An image based approach to recovering the gravitational field of asteroids

Abstract

NASA's DAWN spacecraft is on a mission to recover the gravity and structure of the asteroids Vesta and Ceres. Current approaches for developing a gravitational map of a celestial body rely upon use of the Deep Space Network of radio telescopes in conjunction with camera measurements for highly accurate tracking of orbiting bodies. Unfortunately, large occluding bodies greatly effect the accuracy of the radio tracking system, significantly reducing the time available for scientific experiments. This paper presents a Structure from Motion based approach that recovers the gravitational map as well as the asteroid's structure in a two step optimization process. The approach solves for a set of spherical harmonic coefficients that define the gravitational potential given a spacecrafts relative position to the asteroid without the need for radiometric tracking from Earth based satellites. The resulting procedure can then be used to augment gravitational science during periods of large noise or damaged equipment. Results are shown using the Vesta dataset from the DAWN mission and are compared with the recently published results from the DAWN gravitational team.