Robust adaptive sliding-mode fault-tolerant control with L2-gain performance for flexible spacecraft using redundant reaction wheels

A robust adaptive fault-tolerant control approach for attitude tracking of flexible spacecraft is proposed for use in situations when there are reaction wheels/actuator failures, external disturbances and time-varying inertia-parameter uncertainties. More specifically, a robust controller based on sliding-mode control scheme is first designed to ensure that the equilibrium point in the closed-loop system is uniform ultimate bounded stability, incorporating constraints on actuator failures, whose failure time instants, patterns and values are unknown, as motivated from a practical spacecraft control application. Then, this controller is redesigned such that an assumption on a bound required of the unknown and time-varying inertia matrix is released by using online estimation for this bound. The prescribed robust performance is also evaluated by L₂-gain less than a given small level for the penalty output signal. Complete stability and performance analysis are presented, and illustrative simulation results of an application to flexible spacecraft show that the high precise attitudes control and vibration suppression are successfully achieved using various scenarios of control effect failures.