Analytical redundancy based fault diagnosis scheme for satellite attitude control systems

This paper presents an integrated fault detection and diagnosis (FDD) scheme based on analytical redundancy for satellite attitude control systems (ACS). The faults of actuators, angular rate sensors and attitude sensors are all taken into account, and the nonlinear ACS considered is subject to both space disturbance torques and sensor uncertainties. The proposed scheme is developed in two phases. In the first phase, two nonlinear observers are designed, and based on the proposed strategy which called observer redundancy the fault source (actuators, angular rate sensors or attitude sensors) can be verified. In the second phase, two banks of fault isolation observers (FIOs) activated by the previous detection results are designed to perform the diagnosis within the fault part. The first bank of FIOs are obtained based on nonlinear unknown input observers to isolate the fault actuator and the second bank of FIOs are obtained based on nonlinear adaptive observers to isolate and estimate the fault of angular rate sensor. The effectiveness of the proposed scheme is simulated on a closed-loop satellite attitude control system with some typical faults of these components.