Surface Gravity Fields for Asteroids and Comets

Abstract

The characteristics of the interior gravity field are derived, summarized, and evaluated near the surface of an asteroid for the purpose of small body proximity operations. In order to characterize the gravity field of a body, the exterior gravity field is widely in use. However, the exterior gravity field expression breaks down when computing the potential and its gradients within the Brillouin sphere, meaning that spacecraft dynamics cannot be modeled accurately in close proximity to the body's surface. On the other hand, the convergence of the potential and its gradients are guaranteed within the Brillouin sphere of the interior potential, a feature that enables the gravity field modeling near the surface of a body. After derivation, a technique for converting an exterior gravity field or a polyhedral gravity field into an interior gravity field is outlined, a method to numerically approximate the interior spherical harmonic coefficients for a body with a homogeneous density distribution is introduced, and comparisons between the spacecraft dynamics propagated in the polyhedral gravity field and the interior gravity field are made. The results show that the interior gravity field models the gravity field environment well in close proximity to the body's surface.