Development and testing of the pneumatic lunar drill for the emplacement of the corner cube reflector on the Moon

Abstract

Lunar Laser Ranging provides a highly accurate measurement of the distance between ground stations on Earth and reflectors on the surface of the Moon. Since retroreflectors were initially placed during the Apollo missions, the ground stations improved the ranging accuracy by a factor of 200 and now the Apollo-era arrays on the Moon pose a significant limitation to the ranging accuracy. The new Lunar Laser Ranging Retroreflector (i.e. the Lunar Laser Ranging retroreflector for the 21st century or LLRRA-21) would provide extensive new information on the lunar interior, general relativity, and cosmology.During the day/night lunar cycle, when the thermal variation of the surface is approximately 300°C, the regolith will rise and fall by almost 500μm. Yet, it is estimated that the thermal variation 0.5m to 1m below the surface is less than much 1°C. Thus for the lunar emplacement to support 10s of microns ranging accuracy, the reflectors must be anchored to that thermally stable mass at 0.5m or greater depth.In this paper, we present a novel method of deploying LLRRA-21 with a Corner Cube Reflector (CCR) on the Moon. The emplacement approach uses a gas-powered drill consisting of a >50cm long, slim, hollow rod with a perforated anchor-cone at its lower end and the CCR mounted to the top. Gas supplied from a small tank is directed into and down the rod and out through the cone, lofting the soil out of the hole and allowing the rod to sink under its own weight to a depth of 0.5m.To determine the system performance, we conducted several tests in compacted JSC-1a lunar soil simulant and inside a vacuum chamber. In several tests, the rod successfully sunk under its own weight of 16N to a depth of 50cm in 4–6min.The pneumatic system is the game-changer for subsurface access. The extremely low mass and volume required to reach 50cm, along with very simple penetration method allow the CCR to remain in a variety of payload architectures.