Feasibility study of quasi-frozen, near-polar and extremely low-altitude lunar orbits

Design of long-duration lunar orbiter missions is challenging due to the Moon’s highly nonlinear gravity field and third-body perturbations induced by the Earth, Sun and other large bodies, on the orbiting spacecraft. The absence of a Lunar atmosphere, and hence the lack of orbital atmospheric drag, has encouraged mission designers to search for extremely low-altitude, stable, lunar orbits. In addition to the reduced amount of propellant required for station-keeping maneuvers, these orbits present great opportunities for unique scientific studies such as high resolution imaging and characterization of the polar ice deposits in deep craters. Mission planning for Lunar orbiters has historically suffered from inaccuracies, mainly due to the lack of an accurate Lunar gravity model, which resulted in severe deviations with respect to the spacecraft’s nominal orbit. In 2012, JPL’s Gravity Recovery and Interior Laboratory (GRAIL) mission mapped the Moon’s gravity field with much improved accuracy, allowing future missions to be designed and flown with far better models. In this paper, we perform a station-keeping feasibility study for quasi-frozen, near-polar and extremely low-altitude orbits around the Moon with a high-fidelity lunar gravity model and when perturbations due to the Earth and Sun are taken into consideration. We study the tradespace between mission duration and ΔV budget considering impulsive maneuvers applied once every 2, 6 or 10 orbits.