AUS RESEARCH EXTENDS BATTERY-POWERED VEHICLES LIFETIME AND DRIVING DISTANCE

Dr. Mohamed Okasha

Associate Professor Department of Mechanical and Aerospace Engineering

United Arab Emirates University

The satellite design process has always faced constraints on mass and volume due to the practical limitations of the boosters. These traditional launch methods are not realistic for large satellites and structures. Even if massive boosters capable of launching these large structures existed, the cost would be expensive.

This is why Mohamed Okasha, Associate Professor at the Department of Mechanical and Aerospace Engineering at United Arab Emirates University, worked on a study entitled, “Optimal consensus control for multi-satellite assembly in elliptic orbit with input saturation”. The study sought an alternative method, an in-orbit assembly, that offers a more flexible framework for launching large satellites at a lower cost. This study was supported by the startup grant funded by the College of Engineering at United Arab Emirates University (UAEU).

The Study

The study introduced an approach to assemble satellites in orbit by designing a control system using optimal consensus control.

Okasha states, “Our research focuses on the innovative approach of assembling satellites in orbit, which is crucial for advancing space exploration. This method significantly reduces launch costs and overcomes limitations related to payload size and mass, enabling the construction of largescale space structures. This advancement is pivotal for future ambitious missions and the development of essential space infrastructure.”

The research proposed that, instead of launching an integrated system, the system should be divided into numerous elements. Then, each element would be launched into orbit separately and assembled there. Using this technology would allow the space sector to build large structures such as telescopes and solar panels, as well as the assembly of small satellites to a specific configuration.

However, designing a control system for multi-satellite assembly is challenging because it requires an accurate model of the satellite’s relative motion. In addition, optimal fuel consumption has to be ensured while considering the hardware limitation of the actuators (e.g., input saturation).

The design process becomes more complex when the satellites are partially communicating, where each satellite does not have access to the states of all other satellites in the team.

As such, the paper proposed a control technique that overcame these challenges. The paper proposed a control system based on the discrete-time model of the Tschauner–Hempe (T–H) equations, taking advantage that the T–H equations are linear time-periodic.

Okasha explains, “Optimal consensus control is a sophisticated technique that allows a group of satellites to achieve a common objective efficiently, with minimal central coordination. It uses discrete-time control strategies and optimizes communication between satellites, ensuring stability and precise assembly despite input saturation, which is the incapacity of actuators to exceed certain thresholds. This method stands out for its efficiency and minimal reliance on extensive communication, distinguishing it from traditional control techniques.”

The Optimal Consensus Control is much better than the Model Predictive Control (MPC) which has been widely used in multisatellite systems for solving an online optimization problem. Despite the fact that the Model Predictive Control provides a framework for handling different constraints on the input and the state, it requires high computational processing to solve the optimization problems within the sampling time. Hence, the paper addressed the optimal discrete-time control problem of multi-satellite assembly considering partial communication and input saturation.

The Results of study

The work designed an optimal discrete-time control system for multi-satellite assembly using the discrete-time periodic Riccati equation and analyzed its stability under input saturation using the discrete-time T-H model.

Okasha explains, “The proposed control law in our research exhibits superior tracking accuracy and requires less control effort compared to existing methods. This implies our approach can more precisely control the satellite formation with lower fuel consumption, enhancing the feasibility and sustainability of in-orbit assembly missions. It represents a significant advancement in the field, offering practical and efficient solutions for space operations.”

Benefits for UAE satellite assembly projects

The efficiency and effectiveness of the proposed control law makes it highly applicable to UAE›s satellite assembly projects. According to Okasha, it provides a promising solution for precise and efficient in-orbit assembly, with potential for future advancements.

He adds, “As technology progresses, further research may introduce even more optimized control laws, but our current findings lay a strong foundation for practical application and innovation.”