Fixed-Time Preassigned Performance Attitude Control for Hypersonic Vehicles With Lumped Disturbance and Actuator Saturation

This article proposes a terminal-sliding-mode disturbance observer (TSMDO)-based adaptive control strategy that guarantees fixed-time preassigned performance with small overshoot for hypersonic vehicle attitude tracking in the presence of actuator saturation and lumped disturbances. The approach combines a TSMDO for rapid disturbance estimation, an inner-loop controller that enforces designer-specified transient envelopes, and an adaptive antisaturation outer loop that compensates actuator limits. Rigorous Lyapunov analysis proves global fast finite-time convergence of the observer and closed-loop boundedness with explicit settling-time bounds. Numerical simulations demonstrate that the proposed method achieves substantially smaller steady-state errors and overshoots and faster convergence than benchmark controllers.