Adaptive Fixed-Time Fault Tolerant Control for Rigid Spacecraft Under Harsh Conditions: Simultaneous Actuator and Sensor Faults

Abstract

In-orbit operation of rigid spacecraft fundamentally relies on attitude tracking control. However, tracking performance is highly dependent on the reliability of onboard actuators and sensors, and it can be significantly degraded, or even fail, if any actuator or sensor becomes faulty. The consequences may become more severe when faults occur during transient maneuvers, particularly while the spacecraft is accelerating to track a desired attitude. Furthermore, simultaneous actuator and sensor faults can be especially detrimental. To address these challenging conditions, this study proposes a fault-tolerant attitude tracking scheme that integrates an adaptive fixed-time controller with an unscented transform-based fault estimator. Within the control design, a sliding surface is appropriately constructed to eliminate the singularity issue commonly encountered in many existing fixed-time control methods. In addition, an adaptive law is incorporated to compensate for actuator faults and external disturbances. A rigorous practical fixed-time stability analysis is performed based on Lyapunov theory, which formally establishes the practical fixed-time convergence of the closed-loop system. Meanwhile, the unscented transform is employed to estimate sensor faults. The resulting estimator plays a pivotal role in reconstructing reliable estimates of the system’s true angular rates, which are then fed back into the attitude tracking controller, thereby enhancing overall fault-tolerant performance. Finally, a series of experiments is conducted to validate the feasibility of the proposed approach and to demonstrate its effectiveness in a practical spacecraft system.