LAUSR

In this paper, an improved extended state observer (ESO) based on sigmoid function and a finite-time convergence attitude controller are designed for reusable launch vehicle (RLV) in the re-entry phase. First, a control-oriented model (COM) of the RLV is established. According to the singular perturbation theory, the RLV control system is divided into an outer-loop and inner-loop subsystems. Second, a sigmoid function ESO (SESO) is proposed to estimate the model uncertainties and external disturbance caused by the large attitude maneuver and complicated external environment during the RLV re-entry phase. The continuous differentiable sigmoid function has the significant ability in noise suppression. By selecting the proper Lyapunov function, the stability of the SESO is proved. Then, based on the sliding mode control (SMC) theory, an improved multivariable super-twisting high-order sliding mode controller is designed. The finite-time convergence for the whole system is proven by the Lyapunov function technology. Finally, a 6-degree-of-freedom (6-DOF) RLV model is utilized to simulate to verify the effectiveness and robustness of the proposed control scheme.