Spherical Harmonic Representation of the Martian Gravity Using a Short-Arc Technique

Abstract

Planetary gravity fields are determined primarily from Doppler tracking of orbiting spacecraft, which are typically in high-eccentricity orbits. Thus, the noncentral gravitational components perturb the orbit primarily in the vicinity of periapsis. To find a computationally efficient technique and to reduce the influence of unmodeled forces on the spacecraft, an analysis has been performed of the effectiveness of processing only data in the vicinity of periapsis using multiple short arcs. Although similar short-arc techniques have been utilized for Mascon studies, this analysis is based on a spherical harmonic representation of the gravity field of Mars. Mariner 9 data are processed for the study, using 1-, 2-, 3-, and 4-hr arcs and estimating gravity fields from fourth through seventh degree. The resulting gravity fields are intercompared and also compared with previously published results.