Control of Hovering Spacecraft Using Altimetry

Abstract

The control of a spacecraft hovering over a uniformly rotating asteroid is analyzed. This work builds on the previous analysis of open-loop stability of hovering spacecraft trajectories (Scheeres 1999) by considering the effect of closed-loop control strategies on the overall stability of the hovering trajectory. We characterize the ability of one-dimensional altimetry measurements to stabilize the hovering spacecraft and find some ideal control methodologies that can yield stable hovering trajectories. These ideas are developed initially for the ideal case of a spherical asteroid and are then applied to a rotating ellipsoid and a rotating model of the asteroid Castalia (Hudson and Ostro 1994). The necessary modifications to the measurement and control laws in these more general gravitational cases are characterized.