Magnetically Levitated Cable (MIC) System for Space Applications
James Powell Plus Ultra Technologies www.NewWorlds.com NIAC Phase 1 Fellows Meeting March 7-8, 2006 Atlanta, Georgia
The MIC Concept |
Very large, very strong and rigid MIC structures can be erected in space and on the surfaces of planets and moon’s using high temperature superconducting (HTS) cables z z z
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HTS superconductors are rapidly being commercialized z z
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Current densities of ~100,000 amps/cm2 with zero electrical losses Only power input required is to remove heat leaking through thermal insulation – power requirements are very small
MIC can be launched into space as a very compact, folded bundle of HTS cables and tensile tethers z z
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Very strong magnetic forces (e.g., tons/meter) on a distributed array of HTS cables Magnetic forces on HTS cables are restrained by a network of high strength tensile tethers (e.g., Kevlar, Spectra, etc.) to form the MIC structure MIC structures can be configured as discs, trusses, loops, etc.
Once in space or on the surface of a planet or moon, energizing the HTS cables with current unfolds the MIC array into its final design configuration MIC structures can be kilometers in scale
Thermal insulation is easier for MIC than for superconducting installations on Earth z
Vacuum of space eliminates need to maintain vacuum in Earth (based) thermal
MIC Launch and Deployment Sequence |---1000 meter s---|
MIC Applications In Space
Objectives of the Phase 1 MIC Program | | | | |
Assess the feasibility and advantages of constructing large structures in space using magnetically inflated cables (MIC) Identify and analyze most promising MIC applications Evaluate potential high temperature superconductor (HTS) options for MIC and select best one Carry out baseline designs of most promising MIC applications and determine performance capabilities Layout R&D program to develop and demonstrate MIC feasibility
High Temperature Superconductors: Options and Benefits for MIC |
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HTS (High Temperature Superconductors) have the following benefits over LTS (Low Temperature Superconductors) z Much less refrigeration power required z Much more stable against external thermal and mechanical impulses z Easier to thermally insulate z Does not require liquid Helium coolant Can be cooled with liquid Nitrogen or Helium gas Can use simple, reliable cryocoolers for refrigeration 3 principal HTS options z MgB2 (Magnesium Diboride) z BSCCO (Bismuth Strontium Calcium Copper Oxide) z YBCO (Yttrium Barium Copper Oxide)
Status of BSCCO Superconductor |
Critical temperature of BSCCO is ~90K Useful at 77K (liquid N2 temperature) – for higher current density and field capability, lower operating temperatures, e.g., 20 to 50K, may be desirable z Refrigeration factor very attractive, ~20 Watts(e) per Watt(th) z Examples of engineering current density (A/cm2) capability (parallel to surface) T(°K) Self Field 1 Tesla 2 Tesla 3 Tesla 77 15,000 3,800 1,500 750 70 18,000 10,500 6,000 4,500 64 27,000 15,000 11,000 7,500 50 37,500 29,000 22,500 18,000 35 51,000 39,000 32,000 30,000 20 81,000 58,000 50,000 46,000 z
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Practical BSCCO conductor is commercially produced z z z
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~1000 meter lengths produced Producing ~106 meters/year (~105 kiloamp meters) Will soon double capacity for wire production
Principal limitation is requirement for silver metal matrix – impacts cost and very large scale production capability
Status of YBCO Superconductor |
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Critical temperature of YBCO superconductor is ~100K z Useful at 77K (liquid N2 temperature – for higher current density and field capability, lower operating temperatures, e.g., 20 to 50K, may be desirable z Engineering current densities of 16,000 A/cm2 @ 77K (self field) z Engineering current densities of ~50,000 A/cm2 @ 26K and 3% Present conductor uses single film (0.8 µm) on metal tape substrate z Multi-layer film conductors under development – potential for much higher engineering current densities YBCO conductor is very flexible with minimum bend diameter of 1 inch Goal of 300 Km/year production capacity by 2007 with 1000 meter conductor lengths z No ultimate limit to production capacity
