Attitude control via continuous sliding modes for RLV initial reentry

A robust attitude control method for the implementation of initial reentry for reusable launch vehicle (RLV) was proposed. A robust attitude control method for the implementation of initial reentry for reusable launch vehicle (RLV) was proposed. Giving any feasible attitude commands and the bounds of uncertainties and disturbances, the method could generate firing commands, featuring multiple-time-scale continuous sliding mode control, which met the requirement with accurate, robust, and excellent tracking of both the commanded attitude and angular rate profiles in the presence of modeling uncertainties and external disturbances. Afterwards, by utilizing sliding mode state observer via Lyapunov theorem with adaptive gains to achieve the estimation without high amplitude switching, the method enabled the attitude control system to reduce the control chattering significantly. Hence the switching numbers of RCS jets and fuel cost were reduced, and the applicability was enhanced remarkably. Initial reentry attitude control law design and simulations based on various methods for a reusable launch vehicle model with modeling uncertainties and external disturbances were proposed to demonstrate the capacity and reliability of this proposed method.