Attitude control of spacecraft with actuator uncertainty

Fault-tolerant-control (FTC) design without ground intervention has attracted increasing attention to increase onboard autonomy in fault management. The preceding FTC schemes assume that actuators are free of misalignments. However, finite manufacturing tolerance or warping of structure may introduce actuator alignment errors. The moment of inertia for reaction wheels is finite. The speed range of reaction wheels is also finite in practical aerospace engineering. Attitude stabilization for rigid spacecraft has been investigated in the framework of input-to-state stability. External disturbance, unknown inertia parameters, actuator fault, and misalignments were explicitly addressed. All the signals are shown uniformly ultimately bounded in the absence of actuator misalignments. Also, as a consequence of the input-to-state-stable property, an input-to-statestable characterization of the closed-loop system has been derived with respect to possible actuator misalignments.