Adaptive Terminal Sliding Mode Control for Reentry Vehicle Based on Nonlinear Disturbance Observer

The movement of reentry vehicle is disturbed by the atmospheric environment and changes of aerodynamic parameters. In this paper, an adaptive terminal sliding mode control method based on nonlinear disturbance observers is proposed, which is used to control the attitude of the reentry vehicle. Firstly, the attitude control system is divided into an attitude angular control loop and an angular velocity control loop. Then, novel finite time convergence nonlinear disturbance observers are designed to estimate lumped disturbances. In the design of control law, the super-twist algorithm is used to make the proposed terminal sliding mode variables converge to the origin within a finite time and reduce the chattering of the controller. The estimated value of disturbance is considered in the controller to attenuate the effect of disturbances on the vehicle. Last, the algorithm proposed is applied to reentry vehicle and a good performance can be obtained. The effectiveness and superiority of the proposed algorithm is demonstrated by numerical simulations.