Reaction wheel fault compensation and disturbance rejection for spacecraft attitude tracking

Anovel attitude tracking control scheme is proposed for rigid spacecraft to simultaneously compensate for reaction wheel faults and reject external disturbances. The reconstruction of the reaction wheel faults and disturbances is treated as a problem of observing the state of a linear system with unknown inputs. A terminal sliding mode observer is proposed to reconstruct the reaction wheel faults and disturbances. A Lyapunov-based analysis shows that the observer asymptotically converges to the actual faults and disturbances with a finite time convergence. Then, with the reconstructed faults and disturbance information, a compensation control law is developed to guarantee that the desired attitude trajectories are followed in finite time. The key feature of the proposed control strategy is that it globally asymptotically stabilizes the system, even in the presence of reaction wheel faults and external disturbances. The attitude tracking performance using the proposed compensation control is evaluated through a numerical example.