Fully actuated system-based active disturbance rejection saturated attitude control for flexible spacecraft

Flexible spacecraft, characterized by infinite degrees of freedom, pose challenges in attitude control due to complex coupling effects and significant nonlinearities. This paper addresses the attitude control problem for underactuated flexible spacecraft, considering external disturbances, inertia uncertainties, and control input saturation. A novel active disturbance rejection saturated control strategy, which is based on fully actuated system (FAS) theory, is developed to achieve robust attitude stabilization. The approach involves the construction of a fully actuated attitude model for the flexible spacecraft and implementing an extended disturbance observer to estimate uncertain nonlinearities, such as elastic vibrations, system uncertainties, and external disturbances. These estimates are fed into a nonlinear feedforward compensation control. The feedback controller, designed with the direct parametric method, ensures the desired orientation with high precision. Additionally, the inclusion of a dynamic gain filter effectively controls input saturation and significantly enhances flexible vibration suppression. The simulation results validate the effectiveness of the proposed strategy, demonstrating its potential for use in underactuated flexible spacecraft attitude control in practical scenarios.