Fixed-time extended state observer based non-singular fast terminal sliding mode control for a VTVL reusable launch vehicle

This paper is devoted to developing an extended state observer based non-singular fast terminal sliding mode control with fixed-time convergence for a vertical take-off and vertical landing (VTVL) reusable launch vehicle. The six-degree-of-freedom dynamic model of the VTVL is developed, and then the error tracking state equation is established as well. A novel fixed-time extended state observer is presented to estimate the error state and the total disturbances in the presence of nonlinear, couplings, uncertain parameters and external disturbances. Based on the estimation of the error state, a novel non-singular fast terminal sliding mode surface is designed, and the corresponding fixed-time controller is also designed via the estimation of the total disturbances and the proposed sliding mode surface. The stability analysis for the fixed-time extended state observer and the proposed controller are provided. Numerical simulation results are carried out to illustrate the effectiveness of the proposed control scheme.