Orbital launch window for Moon-to-Earth trajectories

To support China's manned lunar landing mission requirements of high-latitude landing and anytime return, i.e., the capability of safely returning the crew exploration vehicle at any time from any lunar parking orbit, an orbital launch window for Moon-to-Earth return has been established. The launch window is a certain time interval during which the transearth injection may occur and result in a safe lunar return to the specified landing site on the surface of the Earth. Using the patched conic technique, an analytical design method for determining the transearth trajectories is developed with a finite sphere of influence model. Orbital launch window has been established to study the mission sensitivities to transearth trip time and energy requirement, and also to provide the basis for the preparation of an orbital launch timetable compatible with lunar missions and reentry conditions requirements. The results presented here are limited to a single impulsive maneuver. The difference between the results of the analytical model and high-fidelity model is compared. This difference is relatively small and can be easily eliminated by a simple differential correction procedure. The solution can also be used to serve as an initial estimate for future optimization procedures.