Fault Diagnosis and Fault-Tolerant Attitude Control of Spacecraft Based on Combined Observer

Reaction wheels as the main actuators for attitude control of spacecraft are very prone to malfunction, which may significantly degrade the performance of the spacecraft attitude control system. In this paper a novel active fault-tolerant control scheme is proposed to react the reaction wheel faults actively. A combined observer is first designed to detect the reaction wheel faults, by combining a traditional adaptive Luenberger observer and a newly designed neural network (NN) observer. It inherits the advantages of the low computational cost of the Luenberger observer and the high performance of the NN observer. Then, a fault isolation scheme is given to locate faults. Subsequently, an adaptive fault-tolerant controller is designed to achieve graceful performance degradation under reaction wheel faults, based on the diagnosis results of the combined observer and the judgment results of the fault isolation scheme. Finally, simulation results show that the proposed scheme is able to achieve precise fault diagnosis and fault-tolerant control of spacecraft in the presence of external interference and limited computation.