FAS-Based Attitude Tracking Control with Prespecified-Time Sliding Mode for Rigid Spacecraft

This paper proposes a novel attitude tracking control strategy for rigid-body spacecraft, which innovatively integrates the fully actuated system (FAS) approach, error-dependent gain observation, and nonsingular terminal sliding mode techniques with practical prespecified-time convergence properties. Initially, within the FAS framework, the spacecraft attitude tracking error dynamics are reformulated, transforming the original nonlinear and coupled system into a simplified pseudo-linear model, thereby facilitating controller design. To address inertia uncertainties and external disturbances, an extended state observer (ESO) with error-dependent gains is developed. This observer features gain magnitudes that vary with error size, potentially improving convergence under large-error conditions while maintaining precision during small-error regimes. Building upon this framework, a nonsingular terminal sliding mode control strategy is proposed, effectively resolving the singularity issues inherent in conventional terminal sliding mode controllers. Theoretical analysis demonstrates the practical prespecified-time stability of the sliding mode dynamics, with convergence rates being flexibly adjustable through parameter selection, while the overall closed-loop system achieves practical bounded stability. Numerical simulations verify that the presented control method exhibits superior tracking performance, disturbance rejection capability, and control smoothness.