellectual property, technological trends, and coordination of the group at the interorganizational level. Additional data were collected immediately after the workshop through interviews with CEO’s from three companies which are part of the network. Queries in official sources, such as the National Program of Space Activities document (AEB, 2005), sector reports, and websites of the participating institutions provided complementary information. Open innovation and interorganizational relationships Innovation studies have emphasized the growing relevance of external sources of innovation. Rather than relying exclusively on internal research and development (R&D), organizations are reported to increasingly engage in “open innovation” (Chesbrough, 2006). This means that innovation may be considered as resulting from distributed interorganizational networks, rather than from single firms (Powell, Loput and Smith-Doerr, 1996; Coombs, Harvey and Tether, 2003). In the same direction, various concepts of “interactive” innovation have been presented to understand the non-linear, iterative and multi-agent character of innovation processes (Kline, 1985; Lundvall, 1988;Von Hippel, 1988). By definition, open innovation occurs through the establishment of links between innovative firms with other institutions. In open innovation a firm collaborates with technology providers, suppliers and/or customers (Von Hippel, 1988) to improve its internal innovation capabilities or to expand the markets for the external use of internal innovations (Fig. 1) (Chesbrough, 2003). In an open innovation context, firms jointly create value through a number of transactions in so-called value networks.
Figure 1: Open innovation model (Chesbrough, 2003)
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
Open innovation as an alternative for strategic development in the aerospace industry in Brazil
Networking is a crucial dimension of open innovation, and the role of interorganizational relationships in a context of open innovation has been studied in recent years (Vanhaverbeke, 2006; Vanhaverbeke and Cloodt, 2006). Analyzing this context, the authors affirm that organizations are urged to collaborate with others to develop or absorb new technologies, sell new products, or simply keep up with the latest technological advances. According to Von Hippel (1988), the high costs and uncertainty in knowledge creation are powerful reasons to explain why firms frequently resort to external sources of ideas. Research on innovation has emphasized the role of the firm’s external dimension as an important locus of useful knowledge (Arora and Gambardella, 1994; Caloghirou, Kastelli and Tsakanikas, 2004; Cassiman and Veugelers, 2006; Lichtenthaler, 2008a). Such interfirm networks may offer flexibility, speed, innovation, and the ability to easily adapt to changes in market conditions and to new strategic opportunities (Dittrich and Duysters, 2007). Learning how to create and capture value when organizations are highly dependent on one another is an under-explored field in network literature. Most firms are accustomed to make decisions inside their limits, considering the external environment literally as an exogenous variable or as a locus in which firms compete with each other. However, in networks, value is produced together: total value created in the network depends directly on how partners’ objectives are aligned and on their commitment to invest in complementary assets (Vanhaverbeke, 2006). The establishment of cooperative networks seems to be important in processes related to both technological complexities, to make innovation possible in manufacturing firms, and to the increasingly global nature of markets and economies, which results in a global division of labor and in a more intense competition (Álvarez, Marin and Fonfría, 2009). According to these authors, motivations for cooperation are grouped into two items: i) the complex and uncertain (and thus costly) nature of research and technological development, and ii) market access and search for opportunity. In the dynamic capabilities approach, Teece, Pisano and Shuen (1997) consider cooperation as a mechanism through which firms accumulate and combine knowledge and other complementary assets. Finally, the open innovation hypothesis may serve as a useful reference point for guiding research considering the organizational dynamics of collaboration arrangements between universities and industry, which remains underresearched (Perkmann and Walsh, 2007). From the perspective of a firm, the types of networks that influence
its search for university partners are geographically proximate social networks (Jaffe, 1989; Owen-Smith and Powell, 2004 ). The issue of geographic location of innovation and its implication for open innovation has been recently developed by Simard and West (2006). Intellectual property An intellectual property (IP) policy for a network is a challenging arrangement. Multiple parties have different interests that must come into balance. Defining IP rights enables the exchange of ideas and technologies between the many parties who possess useful knowledge (Chesbrough, Vanhaverbeke and West, 2006). In the open innovation paradigm, changes in the general role of IP have been observed, particularly in patenting practices. This may be attributed to technological changes, in which IP rights cease to be the only source of value capturing to firms. Value creation may occur, for example, through the generation of open standards (Simcoe, 2006), in a cooperative fashion, removing the emphasis of a patent as the sole mechanism of competitive advantage. Based on a survey, Cohen, Nelson and Walsh (2002) distinguish between the following channels relevant to industrial innovation: patents, informal information exchange, publications and reports, public meetings and conferences, recently hired graduates, licenses, joint or cooperative research ventures, contract research, consulting, and temporary personnel exchanges. It is argued that in contexts of open and networked innovation, interorganizational relationships between public research organizations and industry play an important role in driving innovation processes. Specifically, it appears that the contribution of relationships to innovative activities in the commercial sector considerably exceeds the contribution of IP transfer (e.g. licensing) (Perkmann and Walsh, 2007). Laursen and Salter (2006) conclude that openness is associated with a moderate level of appropriability through IP rights; therefore, depending on the industrial sector, patents and university research may play a larger or smaller role in innovation. In this direction, other authors (Chesbrough, Vanhaverbeke and West, 2006; Fabrizio, 2006) identify potentially negative impacts of high appropriability upon the cumulative and decentralized aspects of open innovation, with several concerns as to the potential of limited availability of university research and the destruction of norms that support the cumulative, open nature of scientific discovery associated with university research.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
351
Dewes, M. F. et al.
Roadmaps When considering investment in technological innovation, it is suggested that policy makers grasp the broader coverage of scientific and technological research, and make decisions on effective investment in especially promising and emerging technologies, under circumstances where total budget has been constrained or has declined. In this sense, policy makers and R&D managers have to notice global trends in research and emerging technologies, which enables precise forecasting and effective roadmapping. Nowadays, in the increasingly knowledge-based economy, a more reliable growth depends on the application of new science and technology (Kajikawa et al., 2008). Technology roadmaps are a flexible approach, in terms of the different organizational aims they can address. They should integrate commercial and technical knowledge, and their purpose is to give a clear picture of where an organization (or a group of organizations) is headed, in terms of its technology, the local environment of which it is a part, and who are the participants in its market. Roadmap models consider the need to consolidate multiple views of technology development. According to Lichtenthaler (2008b), it is an instrument that may help firms to incorporate external knowledge exploitation in strategic technology planning. Some types focus on integration of technology, in terms of how different technologies combine within products and systems, or to form new technologies. Other models are used for long-range planning. This type of roadmap is often performed at the sector or national level (foresight), and can act as a radar for the organization to identify potentially disruptive technologies and markets, aiming to converge to a specific enterprise, as shown in Fig. 2 (Phaal, Farrukh and Probert, 2004). According to Phaal, Farrukh and Probert (2004), a key challenge to overcome if the roadmap is to be widely adopted is keeping it alive; its full value can be gained only if the information that it contains is current and
kept up-to-date as events unfold. In practice, this means updating the roadmap on a periodic basis, at least once a year, or perhaps linking it to budget or strategy cycles. A few roadmaps have been developed in Brazil, although its use as a strategic planning tool is still quite limited. Some examples include the nanotechnology roadmap for space industry (Fellows and Vaz, 2006) ) and the ethanol technology roadmap (Graziano, 2009). Both were conducted by governmental organizations. Overview of the Brazilian aerospace sector The Brazilian Space Program started in 1979, with the Complete Brazilian Space Mission (MECB). The satellites developed under this program were SCD-1 and 2 (Data Collecting Satellite), launched in 1993 and 1998, respectively. In addition, Brazil and China signed, in 1988, a cooperation agreement for the development of the so-called Chinese-Brazilian Earth Resource Satellite (CBERS), which generates images of the Earth. Three other satellites are being developed by the National Institute for Space Research (INPE), which is responsible for the projects: Amazonia-1, which shall be used to generate images of the Amazon region, Sabia-mar, developed in cooperation with Argentina, and GPMBrasil, for meteorological studies. The Brazilian aerospace sector has two satellite launching programs under development, which intend to offer in the future launching services to the market. The first program is a joint effort of Defense and of Science and Technology Ministries, the VLS program. The second one is related to a bi-national company, the Cyclone 4 program. In the satellite segment, the country does not have yet a communication satellite development program. There are, however, competences in equipment and subsystems.
time Component/ Prototypes / System / subsystem test technology technologies systems demonstrators
Inservice systems Nugget
Figure 2: Roadmap models (Phaal, Farrukh, Probert, 2004, p. 12) 352
J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
Open innovation as an alternative for strategic development in the aerospace industry in Brazil
In the services segment, there are more than 30 communication satellites supplying the Brazilian market. Brazilian companies operate around 10 satellites. Research institutions The Department of Aerospace Science and Technology (DCTA) was created in the 1950s in São José dos Campos to build capabilities in the aeronautical area. Nowadays, its objectives encompass the aerospace area. It comprises several research institutes for aerospace and defense, including: the Technological Institute of Aeronautics (ITA), which has graduate and undergraduate courses, research and extension activities in areas of interest to the Brazilian Air Force and to the aerospace sector in general; Institute of Aeronautics and Space (IAE) and Institute for Advanced Studies (IEAv), where pure and applied science and also technological development in various fields of aerospace area are conducted (DCTA, 2009). DCTA is also in charge of the Brazilian launching centers. INPE, linked to the Ministry of Science and Technology, also located in São José dos Campos, is the main research institute for space, astronomy, meteorology, and related areas in Brazil. It was created in 1971, from the Group for the Organization of National Space Activities Commission, the embryo of the institute, which had been created in 1961. R&D are conducted in areas such as space and atmospheric sciences; weather forecast and climate studies; space engineering and technology; Earth observation; satellite tracking and control; integration and testing laboratory. INPE is the executive organization responsible for coordination and implementation of R&D activities in satellite and payload projects and applications, as well as for the establishment of operational and maintenance activities regarding the infrastructure associated to development, integration, tests, satellite tracking and control, reception, processing and distribution of satellite data. Nowadays, INPE is the main client for spatial subsystems. Industry defines the project and the necessary components, which are purchased by INPE in the international market, with spatial specification when possible. Thus, it is today the main client in Brazil for radiation resistant components applied to the national satellite program, which supplies a satisfactory indicator of the R&D needs for such components, and their qualification for space environment (INPE, 2009). Recently, this orientation seems to be changing and the industries will also be in charge of purchasing parts and components. An example is the Multi Mission Platform (MMP) project, which is expected to follow this new orientation.
Space agency AEB was created in 1994, and is responsible for the formulation and coordination of the national space policy. It is a federal authority under the Ministry of Science and Technology, and has strategically contributed to the efforts undertaken by the Brazilian government to promote autonomy in the space sector since 1961. It is responsible for the National Space Activities Program (PNAE – 2005-2014). In order to face the technological challenges involved in large scale projects, PNAE is configured as an innovation fostering agent. R&D activities, with support of the academic community, play a fundamental role towards leveraging national industrial capacity and competitiveness, through the acquisition of strategic capacities and technology, new work processes and methodologies, in compliance with international quality standards. In the view of AEB, this knowledge shall lead to the modernization and leveraging Brazil’s entire productive sector, through technology absorption mechanisms. The agency also manages international cooperation, which is important for building technological capacity in the space sector. Agreements have been signed with nine countries and one international organization for cooperation on peaceful use of outer space. These agreements lead to new bilateral space programs and eventually to the obtainment of new technologies (AEB, 2005). Companies Companies participating in the network vary in size and age, ranging from 30 to about 450 employees. The first companies were established in the 1980s; others were established during the 1990s to work in the electronics, avionic and space industries, working with both civil and military clients. Most of the companies are located in the State of São Paulo, and have strong ties to universities and research institutions located in the same region. This is a main competitive advantage, because these ties benefit from highly qualified professionals who seek jobs in the region. They have in common research-based origins, since all were created by former researchers. All of them reported to have either formal or informal cooperative relationships with electronic component manufacturers and with Brazilian space institutions such as AEB, INPE and DCTA, and their international counterparts such as the National Aeronautics and Space Administration (NASA), European Space Agency (ESA), French Government Space Agency (CNES), and Indian Space Research Organization (ISRO). One of the companies has participation of EADS Astrium as a shareholder, the largest European company in the aerospace and defense
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
353
Dewes, M. F. et al.
sectors. According to one interviewed CEO, companies in the Brazilian space sector seek ideas for products and applications in foreign space programs, developed also by foreign companies. AIAB is the national entity which represents companies in the Brazilian aerospace sector. Founded on March 18, 1993, with headquarters in São José dos Campos, São Paulo, it operates similarly to associations in other countries. It is member of the International Coordinating Council of Aerospace Industries Associations, together with its counterparts from Canada, United States, and Japan. The position of AIAB is that it should strive to reach significant participation in the space market, analogously to the Brazilian aviation industry. It participates in the segments of ground equipment, mainly DTV, GPS, and other telecommunication satellite equipment. Great demand is foreseen for HDTV, internet access, GPS, and maps (GIS). Universities Brazilian universities, both public and private, state and federal, have expertise and generate new knowledge in many areas related to aerospace science and technology, participating in the main international conferences and publishing research papers in international journals. The ITASAT project, a federally funded project, involves academic participation from Brazilian public universities. It started in 2005, and its goal is to develop a universitybuilt satellite, giving students the opportunity to conduct technological experiments with space applications. The idea is to transfer manufacturing of flight and qualification models to national industry. Initiatives such as ITASAT are extremely relevant to develop space related activities in Brazil, because they contribute to educate highly qualified human resources, bringing the space program closer to universities, and creating means to develop knowledge in science and technology (ITASAT, 2010). Design houses In March 2004, the Brazilian government launched an industrial policy program (CI Brasil) which had the aim to support microelectronics, among other industrial sectors. Design houses for integrated circuits were among the organizations to be fostered by this policy, and they should be directed in either of two strategies: linked to Brazilian technological institutions or to multinational companies in the sector. Brazilian industry would be the potential client for design houses services (Gutierrez and Mendes, 2009).
354
In the context of CI-Brasil, the mission to start organizing the development of the aerospace market niche in Brazilian design houses was delegated to the Center for Information Technology Renato Archer (CTI), especially for building competences in designing radiation-hard components, following strict international standards (Finco, 2009). CTI, which is a R&D unit for information technology of the Ministry of Science and Technology, founded in 1982 in Campinas, São Paulo, has a design house (CTI-DH) with 40 employees, offering consulting services in electronic components and systems design, manufacturing, as well as qualified IP production for the global market, with application in wireless products, sensor networks, automotive, consumer electronics, among others. CTI interacts intensely with academic and industrial sectors through research cooperation agreements, with ten laboratories dedicated to electronic components, microelectronics, systems, software, and IT applications, and with almost 300 employees. Another publicly funded design house in Brazil is CEITEC, located in Porto Alegre (southern Brazil), with almost 100 collaborators. A production facility is also located there. Throughout Brazil, there are over 10 other design houses. Technological restrictions in component development The main differences between conventional component technologies and radiation resistant technologies reside in the design step, and are related to quality, resistance to cosmic radiation, temperature operation range, and resistance to mechanical vibration and operation in high vacuum environment. Conventional integrated circuit design techniques must be upgraded to satisfy requirements for aerospace applications, or specific manufacturing steps should be adopted. There is sufficient consensus that IC design has influence on characteristics related to radiation resistance and quality standards, so the possible solutions to this problem would be to develop local suppliers and component qualification in Brazil, such as dedicated electronic module design (ASIC), module manufacturing on demand, and module qualification for space use (especially radiation). Critical components may be subject to international commercial restrictions (ITAR – International Traffic in Arms Regulations), and must be internally developed (AIAB, 2009). The network Figure 3 shows the links in the network of institutions which participate in the aerospace industry. It should be noted that INPE and AEB play a central role, according to their
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
Open innovation as an alternative for strategic development in the aerospace industry in Brazil
characteristics, as discussed earlier in this section, and have links to almost all other institutions. As it is an illustration, universities, companies and design houses are shown without identification and in smaller number than those which actually participate in the network. The Brazilian Bank for Social and Economic Development (BNDES), founded in 1952, is the countryâ&#x20AC;&#x2122;s largest investment bank, acting as a major supporter of the industrial policy of the government. Among its objectives there are fostering technological innovation and competitiveness of the electronics industry in Brazil, thus establishing links mainly to companies and design houses, and with AEB for creating funding guidelines for the sector (expressed by the dotted lines). Other national funding agencies for science and innovation, such as CNPq, FINEP, and FAPs, which may fund partnerships between public and private institutions, were not included in Fig. 3, but are nonetheless important actors in the technological innovation process. This group of institutions took part of the II Workshop on Radiation Effects on Electronic and Photonic Components for Aerospace Applications, as mentioned above. The proposed objectives of this workshop were: a) to disseminate knowledge on the effect of ionizing radiation on components and materials of aerospace interest; b) to promote integration between policies and funding institutions, research institutions
and companies in the aerospace sector, showing their visions, actions, needs, and perspectives as to the application of electronic and photonic radiation resistant devices in the Brazilian space program; c) to identify short term demands (two to four years) for R&D on ionizing radiation effects on electronic and photonic devices, aiming satellite applications; and d) to foster the creation of workgroups and a national network of institutions for studying the radiation effects on materials and devices, their qualification for space applications, and for developing specific radiation resistant components with Brazilian technology. These objectives suggest that a strategic management approach should be followed by the sector, if it wishes to become technologically independent. Other examples in Brazil, such as deep sea oil drilling, have succeeded in developing critical industrial technology, leading the country to become technologically independent. In this case, there was a government-led movement to foster development in the country, fed by public and private funding of the whole sector, with the leadership of Petrobras. Thus, participants were able to have direct contact with the concerns of the sector, objectives and necessities related to the aerospace sector. Moreover, they were
Company A ITA Company B
IEAv Company C
INPE
AEB
CTI Design house A University A
BNDES Design house B
University B University C
CTI: Center for Information Technology Renato Archer; IEAv: Institute for Advanced Studies; ITA: Technological Institute of Aeronautics; INPE: National Institute for Space Research; AEB: Brazilian Space Agency; BNDES: Brazilian Bank for Social and Economic Development. Figure 3: Network of institutions in the aerospace industry in Brazil. J. Aerosp.Technol. Manag., SĂŁo JosĂŠ dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
355
Dewes, M. F. et al.
able to give precise and valuable orientation on how the community may organize itself to fulfill the fourth objective. This objective is very broad, and should start with the organization of workgroups. The first step in this direction was a set of presentations of all present companies, universities, research institutes, and design houses, involved in the creation of integrated circuits for the aerospace market, focusing on its achievements in the area, involvement with research or problems concerning the radiation effects with which the institution is confronted, as well as competences and needs. These presentations enabled: a favorable environment for promoting collaboration and partnership between universities, research institutions, and companies; the identification and consolidation of common necessities and ways of seeking support in official funding bodies; the discussion of strategic guideline propositions for the sector, and the evaluation of the feasibility of workgroups to study future action. The next step was to create groups to discuss and to propose strategies for the sector. It was established that the workgroups would be formed to continue discussions on common interests following the workshop. One of the objectives of the group (business group) was to include identification of contact areas with the aerospace sector; funding alternatives which would permit the creation of conditions to meet the needs of the Brazilian space industry in robust components; justification for the proposed developments and possible impacts in other areas of interest to the country. To survey problems and strategic solution proposals related to IP is also a concern for the group. Business issues in the Brazilian space program To further advance in the proposed developments, according to AEB, PNAE must be reviewed on topics such as putting more emphasis on a program orientation and building a catalogue of critical technologies. Radiation hardening should be considered in the development cycle of integrated circuits. Ten percent of the cost of digital integrated circuits comes from specification, design (“soft” and silicon design, with many verification steps), manufacturing (with specific “radhard” processes), encapsulation, qualification, and tests. A typical project in Brazil has a two-year schedule, at the cost of a few million dollars. Considering necessary investments, appropriate technological routes must be defined, focusing on increasing scale by reusing shared modules. Other challenges include planning beyond missions, and cheaper and more rapid access to space. This includes, besides low cost, shorter deadlines, reutilization of subsystems, greater volume demand, and the use of more
356
recent technologies than those practiced by all the main agencies (AEB, 2009). According to AEB, the cost of doing business in the market for integrated circuits in Brazil is equivalent to about 10 million dollars per year including assets such as IP, human resources, licenses, silicon foundry runs, encapsulation, and intermediation in Brazil. Funding is a critical issue and should be linked to large programs, managed by public agencies, which include tax incentives for those who invest in innovative projects. At the beginning, it may be public, but later may also include venture capital and angel investors. This will have implications for establishing viable business models for national industry. Related issues such as market niche, IP problems, and business model sustainability (service, IP licensing, fabless) are not clear yet. It is necessary to identify design cycle and manufacturing steps for integrated circuits which are viable in Brazil, and also to define demands to prioritize technological routes in: design (library demands); manufacturing; encapsulation; qualification and tests (internal capacities and external partnerships). There is only one manufacturing facility in Brazil, which may have process restrictions, low yield, and technology use limitations. In this sense, besides investments in manufacturing facilities in Brazil, partnerships with outside foundries may be of interest. An important question concerns IP and where it should focus, whether on the component, on the functional block or on its function (AEB, 2009).
