Conceptual Design of a Communications Relay Satellite for a Lunar Sample Return Mission

NASA is soliciting a new opportunity for robotic exploration of the lunar surface. Proposals are being requested for a lunar sample return mission from the South Pole-Aitken Basin. The basin is of interest because it may contain some of the oldest accessible rocks in the solar system. A mission that will land a spacecraft in the basin, collect a rock sample, and return the sample to Earth is under study. Because the Aitken Basin is on the far side of the Moon, the lander will require a communications relay satellite (CRS) to maintain contact with the Earth during its surface operation. Design of the CRS's orbit is therefore critical. This paper describes a mission design which includes potential transfer and mission orbits, required changes in velocity, orbital parameters, and mission dates. Several different low lunar polar orbits are examined to compare their availability to the lander versus the distance over which they must communicate. In addition, polar orbits are compared to a halo orbit about the Earth-Moon L2 point, which would permit continuous communication at a cost of increased fuel requirements and longer transmission distances. This paper also examines some general parameters of the communication system design for the mission under study. This mission could be the first step in a period of renewed lunar exploration and eventual human landings.