Fixed-time sliding mode controller design for hypersonic vehicles

Purpose Multi-source disturbances present a major challenge to the control systems of hypersonic vehicles, making their rapid estimation and compensation imperative for performance assurance. In response, this study aims to present a novel fixed-time robust control strategy grounded in sliding mode theory. Design/methodology/approach Guided by an analysis of the vehicle model’s dynamics, a control-oriented framework comprising multiple decoupled subsystems is developed. Then, a fixed-time control structure based on filters, observers and controllers is constructed. In this structure, the filters are used to soften the reference signals, while the observers are used to estimate the lumped disturbances arising from the flexible state variables, parameter perturbations, actuator faults and other contributing factors. Finally, the controllers incorporating disturbance compensation are used to drive the velocity and altitude tracking of reference values. Furthermore, the stability of the closed-loop system is analyzed based on Lyapunov theory. Findings A stable control system with fixed-time convergence has been developed for hypersonic vehicles, demonstrating strong robustness against multi-source disturbances and satisfactory velocity and altitude tracking performance. Compared to the robust control system based on disturbance observer, the developed control system has obvious advantages in the fuel equivalence ratio. Originality/value A key advancement presented in this study is a fixed-time control strategy that synergistically integrates filtering, extended state observers and sliding mode control. Such a synthesized strategy opens up new possibilities for maintaining robust flight control of hypersonic vehicles amidst challenging and rapidly changing operational environments.