Fault tolerant control with H_∞ performance for attitude tracking of flexible spacecraft

A fault-tolerant control scheme with thruster redundancy is developed and applied to perform attitude tracking manoeuvres for an orbiting flexible spacecraft. Based on the assumption of bounded elastic vibrations, an adaptive sliding mode controller is proposed to guarantee that all the signals of the resulting closed-loop attitude system are uniformly ultimately bounded in the presence of an unknown inertia matrix, bounded disturbances and unknown faults. An H_∞ performance index is introduced to describe the disturbance attenuation performance of the closed-loop system. This approach is then extended to the problem of elastic vibration without knowledge of the bounds a priori. The presented approach addresses thruster saturation limits and the desired thruster force is guaranteed to stay within the limit of each thruster. Extensive simulation studies have been conducted to demonstrate the closed-loop performance benefits compared to conventional control schemes.