A Lunar L2 Navigation, Communication, and Gravity Mission

Abstract

Most high-priority landing sites on the lunar surface do not have direct communication with the Earth. A mission was designed which would involve two spacecraft, a halo orbiter at Earth-Moon L2 and a microsatellite in a low lunar orbit. The two spacecraft would travel together on a ballistic lunar transfer and arrive on the Earth-Moon L2 halo orbit. No insertion maneuver would be required, which would allow the spacecraft to be about 25% to 33% more massive than if a conventional transfer were used. After that, the microsatellite would only require a small maneuver to depart from the halo orbit and descend to where it can be inserted into a low lunar orbit. The spacecraft would relay communications from the lunar far side and south pole to Earth. They could also be used to track other lunar missions, or broadcast navigation signals. To lower the operations cost, a new method of autonomous orbit determination called “Liaison Navigation” would be used. To perform Liaison Navigation, spacecraft in libration point orbits use scalar satellite-to-satellite tracking data, such as crosslink range, to perform orbit determination without Earth-based tracking. Due to the characteristics of libration orbits, relative tracking between two spacecraft can be used to estimate the relative and absolute positions and velocities of both spacecraft simultaneously. The tracking data from the two spacecraft could also be used to estimate the lunar far side gravity field.