Abstract: This paper investigates the method for evaluating the diagnosability of sensor faults and actuator faults in satellite attitude control systems without depending on the fault diagnosis algorithms. The purpose is to improve the fault diagnosability of the system in the design phase. Considering the existence of feedback control, the single fault may generate a number of abnormal symptoms due to the fault propagation in the closedloop systems. Thus, it is a challenge to the fault diagnosability in the closedloop control systems. The statespace model of a satellite attitude closedloop control system with model uncertainties is established via extending the fault to the state variables. For the extended system, according to the criterion of the observability, the diagnosability conditions of additive faults and multiplicative faults are presented and proved by rigorous mathematical proofs. The achieved conclusions can be used to guide the design of satellite attitude control systems to improve the fault diagnosability.

Key words: satellite attitude control system, closedloop system, model uncertainties, additive fault, multiplicative fault