Observer-based attitude control for flexible spacecrafts under actuator fault and actuator saturation

This paper studies the attitude control problem of flexible spacecrafts in the presence of actuator fault, actuator saturation and space environmental disturbances. It is well known that the performance of the attitude control systems (ACSs) can be degraded by the unwanted flexible vibration and actuator fault, so in order to achieve high-accuracy attitude control, the vibration disturbance of the flexible appendage is modelled by an exogenous system and the actuator is supposed to be derivative-bounded, then the disturbance observer (DO) and fault diagnosis observer (FDO) are utilized to estimate and reject the vibration of flexible appendage and the actuator fault, respectively. Next, a kind of composite hierarchical control scheme combining the observer-based control with state feedback control is presented, where the state feedback control can deal with the observation errors of the observers and space environmental disturbances. Under the proposed composite hierarchical control law, the system states can converge into a small set of the equilibrium points asymptotically even the actuator saturation occurs. At last, numerical simulations are performed to demonstrate the effectiveness of the proposed control law.