Status of MgB2 Superconductors |
Critical temperature of MgB2 is 39K z z z
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Practical MgB2 conductors are being manufactured using multi filament MgB2 in Nb wire matrix z z z z
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Practical operating temperature of 15 to 20 K at high current, high field conditions Practical temperature for present NbTi superconductor is 4 to 5 K at high current, high field conditions Refrigeration factor, watts(e)/watt(th), is ~100, compared to ~500 for NbTi
~1000 meter lengths at present for powder in tube (PIT) conductor – will go to 3000 meters lengths in 2006 λc current density in superconductor now at 175,000 Amp/cm2, compared to ~300,000 Amp/cm2 for NbTi will go higher in future Engineering current densities (superconductor + metal matrix) now at ~30,000 Amp/cm2 – will go higher in future Cost for large scale production will be below $1 per kiloamp meter
Production process is simple and inexpensive – materials are cheap and abundant
Thermal Leakage into MIC Cable as Function of Insulation Thickness and Local Surface Temperature Thermal Leakage into MIC Cable as Function of Insulation Thickness and Local Surface Temperature Basis: Cable diameter = 4 centimeters; cable length = 1 kilometer Insulation thermal conductivity = 0.5 x 10-4 W/MK Superconductor temperature = 20 K
Thermal Leak into MIC Cable, watts per kilometer
140 120 100 Tsurface = 100 K Tsurface = 200 K
80
Tsurface = 300 K 60 40 20 0 2
3
4
5
Insulation Thickness, centimeters
6
Flowsheet for MIC Cooling and Refrigeration System From Heat Rejection Radiator
Coolant Pump
To Heat Rejection Radiator
Electric Power Coolant Heat Exchanger MIC Conductor Cryocooler
Pump
Connection to Alternate Cryocooler
Features of MIC Coolant/Refrigeration System • Leak in MIC conductor coolant circuit is confined to that circuit – Does not compromise other conductor circuits • Refrigeration function of failed cryocooler can be taken over by other cryocoolers – MIC conductor circuit continues to operate • Reject heat from cryocooler can be handled by fail-safe multi-heat pipe radiator
Refrigeration Power of 1 Km MIC Cable as a Function of Superconductor Temperature, Fractional Carnot Efficiency, and Radiator Temperature
Refrigeration Input Power, kilowatts(e)
25
Basis: 1 km long MIC cable 400,000 Amp current 4 cm diameter 2 cm thick insulation 200 K average surface temperature
20
15 Tradiator = 300 K 20% Cryocooler Efficiency
400K 300K
Tradiator = 400 K 20% Cryocooler Efficiency
10 400K
Tradiator = 300 K 10% Cryocooler Efficiency
5
300K
Tradiator = 400 K 10% Cryocooler Efficiency
0 15
20
25
30
35
40
Superconductor Temperature, K
45
50
Illustrative Views of Method 1 for Support of Multiple MIC Conductors on Single MIC Cable Using Central Structural Tube
Reliability and Redundancy Features of MIC Conductor and Cable Systems Potential Event
Consequence
Action Taken
Coolant Tube Leaks
Coolant Leaks Into Space
Coolant Flow to Conductor That Leaks
One of MIC Conductors Fails Locally
Current Locally Shifts to Other Conductors Through Aluminum Tube
No Action Taken
Protective Kevlar Layer Prevents Damage to SubConductor
No Action Taken
Protective Layer Fails to Prevent Damage to Conductor
Coolant Flow to Conductor That Fails Automatically Shuts Off
Very Minor Effect – Many other conductors inductively take over current that was carried by the failed conductor
Coolant Flow to Some Conductors Stops
Standby Cryocooler is Switched into Replace Failed Unit
No Effect – Conductor has sufficient thermal inertia to continue operation while new cooler is switched in
Micro-Meter or Space Debris Strikes Conductor
Cryocooler Fails
Effect on MIC Capability Very Minor Effect – Many other conductors inductively take over current that was carried by the failed sub-conductor
No Effect – Full current continues in other conductors and cables
No Effect – Full current continues in other conductors and cables
Examples of Present Large Scale Superconducting Systems |
High energy particle accelerators z z z
z |
Japan Railways superconducting Maglev system in Yamanashi, Japan z
