Adaptive Integral-Sliding-Mode Control for Spacecraft Single-Axis Pointing Using Two Torques

This paper deals with the attitude control problem of a nearly axis-symmetric spacecraft actuated by two torques perpendicular to its symmetry axis. As a result, the spacecraft symmetry axis is unactuated and the rotation about it is uncontrollable. Our objective aims to stabilize the symmetry axis to an arbitrary inertial direction irrespective of the spinning motion about it. First, a non-smooth controller is derived via homogeneous techniques to align the symmetry axis in finite time when there are no uncertainties. To compensate for perturbations induced by uncertain inertias, unknown external disturbances and actuator faults, an adaptive integral sliding mode controller is developed by combining adaptive control and integral sliding modes with the non-smooth controller. The resultant adaptive controller can stabilize the system states into a small neighborhood around the sliding mode. Consequently, the performance of the non-smooth controller can be approximately recovered, even in the presence of uncertainties, which ensures significant robustness and high control accuracy. Numerical examples are presented to verify the effectiveness and advantages of the proposed methods.