LUNISAT ORBIT MAINTENANCE AND LOW-THRUST MANEUVERS

Lunisat represents a next-generation microsatellite aimed at orbiting the Moon, and equipped with dispensers for the release of nanosatellites. This research is focused on orbital dynamics of the main microsatellite, and specifically addresses orbit maintenance and low-thrust maneuvers. Nonsingular equinoctial orbit elements are employed for orbit propagations, in conjunction with numerical averaging. This is a powerful technique for the numerical integration of the mean elements, and allows substantial computational improvements. Due to the masconian character of the lunar mass distribution, low altitude, near-circular lunar orbits are affected by a considerable number of harmonics of the Moon gravitational field. Thus, in the dynamical modeling a large number of harmonics are included, as well as the Earth and Sun perturbing influence as third bodies. Low altitude lunar satellites turn out to impact the Moon surface after a few weeks or months. In case of unsatisfactory lifetime, two simple orbit maintenance strategies are evaluated, together with the related propellant budget. Moreover, minimum-time low-thrust transfers for reducing the orbit altitude are investigated, either for nanosatellite release or for the conclusive phase of the Lunisat mission, which finally terminates with the impact on the Moon surface.