Robust attitude control for a rigid-flexible-rigid microsatellite with multiple uncertainties and input saturations

In this paper, the attitude tracking system of a microsatellite consisting of a rigid main-satellite, a flexible coilable mast and a rigid sub-satellite is studied. The attitude tracking model is formulated as a highly nonlinear and coupled system subject to parametric perturbations, external disturbances, flexible vibration and input saturations. To realize the high-accuracy attitude tracking control, a robust controller consisting of a nominal controller, an observer-based compensator and a modified proportional-derivative (MPD) controller is proposed with a simple configuration. The nominal controller is introduced based on a disturbance-free nominal system. The observer-based compensator is constructed to compensate a lumped equivalent disturbance representing all uncertainties and disturbances in a finite time. The MPD controller is developed to implement the high-accuracy attitude control under input saturations. Stability analysis indicates that both attitude tracking errors and angular velocity tracking errors of the closed-loop system can converge asymptotically. To verify the effectiveness of the proposed control law, numerical simulations are launched in different cases. Simulation results demonstrate that the proposed control law not only achieves the high-accuracy attitude tracking control, but also suppresses the vibration of the flexible coilable mast.