Novel smooth sliding mode attitude control design for constrained re-entry vehicle based on disturbance observer

This paper investigates the attitude tracking control system design for reusable launch vehicle (RLV) in re-entry phase with input constraint, model uncertainty and external disturbance. The novel control scheme is designed via combining the advantages of the robust property of sliding mode control (SMC), the compensation ability of disturbance observer (DOB) and the systematic design procedure of backstepping technique. By applying DOB technique to estimate the lumped uncertainty, there is no need to choose the switch gain larger than the bound of uncertainty. Through designing the exponential form sliding surface and smooth sliding mode controller, the chattering and discontinuous problem inherent in the traditional SMC is alleviated. An additional system is constructed to handle input constraint. Based on Lyapunov theory, the asymptotic stability of the closed-loop system is proven. At last, compared simulations are presented to verify the effectiveness of the proposed control approach.