A novel global sliding mode control strategy for attitude control of reusable launch vehicles in the reentry phase

The attitude control for reusable launch vehicles (RLV) is responsible for the robust operation to avoid the major deterioration from uncertainties of parameters and external disturbances in the reentry phase. Targeting for these practical issues with the study of the feedback-linearized RLV rotational equations of motion, two global sliding mode control (SMC) strategies are proposed with modified PID-type sliding surfaces. Firstly, this paper begins with a SMC method, which is applied with a modified fixed-gain PID-type sliding surface so that it achieves a global sliding mode and guarantees the global robustness of the controlled system. Furthermore, in order to rationally deal with the contradictory relationship between faster response and smaller overshoot, an improved SMC method is derived with modified variable-gain PID-type sliding surface. Finally, the effectiveness of the proposed strategies is verified by the theoretical analysis and simulation results are presented for the attitude control problem of X-33 RLV in the reentry phase.