Fuzzy Intermediate Variable Observer for Spacecraft Fault-Tolerant Attitude Control Against Complex Actuator Faults

Abstract

This article investigates the attitude fault-tolerant control (FTC) problem for rigid spacecraft subject to actuator faults and input saturation. A Takagi–Sugeno (T–S) fuzzy representation is constructed within a prescribed compact angular-velocity region, which enables systematic observer and controller synthesis for the nonlinear attitude dynamics. To overcome the limitations of overly simplistic static fault models in representing diverse engineering failures, a generalized polynomial function approximation strategy is introduced. This formulation encompasses a wider spectrum of fault profiles and improves fault-reconstruction fidelity. Building upon this, an intermediate variable-based fuzzy fault observer is developed. This design relaxes the restrictive strictly positive real (SPR) condition commonly required in classical observer designs, providing greater flexibility in gain selection. Leveraging the observer’s estimates, an adaptive FTC scheme is synthesized to compensate for actuator faults while respecting input saturation. The region-dependent uniformly ultimately bounded (UUB) of the closed-loop system is rigorously established via Lyapunov stability theory. Finally, simulations on a spacecraft benchmark model verify the effectiveness of the proposed fuzzy-based FTC strategy.