Site Selection and Instrument Considerations for Micro-Rover Exploration of Lunar Polar Ice: The MoonRanger Mission

Abstract:

Lunar ice holds the prospect of water for drinking, growing food, generating oxygen, and producing propellants. Successful ice utilization relies heavily on yet-undetermined knowledge of accessible concentrations at useful scales. This can only be achieved by surface missions. Some explorations will be undertaken by MER-scale rovers (e.g. VIPER in 2023), but a capable new class of micro-rovers may provide complementary coverage over multiple landing sites. Micro-rovers present, however, unique considerations of siting, instrumentation, and operations for high-return missions.

Small rovers can cost less, weigh less, and fly more frequently; however, they also have lower energy storage and more limited slope capability for probing into darkness and reaching stable ice. They likely offer less range from their landers and no direct-to-Earth communication to provide human oversight. Additionally, the small landers that deliver small rovers may provide less precision in landing site targeting and less tolerance of landing slopes and hazards. They require full sunlight and line of sight to Earth. We present a methodology and results for search and site selection based on these considerations. Favorable sites are found to be a minor subset of those acceptable for VIPER-scale roving. Several most-favorable sites are profiled and compared.

Micro-rovers require effective low-mass, low-power instruments for ice measurement. For these reasons, instruments such as the Neutron Spectrometry System (NSS) are most relevant. The NSS consists of two helium-3 gas proportional counter tubes that are sensitive to thermal and epithermal neutrons. Relative fluxes of the two correlate with bulk hydrogen, hence water, in the upper meter of regolith. Micro-rover advantages include instrument mounting close to the surface and minimal componentry over and under the instrument that would otherwise affect readings. The result is an estimation of water content along the robot’s 1 km route. Rover navigation accurately localizes the data in lunar coordinates for interpretation relative to orbital maps. Beyond principles and methodology, the presentation is illustrated with specifics pertaining to the MoonRanger 2022 polar micro-rover ice-seeking NASA CLPS mission.