Thruster Fault Detection, Isolation and Accommodation for an Autonomous Spacecraft

Abstract

The presented work is a result of a research collaboration between European Space Agency, Thales Alenia Space and IMS Laboratory with the aim of promoting fault-tolerant control strategies to advance spacecraft autonomy. A multiple observer based scheme is proposed jointly with an online constrained allocation algorithm to detect, isolate and accommodate a single thruster fault affecting the propulsion system of an autonomous spacecraft. Robust residual generator with enhanced robustness to time delays induced by the propulsion drive electronics and uncertainties on thruster rise times is used for fault detection purposes. A decision test on the residual of the fault detector triggers a bank of nonlinear unknown input observers which is in charge of confining the fault to a subset of possible faults. The faulty thruster isolation is achieved by matching the residual and the thruster force directions using the direction cosine approach. Finally, the fault is accommodated by redistributing the desired forces and torques among the remaining (healthy) thrusters and closing the isolated thruster. Simulation results from the high-fidelity industrial simulator, provided by Thales Alenia Space, demonstrate the fault-tolerance capabilities of the proposed scheme.