RECOMMENDATIONS AND CONCLUDING REMARKS Steps that are considered viable in Brazil should be part of the orientation on long term programs. Strategically, this is more desirable than thinking in terms of specific missions. A catalogue of critical technologies may be put together, in which all participants recognize their role in the development. Issues concerning intellectual property should be discussed between participants at all levels, in order to reach a consensus on which are the critical technologies and the types of licenses involved in each phase, because of the public interest of the program. The main source of funding is public, and this shall trace the guidelines of the IP policy that should be followed. The issues presented above, that have been preliminarily discussed by the group during the workshop, lead to suggestions aiming to develop the sector and to bring plausible solutions to the presented problems. It is
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
Open innovation as an alternative for strategic development in the aerospace industry in Brazil
suggested that a roadmap be developed, adopting a model for integration planning as shown by Phaal, Farrukh and Probert (2004). According to PNAE, an explicit time frame (2005-2014) should be considered for the program. Based on the collected data, roadmap models may be adapted to suit the workgroups that were formed at the workshop, linking participating organizations to each “phase” aiming to support scientific missions, in this case, satellite building in Brazil (Fig. 4). The main technological issues involved in a space mission in the brazilian program are satellite, subsystems, integration and tests, launch, ground segment, operation, management, and project documentation. The business group should consolidate information and establish the actions that the other groups should take (i. Specification group; ii. Design group; iii. Fabrication and encapsulation group; iv. Radiation robustness tests group). The direction − “nugget”, as proposed by Phaal, Farrukh and Probert (2004) − should be the development of “radiation tolerant components for space applications”, which is the critical product demanded by the internal market, impacting the sector as a whole. Considering the existent problem, from a commercial point of view, internal development (inside the network) should be prioritized, therefore efforts should concentrate on establishing, for the whole network, the role that each actor should play in order to deliver the products. In a configuration of open innovation, IP issues are a main concern. Each institution – universities, research institutions, and companies – has distinct objectives concerning IP issues. A well defined patenting policy, considering all actors’ interests, is of main concern in order to guarantee that
Definition and specification of component/ function
INPE
Design cycle
Design houses
Component manufacturing
Foundry in Brazil
critical knowledge and technologies be transferred to companies, and to avoid delays in the innovation process that transforms technological knowledge into products applicable to satellites. This step generally takes place in companies, in close collaboration with INPE, in which the first have to build or acquire capacities to be able to answer demands of the space program, all with cost implications and deadlines. In other words, in order to build value as a network, the appropriability regime, as some authors (Agrawal, Henderson, 2002; Laursen, Salter, 2006) have expressed, must be moderately associated with strict IP rights. The nature of knowledge produced in many of the institutions in the analyzed network is unhindered by commercial considerations, therefore suggesting that a free sharing policy may be adopted. According to the observed interactions, geographical proximity of most of the institutions participating in the aerospace program facilitates knowledge exchange, both formally and informally. The institutional setting also contributes to shape the network of relationships. There is a strong link between what is done in terms of research in universities and public institutions, and sometimes the university-industry link is represented by a person who is at the same time at the university, working as a professor or a PhD student, and as a business partner. This same individual maintains contact with a research group, interacting and searching for new ideas to implement in his/her start-up company. These roles must be sorted out in order to organize a sustainable strategy for the space industry. The client for qualified components (INPE, in this case) must know which competences can be made available inside the country. In this way, this client may specialize in defining mission prerequisites and contracting local companies to conceive, develop, and implement the
Encapsulation
Design houses
Qualification and tests
Satellite assembly
INPE Universities Companies
Other foundries
Research institutes
Figure 4: The proposed roadmap.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
357
Dewes, M. F. et al.
program, establishing development and manufacturing schedules considering all possible partners.
Management Science, Vol. 48, No 1, pp. 44–60. doi: 10.1287/mnsc.48.1.44.14279
The case presented in this paper shows how a large group of research organizations, companies, and government institutions in the aerospace sector in Brazil is trying to discuss its role. A main concern for these actors is building critical professional competences. This includes fostering higher education in order to maintain qualified human resources where they are needed to develop critical technology, mainly in companies, instead of depending exclusively on graduate and undergraduate students with a research profile. This issue poses a difficulty, inasmuch as there is a high staff turnover, causing project discontinuities.
Álvarez, I., Marin, R., Fonfría, A. and 2009, “The role of networking in the competitiveness of firms”, Technological Forecasting & Social Change, Vol. 76, No 3, pp. 410-421. doi:10.1016/j.techfore.2008.10.002
It may be concluded that there is a network; recently, the institutions have been working to define their roles, through participation in federally funded projects to develop robust component technology for the aerospace industry in Brazil. A suggestion to maintain and improve the network would be to adopt long term planning tools, such as technology roadmaps, integrating all members of the network. The open innovation approach may be adopted to increase awareness of and help to clarify IP issues. As the analysis revealed, this may be a significant bottleneck to overcome in order to advance technology. The network shall be recognized if it is able to deliver qualified components for satellites, being competitive by complying with cost, deadline, technological, and commercial restrictions (e.g. ITAR). In spite of revealing valuable insights on network dynamics, the present paper has limitations common to single case studies. Not all requested interviews were granted, mainly from companies, which possibly limited our understanding of certain problems related to the network and its development. We suggest further study in this area. REFERENCES AEB, 2005, “National Program of Space Activities: PNAE/Brazilian Space Agency”, Ministério da Ciência e Tecnologia, Brasília. AEB, 2009, “Panorama do setor de projetos de circuitos integrados no Brasil” II Workshop sobre Efeitos das Radiações Ionizantes em Componentes Eletrônicos e Fotônicos de uso Aeroespacial. São José dos Campos, Brazil. Agrawal, A., Henderson, R.M., 2002, “Putting patents in context: exploring knowledge transfer from MIT”,
358
Arora, A., Gambardella, A., 1990, “Complementarity and external linkages: the strategies of the large firms in biotechnology”, Journal of Industrial Economics, Vol. 38, No 4, pp. 361-379. AIAB, 2009, “O mercado espacial e a indústria brasileira”, II Workshop sobre Efeitos das Radiações Ionizantes em Componentes Eletrônicos e Fotônicos de uso Aeroespacial. São José dos Campos, Brazil. Caloghirou, Y., Kastelli, I., Tsakanikas, A., 2004, “Internal capabilities and external knowledge sources: complements or substitutes for innovative performance?”, Technovation, Vol. 24, No 1, pp. 29-39. doi:10.1016/ S0166-4972(02)00051-2 Cassiman, B., Veugelers, R., 2006, “In search of complementarity in innovation strategy: internal r&d and external knowledge acquisition”, Management Science, Vol. 52, No 1, pp. 68-82. doi: 10.1287/mnsc.1050.0470 Chesbrough, H., 2003, “Open innovation: the new imperative for creating and profiting from technology”, Harvard Business Press, Boston. 272 p. Chesbrough, H., Vanhaverbeke, W. and West, J. (eds.), 2006, “Open innovation: researching a new paradigm”, Oxford University Press, Oxford. Cohen, W.M., Nelson, R.R. and Walsh, J.P., 2002, “Links and impacts: the influence of public research on industrial R&D”, Management Science, Vol. 48, No 1, pp. 1-23. doi: 10.1287/mnsc.48.1.1.14273 Coombs, R., Harvey, M. and Tether, B.S., 2003, “Analysing distributed processes of provision and innovation”, Industrial & Corporate Change, Vol. 12, No 6, pp. 1125-1155. DCTA, 2009, “Organizações do DCTA”, Available at <http:// www.cta.br/organizacoes.php>, Access on Dec 9, 2009. Dittrich, K., Duysters, G., 2007, “Networking as a means to strategy change: the case of open innovation in mobile telephony”, Journal of Product Innovation Management, Vol. 24, No 6, pp. 510–521.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
Open innovation as an alternative for strategic development in the aerospace industry in Brazil
Eisenhardt, K.M., 1989, “Building theories from case study research”, Academy of Management Review, Vol. 14, No 4, pp. 532-550. Fabrizio, K.R., 2006, “The use of university research in firm innovation”, In: Chesbrough, H.W., Vanhaverbeke, W., West, J. (eds.), “Open innovation: researching a new paradigm”, Oxford University Press, Oxford. Fellows, L., Vaz, A., 2006, “Roadmap de nanotecnologia para o setor aeroespacial. Centro de Gestão de Estudos Estratégicos – CGEE”, Available at http://www.ieav.cta.br/ nanoaeroespacial2006/pdf_arquivos/1610%201100%20 CGEE%20-%20Roadmap.pdf, Access on Nov 4, 2010. Finco, S., 2009, “Design House – CTI”, In: II Workshop sobre Efeitos das Radiações Ionizantes em Componentes Eletrônicos e Fotônicos de uso Aeroespacial. São José dos Campos, Brazil. Graziano, P., 2009, “Roadmap tecnológico para o etanol: componente manejo agrícola”, Available at <http://www.apta.sp.gov.br/cana/anexos/wks_rmt_ manejo.pdf> Gutierrez, R.M.V., Mendes, L.R., 2009, “Complexo eletrônico: o projeto em microeletrônica no Brasil”, BNDES Setorial 30, pp. 157-209. IEEE Spectrum Aerospace, 2009, “Norman Augustine on human spaceflight – and what comes next”, Available at <http://spectrum.ieee.org/aerospace/space-flight/normanaugustine-on-human-spaceflight>, Access on: Jan 26, 2010. INPE, 2009, Available at <http://www.inpe.br/ingles/ index.php>, Access on Dec 9, 2009. ITASAT, 2010, “Satélite Universitário”, Available at <http://www.itasat.ita.br>, Access on Sep 12, 2010. Jaffe, A.B., 1989, “Real effects of academic research”, American Economic Review, Vol. 79, No 5, pp. 957–970. Kajikawa, Y. et al., 2008, “Tracking emerging technologies in energy research: toward a roadmap for sustainable energy”, Technological Forecasting & Social Change, Vol. 75, No 6, pp. 771-782. Kline, S.J., 1985, “Innovation is not a linear process”, Research Management, Vol. 28, No 4, pp. 36–45. Kostoff, R.N., Schaller, R.R., 2001, “Science and technology roadmaps”, IEEE Transactions on Engineering Management, Vol. 48, No 2, pp. 132-143. doi: 10.1109/17.922473
Laursen, K., Salter, A., 2006, “Open for innovation: the role of openness in explaining innovation performance among UK manufacturing firms”, Strategic Management Journal, Vol. 27, No 2, pp. 131–150. doi: 10.1002/smj.507 Lichtenthaler, U., 2008a, “Open innovation in practice: an analysis of strategic approaches to technology transactions, IEEE Transactions on Engineering Management, Vol. 55, No 1, pp. 148-157. doi: 10.1109/ TEM.2007.912932 Lichtenthaler, U., 2008b, “Opening up strategic technology planning: extended roadmaps and functional markets”, Management Decision, Vol. 46, No 1, pp. 77-91. doi: 10.1108/00251740810846752 Lundvall, B.A., 1988, “Innovation as an interactive process: from user–producer interaction to the national system of innovation”, In: Dosi, G. et al., Technical Change and Economic Theory, Pinter, London. Owen-Smith, J., Powell, W.W., 2004, “Knowledge networks as channels and conduits: the effects of spillovers in the Boston biotechnology community”, Organization Science, Vol. 15, No 1, pp. 5-21. doi: 10.1287/orsc.1030.0054 PEICE II, 2009, “II Workshop on ionizing radiations effects on electronic and photonics components for aeroand spatial uses (in Portuguese)”, Available at < http:// www.ieav.cta.br/peice/index.php>, Access on Sep 13, 2010. Perkmann, M., Walsh, K., 2007, “University–industry relationships and open innovation: towards a research agenda”, International Journal of Management Reviews, Vol. 9, No 4, pp. 259–280. doi: 10.1111/j.14682370.2007.00225.x Phaal, R., Farrukh, C.J.P. and Probert, D.R., 2004, “Technology roadmapping - a planning framework for evolution and revolution”, Technological Forecasting and Social Change, Vol. 71, No 1-2, pp. 5-26. Powell, W.W., Koput, K.W. and Smith-Doerr, L., 1996, “Interorganizational collaboration and the locus of innovation: networks of learning in biotechnology”. Administrative Science Quarterly, Vol. 41, pp. 116-145. Simard, C., West, J., 2006, “Knowledge networks and the geographic locus of innovation”. In: Chesbrough, H.W., Vanhaverbeke, W., West, J. (eds.), “Open innovation: researching a new paradigm”, Oxford University Press, Oxford.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
359
Dewes, M. F. et al.
Simcoe, T.S., 2006, “Open standards and intellectual property rights”, In: Chesbrough, H.W., Vanhaverbeke, W., West, J. (eds.), “Open innovation: researching a new paradigm”, Oxford University Press, Oxford. Teece, D.J., Pisano, G. and Shuen, A., 1997, “Dynamic capabilities and strategic management”, Strategic Management Journal, Vol. 18, No 7, pp. 509-533. Vanhaverbeke, W., 2006, “The inter-organizational context of open innovation”. In: Chesbrough, H.W., Vanhaverbeke, W., West, J. (eds.), “Open innovation: researching a new paradigm”, Oxford University Press, Oxford.
360
Vanhaverbeke, W., Cloodt, M., 2006, “Open Innovation in Value Networks”. In: Chesbrough, H. W. Vanhaverbeke, W., West, J. (eds.), “Open innovation: researching a new paradigm”, Oxford University Press, Oxford. Von Hippel, E., 1988, “The sources of innovation”, Oxford University Press, Oxford. 218 p. Yin, RK., 2003, “Case study research: design and methods”, Sage Publications, Thousand Oaks, CA. 200 p.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 349-360, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02038110
Ana Maria Vieira
Technological Institute of Aeronautics São José dos Campos – Brazil marianav@uol.com.br
Isabel Cristina dos Santos*
University of Taubaté Taubaté- Brazil isa.santos.sjc@gmail.com
*author for correspondence
Communication skills: a mandatory competence for ground and airplane crew to reduce tension in extreme situations Abstract: Communication skills have been considered a strategic asset for any kind of organization. However, technical-oriented enterprises usually emphasize the virtues of a cluster of technical competences and technological resources availability. So, this paper aimed to discuss communication skills development beyond technical communication in a high technology and technical-based operation, such as ground and flight operations. To do so, this article describes some tragic-ending cases in commercial aviation in which the poor quality of interpersonal communication was identified as the one of the most influential causes of the aircraft, or at least that was seen as a compelling force for creating the perfect backdrop for a disaster involving civilian aircrafts. Methodological procedures were basically addressed to a qualitative approach, supported by a documental research considering some of the most documented cases of aircraft accidents reported by the Aviation System Safety Report, issued by Federal Aviation Administration (FAA), USA, as well as reports of accidents provided by The National Transportation Safety Board (NTSB), USA, and by the Center for Aircraft Research and Prevention (Cenipa), Brasil. Keywords: Airplane operations, Communication skills, Flight safety, Managing risks.
