Method for Transferring a Spacecraft from Geosynchronous Transfer Orbit to Lunar Orbit

The invention presents a trajectory design whereby a spacecraft can be launched as a secondary payload into a Geosynchronous Transfer Orbit (GTO) and through a series of maneuvers to reach lunar orbit. The trajectory analysis begins by identifying acceptable ranges of lunar orbit altitude and inclination values. The unique features of this method includes the use of either a leading or trailing edge lunar flyby to achieve an orbit inclination in the lunar orbit plane from a GTO launched at any time of day. This technique is applicable to secondary spacecraft that share a ride to space resulting in a substantially reduced cost, and with no control of the launch conditions. Major advantages of this design include the relatively short (maximum) lunar transfer duration (<3 months, less than half of that required for a Sun-Earth weak-stability boundary transfer), simplicity and consistency of design (again compared to a Sun-Earth weak stability boundary transfer). This novel innovation from Ames Research Center allows spacecraft to share rides with larger spacecraft which are headed to Geosynchronous Earth Orbit (GEO). The secondary spacecraft is dropped off Geosynchronous Transfer Orbit (GTO) at any time during the day or year and will subsequently enter lunar orbit, with no constraint on the lunar orbit inclination. The secondary spacecraft can be relatively small, riding as a secondary payload with a larger primary spacecraft. The secondary spacecraft is intended to be controllable (i.e., maneuverable).