Fixed-Time Planetary Landing Guidance With Unknown Disturbance and Thruster Constraint

This article proposes a planetary autonomous soft pinpoint adaptive fixed-time feedback landing guidance scheme based on the sliding mode control that is subject to thruster magnitude constraint, unknown control acceleration deviation, and disturbance without a priori knowledge. More specifically, a sliding surface is designed, and its gain is adjusted by the system state, increasing the convergence rate. Then, the adaptive law is proposed to compensate for the thruster magnitude constraint, unknown control acceleration deviation, and disturbance without a priori knowledge. On these bases, a thruster-magnitude-constrained feedback landing guidance is developed to ensure the fixed-time stability of the vehicle even in the presence of unknown control acceleration deviation and disturbance without priori knowledge. Furthermore, numerical simulations are performed to verify the feasibility and effectiveness of the proposed algorithms. Moreover, its near-fuel-optimal performance is illustrated by comparing it with offline fuel-optimal guidance.