Finite-time stabilization-based trajectory tracking under disturbances for entry vehicles

For the entry guidance based on a nominal trajectory, trajectory tracking is an important part, by which the nominal trajectory is followed and several constraints can be observed. In order to reject disturbance and achieve good tracking performance in trajectory tracking, a finite-time trajectory tracking method is presented. Utilizing the differential flatness theory, a linear tracking error system can be derived from the nonlinear point-mass dynamics of an entry vehicle. A disturbance compensator is designed based on linear extended state observers. The compensator observes the disturbances in the tracking error system, and then compensates the disturbances in the following tracking law. To track the nominal trajectory, a finite-time tracking law with disturbance compensation is derived using a linear finite-time stabilization method. This method ensures that the tracking error is finite-time stable and the settling time of the tracking error is within a specified range. Numerical simulation demonstrates the proposed trajectory tracking law. Under various disturbances, good tracking performance is achieved and all constraints are observed. The proposed trajectory tracking method is effective.