Entry control using sliding modes and state observer synthesis for reusable launch vehicle

A robust method for the implementation of entry control for reusable launch vehicle is presented. Given any feasible guidance commands and the bounds of uncertainties and disturbances, the method can generate control commands to each individual effectors including aerosurfaces and reaction control system (RCS) jets, featuring multiple-time-scale continuous sliding mode control, which meets the requirement with accurate, robust, and decoupled tracking of both the commanded aerodynamic angle and angular rate profiles in the presence of modeling uncertainties and external disturbances. Afterwards, utilizing sliding mode state observer via Lyapunov theorem with adaptive gain to achieve the estimation without high amplitude switching for more convenient implementation, the method enables the entry control system to reduce the control chattering significantly and enhance applicability remarkably. To compare with the pure sliding mode control, entry control law design and simulations for a reusable launch vehicle model with modeling uncertainties, wind gust, measuring noises are presented to demonstrate the capacity and reliability of this proposed method.