Smooth second order sliding mode control for reusable launch vehicle in reentry phase

This paper describes the design of nonlinear robust controller for reusable launch vehicle which is nonlinear, multivariable, strong coupling, and includes uncertain parameters and external disturbance. Firstly, the feasible guidance strategy is introduced to obtain the desired guidance commands. Then, the attitude control model is converted to integral chain system. Next, the continuous finite time convergence second order sliding mode controller is designed for the normal system. In order to improve the robustness, the nonlinear disturbance observer is proposed to suppress the uncertainties and external disturbances. Furthermore, the synthesis of controller and disturbance observer is used to achieve the attitude tracking for reusable in reentry phase. Finally, the six-degree-of-freedom (6-DOF) simulation results verify the effectiveness of the control strategy.