Adaptive Integral Variable Structure Attitude Controller Design and Application to Flexible Spacecraft

A robust control system for the rotational maneuver of an orbiting spacecraft with flexible appendages is designed. Based on adaptive 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 variable structure 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 also verified. An additional attractive feature of the control system is that an adaptive mechanism is also embedded such that the unknown upper bound of lumped perturbation is automatically adapted. Simulation results have been shown that the developed control scheme guarantees not only the stability of the closed-loop system, but also yields better performance and robustness in the presence of parametric uncertainties and external disturbance.