Kai Zhang

Whether operating autonomously or assisting humans, multi-degree-of-freedom free-flying space manipulator has shown enormous potential in space missions. Leveraging the fully actuated system approach (FASA), this article proposes a distributionally robust model predictive control (MPC) scheme for trajectory tracking issue of space manipulator with stochastic uncertainties and multiple constraints on the angle, angular velocity, and control torque. First, a nominal FASA-based controller is designed to establish a linear second-order fully actuated (SOFA) model with desired eigenstructure assignment. By adopting an exact penalty function, a gradient-based optimization scheme is developed to optimize the FASA-based controller parameters offline, while avoiding violating of multiple constraints on angle, angular velocity, and control torque. Furthermore, a distributionally robust MPC is proposed to enable real-time optimization of auxiliary input, ensuring constraint satisfaction and enhancing performance in the presence of independent stochastic uncertainties. Recursive feasibility and convergence are proven. Monte Carlo numerical simulations are conducted with a planar space robot system to validate the superiority of proposed strategy.

A sliding mode controller is proposed for the attitude control of spacecraft reorientation with attitude constraints. By introducing a potential function, a novel sliding function is designed. With the structure of the proposed sliding function, uniqueness of the equilibrium and fixed-time convergence are rigorously proven. Another advantage of the proposed controller is that the feasibility of attitude constraints can be proven not only on the sliding surface but also outside it. Moreover, the singularity issue of the proposed controller is resolved. Effectiveness of the proposed method is demonstrated by carrying out two numerical simulation.

For tumbling or non-cooperative targets in space missions, the prior knowledge of the target trajectory is unknown, which leads to the property of prescribed tracking accuracy with assigned settling time hard to achieve. In addition, the unknown inertia characteristics and the presence of actuator faults will also reduce the robustness of the existing spacecraft control methods. To overcome these difficulties, a new approximation-free attitude tracking control scheme of spacecraft with unknown dynamics, external disturbance and actuator fault is proposed. For the designed controller, no inertia matrix is used, and no approximation-based or adaptive method is applied. Besides, it is rigorously proved that the developed control theory can also ensure that tracking error converges to the prescribed accuracy in appointed time even when the actuator fault occurs. Furthermore, a modified tuning function is used to relax the constraint of the initial value, which ensures the global stability of the closed-loop system. Simulation results verify effectiveness of the proposed method.

This paper addresses the event-triggered attitude control problem for spacecraft anti-unwinding reorientation with multiple attitude constraints in the presence of external disturbance. Based on a designed novel potential function(PF), a new sliding mode controller is proposed to guarantee the completeness of anti-unwinding reorientation with multiple attitude constraints and external disturbance. Different from existing continuous attitude reorientation controller, the static and dynamic event-triggered mechanisms, related with the sliding mode variable and disturbance bound, are then constructed. With the designed event-triggered sliding mode control schemes, the attitude system asymptotic stability, the satisfaction of attitude constraints with anti-unwinding action and free of Zeno phenomenon despite on external disturbance are proved theoretically. Numerical simulations results confirm that the proposed methods can significantly reduce resource usage while guaranteeing the desired performance.