NON-LINEAR PULSED GUIDANCE FOR ASTEROID CLOSE-PROXIMITY OPERATIONS

Autonomous close proximity operations (hovering, landing, Touch-And-Go maneuvers) in the low-gravity environment exhibited by asteroids is particularly challenging. A set of non-linear, pulsed guidance algorithms have been developed for spacecraft that are required to execute autonomous closed-loop guidance to a designated point on the asteroid environment. The guidance algorithms development rely on the definition of a Lyapunov-like descent function that has the property of being negative definite along the trajectory defining the motion of the spacecraft. More specifically, we have defined a) a quickest descent pulsed guidance, where at each point along the guided trajectory, one selects a combination of thrusters (on-off mode) that makes the derivative of the descent function as negative as possible and b) a least effort pulsed guidance where one selects the combination of thrusters that ensure the minimum number of pulsing along the guided trajectory. The derived pulsed guidance laws require information about the current state and the target state and generates a class of feedback trajectories that have a built-in proof of global stability. Guidance simulations in asteroid dynamical environment modeling the spacecraft motion around 433 Eros show that the guidance approach is suitable for autonomously targeting positions and velocity during close-proximity operations.