INTRODUCTION As estimated by the Federal Aviation Administration (FAA), human error accounts for 60-80% of accidents and incidents of flight (FAA, 2004). And the dysfunctions related to human communication appear as substantial part of the causes highlighted by the Aviation Safety Reporting System (ASRS), the FAA system that collects voluntarily submitted aviation safety incident/situation reports from pilots, controllers, and others. According to research conducted by Sexton and Helmreich (2000), since the creation of ASRS, over 70% of these reports have directly or indirectly accused problems associated with failures in interpersonal communications. The authors concluded that an effective communication system is not enough to overcome the lack of technical competence in flight operations. But, on the other hand, they also found that technical competence is not sufficient to prevent the catastrophic effects of poor communication. Krifka, Martens and Schwarz (2003, p. 1) postulate that “factors related to interpersonal communication have Received: 03/07/10 Accepted: 22/08/10
been implicated in up to 80% of aviation accidents in the last 20 years”. A recent study performed by Kutz (2000) has detected a significant deficiency in the aviation community’s ability to communicate. To overcome this gap, the author recommends that communication skills should be developed from the basic writing skills, including grammar, spelling and punctuation up to interpersonal relationship. Although the Corporate Resource Management (CRM) may have both positive and detectable effects on the behavior of the crew, its failures continue to be the cause pointed in almost aviation accidents (Wiegmann and Shappell, 2001). According to Shapell et al. (2006, p. 3), “preconditions associated with aircrew were also frequently observed within the accident record. For instance, crew resource management failures were identified in nearly one out of every five air carrier accidents examined. Even more interesting, the nature of the CRM failure differed between the two commercial operations. That is, whileover 60% of the CRM failures associated with air carrier accidents involved “inflight” CRM failures (inflight crew coordination, communication, monitoring of activities,
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
361
Vieira, A.M.; Santos, I.C.
etc.), over 80% of the CRM failures observed during commuter operations involved “preflight” activities (such as planning and briefing). CRM training has shown to be efficacious for pilots, flight attendants and ground staff, but when viewed separately, according to Baron (2010). “Unfortunately, in real flight operations, there are cognitive and physical factors that cause these disparate groups to work less than efficiently between their groups, particularly when a cohesive environment is critical, such as in an emergency”, says Baron. (2010, p. 1). What are the possible causes of communication failures? CRM training is provided by airline companies, focusing on the performance of employees as members of a team. Professionals of this area believe that any feature of management resources, such as CRM training, has strong roots in individual performance. For this reason, there is the need to insert the subject “communication skills” in aviation courses, in which the level of individual communication skill should be the focus of development. This is because everything starts in the individual and, if the individual does not possess such skill, previously developed and assimilated, knowing beforehand his/ her own strengths and weaknesses, it will become very difficult for him/her to think and interact in group, as oriented by the CRM philosophy. If future aviation professionals are not trained and evaluated on their interpersonal communication and social skills, that is, in the significant involvement with others, the result will be, very often, that this professional will represent a serious latent failure, when accepted by an airline company. “Perhaps no other essential activity is as vulnerable to failure through human error and performance limitations as spoken communication”. (Monan, 1988, p. 3). If the ground staff and air crew have not learned, assimilated and developed their individual necessary communication skills, how will they know to properly use the communication tools needed in the practice of their profession? It would be like building the roof before the house. That is, the air crew needs to master this skill, learned and developed in the course they attended, before being hired by an airline company. Without this ability, the CRM will not be efficient, because communication is the key tool to use available resources (human resources, equipment and information) that interact in this situation. The ability of communication supports CRM, by providing means to achieve the team’s situational awareness, problem solving, distributing the workload and many other management functions. A training program of two or three days does not change immediately inappropriate habits that have been acquired since the beginning of professional training. Furthermore, 362
although the CRM training is sufficient to adjust behaviours and attitudes, according to Helmreich, Hines and Wilhelm (1996, p. 5), “not all of its provisions have left the classroom to reality”. Due to the problems raised by the referenced authors, this article aimed to discuss the relevance of training communication as a skill of social interaction to follow the training of all professionals in aviation field throughout the course, identifying the students’ individual skills (not only when they are hired by airline companies and get CRM training), in order to mitigate these errors related to communication skills and thus improve flight safety. COMMUNICATION SKILLS Communication is the main tool of relationship technologies, able to generate best life quality and safety in the work environment. According to Harms (2005), in the Operations Safety Program Manager of FAA, communication is a personal responsibility. One of the factors that contribute to error control is effective communication. Most of us have never received any formal training on effective communication when we learned how to fly except for radio communication. The concept of communication skills expresses social and interpersonal skills. In literature, these terms tends to be used interchangeably. Some scholars have tried to differentiate among these terms; however, such distinctions have not been widely recognized, according to Greene and Burleson (2003). Communication skill, according to Wiemann (1977) is the ability of choosing between different available communicative behaviors, those that successfully fulfill their own interpersonal goals. Brooks and Heath (1993) defined the process by what information, meanings and feelings are shared by people through the exchange of verbal and nonverbal messages. In academic and professional spheres, the term “communication skills” reflects the verbal and nonverbal competence, written and social strategies, used to interact, influence and solve problems within the group (Dickson and Hargie, 2004). The importance of communication skills in aviation safety “There is a general agreement about the importance of interpersonal communication in technological environments and the need for training these skills (sometimes called non-technical skills) to complement the technical education” (Klampfer et al., 2001, p. 5-6).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
Communication skills: a mandatory competence for ground and airplane crew to reduce tension in extreme situations
Johnston (2003, p. 2), from the Aerospace Psychology Research Group, said that “emergencies are rare; however, abnormal situations are common in aviation. An abnormal situation, if not properly addressed, can become an emergency situation”. When operations are no longer routine, action planning, the process of delegating responsibility and monitoring of tasks should be fully explained by an accurate and timely communication. Failures in interpersonal relationships make the team’s synergy difficult, especially in emergency situations, affecting the decision-making process and also making the task of delegating functions more difficult. A research conducted by Segrin and Flora (2000) showed how communication skills can generate benefits in people’s lives. Those with higher levels of skills deal with stress more easily and are more resistant to the harmful effects of a risk, while individuals with few skills suffer a worsening of problems when faced with stressors. The need to start training communicative skills in the initial stage of preparatory courses is similar to the training requirements of football players. We must first determine what specific needs should be developed to work in teams. The abilities of each professional in the field of aviation are different as in a football team (for example, goalkeeper, center forward, forward etc.). Each one has to develop specific skills and understand his or her importance within the team to the best performance; otherwise, it may result in waste of time teaching skills they already have or will not be as useful and end up not really developing skills that are needed or need improvement. Hawley, administrator of the U.S. Transportation Safety, believes that the evolution of security at airports currently focuses on the social skills training of agents. Part of this training is geared towards maintaining a calm state of mind and the recommendation to ensure an organized working environment in order to reduce the occurrence of aggressive approaches in the way of speaking and behaving, mitigating the disruption which may provide answers disproportionately violent, as in the case of terrorist actions (Sharkey, 2008).
of communication skills. Believing that communication skills can be taught and improved, aiming at more assertive future doctors who know how to communicate effectively with patients and colleagues, Lloyd et al. (1996, p. 6) emphasize that this learning process should begin as soon as the students enter to the medical school, and should continue throughout the course. Some studies developed states in which students who receive training are better at communicating with patients than untrained students. Another question must be asked. Are the skills which these students acquired through training retained, or are they lost over a period of time? As part of these studies, the same experimental design was carried out on both groups, four to six years later. These studies showed that the doctors who had received communication training as students retained their skills. They were more empathic, more self-assured, and had better communication skills, including the use of an open style of questioning and responding to verbal cues. “The conclusions are that communication skills can be learned, and doctors who receive training retain the skills” (Lloyd et al., 1996, p. 5). Medical students now must demonstrate technical proficiency, and have a new nationwide test of communication skills to become a doctor. “The Skills Exam, administered by the National Board of Medical Examiners and the Federation of State Medical Boards, is the latest addition to the Medical Licensing Exam” (Fromm, 2004, p. A03). This article proposes that the same line of thinking used in the training of medical professionals should be applied in the training of aviation professionals, integrated training of communication skills, consistently, since the beginning. In aviation, as well as in hospitals, training of communication skills are crucial in emergency situations where the interaction among the group is essential, especially because it often requires that teams be helped by members of several other sections and strategic groups of the company, as well as members of external agencies.
In contrast to the industrial operations, where teams work with the same people over months or years, the flying commercial crew works with a different team in each flight as well as medical staff who also work with different people in stressful environments, such as the surgical centers. “Therefore, we can make an analogy with the medical professionals and the flying crew” (Spencer, 1976, p.1177-1183).
There is a clear need to review the position of the flight schools that, in general, consider the technical content of their responsibility, not having, however, the same attitude about the formation of non-technical skills, which depend on the perception of the student’s need and his/her effort to overcome. In this case, the development of students will occur within their skills, getting on the margins of the development of subjective character skills, such as discernment, decision making and social interaction, which will be critical in circumstances of intense risk.
Recent researches have shown that the overheated atmosphere of an operating room generates enormous problems, and almost all of them are the result of lack
Flight Safety Foundation (2009) believes that technical and non-technical aspects of flight operations are just like two sides of a coin, and we cannot evaluate them separately.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
363
Vieira, A.M.; Santos, I.C.
So the first rule of this principle is that the technical skills and techniques should be considered together. That is why it is important to change the traditional teaching and training for a more holistic assessment of students. Written communication skills and its importance to aviation safety Taylor and Thomas (2003) highlight the importance of written communication in airline in all modes of communication operating in such a system. The authors see the written message at the core. The property of maintaining security within an airline is directly related to how this company is structured to keep the communication flows that support the processes of decision-making. Inadequate or poorly constructed documents could compromise security, create resentment and cause embarrassment. In an industry with very high risk, such as aviation, internal communication should be used as a tool to generate safety and interaction. In aviation schools, writing activities do not represent the writing form expected by the aviation business, and students are not successfully trained to write reports or other documents that are important to their tasks. Ruiz (2004) argues that the writing assignments in flight schools need to realistically reflect the types of communication these professionals will find when they perform their functions. Aviation Safety Reporting System (ASRS) reports, from July 1998 to March 2002, showed that in 1,182 maintenance incidents and accidents, around 8% had communication as one of their contributing factors. Failures in transmitting information may result in greater errors. The work cards depict the work to be done and serve as a mean of documenting their completion in order to allow a release to service (RTS). The study “Shift Turnover Related Errors in ASRS Reports”, conducted by Parke, Patankar and Kanki (2003), showed the work cards as a contributing factor in a much higher proportion of incidents involving turnover communication problems. This fact suggests that increasing the completeness and correctness in writing will result in a significant reduction in shift turnover communication problems. The aircraft maintenance is an ongoing process carried out between shifts; thus, asynchronous communication (where there is a lag time between the responses) is used to a greater extent than synchronous communication (real time). During the professional training, it is important that one be trained in this specific form of communication, 364
knowing how to interpret what is written and knowing how to correctly write what should be done. Poor instructions normally impose loads on working memory which are unnecessary to understand the meaning of the text; in this case, there is the danger of ambiguity, the working memory is challenged to discover the correct meaning of the instructions and run the risk of the message to be misunderstood, which, in aviation, can mean a disaster. An example of poorly written communication can be seen in the crash of ValuJet. The manager who prepared the documentation of oxygen cylinders to send to the ValuJet headquarters in Atlanta, USA, wrote “Oxy Canisters” and then wrote “Empty”. The commander relied on the flight manifest, and believed that as the cylinders were empty, he was not violating FAA regulations prohibiting the transport of hazardous materials in cargo aircraft. The National Transportation Safety Board (NTSB) determined that due to the pressure difference, the oxy cylinders, which were without the protective cover, have become true blow-torches, causing a fire and killing all its occupants. In his work for an insurance company against fire, MacNeal (1997) has analyzed hundreds of reports involving accidents. At first, he considered only the physical conditions, such as faulty wiring, but it became clear that the linguistic meaning, residing in the name or linguistic description commonly applied to the situation was affecting people’s behavior. The word “empty” inevitably suggests a lack of danger. Its default language is associated with zero, void, negative, inert. The word “empty”, used in the analysis of physical situations, does not take into account, for example, steam or traces scattered in the container. Due to the fact the aircraft is a high-technology product, which requires a very distinctive cluster of human resources qualification to work in aircraft and in the airport operations, it is difficult to accept the fact that a single misunderstood word can result in an air disaster, as previously explained. Flight schools should offer specific training in risk communication and specific training in improving written communication included in the curriculum, calling attention to the characteristics of texts, since they influence the interpretation. In this case, where human lives are at stake, students should be trained to develop specific skills of written communication; they should know with whom they are communicating, what message they are sending and through what channels, what are the obstacles and noises of the process, and what effects it produces in the safe operational flight.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
Communication skills: a mandatory competence for ground and airplane crew to reduce tension in extreme situations
VERBAL COMMUNICATION PROBLEMS The NTSB and the Transportation Safety Board of Canada have both found out that inadequate operational control and inadequate collaborative decision making have been contributing factors in air carrier accidents. The greatest causes of these accidents happen due to a lack of vision of the joint responsibility of pre-flight planning, necessary among all those involved. Many problems encountered by flight crews and aircraft dispatchers have very little to do with the technical aspects of flight operations. Instead, most problems are associated with ineffective communication (FAA, 2005). In his book Fatal Words: communication clashes and aircraft crashes, Cushing (1995) raised the main problems of communication in aviation: Much of what we take for granted about language and communication in everyday life is simply false. The processes through which people communicate and understand each other are much more complex than they superficially appear to be. Training should include some sophisticated discussion of the social and cognitive aspects of these processes and the ways these aspects can interact to lead the processes themselves awry. (p. 90). According to the International Civil Aviation Organization (ICAO), between 1976 and 2000, more than 1,100 passengers and crew lost their lives in accidents where language issues played a contributory role (Mathews, 2004). Eurocontrol (2006) organized in Europe a survey among pilots and air traffic controllers to evaluate the communication problems. The survey revealed a large number of reported occurrences of problems of air-ground communication in Europe between March 2004 and April 2005. Problem areas reported included communication loss (due to change of frequency, sleeping VHF radio receivers and equipment failure) and readback errors/ hearback (because of call signs similar expectations of the pilot, changing frequency). Language (accent, speech rate, ambiguous phrasing) was involved in a number of communication problems and could generate major problems if not corrected by the crew or controller. It is crucially important to conduct research in each country in order to provide an effective survey, which allows studying the emotional, cognitive, structural variables, and the components present in the communication process, in order to increase understanding of these variations in the way language is used. Through this research, like the place in Europe by Eurocontrol, it would be possible to isolate aspects of effective communication from the negative ones that present themselves for training aspects and specific
behaviors, producing significant improvements in the preparation of aviation professionals since their training, and developing the ability to communicate more assertively, not based on “what” people say, but “how” they say. If the training is carefully planned to mitigate the problems caused by the negative effects of communication skills related to strong patterns of cultural behavior (e.g. not to question top decisions, to speak more than necessary, not comply with norms and standards etc.) it will certainly transcend negative regional influences to the profession and compete for the creation of an standardized assertive behavior. Cultural habits that may negatively influence communication skills can be tracked in an attempt to transform incongruent behaviors in job performance skills that can contribute to develop a safer flight environment. The hearing perceptive development to detection of red flags Two important elements in human communication are verbal expression, or speech, and non-verbal expression, or body language. We believe it is the power of verbal persuasion that makes the speaker credible, but actually what most influences the credibility is body language. In other words, the best way to listen is through our eyes. And when visualization is not possible, as in the case of radio communication, the ear should play the role of the eyes. “Speech conveys more than syntactic and semantic content of the sentence. It also has prosodic cues that are used by speakers and listeners to express and decode the spoken message” (Mozziconacci, 2002). The communication skills training must sensitize students to hear beyond the voice. It must instruct them to detect speech variations and develop their hearing perceptive capacity to establish the following prosodic aspects: voice quality, pitch, volume, articulation, speech rate, rhythm and pauses. The ability to detect and interpret these nonverbal resources is essential for safety communication, and can serve as an efficient method to evaluate the emotional variables present in the conversation, and to increase understanding of these variations in the way verbal language is used. While it is clear that the intonation, stress and changes in the rhythm of the pilot and the controller’s voices contain valuable information, according to Karlsson (1990), little or no training of prosodic analysis is performed in training courses. Bolinger (1986) reported that intonation is a phenomenon that interests not only linguists, but also all professionals working with communication, for whom the emphasis of an utterance is as important as its content.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
365
Vieira, A.M.; Santos, I.C.
There are a significant number of voice qualities that are universal in all human cultures, according to Karlsson (1990). The training goal of the hearing perceptive is to increase sensitivity and create greater awareness in order to detect the red flags and understand their impact on security of communication. Developing this ability is particularly important when it comes to facilitate the processes of prevention and/or resolve misunderstandings. The expectation is that the hearing perceptive training will develop in students a more professional approach, focused on their security tasks in the future. Nevile (2006), in his study entitled “Communication in context: a conversation analysis tool for examining recorded voice data in investigations of aviation occurrences”, shows the importance of analyzing the recorded conversation by the cockpit voice recorder (CVR) for aviation investigations, in order to increase the level of understanding that researchers can obtain from a voice recording. Conversation analysis (CA), proposed by Nevile (2006), should be used by investigators after the air crash/incident during the transcription of CVR. However, our proposal is to develop this sensitivity in aviation professionals through training perceptual evaluation of communication (PEC) that must be developed in schools of aviation for accident prevention. Nonverbal communication According to McHenry (2008), from Global Jet Services Inc., a U.S. aviation training company, 93% of the content of a message is nonverbal, and the words represent only 7%, while body language represents 55%, and tone, 38%. The goal of the communication skills training (CST) is to make certain elements, such as the appropriate choice of words and gestures, an unconscious competence. Thus, we can learn to control what our bodies say as well as the messages sent through words. There are common occasions when someone may convey a non-consistent verbal message: the words suggest an interpretation, but body language depicts a different scenario. The understanding of nonverbal signs (anger, fear, anxiousness, suspicion or sickness) is crucial to our orientation and safe resolution. Reading body language requires training and practice, so the CST might develop, in the future, professionals with ability to observe, interpret and take correct decisions to properly reduce tension, conflict and crisis. The key to understand nonverbal behaviours is to observe them in the context in which they occur. The visual 366
perceptive sensitivity (observation, interpretation and action) is a proactive tool and should be developed and trained in all courses for aviation professionals, for an effective risk management. Associate visual perceptive sensitivity in the first-aid training may be helpful. It should also be involved in illegal acts, emergencies and also for technical training. For example, when pilots are doing flight simulation training, they can detect signs of tiredness, nervousness and anxiety in the other pilot. They can therefore assess whether he or she is able to perform or not a landing, or perform any other task. LACK OF COMMUNICATION SKILLS IN AVIATION: CASE STUDIES For the present article, we have used some excerpts from the CVR, compiled from the NTSB. We have also used the Aviation Safety Reporting System database, which is the largest repository of voluntary, confidential safety information of the world provided by officials from the front line of aviation, including pilots, controllers, mechanics, flight attendants and dispatchers. Such narratives are rich sources of information for policy development, research, human factors, education and training. In these researched sources, we have used reports that indicate the occurrence of communication skills. The case reported below shows a communication problem between the cockpit and the flight attendants during an abnormal situation, which, due to a lack of communication skills, could turn an emergency into a fatality. Upon arr acft was met by fire and emer vehicles. It was not until i deplaned and asked a fireman what was going on that I was told that our #1 eng was on fire as we taxied in. Why, as flt attendant, were we not told? Why were we not debriefed? Why did we not stop immediately and evac? This is poor communication and does not represent the safety professional image we were taught. The capt spent more time berating the purser as pax deplaned than informing and assuring the pax and flt attendants as to the situation. (ACN 714718). The most common examples of problems in communication during emergencies involve the flight crewmembers not informing the flight attendants of the nature of the emergency, the time available to prepare the cabin, and the necessary special instructions, for example, to use only one side of the aircraft in the evacuation. “This problem has arisen several times, despite instructions in flight manuals to relay such information to the flight attendants” (FAA, 1988, p. 1). The quality and timing of the information given to the flight attendants is extremely important in an
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
Communication skills: a mandatory competence for ground and airplane crew to reduce tension in extreme situations
emergency. Communications from the flight crew should be clear, precise, and instructional. A vague description of the situation without specific instructions may be misinterpreted and result in valuable time being misspent. The timing of the information transfer is as important as the quality of the information. When there is a break in the communication flow, especially in an extreme situation, this loss can be interpreted as a failure and lead people to believe they are considered inferior in office and, for this reason, not included in the exchange of information. [….] I then wanted the Pilot Not Flying to show me the plot he made that proved we had passed the ETP. He did not say a word and stared at the plotting chart. He then threw the chart at me and said ‘You do it.’ Perplexed at that, I plotted our location and we were over an hour before reaching our ETP. At this time the cabin altitude began to fluctuate again, and I told the Pilot Not Flying to ask for a lower altitude again. The Controller asked if we declare ‘Pan Pan,’ and I said to say yes and we need time to advise. I decided to offset 4 miles right off course until we worked out a decision and prepared to descend further. I told the Pilot Not Flying to declare an emergency and request a descent to FL320. He refused to declare an emergency and told me to do that myself as well. The cabin altitude began climbing again so I started a descent to FL320. I got on the radio declared an emergency and descended to FL320. At that altitude we were able to maintain cabin pressure. I told the Pilot Not Flying to get back on the radio and request clearance to return. The Pilot Not Flying then asked to return to ZZZ2. The Radio Controller first cleared us direct XXXXX. I knew XXXXX was too far and told the Pilot Not Flying to ask for a revised clearance towards ZZZ2. The Controller then re-cleared cleared us direct ZZZ2. In conclusion, before the event occurred, the Pilot Not Flying ‘who is also my employer’ had been sitting in the cabin with the Flight Attendant doing nothing to assist me with the Oceanic crossing and was lost when I needed him most. During this flight I realized the importance of CRM and situational awareness of both pilots. If I hadn’t plotted our route and maintained situational awareness I would have listened to the Pilot Not Flying and continued and possibly run out of fuel with no alternate airport for landing. One way to prevent this in the future is to make sure the Pilot Not Flying has been trained properly and knows how to assist the Pilot Flying with important duties. (ACN 818908). In the case above, we see two different styles of communication effectiveness, or better, opposed to a situation of cross communication.
