Mars entry guidance for mid-lift-to-drag ratio vehicle with control constraints

Abstract With the control constraints taken into account, the Mars entry guidance problem of the entry vehicle with a mid-lift-to-drag ratio is investigated in this paper. A dual-loop guidance framework is proposed that the bank angle command is generated in the outer loop and tracked in the inner loop. An innovative energy-based mathematical model is firstly derived. Then, the switching mode of longitudinal guidance and lateral guidance is used in the outer loop, which is based on the velocity. The former is a time-varying sliding mode anti-saturation guidance law considering the amplitude constraint of bank angle, and the latter is obtained by feedback linearization of the heading angle. Hereafter, the heading angle error threshold, which is linear with velocity, is given, and the logic of the bank angle sign is designed to control the lateral motion. Furthermore, the cascade-saturation PD controller is used in the inner loop to meet the angular rate and angular acceleration constraints of bank angle, and the non-overshoot tracking can be realized by reasonably selecting the parameters to satisfy the bank angle amplitude constraint. Numerical examples are presented to demonstrate that the guidance law developed in this paper has a clear physical meaning, a small deviation from the expected state on the basis of meeting the terminal energy requirements, and strong robustness, which is convenient for engineering application.