A global sliding mode control with pre-determined convergence time design for reusable launch vehicles in reentry phase

This paper addresses the robust attitude control problem of reusable launch vehicles (RLV) with parametric uncertainties and external disturbances in reentry phase. Based on the feedback-linearized RLV rotational equations of motion, a global sliding mode control (SMC) strategy with a priori stated convergence time is first proposed, which ensures the global robustness of the controlled system. As compared with the existing sliding mode attitude control method, an improved system performance can be obtained in terms of convergence time and robustness. Then, the steady-state error problem caused by the continuous approximation techniques such as the boundary layer method (which is used to alleviate the control chattering) is considered. A disturbance observer (DO) based global SMC strategy is presented to improve the control accuracy. Finally, the validity of the proposed strategies is verified by both theoretical analysis and simulation results for the attitude control problem of X-33 RLV in reentry phase.