Adaptive Fault-Tolerant Spacecraft Pose Tracking with Control Allocation

The concurrent position and attitude (pose) tracking of a rigid spacecraft is addressed in the presence of actuator faults, mass and inertia uncertainties, and unknown external disturbances. The control design relies on a novel hybrid dual-quaternion integral sliding mode that incorporates a hysteretic switching to avoid the quaternion unwinding problem. On the sliding mode, the pose tracking error is globally finite-time convergent. The resultant control law has a simple structure and consists of a nominal control input, which realizes the sliding mode in the fault-free uncertainty-free case, and an adaptive part, which dynamically compensates for the perturbations due to actuator faults and other uncertainties. Moreover, a real-time control allocation algorithm is devised to deliver the control command to position and attitude actuators in proportion to the effectiveness degree of each actuator. Rigorous proof shows that the proposed strategies can stabilize the spacecraft pose trajectory to a small neighborhood of the sliding mode in finite time. Formation flying of earth-orbiting spacecraft and asteroid body-fixed hovering are simulated to demonstrate the efficacy and broad applicability of the proposed method.