The pilot not flying is an aggressive communicator, whose goal is to dominate the other. Its main features are: dominance, coldness, authoritarianism, intolerance, disregard for the person who is in a dependency position, and hostility. Communicators adopt aggressive behaviors to defend their rights, downplaying the rights of others. Pressure obliges viewers to react against their own wills or downplay the abilities of others. According to Del Prette and Del Prette (2004), a person who has low level social skills can cause flaws in the balance of a positive and mutual communication. The main consequence would be the onset of aversive behavior to the others involved. The pilot who was in command, on the other hand, is a passive communicator, whose goal is to please others, order to avoid conflicts. His weaknesses are: difficulty in solving problems, inability to self-assertion, poor self-esteem and anxiety. The passive communicators avoid expressing opinions, easily submitting themselves to others. In CST, students learn how to identify the various styles of communication effectiveness and even identify their own style and apply techniques to improve their assertiveness. Behavior changes according to time and situation. This finding confirms the idea that we can change a behavior if we perceive it is not worth; in other words, it does not satisfy our needs. CST may help to develop assertive behavior which enables one to deal with the conflict with greater ease and satisfaction, feel less stressed, gain greater confidence. Then one can act with more tact, improve his/her image and credibility, express his/her disagreement in a convincing way, but without sacrificing relationship, besides resist the attempts of manipulation, threats, emotional blackmail etc. and make others also act with greater assertiveness. CST will develop in students their innate abilities and skills to practice effective communication in difficult situations. In these situations, it is important that such professionals have already explored their feelings about these issues and developed through training a skilled behaviour for conflict resolutions. The excerpt below is part of the final report concerning the accident on September 29, 2006, in Brazil, involving a regular air transport aircraft and another executive one. The controller, by having mistakenly understood or not having understood, felt himself uncomfortable to ask again and did not respond to the pilot’s question. This initial lack
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
367
Vieira, A.M.; Santos, I.C.
of knowledge was the first link of the events chain that arose during the flight, which resulted in an accident. PILOT: key, frequency one two six decimal one five, One three three decimal five for alternate. And what initial altitude for clearence? ATC: ahn..., say again, please? PILOT: altitude for take-off? ATC: eh.... clear taxi to holding point runway one five, and report ready for take-off. PILOT: okay, clear taxi to holding point one five, six zero zero x-ray lima. (Cenipa, 2008, p. 52) In the dialogue transcribed above, the pilot asked about his initial altitude. The controller uses a marker of hesitation at the beginning of his response, signalling a red flag that he had not understood or was in doubt (“ahn...”), and then makes more general questions indicative of an understanding failure, used in aviation, denoting that the listener had not understood the wording of what he was told, and asked the transmitter to repeat (“Say again, please?”). The repetition of the phrase (“Say again, please?”), by the controller, means a request for clarification. It is evident that there is a difficulty in understanding what was spoken. The pilot, therefore, should have repeated the question in a clear and paused voice, as follows: “What initial altitude for take-off?” When you receive the answer, consider whether this corresponded to what was asked. The ability to process communication means that the information needs of pilot/ATC will be properly interpreted. Communication ambiguities can be resolved through a standard routine of active listening, which means to investigate and ask for clarification when and if it is necessary to prevent misunderstanding and fatal errors. In the above situation, the controller did not answer the question of the pilot. There was a tangential response, the controller recognized the other in the communication process, but did not answer the substance of what was asked. The pilot, at that very moment, realizing that there was no answer to his question should have called the attention of the controller for this failure. Pilots and controllers can avoid misunderstandings by providing timely information to each other in advance and asking again when they notice a lack of information, besides confirmation or correction. 368
Instead of calling the attention of the flight controller for the lack of an adequate response, the pilot chose not to clarify the altitude and went on performing the readback, neglecting to mention the lack of information about the altitude to be maintained during takeoff execution. When callers did not seek to resolve such discrepancy, in which there is divergence between the question asked and answer that did not happen, they are communicating without using the skills of critical thinking, which is also part of the CST. The perceptual evaluation of communication (PEC) aims to sensitize students to hear beyond the voice. Red-flag words sometimes cause minor differences or misunderstandings. When a listener disagrees or feels a reaction of uncertainty from the transmitter as, for instance, a different tone, a question rather than an assertion, even silence, which may mean a hesitation, he/she should immediately clarify the situation before too late. In the narratives below, the reporters specifically referred to deficient communication in the form of work cards, maintenance manuals, logbooks, and turnover documentation. They have better written documentation improving communication especially in the work cards, since it would dramatically reduce communication problems. Synopsis: Callback conversation with rptr revealed the following info: reporter stated the cabin pressure controller on the dhc-100 is also the computer for this system. The lack of communication between the avionics group and the quality control inspectors, including the wording used on their maint writeup form for the pressure controller, contributed to inspection not accomplishing the required pitot/static leak check rii inspection. (ACN 803646). Synopsis: A B767 was dispatched with an interim repair that required progressive inspections. Inspection was accomplished but deferred item was not updated in logbook or acft maint history. Communication between the depts was not adequate and there was no follow-up between the 2 depts. (ACN 681898). Synopsis: A B737-500 during a ‘b’ chk upper wing fasteners were found corroded and written up by an inspector. Engineering wrote up a repair that was in conflict with the inspector’s write-up. (ACN 628475). CONCLUSION This paper can be identified as an experience report, whose central objective was to present a proposal to
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
Communication skills: a mandatory competence for ground and airplane crew to reduce tension in extreme situations
integrate communication as a skill of social interaction in the curriculum of all schools focused on aviation, as a requirement for certification of the student, in order to mitigate these errors related to communication skills, especially in extreme situations and, consequently, improve flight safety. Therefore, the theoretical approach and case studies conclude that: - communication is the biggest obstacle in an extreme situation, because interpersonal interactions tend to deteriorate. The key to prevent that an extreme situation turns into a disaster is to bring communication back on track; - another basic rule for this principle is that technical skills should be evaluated in an operational context that allows the integration of communication skills to evaluate overall performance of flight crew/ground staff; - schools must have pilots, stewards and flight engineers acting as instructors who will work in cooperation with professionals specialized in communication training, producing significant programs. The development team is essential to integrate communication skills with technical skills in training; - typically, the process of training the future professional is focused more on technical development and less on interpersonal issues. It makes professionals face a new challenge when working, to communicate interactively and assertively with their peers, especially in an extreme situation, under continuing pressures;
topic for further training, enabling students to become proficient in this vital part of their work. Inefficient communicators increase the possibility of human error. REFERENCES Baron, R., n.d., The Cockpit, the Cabin, and Social Psychology Airline Safety. Airline Safety.com, Available at http://www.alirlinesafety.com/editorials/ CockpitCabinPsicology.htm, Access on Sept 18th, 2010. Bolinger, D.,1986, “Intonation and its parts: melody in spoken English”, Stanford University Press, Stanford, CA, USA. Brooks, W.D., Heath, R.W., 1993, communication”, Dubuque: W. C. Brown.
“Speech
CENIPA, 2008, “Relatório Final A-022/CENIPA/2008”, Brasília: Cenipa. Cushing, S., 1995, “Fatal Words: communication clashes and aircraft crashes”, Chicago: Chicago University Press. Del Prette, A., Del Prette, Z.A.P., 2004, “Psicologia das relações interpessoais: vivências para o trabalho em grupo”, 3rd ed., Petrópolis: Vozes. Dickson D., Hargie O., 2004, “Skilled interpersonal communication: research, theory, and practice”, London: Routledge, pp. xi -3.
- nobody chooses to be a bad communicator; however, practicing good communication skills are not easy, but it is possible. It involves personalities, styles and habits, and changing habits can be an overwhelming task, but training can break old habits and develop skills that lead to a reduction of accidents. Possessing excellent communication skills should be an important part in hiring staff;
European Organisation for the Safety of Air Navigation (Eurocontrol), 2006, “Air-ground communication safety study causes and recommendations”, Brussels: Eurocontrol.
- at least, the habits of good communication have profound effects on flight safety, which raises the question: why do not we train professionals committed to the excellence of communication? The communication has to be evaluated and attacked on all levels: managers, pilots, flight attendants, aircraft dispatchers, flight controllers and aircraft mechanics. These levels are all connected and poor communication is contagious.
Federal Aviation Administration (FAA), 1988, “Advisory Circular Nr. 120-48. Change Description: Subject: Communication and Coordination Between Flight Crewmembers and Flight Attendants”, Federal Aviation Administration.
In summary, communication skills should be incorporated into the curriculum – since the beginning of learning, through clearly defined goals in the evaluation process, with clear performance standards – and not just relegated to a curriculum module in human factors. It should be a
Federal Aviation Administration (FAA), 2004, “Advisory Circular Nr. 120-51E. Change Description: Subject: Crew Resource Management Training”, Federal Aviation Administration.
Federal Aviation Administration (FAA), 2005, “Advisory Circular Nr.121-32A. Dispatch Resource Management Train”, Federal Aviation Administration. Flight Safety Foundation Assessment and Feedback of Non-Technical Skills. SKYbrary, Available at: http://www. skybrary.aero/index.php/Assessment_and_Feedback_of_NonTechnical_Skills_(OGHFA_BN), Access on Sept 24th, 2009.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
369
Vieira, A.M.; Santos, I.C.
Fromm, M., 2004, “Medical Students Tested for People Skills”, The Washington Times, June 28th, 2004, pp. A03. Greene, J.O., Burleson, B.R., 2003, “Handbook of communication and social interaction skills”, New Jersey: Lawrence Erlbaum Associates. Harms, F., 2005, “Aviation Safety Newsletter”, Available at: http://www.rollanet.org/~mopilots/stlouis/ nov2005nws.htm, Access on Nov 4th, 2010. Helmreich, R.L., Hines, W.E. and Wilhelm, J.A., 1996, “Issues in crew resource management and automation use: data from line audits”, Austin: University of Texas Aerospace. Johnston, N., 2003, “Responding to emergencies and abnormal events”, Dublin: Aerospace Psychology Research Group. Trinity College Dublin. Karlsson, J., 1990, “The integration of automatic speech recognition into the air traffic control system”, Princeton, NJ, USA: Mechanical and Aerospace Engineering Princeton University. Klampfer, B. et al., 2001, “Enhancing performance in high risk environments: Recommendations for the use of behavioural markers”, Zurich: Group Interaction in High Risk Environments GIHRE Swissair Training Center.
Mozziconacci, S.J., 2002, “Prosody and emotions: speech prosody”, In: Proceedings of the Conference Aix-enProvence, April 11th-13th, 2002, France. Nevile, M., 2006, “Communication in context: a conversational analysis tool for examining recorded data in investigations of aviation occurrences”. ATSB Research and Analysis Report B2005/0118”. Parke, B., Patankar K. and Kanki, B., 2003, “Shift turnover related errors in ASRS reports”, In: Proceedings of the Twelfth International Symposium of Aviation Psychology, April 14th -17th, Dayton, Ohio, pp. 918-923. Ruiz, L.E., 2004, “Perceptions of communication training among collegiate aviation flight educators”, Journal of Air Transportation, Vol. 9, Nº 1, pp. 36-57. Segrin, C., Flora, J., 2000, “Poor social skills are a vulnerability factor in the development of psychosocial problems”, Human Communication Research Journal, Vol. 26, Nº 3, pp. 489-514. Sexton J.B., Helmreich, R.L., 2000, “Analyzing cockpit communication: the links between language, performance, error, and workload”, Human Performance in Extreme Environments, Vol. 5, Nº 1, pp. 63-68.
Krifka, M., Martens, S., Schwarz, F., 2003, “Group interaction in the cockpit: some linguistic factors”, Berlin: Humboldt University.
Shappell, S. A., et al., 2006, “Human error and commercial aviation accidents: a comprehensive, fine-grained analysis using HFACS. DOT/FAA/AM-06/18”, Washington, DC: FAA Office of Aerospace Medicine.
Kutz, M.N., 2000, “Developing future aviation leaders: Advice from today’s leaders!”, The Journal of Aviation/ Aerospace Education & Research, Vol. 9, Nº 3, pp. 24-32.
Sharkey, J., 2008, “New focus on behavior as airport security evolves”, The New York Times, December 29th, 2008, p. B7.
Lloyd, M. et al., 1996, “Communication Skills for Medicine”, New York: Churchill Livingstone.
Spencer, F.C., 1976, “Deductive reasoning in the lifelong continuing education of a cardiovascular surgeon”. Archives of Surgery, Vol. 111, Nº 11, pp. 1177-1183.
MacNeal, E., 1997, “Fatal words: bad mathsemantics can have fatal results”, ETC: A Review of General Semantics, Vol. 54, Nº 1, pp. 54. Mathews, E., 2004, “New provisions for English language proficiency are expected to improve aviation safety”, ICAO Journal, Vol. 59, Nº 1, pp. 4-6. McHenry, J.D., 2008, “Technical maintenance and maintenance management training classes. AMT Society MX Logs Update”, Weatogue, CT, USA: Global Jet Services. Monan, W.P., 1988, “Human factors in air-carrier operations: the hearback problem. NASA Report CR 177398”, Moffett Field, CA: National Aeronautics and Space Administration. 370
Taylor, J. C., Thomas R.L., 2003, “Written communication practices as impacted by a maintenance resource management training intervention”, Journal of Air Transportation, Vol. 8, Nº 1, pp. 69-90. Wiegmann, D.A., Shappell, S.A., 2001, “A human error analysis of commercial aviation accidents using the human factors analysis and classification system (HFACS). DOT/FAA/AM-01-/3”, Washington: Office of Aviation Medicine. Wiemann, J.M., 1977, “Explication and test of a model of communication competence”, Human Communication Research, Vol. 3, pp. 195-213.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 361-370, Sep-Dec., 2010
doi: 10.5028/jatm.2010.02038710
Eric Julius Wurts
Exército Brasileiro Rio de Janeiro – Brazil ericwurts@superig.com.br
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas Resumo: Este artigo trata do Sistema de Identificação Amigo-Inimigo (IFF) com tecnologia genuinamente nacional, incluindo o Modo 4 com criptografia autóctone. São apresentados fratricídios reais e os métodos do país para reduzi-los. Aspectos técnicos dos sistemas IFF em uso pela Organização do Tratado do Atlântico Norte (OTAN), são revistos e atualizados com base nas Normas de Padronização da OTAN 4193. A análise mostra que o estágio atual de desenvolvimento da Indústria Nacional de Defesa, combinado à sua capacidade de integração com os centros tecnológicos das Forças Armadas, bem como as disponibilidades orçamentárias para a pesquisa e o desenvolvimento, fruto da Política de Defesa Nacional, são fatores para o êxito do projeto. Também expõe a importância da combinação da defesa aérea e controle do tráfego aéreo no Brasil como fator de sucesso do trabalho. A solução deve ser baseada na manutenção dos padrões da OTAN das características técnicas dos interrogadores e transponders do IFF Mark XII, mantidos os processos de interrogação e “resposta”. Indica-se a necessidade de subsídios para estudo da incorporação do Modo 5 e Modo S, em segunda etapa. Palavras-chave: IFF nacional com Modo 4, Fratricídios, Indústria Nacional de Defesa, Tecnologia autóctone.
The native identification friend-foe of Brazil: questions and replies Abstract: This paper discusses the System of Identification Friend-Foe (IFF) with genuinely national technology, including Mode 4 with native encryption. Actual fratricides are illustrated and the Brazilian processes to reduce them are shown. Technical aspects of IFF systems in use by the North Atlantic Treaty Organization (NATO), are reviewed and updated based on the standards of NATO Standardization Agreement (STANAG 4193). The analysis shows that the current stage of development of the industry of National Defense, coupled with its ability to integrate with the technological centers of the Armed Forces, as well as the availability of budget for research and development, resulting from the National Defense Policy, are factors for the success of the project. Also, it exposes the importance of combining air defense and air traffic control in Brazil as a determinant factor for the success of the task. The solution should be based on maintaining the standards laid down in STANAG 4193 technical characteristics of interrogators and transponders of IFF Mark XII, keeping the processes of interrogation and “response”. Results indicate the need of providing grants to study the incorporation of Mode 5 and Mode S, in a second step. Keywords: National IFF with Mode 4, Fratricide, National Defense industry, Indigenous technologies.
Nota: Este artigo reflete a opinião do autor e não necessariamente de sua Instituição.
