Searching for Subsurface Lunar Water Ice using a Nuclear-Powered Rover

Abstract

The Vision for Space Exploration has identified the Earth’s moon as a future destination for human explorers as a stepping‐stone for further manned deep space exploration. The feasibility of building and maintaining a human presence on the moon could be directly related to whether in‐situ resources, especially water ice, can be obtained and utilized by astronauts. With the recent success of both Mars Exploration Rovers (MERs), it is clear that a lunar rover could be a desirable platform with which to search for evidence of lunar water prior to the arrival of astronauts. However, since surface water can only exist in permanently shadowed areas of the moon (i.e., deep craters near the poles), conventionally powered rovers would not be practical for exploring these areas for extended periods. Thus, a study was performed to assess the feasibility of a lunar rover mission enabled by small radioisotope power systems (RPS), i.e., systems that use single GPHSs. Small RPSs, the feasibility of which has been looked at by the Department of Energy, would be capable of providing sufficient electrical and thermal power to allow scientific measurements and operations of a small rover on the floor of dark lunar craters. A conceptual study was completed that considered the science instruments that could be accommodated on a MER‐type rover using RPS power. To investigate the subsurface characteristics of the crater floor, a pulsed gamma ray/neutron spectrometer and a ground‐penetrating radar would be used. Also, a drill would provide core samples from a depth of 1 meter. A rover architecture consistent with MER capabilities included a mast with panoramic cameras and navigation cameras as well as an instrument deployment device (IDD) that allowed direct contact between the instrument head and surface materials to be measured. Because the crater floor is eternally dark, artificial illumination must be used for both landing and roving operations. The rover design included of dual headlights that would be operated during visual imaging observations. During the landing approach, the lander would use a laser imaging technique to image the approaching surface and react to that image to avoid hazards. The baseline rover concept used four GPHS power sources for a total of about 50 We in conjunction with a 25 A hr battery to supply power during peak loads. A detailed analysis of energy usage for various operational scenarios (e.g. roving, science instrument operations, and telecommunications) was completed using an elaborate power simulation tool. The results show that very demanding activities are possible on a daily basis while maintaining the battery charging.