Fault-Tolerant Reduced-Attitude Control for Spacecraft Constrained Boresight Reorientation

Abstract

This paper is devoted to investigating the fault-tolerant reduced-attitude control problem for boresight reorientation of an uncertain spacecraft subject to pointing and angular velocity constraints. First, the stereographic projection is used to transform this problem to an obstacle avoidance problem on a two-dimensional Euclidean sphere world with circular obstacles. Then, an adaptive fault-tolerant control strategy is proposed to solve the transformed problem, by designing two potential functions for constraint handling in conjunction with a sliding vector containing hyperbolic tangent functions. Stability analysis shows that the derived controller can achieve asymptotic convergence of the gradient of the obstacle avoidance potential and angular velocities, while ensuring the satisfaction of both pointing and angular velocity constraints, despite the presence of unknown time-varying inertia parameters, disturbances, and actuator faults. In particular, benefiting from incorporating the spacecraft principal moments of inertia into the potential field design, the risk of the system losing strong controllability under multiplicative actuator faults is greatly reduced. To accommodate actuator faults under input saturation, the adaptive fault-tolerant controller is further extended to a saturated counterpart, which is capable of making full use of the remaining actuation power to react to actuator faults. Finally, simulation results are presented to demonstrate our theoretical findings.