Received: 13/09/10 Accepted: 28/09/10 J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
371
Wurts, E. J
INTRODUÇÃO No moderno combate aeroespacial, aí inclusos os embates aéreos (ar-ar) e a defesa antiaérea (terra-ar e mar-ar), são crescentes as buscas para incrementar o alcance dos armamentos: às aeronaves incorporam-se mísseis ar-ar e ar-superfície além do alcance visual (BVR − beyond visual range), conferindo alta possibilidade de acerto sem “o reconhecimento visual”; os sistemas antiaéreos de solo, de plataformas terrestres ou navais, aumentam seu raio de ação, buscando estender a letalidade de seus mísseis aos vetores de ataque com armas “fora do alcance” (stand off weapons) e em voo na casa dos 15 mil metros, também sem chance de identificação a vista pelos artilheiros antiaéreos. Aumentar o alcance significa maior probabilidade de vitória. A identificação a vista dos alvos torna-se inexequível diante dos alcances estendidos das modernas armas de combate, apesar de a percepção (reconhecimento) visual de objetivos ser motivo de intenso treinamento para pilotos e integrantes da artilharia antiaérea de todos os países; portanto, aumenta-se o risco de fratricídios com o combate.
na Guerra de 1991, cerca de 17% do total (Lum, 1995), índice também apresentado com o valor de 25% (Hess, 2003); na guerra de 2003, o índice foi de 28% (Hess, 2003). A média, se considerados todos os conflitos envolvendo os Estados Unidos no século 20, é de 15% (Lum, 1995). Na Guerra do Golfo de 1991, os incidentes foram limitados ao engajamento de alvos terrestres por plataformas aéreas e entre alvos terrestres. Já na Guerra do Golfo de 2003, fratricídios no combate aeroespacial aumentaram os índices. Como exemplos envolvendo aeronaves e a artilharia antiaérea (Hess, 2003), ficaram marcados o míssil Patriot, que abateu um tornado da Royal Air Force (Fig. 1), e a destruição de uma unidade de tiro Patriot por um F-16. Posteriormente, em 2 de abril de 2003, um míssil Patriot abateu um F-18 a oeste de Karbala, no Iraque. O corpo do Tenente Nathan White, de 30 anos, foi resgatado numa operação com cerca de uma centena de militares da Marinha, dos Fuzileiros, Exército e Forças Especiais no dia 12 de abril de 2003. Hoje jaz, para o sofrimento dos militares e da família, no Cemitério Nacional de Arlington, Texas, Estados Unidos (Riggs, 2004).
No controle de tráfego aéreo, surgem pleitos para atender ao vertiginoso aumento do número de aeronaves em circulação e para identificar aeronaves em situação de arresto, o que é preocupante nos dias atuais. Este artigo aborda o desenvolvimento nacional do Sistema de Identificação Amigo-Inimigo (IFF − Identification Friend or Foe), que inclui a criptografia autóctone (Modo 4) e o interrogador e transponder compatíveis para o controle aéreo (militar e civil), contido no convênio firmado pelo Ministério da Ciência e Tecnologia com o Comando da Aeronáutica (Brasil, 2008a), num momento em que soluções nacionais para produção de sistemas de armas e meios de comando e controle têm crescido no ritmo da Política de Defesa Nacional (Brasil, 2008c) e da Estratégia Nacional de Defesa (Brasil, 2008b). OS FRATRICÍDIOS E OS MÉTODOS DE RECONHECIMENTO DO BRASIL O emprego do vetor aéreo no combate moderno e a crescente capacidade dos armamentos por ele utilizados, num ambiente envolvendo forças blindadas de deslocamento rápido, não têm sido acompanhados por igual desenvolvimento nos sistemas de identificação. Agrava-se o risco de fratricídios nos dias atuais. O pico do problema ocorreu nas Guerras do Golfo de 1991 e 2003, em que as perdas causadas por fratricídios nas forças americanas e aliadas atingiram índices alarmantes:
372
Figura 1: Tornado abatido por Patriot. Fonte: Trim (2007).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas
Tais fratricídios revelam-se ainda mais assustadores dada a farta disponibilidade de meios de identificação e o amplo aparato de comando e controle dos Estados Unidos. A Guerra das Falklands (Malvinas) deixou na memória dos militares argentinos recordações dolorosas, conforme relato de combate real do Major Luiz Alberto Puga Ramirez, da Força Aérea Argentina, em entrevista à Revista Aeronáutica (Souza, 1983, p. 19): [...] tem que se mencionar o gesto heróico, em que perde a vida o Cap GARCIA CUERVA, que é abatido pela própria artilharia. Este homem regressava de um provável ataque ao Hermes, que não foi até hoje confirmado, mas como o avião estava intacto [sic] mas não tinha combustível para chegar ao Continente, quis salvá-lo pois o país necessitava dele. Então tentou pousar em Porto Argentino [Port Stanley]. No Brasil, os acréscimos de células na Aviação do Exército e Naval, somados à difusão de mísseis antiaéreos portáteis (IGLA 9K-38, IGLA S e MISTRAL) nas três Forças Armadas, sem sistemas de IFF como os da Fig. 2, aumentam os riscos de fratricídios em combate no país e sugerem maior coordenação entre as forças. Contudo, a adoção do Radar SABER M60 na artilharia antiaérea (AAAe) de baixa altura, dotada de mísseis portáteis (1ª Bda AAAe, 2007) com IFF incorporado nos Modos 1, 2 e 3/A (Tabela 1), reduz o problema, mas ainda carece do Modo 4, com criptografia.
Figura 2: Interrogadores para sistemas de artilharia antiaérea de curto alcance: AN/TPX-56 IFF Interrogator Set (esquerda) e AN/TPX-57(V) Common MK XIIA/ Mode 4/5 IFF Interrogator (direita). Fonte: Raytheon (2006, 2007).
No Brasil, evitam-se os fratricídios nos combates aeroespaciais com os processos ora disponíveis (Brasil, 2001), a saber: -
a identificação eletrônica amigo-inimigo do IFF (Seção 3) entre as plataformas aéreas, terrestres e navais que já possuem os equipamentos, principal forma de evitar o fogo amigo e controlar a localização de vetores; o Brasil está carente do Modo 4, mas estará acessível após o convênio (Brasil, 2008a) citado na Introdução;
-
análise espectral de sinais do sensor primário do Radar SABER M60, capaz de indicar o modelo de
Tabela 1: Modos de Funcionamento (Operação) do IFF Mk X(A), XII e XII(A)
Modos militares
Modos civis
Utilização
∆t entre P1 e P3 (µs)
Mk (OTAN)
1
-
Controle e identificação de tráfego aéreo militar
3
X(A)
2
-
Utilização militar em combate (regulado nas Normas Operacionais do Sistema de Defesa Operacional Brasileiro – NOSDA)
5
X(A)
3
A
Controle e identificação de tráfego aéreo civil e militar (compartilhado)
8
X(A)
B
Controle e identificação de tráfego aéreo civil
17
-
C
Transmissão automática da altura da aeronave
21
-
D
Utilização civil
25
-
4
-
Modo militar com criptografia
-
XII
5
-
Modo militar com espalhamento espectral
-
XII(A)
-
Fonte: The United States of America (2000b) (adaptado). J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
373
Wurts, E. J
aeronaves de asas rotativas constante de seu banco de dados. O SABER diferencia alvos de asas fixas dos de asas rotativas (helicópteros), pela análise espectral do sinal refletido, que produz características específicas no caso dos helicópteros. Pode-se apontar o modelo do helicóptero pelo número e frequência de giro das pás, o que complementa o uso do radar secundário na identificação das plataformas. Por exemplo, se somente as forças amigas possuem o tipo de helicóptero indicado, este será identificado como amigo. Esse método possui limitações, pois há plataformas iguais em diferentes países e a alimentação do banco de dados depende da detecção do vetor para gravar a onda refletida ou de dados precisos das asas rotativas; -
identificação (percepção) visual das plataformas amigas e de outros países, processo incansavelmente treinado nas forças armadas, limitado ao alcance da vista humana e dependente da luminosidade, mas que pode ser incrementado por instrumentos óticos, como binóculos e câmeras com amplificação e dispositivos de visão noturna;
-
análise do comportamento em voo das plataformas e das regras de circulação aérea nos volumes de responsabilidade da artilharia antiaérea. Se um vetor “quebra” as regras, como, por exemplo, ingressando no setor de defesa fora de um “corredor de segurança” arbitrado e com velocidade acima da permitida, poderá ser identificado como inimigo.
A capacidade adquirida para o reconhecimento de vetores aéreos pelo Sistema SABER M60 merece destaque, pois avanços significativos foram alcançados graças aos estudos da Universidade Estadual de Campinas (Unicamp), em parceria com a Orbisat da Amazônia Indústria e Aerolevantamento S.A., sob a coordenação do Centro Tecnológico do Exército (Unicamp, 2008). Para evitar os fratricídios na terceira dimensão do combate, exercer o controle e executar as medidas de coordenação é fundamental, assim como o conhecimento prévio dos critérios de identificação no combate aeroespacial (ar-ar, superfície-ar e ar-superfície). As ações de controle da artilharia antiaérea (superfíciear), que podem ser válidas também de ar para superfície e entre vetores aéreos, desenvolvem-se sob as formas de: -
374
controle positivo, alicerçado na obtenção de dados em tempo real por emissões eletromagnéticas: sistemas de IFF, sensores primários que permitam a análise espectral do sinal recebido, processadores e enlaces de comunicações;
-
controle de procedimentos que complementa o positivo e baseia-se na delimitação do espaço aéreo por volumes e no estabelecimento de estado de ação (grau de liberdade para abrir fogo das armas – Fogo Livre, Restrito, Interdito e Designado);
-
controle misto, método completo, uma vez que engloba os dois anteriores (Brasil, 2001).
A definição de ação hostil é particularmente importante para os critérios de identificação de vetores amigos. A ação hostil classifica automaticamente como inimigo o vetor aéreo que a comete e acarreta a imediata abertura do fogo antiaéreo (ou aéreo). Uma aeronave ou veículo aéreo não tripulado comete uma ação hostil quando ataca força amiga ou aliada; ataca instalações militares ou civis, amigas ou aliadas; ataca aeronave amiga ou aliada; executa ações de guerra eletrônica contra forças ou instalações, amigas ou aliadas; lança paraquedistas ou desembarca material de uso militar em território sob controle de forças amigas ou aliadas, sem a devida autorização. Uma aeronave que adentra um volume de responsabilidade de uma defesa antiaérea ou o raio de ação de um vetor aéreo pode ser classificada como amiga, inimiga ou desconhecida (Brasil, 2001). Será amiga, a menos que cometa uma ação hostil, quando for reconhecida como tal por um centro de controle da Força Aérea ou centro de operações de artilharia antiaérea; seu comportamento em voo a faz reconhecida como amiga; é reconhecida a vista como amiga ou emite código de reconhecimento eletrônico correto que permite sua identificação (IFF), ou a análise espectral indica ser de padrão de aeronave amiga (Brasil, 2001). Será classificada como inimiga quando cometer uma ação hostil; quando for reconhecida como inimiga por um centro de controle da Força Aérea ou centro de operações de artilharia antiaérea como tal; quando seu comportamento em voo a faz reconhecida como inimiga; quando for reconhecida a vista como inimiga; quando permanecer em silêncio diante da interrogação ou emitir código de reconhecimento eletrônico (IFF) incorreto ou diferente do código em vigor, ou a análise espectral indica não ser de padrão de aeronave amiga (Brasil, 2001). Será desconhecida quando for reconhecida como tal por um órgão de controle da Força Aérea ou centro de operações de artilharia antiaérea, ou não for possível identificá-la como amiga ou inimiga (Brasil, 2001).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas
O SISTEMA Identification friend or foe Generalidades O Sistema IFF é uma “forma de reconhecimento” entre plataformas navais, terrestres e aéreas, executada por intermédio de uma “pergunta” padrão (pulso de interrogação) – feita por um “interrogador” a bordo de uma das plataformas, para a qual é emitida – e uma “resposta” codificada (pulso de resposta) por um transponder em outra plataforma. Caso a “resposta” esteja correta, ou seja, conste de uma lista de códigos do sistema de inteligência, o possível alvo pode ser reconhecido como amigo. Se o alvo não “responde”, ou seja, permanece “passivo”, não é possível identificá-lo eletronicamente.
Figura 3: ARC (Cessna) RT-359A Transponder. Fonte: Bennet Avionics (2010).
antenas solidárias, por vezes com emissão defasada em 180°, como no caso do Radar SABER M60: a antena do radar primário emite para frente e a do secundário, para trás do dispositivo (Fig. 4).
Uma só plataforma pode estar equipada com interrogadores e transponders, caso típico de aeronaves destinadas à interceptação aérea e de navios destinados ao combate naval; Sistemas IFF (Combat Id) ainda são raros em viaturas terrestres blindadas de combate, existentes em relação seleta de países, em uma lista que não inclui o Brasil. O Sistema IFF difere do radar primário, pois não há simples reflexão de energia pelo alvo; no caso do IFF, há uma comunicação codificada entre as plataformas interrogadora e interrogada. Pode-se dizer que o IFF complementa o radar primário, sem dispensá-lo. Por esse motivo, também é dito “radar secundário” (SSR – Secondary Surveillance Radar). O radar primário é essencial em combate, dada a falta de “resposta” de inimigos; no caso do controle do tráfego aéreo, o SSR sobressai em importância, por ter maior probabilidade de detecção e permitir troca de dados. O Sistema IFF possui formas diferentes de operação, ditos Modos de Funcionamento (Operação), que definem os padrões do sinal, conforme mostra a Tabela 1.
Figura 4: Radar SABER M60 (antenas do radar primário e IFF solidárias, com emissão defasada em 180°). Fonte: adaptado de Abdalla (2008).
Os Modos de Interrogação e as respostas dos sistemas IFF constam na Fig. 5.
O Pulso de Interrogação do IFF nos modos convencionais (exceto nos Modos 4 e 5) é formado por “trem” de três pulsos (P1, P2 e P3) e o tempo em microssegundos (µs) entre P1 e P3 define o Modo de Interrogação; P2 destinase à supressão dos lóbulos secundários. As “respostas” dos transponders, mesmo dos mais simples como o da Fig. 3, nos modos convencionais (exceto 4 e 5), têm a mesma estrutura, com dois pulsos (F1 e F2) separados por um tempo fixo (µs). No tempo entre F1 e F2 encontramse até 12 pulsos, cujas presenças ou ausências permitem obter as combinações, os “códigos” (STANAG 4193). As plataformas navais e terrestres normalmente têm os dispositivos eletrônicos associados fisicamente e com
Figura 5: Modos de interrogação e resposta do IFF MARK X(A). Fonte: NATO (1990a) (adaptado).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
375
Wurts, E. J
A Organização do Tratado do Atlântico Norte e suas normas de padronização A Organização do Tratado do Atlântico Norte (OTAN), principal pacto militar de coligação de países na Europa Central e Ocidental, possui padrões para a produção dos seus sistemas de defesa. O Sistema IFF da OTAN é um processo de reconhecimento entre plataformas de combate muito difundido nos países de cultura ocidental. Os padrões do IFF estão listados nas Normas de Padronização da OTAN 4193 (Standardization Agreement − STANAG 4193) nos fascículos a seguir: •
Parte I: Descrição Geral dos Sistemas IFF;
•
Parte II: Performance do IFF na Presença de Contramedidas Eletrônicas;
•
Parte III: Características Técnicas dos Equipamentos Instalados em Interrogadores e Transponders dos Sistemas IFF Mk X(A) e XII;
•
Parte IV: Características Técnicas dos Interrogadores e Transponders dos Sistemas Militares de IFF Mk X(A) e Mk XII no Modo S;
•
Parte V: Requisitos de Interoperabilidade no Modo 5;
•
Parte VI: Especificações de Criptografia para a Interoperabilidade no Modo 5.
As versões do IFF e seus aperfeiçoamentos O Mk I, primeiro Sistema IFF em uso, foi projetado em 1939 e entrou em serviço em 1940 (Carroll, 1999). Desde então, o IFF evolui com constância, destacando-se as seguintes versões (The United States of America, 2000b): •
Os equipamentos IFF em uso atualmente no Brasil seguem os padrões da OTAN, apesar de o país não estar contido no bloco, ou seja, não é signatário da OTAN. Os padrões da OTAN devem ser mantidos no projeto ora em desenvolvimento, de acordo com o previsto pelo contrato que regula o Convênio (Brasil, 2008a) – será baseado nos requisitos operacionais descritos nas STANAG 4193 I e III (Brasil, 2008a). 376
-
Mk X (BASIC): o sistema pode “responder” apenas por um Modo de Funcionamento, pois códigos não estão disponíveis no transponder. Apesar de ser considerado obsoleto, ainda está em uso por alguns países, inclusive o Brasil. O Mk X (BASIC) não é compatível com IFF Mk X (SIF), IFF Mk X(A) e IFF Mk XII;
-
Mk X (SIF – Selective Identification Feature): acresce ao Mk X (BASIC) a capacidade de interrogação com códigos de resposta, diferenciados em quantidade de acordo com os Modos de Funcionamento (Interrogação), que são o Modo Militar 1 (32 códigos), Modo Militar 2 (4096 códigos) e Modo Militar 3 (64 códigos). Funcionalidades para identificação especial de aeronaves e em situação de emergência também estão disponíveis, assim como a Supressão de Lóbulos Secundários no Pulso de Interrogação (ISLS – Interrogation Sidelobe Supression);
-
Mk X(A): incorpora ao Mk X (SIF) o Modo “C”, modo de vigilância adequado ao controle do tráfego aéreo, pois a altitude da aeronave, medida pela própria aeronave, é transmitida e recebida automaticamente pelo sistema. Também acresceu ao Modo Militar 3 a capacidade de operar com 4096 códigos. O Modo Militar 3 passou a ser compartilhado com o civil, sendo designado como 3/A, como exibe a Fig. 5. A maioria dos IFF em uso no Brasil são Mk X(A), e os códigos sigilosos do Modo 2 têm o uso regulado nas Normas Operacionais do Sistema de Defesa Operacional Brasileiro (NOSDA) (Brasil, 2002).
•
Mk XII, com duas versões:
As Partes I e III foram publicadas em 12 de novembro de 1990 e a Parte IV, em 12 de abril de 1999. A Parte II das STANAG 4193 possui classificação sigilosa e seu acesso é restrito. As partes V e VI não estão acessíveis a consulta por países não signatários da OTAN, caso do Brasil. Os modos civis do IFF são regulados pelo órgão encarregado da normatização para a segurança do desenvolvimento da aviação civil e do uso do espaço aéreo, a Organização Internacional de Aviação Civil (ICAO − International Civil Aviation Organization).
