Test Results of Core Drilling in Simulated Ice-Bound Lunar Regolith for the Subsurface Access System of the Construction and Resource Utilization eXplorer (CRUX) Project

A major component of the Construction & Resource Utilization eXplorer (CRUX) project is a drill system capable of reaching to a depth of 2 m or more in lunar regolith that is hypothesized to contain frozen water. In an initial phase of the project, coring drills were tested in two lunar soil simulants, JSC-1 and FJS-1. Prior to drilling, the soil samples were mixed with 10 wt% water, compacted to 2 g/cc and refrigerated at –85 °C. These conditions aimed to simulate the realistic worst case for drilling conditions at the lunar cold traps. A rotary coring bit, with a 38mm outer diameter, and Polycrystalline Diamond Compact (PDC) cutters, was used to obtain 25 mm cores. Cuttings removal was done by an auger with flutes placed at a pitch angle of fifteen degrees. To prevent the ice in the simulants from thawing during the drilling process, and to reduce convective heat dissipation, all tests were conducted at an atmospheric pressure of 4 torr. The results of these tests showed that the simulated frozen lunar soil was as hard and strong as ice bound sandstone. The data showed a large improvement in the efficiency of drilling and cuttings removal when the rotational speed was increased. It was found that strategically placed channels in the drill bit, designed to convey cuttings from the bottom of the hole to the auger, drastically reduced chances of auger choking and made drilling more steady and predictable. Drilled cuttings were found to be composed of smaller particles than the original soil, indicating that the drill bit crushed the ice-soil mixture rather than detaching individual soil particles from the ice matrix. Drilling data was very similar when tests were conducted in JSC-1 and FJS-1 simulants. The results of these tests are being used to guide the development of the eventual CRUX drilling approach, in terms of both hardware and operational algorithms.