Trafficability and excavatability of icy lunar regolith simulants quantified using cone penetration

Abstract This article outlines the experimental equipment and techniques used to quan- tify how ice content and microstructure influences the geotechnical behavior of icy lunar regolith simulants, using cone penetration tests. It addresses two pri- mary research questions: (1) What is the relationship between ice microstructure and geotechnical behavior for icy lunar regolith simulants: and (2) How can this knowledge improve excavation and traffcability on the Moon. Unsintered, pressure sintered, ice-cemented, and vapor deposited icy regolith simulants were systematically studied at ice contents from 0.1 to 30 wt.% and bulk densities between 1.5 and 1.8 g cm−3 . Sample and probe temperatures were maintained at −180 ± 5◦ C and −160◦ C to −140◦ C, respectively. Traffcability was estimated using the cone index gradient (G, kPa mm −1 ). After correcting for lunar grav- ity ( G Lunar ) and experiemntal penetration depths to 30 mm, a vapor deposited sample with 6.68 wt.% ice was found to be 3.92 times stronger than a pressure sintered sample containing 8 wt.% ice, and 1.23 times stronger than the upper bound of in-situ G values measured in the Descartes Highlands during Apollo 16. The excavatability of pressure sintered samples, defined as the energy expended per unit mass of excavated water ( η exc , J/g), became more effcient with increas- ing ice content, falling from 0.35 J/g at 1 wt.% to 0.11 J/g at 30 wt.% (3.2 fold decrease), compared to an increase from 2.74 J/g at 1 wt.% to 143.03 J/g at 12 wt.% (52 fold increase) for ice-cemented samples. This work provides the first quantitative geotechnical measurements of vapor deposited icy simulants and demonstrates that ice-cemented simulants can exhibit strength several orders of magnitude higher than other morphologies under identical conditions. If icy lunar regolith occurs as loose granular, pressure sintered or as vapor deposited morphologies these results suggest that icy lunar regolith may be easier to exca- vate and traverse than previously thought, given widespread use of ice-cemented simulants, rocks and concrete analogues - questioning their continued use. Con- sequently, excavation of water-ice within PSRs may be more economically viable, whilst also offering improved traffcability compared to dry regolith.