Output-Feedback Control for Spacecraft: A Fully Actuated System Approach

This paper investigates the modeling and output-feedback tracking control issues for the attitude-orbit integrated spacecraft based on the fully actuated system approach. As traditional spacecraft attitude and orbit control schemes treat the attitude and orbit motions as isolated subsystems, they ignore the coupling characteristics between the attitude dynamics and the orbit dynamics, failing to improve the control performance. Although attitude-orbit integrated control systems enable the integrated description and control of the six degrees-of-freedom (DoF) pose systems, they have strong nonlinearities which bring difficulties to the control design and analysis. In practical engineering circumstances, the physical conditions and the measurement accuracy make part of the system states unknown, which limits the application of the state-feedback control techniques. The development of the fully actuated control theory provides solutions to the above issues. Hence, the twistor, variable elimination, and order elevation techniques are adopted to transform the spacecraft relative dual quaternion model into the fully actuated attitude-orbit integrated system. For the output-feedback tracking control objective, a state-observer is designed to estimate the unknown states, and the tracking control law is given based on the estimation signals. A Lyapunov function is selected to analyze the stability of the closed-loop system, and the estimation and tracking errors are proved to be asymptotically convergent. Finally, a numerical simulation is carried out to verify the effectiveness of the proposed control scheme.