Observer-based robust actuator fault isolation and identification for microsatellite attitude control systems

Purpose - The purpose of this paper is to accomplish robust actuator fault isolation and identification for microsatellite attitude control systems (ACSs) subject to a series of space disturbance torques and gyro drifts. Design/methodology/approach - For the satellite attitude dynamics with Lipschitz constraint, a multi-objective nonlinear unknown input observer (NUIO) is explored to accomplish robust actuator fault isolation based on a synthesis of Hinf techniques and regional pole assignment technique. Subsequently, a novel disturbance-decoupling learning observer ((DLO)-L-2) is proposed to identify the isolated actuator fault accurately. Additionally, the design of the NUIO and the (DLO)-L-2 are reformulated into convex optimization problems involving linear matrix inequalities (LMIs), which can be readily solved using standard LMI tools. Findings - The simulation studies on a microsatellite example are performed to prove the effectiveness and applicability of the proposed robust actuator fault isolation and identification methodologies. Practical implications - This research includes implications for the enhancement of reliability and safety of on-orbit microsatellites. Originality/value - This study proposes novel NUIO-based robust fault isolation and (DLO)-L-2-based robust fault identification methodologies for spacecraft ACSs subject to a series of space disturbance torques and gyro drifts.