Small Body Landings Using Autonomous Onboard Optical Navigation

Spacecraft landings on small bodies (asteroids and comets) present special challenges from a navigation perspective as the size of the bodies is relatively small, with the resultant accuracy requirement to target landing areas fairly tight. Because the accuracies obtainable from ground-based navigation processes may not be sufficient, onboard navigation techniques are needed. Recent developments in deep space navigation capability include a self-contained autonomous navigation system (used in flight on three missions) and a landmark tracking system (used experimentally on the Japanese Hayabusa mission). The merging of these two technologies forms a methodology to perform autonomous onboard navigation around small bodies. This article presents an overview of these systems, as well as the results from Monte Carlo studies to quantify the achievable landing accuracies by using these methods. Two cases are presented, a landing on a small asteroid and on a mid-size comet.