SURFACE PROXIMITY GRAVITATIONAL FIELD ANALYSIS OF THE ASTEROID 433 EROS

Regular spherical harmonics representation of the gravitational field of an object is not accurate within a circumscribing sphere of the body of mass, called the Brillouin sphere. This is a major issue in modeling the gravitational field of asteroids and comets with significant non-spherical shapes, as certain regions in the close proximity of the surface of such objects fall well within the Brillouin sphere. We implement a so called "interior" spherical harmonics expansion to model the surface proximity gravitational field of the asteroid 433 Eros. This model is shown to be able to accurately represent the gravitational field of an object in the close proximity of its surface. However, estimating the coefficients of such model is challenging. This work studies the feasibility of estimating the coefficients of an interior gravity field via orbit determination. The paper presents the expected level of the estimation precision and characterizes the effect of the size of the field radius on the estimation performance.