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Fermi doubler accelerator/storage ring; 6 kilometers of high field superconducting magnets; operating for >10 years Large Hadron Collider; 42 kilometers of high field superconducting magnets, nearing completion in Switzerland Superconducting collider; 76 kilometers of high field superconducting magnets (>10,000 total magnets); started by SSC funding went to International Space Station (ISS) All superconducting magnets in such facilities must operate perfectly, otherwise, facility cannot operate
350 mph Maglev vehicles levitated and propelled by superconducting magnets – many thousands of passengers carried
MRI medical scanners z
Superconducting magnets operate reliably and accurately in thousands of MRI units around the World
MIC Solar Electric Applications |
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3 MIC solar electric applications evaluated z 100 KW(e) system @ 3 AU for electric propulsion z 1 MW(e) system @ manned lunar base z 200 MW(e) system @ GEO for power beaming to Earth 1 MW(e) MIC system @ lunar base selected for further detailed baseline design effort z High priority for first application z Lunar system can lead to other applications Specific mass of MIC solar concentrator is < 1 kg/KW(e) z With concentration factor of > 10 Suns, total system mass is ~1.5 kg/KW(e) Lunar base can use multiple MIC solar electric system for reliability and redundancy z Electric capacity can quickly be increased as size of base grows
Nominal Design Parameters for Potential MIC Solar Electric Applications Basis: 100,000 A/cm2 engineering current density in MgB2 superconductor 2 cm thick multi- layer thermal insulation 15,000 psi tensile stress in tethers MIC Solar Electric Application Electric Propulsion
Lunar Base
Power Beaming to Earth
100 KW(e)
1 MW(e)
200 MW(e)
Solar cell efficiency
20%
20%
20%
Distance from Sun (2)
3 AU
1 AU
1 AU
Concentrator Area, m2
3750
4170
8.34 x 105
Concentrator diameter, m
69
73
913
Length of primary MIC cable, m
217
229
2870
MIC primary cable current, kiloamp (3)
250
250
950
Diameter of primary MIC cable, centimeters (4)
2.5
2.5
9.5
Mass of MIC primary cable, kg
430
430
22,600
Mass of tether and mirror surface, kg (5)
370
370
65,000
Other mass (secondary cable, coolant and refrigeration equipment), kg
100
100
5,000
Total MIC concentrator mass, kg
900
900
92,600
9
0.9
0.46
Parameter Unit output power (1)
Specific mass of MIC concentrator, kg/KW(e)
Nominal Design Parameters for Potential MIC Solar Thermal Propulsion Applications Basis: 100,000 Amps/cm2 engineering current density in MgB2 superconductor 2 cm thick multi- layer thermal insulation 15,000 psi in tensile tethers MIC Solar Thermal Propulsion Application Orbital LEO to GEO
Earth to Moon Tug
Mars Cargo Vessel
1
5
10
H2 propellant temperature, K
2500
2500
2500
H2 flow rate, kg/sec
0.025
0.13
0.25
220
1100
2200
1
1
1
Concentrator area, m2
830
4170
8340
Diameter of MIC concentrator, meter
32
73
103
Length of primary MIC cable, meter
100
229
460
MIC primary cable current, Kilo Amp
180
250
320
Diameter of MIC primary cable, cm
1.8
2.5
3.2
Mass of MIC primary cable, kg
150
430
1120
Mass of tether and mirror surface, kg
80
370
740
Other mass (secondary cable & refrig eq.) kg
50
100
200
Total MIC concentrator mass, kg
280
900
2060
High temperature receiver plus misc mass, kg
200
1000
1500
Total solar thermal propulsion system mass
560
1900
3560
Nominal V(kg/sec)/thrust time, days
5/3.7
5/2
5/3.6
Payload mass, metric tons
10
30
100
Total weight of H2 propellant, metric tons
8.1
24
79
Parameter Thermal power, megawatt
Thrust Newtons (Isp = 900 sec) Distance from Sun, AU
Nominal Design Parameters for Potential MIC Energy Storage Applications Basis: 100,000 A/cm2 engineering current density in MgB2 superconductor 2 cm thick multi- layer thermal insulation (4 cm for rover) 30,000 psi tensile strength in tethers and support tube MIC Energy Storage Application Spacecraft
Lunar Base (1)
Robotic Rover
100
2000
5
Circular loop
Circular loop
Linear quadrupole
50 meters diameter
100 meters diameter
10 meters length, 2 meters width
11
33
5.5
Current in MIC cable, Amps
1.1 x 106
3.3 x 106
500,000
Length of MIC cable, meters
160
320
50
Mass of MIC superconductor, kg
1000
6000
150
Mass of thermal insulation, kg
360
1920
70
Mass of support tube, kg
125
2400
25
Mass of tether network, kg
190
300
40
Mass of refrigeration equipment, kg
50
300
10
Total mass of MIC storage unit, kg
1725
10,920
295
7
42
