Mixed-model gravity representations for small celestial bodies using mascons and spherical harmonics

When designing and navigating space missions to asteroids and comets, mascon models can be attractive because they are simple to compute, implement, and parallelize. However, to achieve a reasonable surface accuracy, mascon models typically require too many elements to compete with other models. Here, mascon models are revisited, with the intent to minimize the number of elements, optimize the placement of the elements, and modify the base model of elements in order to improve computational efficiency, while enabling their use at low altitudes. The addition of small radius spherical harmonics elements, buried within a mascon model, is shown to offer model evaluation speedups and reduced memory footprints at little or no accuracy cost over homogeneous mascon models. In addition, such hybrid models are shown to provide runtimes over an order of magnitude faster than low-resolution polyhedral models for equivalent accuracy. This hybrid gravity model approach is designed for use at small celestial bodies having any regular or irregular shape; a demonstrative and detailed analysis is presented for the case of 433 Eros.

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