Fault detection and isolation in spacecraft attitude control system using parity space method

In this thesis, the problem of fault detection and diagnosis in the spacecraft attitude control system is considered. For this purpose, a fault or a failure in a spacecraft is first defined. This is followed up by description and details on the spacecraft architecture, and specifically the spacecraft attitude control system (ACS). The method developed for fault detection and diagnosis is the parity space or the parity equation approach. This method is applied to one type of actuators, namely reaction wheels that are commonly used in the spacecraft attitude control system. The capabilities of this method for fault detectability are studied through extensive numerical simulations. The proposed method is validated by comparing the obtained results with those of a fault detection method based on linear observer approach. Among the various variables in a reaction wheel of the attitude control system, bus voltage and actuator current components are of particular interest in this thesis, due to their influence in performance of the ACS of the spacecraft. Different types of fault signatures are used for these two components, and the simulated results are compared through two different approaches for fault detection. The advantages of the proposed and designed parity space-based method over a linear observer-based approach for fault detection and diagnosis is shown to be significant especially in detecting faults in the pitch axis of the spacecraft