2
Solar power generated at 1 AU using integrated solar cell array , KW(e)
500
2000
5
Specific mass, kg/MJ(e) stored
17
5.5
59
Specific mass, kg/KW(e) generated at 1 AU
3.4
5.5
59
Parameter Energy storage, Megajoules Form of storage Dimensions of storage unit
Diameter of support tube, centimeters
Refrigeration load, watts(th)
1) several independent storage loops, each of 2000 MJ capacity, would be used for the lunar base
New Astronomical Discoveries Enabled by MIC Space Telescope Imaging of First Stars and Galaxies forming in the Early Universe
Early detection and location of potential Earth impacting objects
Detection and imaging of terrestrial planets out to 100 light years
High resolution imaging of black hole boundaries
MIC Space Telescope
Spectroscopic imaging to detect life on planets around other stars
Detailed measurement of dark energy effects on the expanding universes
Very high resolution of Earth processes, e.g., ground movements
High resolution imaging of distant bodies in solar system (Pluto, etc.)
MIC Summary and Conclusions |
Strong, rigid large space structures based on a network of superconducting (SC) cables and tensile tethers appear practical z z
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MIC applications include large solar collectors for solar electric generation and solar thermal propulsion, electric energy storage, large space telescopes, etc. z z
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Structure is launched from Earth as a compact packaged payload of SC cables and tethers After delivery to desired location in space, SC cables are energized with current, causing the MIC structure to automatically deploy into its final desired shape Final dimensions of MIC structures can be a kilometer or more
Structures are very lightweight Refrigeration requirements are small
Presently high temperature superconductors (HTS) are practical for MIC applications z z z
Can operate at temperature up to those of liquid N2 MgB2 and YBCO conductors favored options Existing high current densities in HTS conductors expected to go higher
Backup
Potential MIC Applications â&#x20AC;&#x201C; On Surface |
Solar electric power z
z
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Large scale electric energy storage z
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MIC structure provides a very large, lightweight solar collector that focuses sunlight into a solar cell array or solar dynamic power cycle Potential for high power, 100â&#x20AC;&#x2122;s of KW(e) and low specific weight (kg/KW(e)) systems Provides very lightweight (kg/KWH) storage of large amounts of electric energy for bases on the Moon and other bodies
Magnetically shielded habitats for astronauts z
Quickly and automatically erected when energized
Potential MIC Applications â&#x20AC;&#x201C; In Space |
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Solar thermal propulsion z MIC structure provides a very large lightweight solar collector that focuses sunlight into a high temperature propulsion unit to heat H2 propellant z Potential for high thrust, high Isp (~1000 seconds) propulsion Solar electric power z Similar to MIC surface solar electric system Large scale electric energy storage z Similar to MIC surface electric storage system Magnetically shielded habitats for astronauts z Similar to MIC surface habitats Large scale space telescope z MIC structure supports reflecting surfaces to produce ~1 km diameter telescope Propellantless propulsion using planetary magnetic fields
Functional Requirements for MIC Superconductor •
MIC superconductors able to operate at 20 K or above in strong magnetic field with good current density
•
Engineering current density of conductor (superconductor plus substrate) can be 100,000 Amp per cm2 or greater Can operate in magnetic fields up to 4 Tesla
Operating Temperature
Current Density & Magnetic Field Capability
•
MIC Superconductor •
Remains superconducting for all anticipated conditions including local flux jumps and conductor micro-movements
•
Operates at anticipated conditions without mechanical fracture or cracking Can be wound into compact package for launch
Operational Stability
Mechanical Integrity
•
Preliminary Assessment of High Temperature Superconductors for MIC Applications | |
