Robust adaptive backstepping attitude stabilization and vibration reduction of flexible spacecraft subject to actuator saturation

This paper presents a dual-stage control system design method for flexible spacecraft attitude stabilization control and active vibration suppression. In the design method, the attitude control system and vibration suppression are designed separately using a lower order model. As a stepping stone, a backstepping controller with the assumption of knowing system parameters is designed that ensures asymptotical convergence of attitude described by Modified Rodrigues Parameters (MRPs) vector and velocity in the presence of bounded parameter variation/disturbances. Then this controller is redesigned such that the need for knowing the system parameters in advance is eliminated by using an adaptive update law. Lyapunov analysis shows that this adaptive controller can also guarantee the asymptotical convergence. In addition, for the actuator restricted by physical structure, a modified adaptive backstepping attitude controller is also developed in the presence of external disturbances and input saturation. The undesirable vibration is also actively suppressed by applying feedback control voltages to piezoceramic actuators, in which the modal velocity feedback (MVF) control method is adopted here for determining the control voltages. Compared with conventional methods, the developed control scheme guarantees not only the stability of the closed-loop system, but also yields better performance and robustness. Simulation results are presented for the spacecraft model to show the effectiveness of the proposed control techniques.