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

This paper 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 anti-saturation 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.