Adaptive sliding mode backstepping control for entry reusable launch vehicles based on nonlinear disturbance observer

Abstract

To attenuate the effects of parameter uncertainties and disturbances on the attitude control performance of entry reusable launch vehicles, an adaptive sliding mode backstepping controller based on nonlinear disturbance observer, here referred to as disturbance observer-based nonlinear controller, is proposed in this paper for the reusable launch vehicles nonlinear and fast time-varying system. The disturbance observer-based nonlinear controller comprises a nonlinear disturbance observer and an adaptive sliding mode backstepping controller with feedforward. First, multiple disturbances resulting from parameter uncertainties, unmodeled dynamics, and environmental disturbances are regarded as an “equivalent” disturbance and can be estimated by the nonlinear disturbance observer. Then, the estimated disturbance can be compensated by the feedforward, and the desired flight attitude can be tracked asymptotically by the adaptive sliding mode backstepping controller. Compared with other reusable launch vehicles flight controllers, the key contributions of the proposed control law are that the controller is independent from the moment of inertia and can achieve a fast convergence rate through an effective compensation for various disturbances. Simulation results of specific reusable launch vehicles demonstrate that the proposed disturbance observer-based nonlinear controller is feasible.