ABSTRACT:

Returning to the Moon and going on to Mars will require the use of local resources to bring launch masses and costs to feasible levels. Attention is focused on mining regolith containing water ice and/or implanted hydrogen ions. Trenches, foundation pits, etc. also will be excavated in the regolith. Effective design of tools for these tasks requires a thorough understanding of regolith behavior. Therefore, in Phase I of a NASA Small Business Innovation Research grant, the forcepenetration behaviors of frozen, compacted samples of JSC-1 lunar and JSC-1 Mars regolith simulants were measured at water contents from zero to 22%. A 19 mm-diameter hemispherical indenter was forced into each sample while the required force, the resulting penetration, and the fragmented volume were measured. The results show that as water ice content increases to saturation, the penetration depth needed to cause failure decreases, the fragmented volume decreases, and the required force increases. The highest strength mix (approximately saturated) behaves like strong limestone or sandstone. This paper discusses the test procedures, differences between the test parameters and in situ conditions, and the results. Additional tests are underway for Phase II.

INTRODUCTION

Successful return to the Moon and continuance to Mars requires the sustained ability to use locally available resources at both locations. The hydrogen signal detected by the Lunar Prospector orbiter near both lunar poles [1] could be due either to water ice from cometary impacts, preserved within permanently shadowed regolith, or to solar wind protons implanted in regolith grains [2]; both resources would provide useful materials. Subsurface water has been detected less ambiguously on Mars [3], [4]. Other materials, such as the iron contained within the fine fraction of the lunar regolith, are of interest as well for infrastructure construction and maintenance. Even unimproved regolith may be used to shield humans and delicate electronics from radiation hazards. All raw materials must be excavated first, however. Indeed, reliable excavation capability is crucial for all lunar and martian surface activity. Foundations, roads, trenches, and pits will be necessary for any scenarios of surface activity, in addition to mining. The effective design of mechanical excavators relies on accurate characterization of the target material and on repeated field testing. The work reported here addresses the first requirement. The physical processes underlying fragmentation are too complex for reliable excavator performance prediction from basic principles, but centuries of rock and soil excavation research have provided useful semiempirical relationships that can be used for extraterrestrial operations if the input parameters are well-determined and their three-dimensional variation is known. The goal of this project was to measure material behavior indices as the first step of excavator design. The force-penetration test [5] was chosen to provide two basic material excavatability indices: specific penetration and specific energy.

Some previously measured or estimated properties of dry regolith are available [6], [7], but very little is known about the mechanical properties of iceregolith mixtures under in situ conditions.

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