An extended high gain state and perturbation observer combined with feedback linearization was applied in drag tracking for Mars entry longitudinal guidance. The observer estimates the drag, the drag rate and the perturbation due to model uncertainty and disturbance for drag tracking. Mars entry simulation was performed to assess the performance of the adaptive guidance law. The results demonstrate that the proposed guidance law is robust to model error, and can recover the ideal performance of the feedback linearization control.

With the development of Mars exploration, NASA has been preparing plans for a crewed mission to Mars in the next few decades. One challenge associated with crewed missions to the Mars is the high ballistic-coefficient and human-class payloads. Because of the high ballistic-coefficient, the maximum limit value of the reference flight path angle is always the reference flight path angle meeting the downrange and altitude for the constant flight path angle algorithm. So this paper presents an improved algorithm which the terminal velocity is controlled by dynamic pressure controller, and the controller is used to modulate the velocity and altitude to meet final constraints. Simulations results of a Mars entry scenario illustrate that the improved algorithm achieves the final constraints within allowable tolerances.