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HTS conductors already in commercial production Practical applications already demonstrated z High power motors – 5MW built, 36MW under construction z High power generators and synchronous condensers z Power transmission z Maglev Substantial improvements likely in next few years – higher current density and field capability lower cost, longer conductor length BSCCO conductor production capacity limited by availability of silver for matrix – MgB2 and YBCO conductors not limited MgB2 probably ultimately lower in cost than YBCO – however, both are promising candidates for MIC
Design Issues for MIC Superconducting Cables |
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Thermal insulation z Type and thickness z Method for expansion from compressed thin layer to full thickness Refrigeration z Optimum operating temperature z Cooling system design Superconductor z Design and operating current of multiple independent conductors z Attachment/support of multiple conductors on MIC cable Reliability and redundancy of MIC SC cable z Capability to continue operation if individual conductors or coolant circuits fail
Erection Process for MIC Thermal Insulation 1
Package MIC Cable Structure into Compact Payload
2
Launch and Deploy MIC Payload into Orbit
6
Thermal Insulation Layer Expands to Full Thickness
Energize MIC Cable with Partial Current
5
Energize Aluminum Conductors to Expand Thermal Insulation
7
Energize MIC Cable to Full Current
3
8
MIC Structure Expands to Final Shape
4
MIC Structure Expands to Initial Shape
Thermal Insulation Parameters for Illustrative MIC Applications A p p lic a t io n s P a r a m e te r
S o la r E le ct r ic
S o la r T h e r m a l P ro p u ls io n
E n e rg y S to ra g e
S pace T e le s c o p e
L o c a tio n
L u nar B ase
S p ac e
L un ar B ase
S p ac e
P er form a n c e
5 M W (e ) @ 20 % s o la r c e l l e ff ic ie n c y
5 0 M W (t h) H 2 p r o p u ls io n I sp = 9 5 0 s e c [ 1 0 ,0 0 0 N e w to n th r u s t ]
30 M W H [1 00 K W fo r 2 w eek s]
30 0 m eter [ 2 0 0 t im e s H u b b le d ia m e te r ]
# o f M I C c ab le s o n lo o p @ 4 0 0 ,0 0 0 A m p s p e r c a b le
1
1
1 6 (c ) [ i n s i d e 0 .5 m in s u la te d tu b e ]
1
M I E lo o p d ia m e t e r , m e te r s
160
230
1 00 0
300
T o ta l M I C c ab le le n g t h , k m
0 .5 1
0 .7 3
3 .1
0 .9 4
T o ta l m a s s o f i n s u l a t i o n (a ) p a c k a g e , k ilo g r a m s
260
370
25 0 0
M a s s o f in s u la tio n , k g p e r s q u a r e m e te r o f lo o p H e a t le a k , w a tts
(b )
1 .2 x 1 0
42
-2
8 .8 x 1 0
60
-3
(d )
3 .5 x 1 0
5 00
(e )
480
-3
6 .8 x 1 0
-3
77
N o te s : a) b) c) d) e)
In s u la t i o n t h ic k n e s s o n M I C c a b l e i s 2 c e n t im e t e r s D e n s ity = 1 2 0 k g /m 3 H e a t le a k b a s e d o n 2 0 0 K a v e ra g e s u r f a c e t e m p e ra t u r e M u l t i p l e M I C c a b le s ( 1 6 t o t a l) r e q u ir e d t o a c h ie v e t o t a l c u r r e n t o f 7 x 1 0 6 A m p s i n e n e r g y s t o r a g e c o o p . T h e 1 6 c a b le s a r e c o n t a in e d i n s i d e a 0 .5 m e t e r d ia m e t e r t h e r m a ll y i n s u l a t e d t u b e , w it h 4 c e n t i m e t e rs o f i n s u l a t i o n M a s s o f i n s u l a t i o n b a s e d o n 4 c e n t i m e t e r s t h i c k n e s s , w it h d e n s i t y o f 1 2 0 k g / m 3 R e f r i g e r a t i o n d u r i n g 2 w e e k n i g h t p e r i o d is s u p p l i e d f r o m c o l d s i n k r e f r i g e r a t e d b y p o w e r g e n e r a t e d d u r i n g 2 w e e k d a y p e r io d
Design Approach for MIC Superconducting Cables |
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Individual MIC conductors are independent of other MIC conductors z ~10,000 Amp nominal current in individual MIC conductor z Each conductor has its own cooling circuit and current input/output leads z Each conductor several multiple SC sub-conductors (e.g., 8) MIC SC cable incorporates many individual independent MIC conductors onto common support tube to provide desired total current z MIC cable carrying total of 400,000 Amps would have 40 individual conductors, for example If an individual conductor fails (e.g., coolant circuit leak, mechanical failure, space debris impact, etc.), MIC cable continues to operate z Failed conductor transfer its current to other conductors by magnetic induction
Procedure to Maintain MIC Current if One of the Sub-Conductors in a MIC Cable Were to Fail or Leak Action 1 No Additional Action Taken MIC Conductor Fails due Either to Coolant Leak or Micro Meteor Impact
