Heliotropic orbits at oblate asteroids: balancing solar radiation pressure and J2 perturbations

The combined effect of significant solar radiation pressure and perturbations on spacecraft orbits is investigated using both singly and doubly-averaged disturbing potentials with the Lagrange Planetary Equations. The resulting dynamics are applied to a spacecraft around an oblate asteroid. Several Sun-frozen families of orbits are identified using the singly-averaged potential, including two new families of orbits and a previously-discovered equatorial heliotropic orbit family. Families of both stable and unstable Sun-frozen orbits are mapped and characterized in the singly-averaged case. In addition, a heliotropic constraint is implemented to locate heliotropic orbits out of the equatorial plane using a constrained, doubly-averaged potential. Dynamic bounds for these 3D heliotropic orbits are shown to have an inclination limit of approximately 46 degrees for oblate bodies, and this limit is independent of the value of and radiation parameters. The resulting heliotropic and related periodic families of orbits are good candidates to consider for low-altitude science orbits around small oblate bodies with low or near-180 degree obliquity like Bennu, the target for the OSIRIS-REx mission.