Adaptive variable structure fault tolerant control of rigid spacecraft under thruster faults

A novel fault tolerant attitude control system is investigated for a rigid spacecraft with redundant thrusters, in which unknown inertial parameters, thruster faults, control input saturation and even external disturbances are explicitly considered simultaneously, and the control torque is limited in one established scope via thruster output saturation function which is explicitly introduced. More specifically, in this proposed control scheme, the control parameters are adjusted dynamically by online adaptive control technique in such a fashion that no fault detection and isolation mechanism is required in advance, and only the remaining active thrusters are assumed to be able to produce a combined force sufficient enough to allow the spacecraft to perform the given operations within the saturation magnitude. Moreover, the effect of the thruster force magnitude deviation is analyzed and the system performance is evaluated by L2 gain from this magnitude deviation to the penalty output, and Lyapunov stability analysis shows that the resulting closed-loop system is proven to be stable. Finally, numerical examples are also presented to demonstrate that the control algorithms developed are not only robust against external disturbances and parameter uncertainties, but also able to accommodate thruster failures under limited saturation value.