Evaluation of GNC Strategies for Descent on Solar System Bodies

Due to the increasing vehicle miniaturization and to the obvious requirements for autonomy, the descent on extra terrestrial bodies poses serious concerns with respect to the accuracy and the robustness of the guidance function. Closed loop guidance will depend on the accuracy on the knowledge of the kinematic state. The paper investigates the behavior of different estimators applied to two classes of trajectories, namely a gravity turn - introduced before as an open and then as a closed-loop configuration, and a path shaped descent. All investigations have been referred to quite simple sensors’ architectures, providing only altitude or slant-range measurements. Numerical simulations are provided for the atmosphere-less lunar case, as well as for the descents on Mars and Titan, where the air drag is present.