Coolant Flow to Conductor Ceases
Outcome Other MIC Conductors Inductively Takes Over Most of the Current from the Failed One
OR Action 2
Outcome
One of the Remaining MIC Conductors is Re-connected to Power Supply
Current is Increased Slightly in Re-Connected Conductor Which is Inductively Coupled
Notes Action 1: Total current carried by MIC cable will drop slightly. For 40 conductor cable, total current will decrease by <0.1%, due to inductive coupling of the MIC conductors
Action 2: Total current carried by MIC cable can be kept at original level, by temporarily reconnecting just one MIC sub-conductor to its power supply
MIC Solar Thermal Propulsion Application | |
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3 MIC solar thermal propulsion applications evaluated 1 MW LEO to GEO tug z 5 MW Earth to Moon tug z 10 MW Mars cargo vessel 5 MW Earth to Moon tug chosen for further detailed baseline design effort z High priority for first application z System can be readily scaled for other applications Specific mass of MIC solar concentrator is 0.2 kg/KW(th) z Specific impulse of hot H2 propellant is 900 seconds z 73 meter diameter MIC solar concentrator Potential for generation of electric power as well as solar thermal propulsion
MIC Energy Storage Application |
3 MIC energy storage applications evaluated z z z
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2000 megajoule system for lunar base chosen for further detailed baseline design effort z
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z z
MIC loop diameter is 100 meters SC current is 3.3 megamps Total mass is 1 metric tons
MIC mass dominated by superconductor needed to carry very large currents, plus conservative tensile stress in tethers z
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High priority for first application
Specific mass of MIC lunar base energy storage system is 5.5 kg/MJ(e) z
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100 megajoule system for spacecraft 2000 megajoule system for lunar base 5 megajoule system for robotic power
Mass could be reduced by factor of ~3, with higher current densities and tether stress
MIC energy storage system can also be used to generate MW(e) power levels
MIC Technical Issues |
Ability to pack MIC superconducting (SC) cables and tethers into compact payload for launch which is then deployed once in space to form extended structure z z z
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For certain applications, ability to carry currents >>500,000 Amps in compact flexible SC cables without exceeding maximum field capability z z
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Single small cable can carry up to ~500,000 Amps Very large currents can be carried by array of multiple cables separated by tether network to keep magnetic fields at acceptable levels
Robust and reliable operation of SC network z z
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SC and coolant tube flexibility Expansion of compacted thermal insulation around SC and coolant tubes once in space Practical solutions identified for packing/deployment operations
Not vulnerable to single point failure Use of independent multiple SC/coolant circuits that are inductively coupled so that remaining circuits can compensate for circuits that fail
Optimize choices for SC, coolant, and operating temperature
MIC Development â&#x20AC;&#x201C; Preliminary Assessment |
High temperature superconductor (HTS) development rapidly proceeding z z z
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Present HTS conductors can be used to test and demonstrate MIC concept z z z
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HTS current density expected to substantially increase HTS cost rapidly decreasing MgB2 and YBCO conductors are leading candidates Tests/demonstrations can be done on Earth laboratories, both in atmosphere, and in large vacuum chambers Tests can be carried out starting with compact package of HTS conductors and tethers that are energized to form final structure Tests can measure thermal input to HTS conductors, temperature distributions, forces, geometric tolerances, etc. in deployment structure
Variety of structures can be tested at sub-scale including MIC z z z
Solar collector Energy storage Telescope