Mk X, disponível em três variantes:
-
Mk XII: equipamento compatível com o IFF Mk X (SIF) e Mk X(A), mas que pode operar também no Modo de Funcionamento (Operação) 4, Modo Militar com criptografia para maior segurança do sigilo da codificação. O Modo 4 é empregado com codificação “encriptada” por algoritmos próprios, podendo servir a um único país ou a coligação de países.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas
O IFF Mk XII também é conhecido nos Estados Unidos pela sigla AIMS: ATCRBS – Air Traffic Control Radar Beacon System IFF – Identification Friend or Foe Mk XII – Mark XII S – System -
Mk XII(A): o Mk XII(A) - Modo 5 é o último acréscimo ao IFF e seu maior aperfeiçoamento. Os níveis 1 e 2 do Modo 5 são criptografados, pois a informação possui codificação como no Modo 4 e a modulação é feita com “espalhamento espectral” do sinal, por variação de frequência da onda portadora, além de autenticação temporal de hora e dia.
O nível 3 do Modo 5 pode operar com a “interrogação seletiva” de uma só plataforma e a resposta com os dados das questões feitas (como situação das armas). Todas as “perguntas” feitas à plataforma são por ela respondidas, e só por ela. O nível 4 do Modo 5 é o mais completo de todos e contribui decisivamente para atingir a desejada “consciência situacional”1 (situation awareness), tão necessária para esclarecer a “confusão” do combate moderno. Dados como PIN, proa, posição, nível de combustível, velocidade, identificação, estado das armas, entre outros, de todos os vetores, sejam aéreos, navais ou terrestres, podem ser trocados (Fig. 7).
O nível 1 do Modo 5 é semelhante ao Modo 4, mas acrescido da identificação do número exclusivo da aeronave (PIN – Platform Identification Number). O nível 2 do Modo 5 é o mesmo do nível 1, com a informação adicional da posição do vetor (GPS) e outros atributos (Fig. 6). Com o Modo 5, a identificação em combate (Combat ID) é obtida entre plataformas aéreas, navais e terrestres.
Figura 7: Níveis 3 e 4 do Modo 5 do IFF. Fonte: Trim (2007).
Por isso, ao utilizar o Modo 5, duas deficiências do Sistema IFF das versões e modos anteriores são resolvidas: - Figura 6: Níveis 1 e 2 do Modo 5 do IFF. Fonte: Trim (2007).
a facilidade de interferência intencional ou acidental, seja por parte de força adversa ou causada sem intenção deliberada, o que diminui a confiabilidade do sistema num ambiente de intenso
A consciência situacional é a percepção dos elementos de um ambiente complexo, dentro de um volume de espaço e no tempo presente, a compreensão dos seus significados, a projeção do seu status para um futuro próximo e suas implicações para o processo decisório (Endsley et al., 1998). 1
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
377
Wurts, E. J
combate eletrônico ou próximo a grandes centros que não controlam as emissões eletromagnéticas proibidas pela ICAO, dado o estabelecimento de frequências padrão para interrogação e respostas dos transponders, respectivamente 1.030 e 1.090 MHz. O Modo 5, com espalhamento espectral, é menos suscetível às atividades de guerra eletrônica e emissões geradas sem licenças, tais como de rádios “piratas”;
O Modo S
a impossibilidade de obter-se a “consciência situacional” por apenas indicar se a plataforma é amiga ou inimiga, com necessidade de processos adicionais de identificação (visual, procedimentos em voo e análise da situação, entre outros) e sem localizá-la com precisão; o Sistema IFF sem o Modo 5 não identifica de imediato a plataforma e não obtém acuidade na localização do vetor. Não é obtida a “consciência situacional”, resumida de uma maneira geral em três perguntas: “Onde estou?”, “Onde estão os inimigos?” e “Onde estão os amigos?”, referenciadas ao tempo presente e inseridas num sistema de comando e controle para a interpretação de seus operadores. Por intermédio do combat ID, o Modo 5 responde essas perguntas essenciais.
Os interrogadores e transponders do Modo S, como mostrado na Fig. 8, foram programados para serem compatíveis com os Modos A e C.
Em outubro de 2004, testes liderados pela Marinha NorteAmericana (US Navy), com a presença de plataformas da Força Aérea Norte-Americana (US Air Force), obtiveram sucesso em testes do Modo 5 do IFF, segundo artigo de Randy Geck, repórter do periódico dcmilitary.com para o Programa PMA-213:
Figura 8: Interface homem-máquina do IFF AN/APX-100 Mark XII/Mode S IFF Transponder. Fonte: Raytheon (2008).
-
O Escritório do Programa de Identificação de Combate e Controle do Tráfego Aéreo - PMA 213 gerencia os esforços para a aquisição pela Marinha do EUA desta nova capacitação. Planejamentos para este voo começaram aproximadamente três anos atrás e culminaram em outubro com o sucesso da aplicação do Modo 5 em três separadas plataformas aéreas, bem como em duas estações de superfície, de acordo com o líder de Testes de Voos da Marinha, Ken Senechal. Os outros membros de equipe foram o Capitão Maghan McNiff, da Força Aérea, e Andy Leone, da Administração Federal de Aviação (FAA). (Geck, 2004, tradução nossa). De acordo com os Termos de Referência (TOR – Terms of Reference) do Grupo de Estudo do Modo 5 do IFF da Organização de Simulação dos Padrões para a Interoperabilidade (SISO – Simulation Interoperability Standards Organization), a maioria das plataformas de combate e unidades estariam com equipamentos de IFF aperfeiçoados no Modo 5 num prazo de cinco anos, a contar de 2005 (Berry, Byers and Madison, 2004).
378
O vertiginoso crescimento da circulação aérea civil e militar aumentou a necessidade de aperfeiçoamentos no desempenho do IFF nos Modos Civis A e C. Por isso, a Organização Internacional da Aviação Civil realizou estudos que resultaram no Modo S, ferramenta poderosa para facilitar o tráfego aéreo nos céus congestionados.
O Modo S incorpora melhorias na vigilância e nas comunicações para a automação do tráfego aéreo, com possibilidade de controle de um número muito maior de aeronaves, com uso de datalink. O Modo S, quando adotado pelos países ou bloco, marca o fim da divisão do controle do espaço aéreo por áreas. No Brasil, os Centros Integrados de Defesa Aeroespacial e Controle de Tráfego Aéreo (Cindacta) poderiam ser fundidos em uma só unidade, por exemplo. O datalink do Modo S reduz a possibilidade de acidentes com choque aéreo devido à melhoria do Sistema para Evitar Colisão Aérea (ACAS – Airborne Collision Avoidance System). Além dos incrementos do Modo S já citados, destacamse também a sua técnica monopulso, que reduz o número de interrogações necessárias para identificação da aeronave, e o emprego do “código de endereço” (Adress Code), como código único de uma aeronave em qualquer área de tráfego (PIN), permitindo interrogação direcionada para uma aeronave em particular e resposta recebida sem ambiguidade; no Modo S, não há interferência entre as respostas de transponders de aeronaves próximas.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas
Veículos aéreos não tripulados Uma nova vertente na defesa aeroespacial e no controle do tráfego aéreo surge com a desenfreada difusão dos veículos aéreos não tripulados (VANT), de tamanhos e pesos variados, operando com raios de ação cada vez maiores e cumprindo as mais diversas finalidades, desde ações de vigilância eletrônica em grandes centros até diversas ações de combate. Nos dois casos, os estudos crescem, seja para uso dos VANT em ações de combate ou para defender-se deles com a AAAe, seja para a sua inserção nos domínios dos centros de controle do tráfego aéreo, pois sua circulação ainda não está regulamentada. O problema dos VANT é complexo, pois envolve diversificados modelos com maneiras distintas de controle, desde veículos remotamente controlados até pré-programados, com autonomias diversas e cargas úteis (payloads) muito diferenciadas. Como os custos dos VANT diferem muito e o seu emprego nem sempre requer um controle por centros de tráfego aéreo, permanece a dúvida sobre como dotá-los de IFF e regulamentar seu uso. O MODO 4 Para evitar uma intromissão não autorizada ou interferência nos equipamentos IFF, seja nos interrogadores ou transponders, incluindo o caso em que os dispositivos venham a cair em mãos hostis, o Modo 4 do IFF surgiu como solução ao empregar um código de chaves de difícil quebra e que devem ser periodicamente inseridas em cada equipamento, evitando a ação inimiga no comando e controle. Será, no caso do convênio em andamento (Brasil, 2008a), o diferencial para os IFF em uso no Brasil. O equipamento criptográfico As interrogações codificadas são dependentes do modo de operação. As respostas codificadas recebidas a partir de um transponder cooperativo são processadas para verificar sua validade e fornecer indicações adequadas para o operador. No IFF Mk XII, Modo 4 do Sistema IFF, a codificação dos interrogadores e transponders é realizada por uma unidade de criptografia, existente somente se o Modo 4 está em operação. A solução padrão normalmente adotada é o interrogador e o transponder (ou o equipamento com as duas finalidades) possuírem uma unidade criptográfica exclusiva para tal fim, projetada para realizar a formulação dos códigos de interrogação e a verificação das respostas, gerando a codificação de forma autônoma e independente (Fig. 9).
Figura 9: IFF 4760 com criptógrafo (direita) e sem criptógrafo (esquerda). Fonte: Jane’s 1995-1996.
Observa-se que esse modelo de solução acarreta maior necessidade de componentes eletrônicos nos vetores, sejam aéreos, terrestres ou navais. Em plataformas de menor porte e com pouco espaço − como aeronaves dotadas de grande quantidade de visores e controles, casos de aviões de caça de interceptação, por exemplo − criptógrafos podem ser de difícil instalação em face das limitações físicas de espaço. Se um equipamento de interrogação ou transponder não suporta tal unidade criptográfica por limitação física ou se deseja um equipamento mais simples e de menor volume e tamanho, pode-se criar uma facilidade ao instalar-se uma “unidade de armazenamento” de códigos do Modo 4. Nesse caso, a “unidade de armazenamento” estocará um bloco de informações que contém uma quantidade de interrogações no Modo 4 e os correspondentes atrasos das respostas dos transponders; a cada código armazenado corresponde uma combinação “código de interrogação do Modo 4/atraso do transponder”. Quando há limitações no tamanho do armazenamento dos códigos do Modo 4, a interrogação poderá ser randomicamente ou pseudo-randomicamente selecionada da caixa de armazenamento (STANAG 4193-I). O código é derivado de uma unidade externa de criptografia do Modo 4 e “carregado” por pequenos dispositivos eletrônicos, e sugere-se que até pen drives ou diminutos cartões de dados possam ser utilizados pelo IFF nacional, dada a evolução dos meios eletrônicos e a facilidade de sua obtenção. Uma acurada análise dos equipamentos IFF já existentes nas três Forças Armadas − e de amostras de SSR de plataformas civis, de diferentes origens, e das limitações físicas das plataformas − pode conduzir a soluções diferenciadas. Um exemplo de solução para o Brasil poderia ser a instalação de criptógrafos externos para plataformas aéreas e criptógrafos embutidos em navios da Marinha do Brasil. Como uma saída possível, aponta-se que os aviões, e com mais ênfase os caças, podem possuir restrições
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
379
Wurts, E. J
nas instalações físicas, porém mobilidade suficiente para “carregar” os códigos em aeroportos diversos. Em situação oposta está o caso dos navios, pois possuem amplas instalações e o longo isolamento da belonave no mar pode dificultar as cargas de códigos. Indica-se que os padrões criptográficos e o número de códigos a ser armazenado nas plataformas, originados em criptógrafos externos, sejam determinados pela própria Força Aérea, por intermédio do Instituto Tecnológico da Aeronáutica (ITA), sob a coordenação do Ministério da Defesa, para manter a padronização. Contudo, indica-se que a decisão da solução do tipo de criptógrafo (externo ou embutido) a ser instalado nas plataformas militares navais, terrestres ou aéreas deva caber a cada uma das Forças Armadas, por melhor conhecerem suas plataformas. É adequado que plataformas de mesmo modelo, mas de Forças Armadas diferentes, possuam o mesmo padrão físico de Sistema IFF (interrogadores e transponders), por facilitar a logística, propiciando aquisições centralizadas pelo Ministério da Defesa, cabendo, portanto, a sua supervisão. Recomenda-se, por fim, que os padrões físicos e criptográficos dos interrogadores e transponders do Sistema IFF devam ser mantidos pelas três Forças Armadas, em qualquer das soluções adotadas, por favorecerem as atividades logísticas e facilitarem a produção em série, adequada às vendas no Brasil pela indústria nacional de defesa.
Figura 10: Interrogação e resposta do IFF MARK XII (Modo 4). Fonte: adaptado de NATO (1990a).
Os padrões de funcionamento do Modo 4 A Interrogação do IFF no Modo 4 As STANAG 4193 preconizam que cada interrogação do IFF no Modo 4 seja composta de um grupo de pulsos sincronizados e uma informação do grupo de pulsos (P1, P2, P3 e P4), como mostra a Fig. 10. De forma diferente dos demais Modos do IFF, no caso do Modo 4, a ISLS é feita pelo pulso P5, emitido 8 µs após P1. Uma “palavra-teste” não irradiada, designada “PalavraTeste” A resulta em uma resposta posicionada no primeiro grupo, gerada pela unidade criptográfica e com chave de códigos de manutenção, quando o Código A é selecionado no painel de controle. Da mesma forma, quando o Código B é selecionado no painel de controle (Fig. 11), uma “palavra-teste” B é gerada no 16º grupo de respostas.
380
Figura 11: Interface homem-máquina do IFF AN/APX-100 (V) IFF Mark XII Transponder Set. Fonte: Raytheon (2008).
Respostas de um transponder no Modo 4 A posição do primeiro grupo de respostas de um transponder no Modo 4, como descrito nas STANAG 4193, ocorre num tempo de retardo fixo de 202 µs, após o pulso de interrogação P4 (Fig. 10).
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas
Cada resposta do Sistema IFF no Modo 4 consiste de um grupo de três pulsos. O intervalo entre o primeiro e o segundo grupo é de 1,75 µs (±0,03 µs), e o intervalo entre o primeiro e terceiro é de 3,5 µs (±0,03 µs). O primeiro pulso do Grupo de Respostas ocorre aleatoriamente em uma das 16 posições nominais múltiplas de 4 µs, após o retardo fixo de 202 µs. O Grupo de Respostas é posicionado no Primeiro Grupo de Respostas, para a “Palavra-Teste” A, e no Décimo Sexto Grupo de Respostas, para a “Palavra-Teste” B. O Grupo é originado numa unidade criptográfica com chaves apropriadas, em resposta à “Palavra-Teste” do interrogador, mencionada na subseção anterior. Os controles da interface homem-máquina do Modo 4 Como previsto na STANAG 4193-I, os controles da interface homem-máquina do Modo 4 do Sistema IFF permitem a seleção do código de operação (Code Select A/B), o acionamento da alimentação autônoma (Hold), a função de “reinício” (Zeroize) e de seleção de supressão do alarme sonoro (Override). Seleção de código (Code Select A/B) A função de seleção no Modo 4 permite ao operador habilitar os dois grupos de códigos do Modo 4 préestabelecidos, A ou B (Fig. 12, item 16). Alimentação autônoma A função de alimentação autônoma (Hold) habilita a retenção dos códigos selecionados do Modo 4 nos computadores de interrogação (Kit) e dos transponders (Kir), se toda a energia é removida do sistema. Para fornecer segurança física para as seleções feitas no Modo 4, considerações operacionais devem ditar o mais prudente método de prover a função Hold. Nas plataformas aéreas, com os equipamentos reduzidos (ou sistemas funcionais equivalentes) e com fonte primária ou emergencial aplicada aos computadores Kit/Kir, a seleção da função Hold (automática ou manual) deve ser desabilitar a função Zeroize, se há uso da função Hold nos dispositivos Kit/Kir. Nas aeronaves em que a alimentação de corrente contínua de emergência está disponível, o seu uso é preferível, ao invés da função Hold, para prevenir perda acidental dos
Figura 12: Interface homem-máquina do Transponder Set Control C-6280A(P)/APX in Control Enclosure CY6816/APX-72. Fonte: The United States of America (2000b).
códigos do Modo 4, quando a energia primária é removida do sistema. Nas aeronaves em que a alimentação de corrente contínua não é viável ou seu uso é impraticável, deve ser incorporada a função Hold automaticamente quando o equipamento de pouso tem energia reduzida. A retração do equipamento de pouso (ou equivalente funcional), com a fonte de energia primária aplicada, pode reiniciar as unidades de criptografia Kit/Kir e causar a perda da codificação e, por isso, manter o que propõe as Normas de Padronização da OTAN (STANAG 4193) é aconselhável. Assim, considera-se correta a recomendação das STANAG 4193 de que o uso contínuo da função Hold em aeronaves não é aconselhável, sugerindo-se ser inadequada a sua utilização pelo Sistema IFF nacional do Modo 4. Nos navios da Marinha do Brasil, em que a alimentação de corrente contínua não está disponível ou seu uso é impraticável, aconselha-se que deva ser fornecida a função Hold continuamente, como sugerem as STANAG 4193.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
381
Wurts, E. J
Para os sistemas de superfície, o uso da função Hold é desaconselhado pelas STANAG, também coerentemente. “Reinício” (Zeroize) A função Zeroize do Modo 4 consiste em fazer a unidade criptográfica apagar os Códigos A e B, quando o Modo 4 da unidade de criptografia é capaz de responder ao comando. Como recomendam as STANAG 4193 para o Modo 4, no IFF nacional devem ser providenciados meios para impedir a seleção involuntária da função Zeroize, o que normalmente é feito por controle de pressão e giro (Fig. 12, item 16). Supressão do alarme sonoro (Override) A função Override permite ao operador anular os efeitos do ruído de alarme e restaurar a unidade de criptografia para a condição de “não alarme”. Essa função existe, pois, por vezes, a repetição do alarme sonoro atrapalha a atenção do(s) operador(es) ou piloto(s), além de concorrer com outros sons, como dos receptores alerta-radar (RWR – Radar Warning Receiver), caso bastante comum nas plataformas aéreas de alta performance destinadas ao combate aeroespacial, os caças aéreos, mas que também ocorre com outros tipos de aviões. Por isso, uma verificação dos equipamentos com alertas sonoros das plataformas aéreas nacionais deve preceder à adoção do Sistema IFF nacional com o Modo 4, de modo a evitar sons coincidentes que possam confundir os pilotos.
