Control of hovering spacecraft near small bodies: Application to Asteroid 25143 Itokawa

The small gravitational forces associated with a minor celestial body, such as an asteroid or comet nucleus, allow visiting spacecraft to implement active control strategies to improve maneuverability about the body. One form of active control is hovering, where the nominal accelerations on the spacecraft are canceled by a nearly continuous control thrust. We investigate the stability of realistic hovering control laws in the body-fixed and inertial reference frames. Two implementations of the body-fixed hovering thrust solution are numerically tested and compared with an analytical stability result presented in the previous literature. The perturbation equations for inertial frame hovering are presented and numerically simulated to identify regions of stability. We find that body-fixed hovering can be made stable inside a region roughly approximated by the body's resonance radius and inertial frame hovering is stable in all regions outside the resonance radius. A case study of hovering above Asteroid (25143) Itokawa, target of the Hayabusa mission, is also presented.