Fault Tolerant Attitude Control for Spacecraft Considering Input Delay and Actuator Saturation: Theory and Experiment

This study presents an advanced fault estimation and control strategy for spacecraft attitude control systems operating under time‐varying input delays and actuator saturation. An adaptive fast terminal sliding mode fault‐tolerant control (AFTSMFTC) framework is proposed to mitigate actuator faults, estimation errors, and input constraints. Two adaptive laws are designed to dynamically tune the control gains, thereby enhancing performance and robustness under fault conditions. A multipurpose sliding surface is formulated to ensure that the reaction wheels come to rest after maneuvering, improving momentum management and energy efficiency. Furthermore, a nonlinear disturbance observer (NDO) is developed to estimate external disturbances, unmodeled inertia variations, and time‐varying input delays, while an integrated fault detection mechanism identifies actuator failures in real time. The closed‐loop stability is rigorously proven using Lyapunov theory. The proposed controller and observer are validated through a high‐fidelity spacecraft attitude control simulator, with results demonstrating superior performance and robustness compared to state‐of‐the‐art methods.