No Brasil, a perspicaz e audaciosa decisão de agregar a defesa aeroespacial ao controle do tráfego aéreo é fator de peso para a escolha do modelo de desenvolvimento de sistemas de IFF militares, pois o seu fomento e solução podem atender às duas demandas simultaneamente. Sem dúvida alguma, o recebimento de recursos para o controle de tráfego beneficia o competente Comando de Defesa Aeroespacial Brasileiro (COMDABRA), um dos motivos que o torna tão eficiente. Em ambos os casos – defesa aeroespacial e controle do tráfego aéreo – o desenvolvimento nacional dos sistemas de identificação e controle (IFF) tem importância vultosa. Assim, o segmento científico-tecnológico do país voltado para a defesa aeroespacial, única área bélica do Brasil que possui um comando combinado das Forças Armadas ativo desde os tempos de paz, o COMDABRA, busca, com veemência, produzir e aprimorar seu poderio, coordenando os esforços e baseando-se na integração das indústrias de materiais de defesa com institutos tecnológicos, exercendo o seu papel de líder na área de monitoramento, como preconiza a Estratégia Nacional de Defesa (Brasil, 2008b, grifo nosso, p. 20): O Comando de Defesa Aeroespacial Brasileiro (COMDABRA) será fortalecido como núcleo da defesa aeroespacial, incumbido de liderar e de integrar todos os meios de monitoramento aeroespacial do país. A indústria nacional de material de defesa será orientada a dar a mais alta prioridade ao desenvolvimento das tecnologias necessárias, inclusive aquelas que viabilizem independência do sistema de sinal GPS ou de qualquer outro sistema de sinal estrangeiro.
Aumentar a eficiência dos armamentos, resolver os problemas de fratricídios e da possibilidade de “caos” aéreo são preocupações latentes no país, representado nesses preitos pelo Ministério da Defesa.
É compreensível a ideia de buscar tecnologias que minimizem a perda, em combate, das facilidades oferecidas pelo GPS; o fato de os Estados Unidos terem decidido retirar o erro de degradação intencional do sistema GPS (SA – Selective Availability) – entre o transcorrer dos anos de 2000 e 2006, gradativamente, conforme anúncio da Imprensa Oficial dos Estados Unidos, de 1º de maio de 2000 – não os impede de negar a disponibilidade do sinal, onde e quando entendam ser necessário (The United States of America, 2000a, grifo nosso):
Soluções nacionais decorrem da Política de Defesa Nacional em vigor (decreto nº 5.484, de 30 de junho de 2005), que tem por diretriz, entre outras, “a busca de um nível de pesquisa científica, de desenvolvimento tecnológico e da capacidade de produção, de modo a minimizar a dependência externa do País quanto aos recursos de natureza estratégica de interesse para a sua defesa”.
[...] My decision to discontinue SA was based upon a recommend by the Secretary of Defense in coordination with the Departments of State, Transportation, Commerce, the Director of Central Intelligence, and other Executive Branch Departments and Agencies. [...] Along with our commitment to enhance GPS for peaceful applications, my administration is committed to preserving fully the military utility of
O FATOR POLÍTICO E A PRODUÇÃO DA INDÚSTRIA NACIONAL DE DEFESA
382
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas
GPS. The decision to discontinue SA is coupled with our continuing efforts to upgrade the military utility of our systems that use GPS, and is supported by threat assessments which conclude that setting SA to zero at this time have minimal impact on national security. Additionally, we have demonstrated the capability to selectively deny GPS signals on a regional basis when our national security is threatened[!]. Surgem exemplos da produção de armamentos nacionais usados na defesa aeroespacial: o míssil Anti-radiação MAR-1 (BVR) (Centro Tecnológico da Aeronáutica/ Mectron) vem sendo incorporado ao poderio da Força Aérea Brasileira (Vitorino, 2000) e a linha dos Radares de Vigilância e Busca SABER tem projeto em andamento (M200) ou já está em fase de incorporação (M60) (Centro Tecnológico do Exército (CTEx)/Orbisat da Amazônia Indústria e Aerolevantamento S.A.) (Jones and Pimentel, 2009). No caso do Radar SABER M200, a intenção é buscar a capacitação nacional para a produção de sensores a serem usados nos sistemas de artilharia antiaérea de média altura, ainda inexistentes no Brasil e, por extensão, no controle de tráfego aéreo, para cumprir o previsto na Estratégia Nacional de Defesa (Brasil, 2008b, p.16 grifo nosso): Nos centros estratégicos do país – políticos, industriais, tecnológicos e militares – a estratégia de presença do Exército concorrerá também para o objetivo de se assegurar a capacidade de defesa antiaérea, em quantidade e em qualidade, sobretudo por meio de artilharia antiaérea de média altura. A incorporação de uma artilharia antiaérea de média altura no país aumentará consideravelmente o nível de dissuasão, mas acrescerá necessidades extras de coordenação para evitar fratricídios, em exercícios de tempos de paz e, mais ainda, em combate. Constata-se como estratégica a capacitação técnica e estrutural da Orbisat da Amazônia Indústria e Aerolevantamento S.A. na produção de radares de busca (aquisição) e vigilância, fruto da parceria com o CTEx (Poggio, 2009), na linha de sensores radares (SABER), e que teve aproveitamento do êxito pelo Comando da Aeronáutica, por intermédio do ITA, executor do convênio (Brasil, 2008a), e do Instituto de Aeronáutica e Espaço (IAE), co-executor, suscitando o nascimento da produção nacional de antenas, interrogadores e transponders de IFF nos Modos 1, 2, 3/A e 4 (Projeto S200). Por isso, sugerese que deva ter início um protocolo de entendimento do CTEx, com o Centro Tecnológico da Aeronáutica e, por extensão, entre o Exército Brasileiro e a Força Aérea Brasileira, sob a égide do Ministério da Defesa, para troca de informações.
Convém ressaltar a necessidade que surgirá de a Força Aérea rever as NOSDA, para atender à nova demanda de regular o emprego do Modo 4, quando estiver disponível. Para o aproveitamento das informações geradas pelo radar secundário produzido no Brasil, seja na defesa aeroespacial ou no controle de tráfego aéreo do país, deve-se prever a camada de aplicação com o formato dos protocolos de transmissão de dados já adotado pela Força Aérea Brasileira, o ASTERIX (All Purpose Structured Eurocontrol Radar Information Exchange Format), como já prescreve o escopo do projeto em sua intenção (Brasil, 2008a). Nesse caso, as relações já existentes entre a Força Aérea e a Fundação ATECH Tecnologias Críticas suprem as demandas, existindo softwares autóctones disponíveis. Outra avaliação necessária, no mais alto nível da Defesa, é a verificação da validade de ingresso do Brasil no Bloco da OTAN, o que facilitaria a produção de equipamentos em conjunto com integrantes desse bloco, de modo a facilitar a obtenção de tecnologia e também dos padrões já existentes, bem como a troca de experiências nos processos de produção. O desenvolvimento de sistemas de armas e de comando e controle no Brasil, como mísseis e radares (primários e secundários), contribui para aumentar o poderio bélico do Brasil, mas ainda é preciso buscar, com muita ênfase, a escala industrial de produção e a criação de facilidades para a sobrevivência das indústrias de material de defesa. Não se pode também deixar de atender à celeridade no desenvolvimento e produção nacionais de materiais de emprego militar, que pode ser obtida por aquisições pontuais de produtos bélicos com valor tecnológico agregado, de maneira a aumentar rapidamente o poder dissuasório do país em face de ameaças externas episódicas, posto que o desenvolvimento independente, por vezes, alonga-se no tempo. CONCLUSÕES Os fratricídios representam uma preocupação durante as ações de combate aeroespacial no Brasil; é evidente a importância da produção de um Sistema de IFF nacional com o Modo 4, controle positivo em tempo real, para evitar e reduzir os riscos de fratricídios no país. O emprego do IFF nacional deve atender às Forças Armadas e ser complementado pelas medidas de coordenação e controle do espaço aéreo, comuns às Forças irmãs, com a padronização de normas e procedimentos e a necessária integração das Forças Armadas no nível operacional, coordenada pelo Ministério da Defesa.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
383
Wurts, E. J
A existência de Normas de Padronização da OTAN − já utilizadas nos modelos atuais de IFF integrados às diversas plataformas brasileiras − é fator de muito peso na produção do Sistema de IFF autóctone.
materiais bélicos de ponta por países diversos, inclusive da América do Sul, mas ainda carece de maiores investimentos para sair da prospecção tecnológica e alcançar a produção em escala, que depende de encomendas regulares.
A dotação de equipamentos de IFF distribuídos às Forças Armadas com controles na interface homem-máquina que seguem os padrões da OTAN contribui para a manutenção dos equipamentos nos moldes já existentes. Também é de suma importância considerar a normatização da ICAO, pois, no Brasil, os sistemas de radares primários e secundários para o tráfego aéreo e a defesa aeroespacial são coincidentes e devem continuar, pela conveniência e economia de recursos.
A produção dos armamentos e meios de detecção utilizados na defesa aeroespacial do Brasil passou a ser acompanhada pelo desenvolvimento de sistemas de identificação, graças ao convênio para a produção de IFF nacional entre o CTA e a Orbisat (Brasil, 2008a), e surge como uma forte luz no fim do túnel para clarear a escuridão dos fratricídios, além de contribuir para aumentar o poder dissuasório do país, pois a coordenação e o controle proporcionados pelo IFF são fatores multiplicadores do poder bélico de uma nação.
Assim, a correta decisão de agregar a defesa aérea ao controle do tráfego aéreo é também fator a ser considerado para o desenvolvimento de sistemas de IFF militares, pois as necessidades dos equipamentos civis também podem ser contempladas com a produção de equipamentos de emprego dual.
Por fim, a reconhecida competência dos envolvidos no desenvolvimento é vital para que se obtenha a solução que ofereça a melhor relação custo-benefício ao país no projeto do IFF nacional com o Modo 4, a fim de evitar que os militares brasileiros provem o mais amargo dos remédios em combate: o fratricídio.
Neste momento, buscar o estado da arte na produção de IFF, que seria a obtenção do Modo 5, não é o mais importante, tampouco imperativa a sua tempestividade, sob a pena de representar a estagnação do projeto. Contudo, o desenvolvimento de um IFF nacional com o Modo 4 deve suscitar a capacitação de pessoal e a previsão de incorporação, em momento posterior, do Modo 5. A compatibilização do IFF com uso civil e a extensão Modo S são importantes e devem ser consideradas no Projeto do IFF nacional. Deve ser feita uma análise acurada dos sistemas IFF já disponíveis nas plataformas das três Forças Armadas para verificar a viabilidade de incrementá-los com o Modo 4, e até em vetores civis, para padronização dos transponders civis e militares, se cabível, otimizando o uso dos recursos orçamentários disponíveis para o convênio. Por isso, é necessária a coordenação do Ministério da Defesa. Outro fator importante é a previsão de facilidades para a indústria nacional realizar a posterior produção em série dos equipamentos. Para tanto, as aquisições em escala terão maior amplitude se a produção do IFF nacional atender às três Forças e também aos órgãos civis de tráfego aéreo. O caminho da produção nacional de equipamentos de defesa, sem dúvida, foi acertadamente escolhido para o poder dissuasório atingir a estatura política do Brasil e, até mesmo, para contrabalançar a importação crescente de
384
REFERÊNCIAS Abdalla, J., 2008, “Operação do Radar SABER M60 pelos Fuzileiros Navais”, Jornal CTEx Notícias, Ano III, Nº 10, pp. 6, Disponível em: <http://www.ctex.eb.br/jornal_ ctex/jornal_010_ctex.pdf>, Acesso em: 1º de outubro de 2010. Bennet Avionics, 2010, “ARC (Cessna) RT-359A Transponder”,Disponívelem:<http://www.bennettavionics. com/rt359a.html>, Acesso em: 1 out. 2010. Berry, A., Byers, R., Madison, K., 2004, “Terms of Reference for the SISO Study Group on: Mode 5 IFF”, Simulation Interoperability Standards Organization”, Disponível em: <www.sisostds.org/index.php?tg=filem an&idx=get&id=31&gr=Y&path=&file=SISO-SG-ORMode5>, Acesso em: 7 de dezembro de 2007. Brasil, 2008a, “Extrato de Convênio Encomenda Vertical de Projetos de Pesquisa Ref. 0402/08: Projeto do IFF e Transponder Compatível com o IFF”, Ministério da Ciência e Tecnologia. Financiadora de Estudos e Projetos. Diário Oficial da República Federativa do Brasil, N. 253, pp. 25. Brasil, 2008b, “Estratégia Nacional de Defesa”. Ministério da Defesa, pp. 17-20. Brasil, 2008c, “Política de Defesa Nacional”. Presidência da República.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
A identificação amigo-inimigo nativa do Brasil: perguntas e respostas
Brasil, 2002, “Normas Operacionais do Sistema de Defesa Aeroespacial Brasileiro”. Ministério da Defesa. Comando de Defesa Aeroespacial Brasileiro. Brasil, 2001, “C 44-1: Emprego da Artilharia Antiaérea”, 4. Ed., Ministério da Defesa. Estado-Maior do Exército. Carroll, S., 1999, “The mark of Cain: avoiding fratricide”, Journal of Electronic Defense, Vol. 22, N. 1, pp. 40, Disponível em: <http://www.jedonline.com/default.asp?func=articles& year=1999&month =1&page=9901j13&doct=cover%20 story>, Acesso em: 26 de junho de 2002. Endsley, M.R. et al., 1998, “A comparative analysis of SAGAT and SART for evaluations of situation awareness”, Proceedings of the 42nd Annual Meeting of the Human Factors and Ergonomics Society, Chicago, IL, USA, pp. 1, Disponível em: <http://www.satechnologies.com/ Papers/pdf/HFES98-SAGATvSART.pdf>, Acesso em: 1º de outubro de 2010. Geck, R., 2004, “New IFF passes the test”. dcmilitary. com. Disponível em: <http://www.dcmilitary.com/navy/ tester/9_49/national_news/32555-1.html>. Acesso em: 30 de maio de 2010. Hess, P., 2003, “Feature: The Patriot’s fratricide record”, Disponível em: <http://www.washtimes.com/upibreaking/20030424-042117-6399r.htm>, Acesso em: 11 de junho de 2004. Jane’s, 1995-1996, “IFF 4700 SERIES TRANSPONDERS”, Radar and Electronic Warfare Systems, pp. 337 e p. 334. Jones, L., Pimenta, V., 2009, “Radar BRASILEIRO SABER M60 é um dos destaques da LAAD”. Disponível em: <http://defesabrasil.com/laad2009/index.php?option=com_ content&view=article&id=73:radar-brasileiro-saber-m60-eum-dos-destaques-da-laad&catid=39:noticias&Itemid=78>. Acesso em: 20 de junho de 2010. Jorge, R.C.B., Wurts, E., 2006, “Radar SABER X60 – Um radar do Exército destinado à defesa aeroespacial brasileira”, Revista CTEx P&D, Ano I, No. 1, pp. 3-9, Disponível em: <http://www.ctex.eb.br/revista_ctex/ edicao_01_2006/sumario_2.htm>, Acesso em: 31 de setembro de 2010. Lum, Z.A., 1995, “Friend? ...Foe? ... Fire !!!”, Journal of Electronic Defense, Vol. 18, No 5, p. 35-38. Lum, 1990b, “STANAG 4193. Technical Characteristics of IFF Mk XA and Mk XII Interrogators and Transponders
- Part III: IFF Installed System Characteristics”, IHS, Englewood, CO, USA. Lum, 1999, “STANAG 4193. Technical Characteristics of IFF Mk Xa and Mk XII Interrogators and Transponders Part IV: Technical Characteristics of Mode S in Military Interrogators and Transponders”, IHS, Englewood, CO, USA. Poggio, G., 2009, “Radar de defesa antiaérea é destaque na LAAD 2009”, Jornal Poder Aéreo, Disponível em: <http://www.aereo.jor.br/2009/04/15/radar-de-defesaantiaerea-e-destaque-na-laad-2009/>, Acesso em: 31 de setembro de 2010. Primeira Brigada de Artilharia Antiaérea (1ª Bda AAAe), 2007, “Experimentação Doutrinária de Comando e Controle de Artilharia Antiaérea com o Radar SABER M60”. Raytheon, 2006, “AN/TPX-57(V) Common MK XIIA/ Mode 4/5 IFF Interrogator”. Disponível em: <http:// www.raytheon.com/capabilities/rtnwcm/groups/ncs/ documents/content/rtn_ncs_products_tpx57_pdf.pdf>. Acesso em: 11 de junho de 2010. Raytheon, 2007, “AN/TPX-56 IFF Interrogator Set”, Disponível em: <http://www.raytheon. com/capabilities/ rtnwcm/groups/ncs/documents/content/rtn_ncs_products_ tpx56_pdf.pdf>, Acesso em: 11 de junho de 2010. Raytheon, 2008, “AN/APX-100 (V) IFF Mark XII Transponder Set”, Disponível em: <http://www.raytheon. com/capabilities/rtnwcm/groups/ncs/documents/content/ rtn_ncs_products_apx100v.pdf>, Acesso em: 11 de junho de 2010. Riggs, R., 2004, “Blue On Blue. How did an Army patriot missile battery shoot down a navy F-18?”. Disponível em: <http://www.globalsecurity.org/org/news/2004/040205patriot-shootdown.htm>, Acesso em: 31 de maio de 2010. Souza, C.A.M., 1983, “Major Puga e LT CMDR Francis W. G. O’Shaughnessy”, Revista Aeronáutica, N. 142, pp. 27-40. The United States of America, 2000a, “Statement by the president regarding the United States decision to stop degrading Global Positisioning System”, White House, Office of the Press, Secretary, Disponível em: <http://www.whitehouse.gov/library/PressReleases. cgi?date=3&briefing=0>, Acesso em: 5 de maio de 2000. The United States of America, 2000b, “Non Resident Training Course”, Operations Specialist. United States Navy, Vol. 1.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
385
Wurts, E. J
Trim, R.M., 2007, “Identification Friend or Foe”, Presentation in IET Sussex Centre, Hawth Theatre Crawley. Disponível em: <http://www.theiet.org/local/ uk/southeast/sussex/docs/iff.cfm>, Acesso em: 10 de novembro de 2010. Universidade Estadual de Campinas (Unicamp), 2008, “Parceria com indústria resulta no primeiro radar brasileiro”, Jornal da Unicamp, Disponível em: <http:// www.unicamp.br/unicamp/unicamp_hoje/jornalPDF/ ju392pag07.pdf>, Acesso em: 31 de setembro de 2010.
