Design of robust adaptive integral variable structure attitude controller with application to flexible spacecraft

A robust control system for rotational maneuver of an orbiting spacecraft with flexible appendages is designed. Based on variable structure control theory, a discontinuous attitude control law is derived to achieve the desired position of the spacecraft, taking explicitly into account external disturbance and nonlinearity. To reconstruct estimates of the system states for use in a full information control law, an asymptotic variable structure observer is also employed and the fulfillment of sliding condition, including the case when estimated states are used, is verified as well. An additional attractive feature of the control system design is that an adaptive mechanism is embedded such that the unknown upper bound of lumped perturbation is automatically adapted. Compared with conventional adaptive proportional-derivative (APD) control, the developed control scheme not only guarantees the stability of the closed-loop system, but also yields better performance and robustness in the presence of parametric uncertainties and external disturbance. Simulation results are presented for the spacecraft model to show the effectiveness of the proposed control techniques.