Saturated Control for Spacecraft Rendezvous and Proximity Operations under Loss of Control Effectiveness

A saturated controller is developed for the final phase of rendezvous and proximity operations in the presence of disturbances, parametric uncertainties and loss of control effectiveness. To achieve this, an integrated auxiliary filter structure is first established using hyperbolic functions that work in tandem with filtered tracking error. Then a robust saturated controller for nominal system is proposed. Furthermore, saturated fault-tolerant controller based on the nominal control law and sliding-mode-like method is derived. The bound on the proposed controller can be adjusted by changing the feedback gains. A Lyapunov-based stability analysis is provided to prove uniformly ultimate bounded (UUB) tracking despite uncertainties, disturbances and even actuator faults in the six-degree-freedom dynamics. A numerical simulation is presented to demonstrate the performance of the controller.