Adaptive Sliding Mode-based Control System for Flexible Spacecraft

Abstract

A design of a robust attitude control system for flexible spacecraft is proposed in this paper, since satellites are often characterized by complicated shapes, with large appendages. The mathematical model of the spacecraft is derived, considering a rigid main body, i.e. the hub, and bending motion of the movable appendage. The Lagrangian approach is used to derive a set of five differential equations for the attitude dynamics of the spacecraft and for the vibrations of the appendage. Since the dynamics of the flexible system includes nonlinearities and parametric uncertainties, an adaptive variable structure controller, based on the theory of Sliding Mode Control (SMC), is proposed for the attitude tracking. The main objective is to analyze the effectiveness of the proposed control methodology for both precise tracking of the attitude dynamics and for suppression of the structural vibration, handling actuation and hardware limitations. Moreover, external disturbances and parametric variations are included, to show the robustness and the adaptability of the proposed control methods. The proposed control strategy is validated by extensive simulations performed in MATLAB and it appears easy to be converted on C language and suitable for real-time on-board implementation.