Observer-Based Fault-Tolerant Spacecraft Attitude Tracking Using Sequential Lyapunov Analyses

The spacecraft attitude tracking problem is addressed with actuator faults and uncertainties among inertias, external disturbances, and, in particular, state estimates. A continuous sliding-mode attitude controller is designed using attitude and angular velocity estimates from an arbitrary stable stand-alone observer. Rigorous analysis shows that the controller ensures robust stability of the entire closed-loop system as long as the observer yields state estimates with uniformly ultimately bounded estimation errors. In addition, a sequential Lyapunov analysis is utilized to obtain a convergent sequence of analytical successively tighter upper bounds on the steady-state tracking error. Therefore, our results can be used to predict steady-state performance bounds given selected gains or facilitate gain selection given steady-state performance bounds. Numerical examples demonstrate the utility of the proposed theory.