386
Vitorino, R., 2000, “Mectron faz míssil anti-radiação”, Disponível em: <http://jornal.valeparaibano.com. br/2000/07/29/sjc/mectron.html>, Acesso em: 21 de junho de 2010. Wurts, E., 2001, “Identificação amigo ou inimigo: perguntas e respostas...”, Revista da Escola de Artilharia de Costa e Antiaérea, Nº 7, pp. 44-47.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 371-386, Sep-Dec., 2010
Thesis abstracts This section presents the abstract of most recent Master or PhD thesis related to aerospace technology and management
Environmental and energetic impacts from use of fuel cells instead internal combustion engine in automotive vehicles Cleber Eduardo Lorenzi Mauá Institute of Technology lorenzi@maua.br Thesis submitted for Masters in Engineering at Mauá Institute of Technology, São Caetano do Sul, São Paulo State, Brazil, 2009. Advisor: Prof. Dr. Roberto Aguiar Peixoto Keywords: Fuel cell, Hydrogen, Greenhouse effect, Electrolysis, Carbon dioxide. Abstract: This work analyzes the application of the space technology spin-off fuel cells in passenger vehicles as a substitute of the current model based on burned fossil fuels in internal combustion engines. The fuel cells were developed to supply electrical energy, substituting the heavier batteries systems on the very small space capsules of the Project Mercury, and are being used in all spaceships since then. Its use is safe, reliable and clean. This paper analyzes the future scenario, considering that all vehicles of the global automotive fleet could have their powertrain system changed from internal combustion engine to fuel cells, and its positive or negative impacts in the environment, and in the reduction of the carbon dioxide emission to the atmosphere, comparing these results to the vehicles moved by gasoline in internal combustion engines. One of the results reveals that the reduction of the carbon dioxide is balanced by the emissions during the phase of electricity generation for hydrogen production by water electrolysis, where it could affect directly the global carbon dioxide emissions to the atmosphere. In this article, hydrogen is presented as an excellent alternative in countries like Brazil − which has a clean energy production of electricity, due to his hydraulic potential − and could reduce the carbon dioxide emissions from the use of automobiles in 79%; however, it is not viable from the point of view of mitigating the greenhouse effect in countries which have a fossil based electricity generation, like the USA, that could increase the emissions in 47%. In spite of not emitting carbon dioxide during the phase of
use of the vehicles with hydrogen fuel cells, the emissions of CO2 in the phase of electric power generation for production of the hydrogen by electrolysis can overcome the emissions of gasoline in conventional vehicles.
Application of AHP method with ratings and BOCR approaches: F-X2 Project Leila Paula Alves da Silva Nascimento Technological Institute of Aeronautics leilapasn@gmail.com Thesis submitted for Masters in Aeronautical and Mechanical Engineering at Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2010. Advisor: Dr. Mischel Carmen Neyra Belderrain Keywords: Multi-criteria Decision Making, Analytic Hierarchy Process, Ratings, BOCR, F-X2 Project. Abstract: During the progress of studies on decision making, several methods have emerged, aiming to provide support to those who participate in decision process. Multi-criteria Decision Making (MCDM) methods offer different ways of decomposing a complex problem, and to consider criteria for measuring the degree of achievement of objectives by alternatives. Among these methods, there is the Analytic Hierarchy Process (AHP) characterized by decomposition of the decision problem in a hierarchical structure. The objective of this thesis was to apply the AHP with Ratings and Benefits, Opportunities, Costs and Risks merits (BOCR) approach to the F-X2 Project Case Study, in order to provide proper organization of information and orderly conduct the decision process. The F-X2 Project, a Brazilian Air Force (FAB) program, aims to retrofit FAB fighters to next-generation supersonic aircraft. Results obtained in the case study demonstrated the suitability of the method also for problems of military decision issues. Addition of the Ratings approach and BOCR contributed effectively to make the solution stronger, because it classifies alternatives into categories of intensity and introduces the influence of negative priorities in the decision problem.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 387-388, Sep-Dec., 2010
387
Thesis abstracts
Study of thermoplastic composite processing of PPS/carbon fiber by consolidation in autoclave Luciana Selmi Marques Embraer luciana.marques@embraer.com.br Thesis submitted for Masters in Aerospace Engineering at Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2010. Advisor: Dr. Mirabel Cerqueira Rezende Keywords: Polyphenylene Sulfide, PPS/Carbon Composites, Autoclave, Mechanical Properties. Abstract: Usually, the hot compression molding technique is utilized to obtain structural thermoplastic parts; however, the size and capacity of the used press limit the dimension of the processed component. Thus, this study aimed to increase the thermoplastic composite applications, by the possibility of processing larger and more integrated parts by the use of infrastructure available in thermoset composite manufacturing. For this, carbon fiber reinforced polyphenylene sulfide (PPS) laminates are consolidated in autoclave, under four different cycles. Ultrasound inspection maps reveal homogeneous and continuous laminates with quality equivalent to laminates processed by hot compression molding. DSC analysis shows that the crystallinity varies from 18 to 30% as a function of the processing parameters applied. In this case, the cycle with the lowest cooling rate (1-5°C/ min) presents the highest crystallinity degree (~30%). Mechanical tests show equivalent results compared with the literature for laminates obtained by compression molding and the highest crystallinity degree presents the lowest compression strength, because the crystallinity becomes the matrix more brittle.
388
Design and performance analysis of an axial turbine used in turbopump unit of a liquid propellant rocket engine of 55 kN of thrust Juraci de Sousa Araujo Filho Technological Institute of Aeronautics juraciaraujo@hotmail.com Thesis submitted for Master in Aerospace Engineering at Technological Institute of Aeronautics, ITA, São José dos Campos, São Paulo State, Brazil, 2009. Advisor: Dr. João Roberto Barbosa Keywords: Turbopump, Liquid Rocket Engine, Axial turbine. Abstract: The turbine of a turbopump for liquid rocket engine must be designed according to its exhaust environment, to operate either on open cycle or closed cycle. For the operation on open cycle, the turbine is usually supersonic, of impulse type and of partial admission. Otherwise, it is usually sonic, of reaction type and full admission. Partial admission is used when blade height is too small, so that losses and tip leakage make the stage inefficient. The blades must be of a minimum height in order to attain a minimum of efficiency.
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 387-388, Sep-Dec., 2010
AD HOC REFEREES
AD HOC REFEREES Besides the participation of the Editorial Board, the Journal of Aerospace Technology and Management (JATM) had the collaboration of specialists as reviewers to evaluate the manuscripts. JATM thanks them for the contribution in Vol. 2 (2010). Adriano Gonçalves - Institute of Aeronautics and Space - São José dos Campos - Brazil Algacyr Morgenstern Junior - Institute of Aeronautics and Space - São José dos Campos - Brazil Amilcar Porto Pimenta - Technological Institute of Aeronautics - São José dos Campos - Brazil Ana Maria Ambrosio - National Institute for Space Research - São José dos Campos - Brazil Anderson Ribeiro Correia - Technological Institute of Aeronautics - São José dos Campos - Brazil Avandelino Santana Jr. - Institute of Aeronautics and Space - São José dos Campos - Brazil Claudio Jorge Pinto Alves - Technological Institute of Aeronautics - São José dos Campos - Brazil Clésio Luis Tozzi - State University of Campinas - Campinas - Brazil Cristina Moniz Araújo Lopes - Institute of Aeronautics and Space - São José dos Campos – Brazil Cristiano Panásio - São Paulo University- São Paulo-Brazil Constança Amaro de Azevedo - Naval Research Institute – Rio de Janeiro – Brazil Daniel Soares de Almeida - Institute of Aeronautics and Space - São José dos Campos David Fernandes - Technological Institute of Aeronautics - São José dos Campos - Brazil Donizeti de Andrade - Technological Institute of Aeronautics - São José dos Campos - Brazil Edson Luis Zaparoli - Technological Institute of Aeronautics - São José dos Campos - Brazil Edvaldo Simões da Fonseca Jr. - University of São Paulo - São Paulo - Brazil Elizabete Yoshie Kawach - Technological Institute of Aeronautics - São José dos Campos - Brazil Elizangela Camilo - Institute of Aeronautics and Space - São José dos Campos - Brazil Emerson Sarmento Gonçalves - Institute of Aeronautics and Space - São José dos Campos - Brazil Enda Dimitri Bigarella - Embraer - São José dos Campos - Brazil Evaldo Corat - National Institute for Space Research - São José dos Campos - Brazil Evandro Marconi Rocco - National Institute for Space Research - São José dos Campos - Brazil Flávio Donizete Marques - University of São Paulo - São Carlos - Brazil Francisco Piorino Neto - Institute of Aeronautics and Space - São José dos Campos – Brazil Gilmar Patrocinio Thim- Technological Institute of Aeronautics - São José dos Campos - Brazil Inácio Malmonge Martin - University of Taubaté - Taubaté - Brazil Ivan Casella-Universidade Federal do ABC- Santo Andrá- Brazil Isabel Cristina dos Santos– University of Taubaté-Taubaté - Brazil João Batista P. Falcão Filho - Institute of Aeronautics and Space - São José dos Campos - Brazil José Alberto Fernandes Ferreira - University of Taubaté - Taubaté - Brazil Jose Maria Fernandes Marlet - Embraer - São José dos Campos - Brazil José Rufino de Oliveira Jr. - National Industrial Property Institute - Rio de Janeiro - Brazil Lais Maria Resende Mallaco- Institute of Aeronautics and Space - São José dos Campos - Brazil Leandro Franco de Souza- University of São Paulo- São Paulo- Brazil Luciene Dias Villar - Institute of Aeronautics and Space - São José dos Campos - Brazil Luis Augusto T. Machado - National Institute for Space Research - Cachoeira Paulista - Brazil Luis Carlos de Castro Santos - Embraer - São José dos Campos - Brazil Luis Cláudio Rezende - Institute of Aeronautics and Space - São José dos Campos - Brazil Luis E. Loures da Costa - Institute of Aeronautics and Space - São José dos Campos - Brazil Luiz Alberto de Andrade - Institute of Aeronautics and Space - São José dos Campos - Brazil Luiz Carlos Sandoval Goes - Technological Institute of Aeronautics - São José dos Campos - Brazil Luiz Claudio Pardini - Institute of Aeronautics and Space - São José dos Campos - Brazil Marcilio Faria Pires -Technological Institute of Aeronautics - São José dos Campos - Brazil Márcio S. Luz - Department of Aerospace Science and Technology - São José dos Campos - Brazil Marcio Barbosa Lucks - Institute of Aeronautics and Space - São José dos Campos - Brazil Márcio T. Mendonça - Institute of Aeronautics and Space - São José dos Campos - Brazil Marco Antonio Chamon -National Institute for Space Research -São José dos Campos - Brazil Marco Antonio da Silva Ferro -Institute of Aeronautics and Space - São José dos Campos - Brazil Marcos Aurélio Ortega - Technological Institute of Aeronautics - São José dos Campos - Brazil Marcos Daysuke Oyama - Institute of Aeronautics and Space - São José dos Campos - Brazil
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 389-390, Sep-Dec., 2010
389
AD HOC REFEREES
Maria Aparecida Pinheiro dos Santos - Naval Research Institute – Rio de Janeiro – Brazil Maria Luisa Gregori - Institute of Aeronautics and Space - São José dos Campos - Brazil Maria Filomena F. Ricco - Department of Aerospace Science and Technology - S. J. Campos - Brazil Marisa Roberto - Technological Institute of Aeronautics - São José dos Campos - Brazil Michelle Leali Costa - São Paulo State University - Guaratinguetá - Brazil Osvaldo Catsumi Imamura - Institute for Advanced Studies - São José dos Campos - Brazil Paulo Giácomo Milani - National Institute for Space Research - São José dos Campos - Brazil Pedro José de Oliveira Neto - Institute of Aeronautics and Space - São José dos Campos - Brazil Pedro Paulo - Institute of Aeronautics and Space - São José dos Campos - Brazil Pedro Teixeira Lacava - Technological Institute of Aeronautics - São José dos Campos - Brazil Pedro Paglione - Technological Institute of Aeronautics - São José dos Campos - Brazil RicardoSuyama- Universidade Federal do ABC- Santo Andrá- Brazil Romis Ribeiro Faissol Attux - State University of Campinas - Campinas - Brazil Sergio Frascino M. Almeida - Technological Institute of Aeronautics - São José dos Campos - Brazil Valcir Orlando - National Institute for Space Research - São José dos Campos - Brazil Valeria Serrano Faillace Oliveira Leite- Institute for Advanced Studies - São José dos Campos - Brazil Vera Lúcia Lourenço - Institute of Aeronautics and Space - São José dos Campos - Brazil Wilson F. N. Santos - National Institute for Space Research - Cachoeira Paulista - Brazil
390
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 389-390, Sep-Dec., 2010
Instructions to the Authors
Scope and editorial policy The Journal of Aerospace Technology and Management is the official publication of Institute of Aeronautics and Space (IAE) of the Department of Aerospace Science and Technology (DCTA), São José dos Campos, São Paulo State, Brazil. The journal is published three times a year (April, August and December) and is devoted to research and management on different aspects of aerospace technologies. The authors are solely responsible for the contents of their contribution. It is assumed that they have the necessary authority for publication. When submitting the contribution the author should classify it according to the area selected from the topics: • Acoustics • Aerodynamics • Aerospace Systems • Applied Computation • Automation • Chemistry • Defense • Electronics
• Management Systems • Materials • Mechanical Engineering • Meteorology • Propulsion • Structures • Vibration
The journal uses the “double blind peer review process” for evaluation of the manuscript. The submissions, except thesis and book reviews, will be evaluated by three Editorial board members or ad hoc referees, and may be selected for publication according to the editorial policy of the journal.
Mandatory requirements All papers must include: type of contribution (review article, original paper, short communication, case report, book reviews or theses), title, authors’ names, abstract and key words (three to six items that should be based on NASA Thesaurus volume 2 – Access Vocabulary). All authors should be identified with full name, e-mail, institution to which they are related, city and country. One of them should be indicated as the author for correspondence.
Contents • Editorial Any researcher may write the editorial on the invitation of the Editor-in-Chief. The article should not exceed two pages. • Review articles They should cover subjects falling within the scope of the journal. These contributions should be presented in the same format as a full paper, except that they should not be divided into sections such as introduction, methods, results and discussion. However, they must include a 150 to 200-word abstract, key words, concluding remarks, acknowledgment and references. The article should not exceed 20 pages. • Technical papers These articles should report the results of original research and must include: a 150 to 200-word abstract, key words, introduction, methods, results and discussion, acknowledgment, references, tables and/or figures. The article should not exceed 16 pages. •Communications These articles should report previous results of ongoing research. They should include a 150 to 200-word abstract, key words, tables and/or figures, acknowledgment and references. The communication should not exceed eight pages. • Thesis abstracts The journal welcomes Masters and PhD thesis abstracts for publication.
Paper submission Manuscript should be written in English or Portuguese and submitted electronically. The manuscripts written in Portuguese must present the title and the abstract translated into English, with the exact same content. If there is any conflict of interest with regard to the evaluation of the manuscript, the author must send a declaration indicating the reasons, for the review process occur fairly. See the instructions on www.jatm.com.br/papersubmission. J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 391-392, Sep-Dec., 2010
391
After submitting the manuscript, the corresponding author will receive an e-mail with the Term of Copyright Transfer, in which the author agrees to transfer copyright to the Institute of Aeronautics and Space (IAE), in case of acceptance for publication, thus being forbidden any means of reproduction (printed or electronic) without previous authorization of the Editor-in-Chief. If the reproduction is allowed, it is mandatory to mention the Journal of Aerospace Technology and Management. The author also declares that the manuscript is an original paper and that its content is not being considered for publication in other periodicals and that all co-authors participated satisfactorily in the paper elaboration as to make public the responsibility for its content. The declaration must be printed, signed by the main author and sent back by mailing to the following address: Instituto de Aeronáutica e Espaço (IAE)/ATTN: Helena Prado/ Praça Mal. Eduardo Gomes, 50 – Vila das Acácias/ CEP 12228-901/São José dos Campos/ São Paulo/Brazil. References References should be cited in the text by giving the last name of the author(s) and the year of publication. Either use “Recent work (Smith and Farias, 1997)” or “Recently Smith and Farias (1997)”. With four or more names, use the form “Smith et al. (1997)”. If two or more references would have the same identification, distinguish them by appending “a”, “b” etc., to the year of publication. Acceptable references include journal articles, numbered papers, books and submitted articles, if the journal is identified. References from private communications, dissertations, thesis, published conference proceedings and preprints from conferences should be avoided. Self citation should be limited to a minimum. It is recommended that each reference contains the digital object identifier number (DOI). References retrieved from the internet should be cited by the last name of the author(s) and the year of publication, or n.d. if not available, followed by the date of access. Standards should be cited in text by the acronym of entity followed by their number, and doesn’t need to appear in the reference list. References should be listed in alphabetical order, according to the last name of the first author, at the end of the article. Some sample references follow: Alves, M. B., Morais, A. M. F., 2009, “The management of Knowledge and Technologies in a Space Program”, Journal of Aerospace Technology and Management, Vol. 1, No 2, pp. 265-272. doi:10.5028/jatm.2009.0102265272 Bordalo, S. N., Ferziger, J. H. and Kline, S. J., 1989, “The Development of Zonal Models for Turbulence”, Proceedings of the 10th Brazilian Congress of Mechanical Engineering, Vol. 1, Rio de Janeiro, Brazil, pp.41-44. Coimbra, A. L., 1978, “Lessons of Continuum Mechanics”, Ed. Edgard Blücher, São Paulo, Brazil, 428p. Clark, J. A., 1986, Private Communication, University of Michigan, Ann Harbor. Silva, L. H. M., 1988, “New Integral Formulation for Problems in Mechanics” (In Portuguese), Ph.D. Thesis, Federal University of Santa Catarina, Florianópolis, S.C., Brazil, 223p. EMBRAPA, 1999, “Polítics of R&D”, Retrieved in May 8, 2010, from http://www.embrapa.br/publicacoes / institucionais/polPD.pdf,. Sparrow, E. M., 1980a, “Forced Convection Heat Transfer in a Duct Having Spanwise-Periodic Rectangular Protuberances”, Numerical Heat Transfer, Vol. 3, pp. 149-167. Sparrow, E. M., 1980b, “Fluid-to-Fluid Conjugate Heat Transfer for a Vertical Pipe-Internal and External Natural Convection”, ASME Journal of Heat Transfer, Vol.102, pp. 402-407. Illustrations All illustrations, line drawings, photographs and graphs should be referred as “Figure” and submitted with good definition (1 to 2 mega pixels). References should be made in the text to each illustration using the abbreviated form “Fig.”, except in the beginning of the phrase. Explanations should be given in the figure legends, so that illustrations are kept clean Tables Authors should take notice of the limitations set by the size and layout of the journal. Therefore, large tables should be avoided. All tables must be numbered and mentioned in the text as “Table”. Equations Equations should be typed on individual lines, identified by numbers enclosed in parenthesis. References should be made in the text to each equation using the abbreviated form “Eq.”, except in the beginning of the phrase, where the form “Equation” should be used. Acknowledgments The financial support received for the elaboration of the manuscript must be declared in this item.
392
J. Aerosp.Technol. Manag., São José dos Campos, Vol.2, No.3, pp. 391-392, Sep-Dec., 2010
Vol. 2 N. 3 Sep/Dec. 2010
ISSN 1984-9648 ISSN 2175-9146 (online) www.jatm.com.br
Journal of Aerospace Technology and Management V.2, n. 3, Sep/Dec. 2010