Using Boulder Tracks as a Tool to Understand the Bearing Capacity of Permanently Shadowed Regions of the Moon

H M Sargeant,A Rogaski,S K Bell,S N Martinez,G D Tolometti,E C Czaplinski,E M Harrington,V T Bickel,B E Farrant,C I Honniball,D A Kring

doi:10.1029/2019je006157

Abstract

AbstractPermanently shadowed regions (PSRs) are abundant at the lunar poles. They experience no direct sunlight and reach temperatures as low as 30 K. PSRs are of interest as evidence suggests that some may contain water ice (H2O/OH‐), which could provide a record of the evolution of volatiles in the inner solar system. This water ice is also a critical resource for life‐support systems and rocket propellant. A better understanding of mechanical properties of PSR regolith, such as its bearing capacity, will help optimize the design of future exploration rovers and landers. Thirteen boulder tracks were identified on the edge of, or inside, south polar lunar PSR enhanced imagery and used to estimate the strength of the PSR regolith at latitudes of 70° to 76° in sites with maximum annual temperatures of 65 to 210 K. PSR boulder track features are similar to those observed in highland, mare, and pyroclastic regions of the Moon, implying similar properties of the regolith. Measured features were used to estimate bearing capacity for PSR regolith at depths of ~0.28 to 4.68 m. Estimated bearing capacity values suggest that these PSRs may be somewhat stronger than highland and mare regions at depths of 0.28 to 1.00 m. Bearing capacity in these PSRs is statistically the same as those in other regions of the Moon at depths of 1.00 to 2.00 m. The results of this study can be used to infer bearing capacity as one measure for the trafficability of lower‐latitude PSRs of the type measured here.

Highlights

The International Space Exploration Coordination Group (ISECG) Global Exploration Roadmap (2018) outlines the shared goals of the ISECG space agencies to expand human presence in low Earth orbit, to the Moon, and to Mars
This study investigates the geomechanical properties of regolith within and on the edge of south polar lunar permanently shadowed regions (PSRs) using rockfalls and their associated boulder tracks, both of which are abundant on the Moon (Bickel et al, 2019; Kumar et al, 2016)
We began with a qualitative study of PSR boulder tracks in Narrow Angle Camera (NAC) images

Summary

Introduction

The International Space Exploration Coordination Group (ISECG) Global Exploration Roadmap (2018) outlines the shared goals of the ISECG space agencies to expand human presence in low Earth orbit, to the Moon, and to Mars. Indirect evidence and more recent direct evidence support these findings using data from the Lunar Crater Observation and Sensing Satellite (LCROSS) lunar impactor and the Moon Mineralogy Mapper, respectively (Colaprete et al, 2010; Li et al, 2018). These volatiles have a range of important applications for in situ resource utilization (ISRU), such as life‐support systems and rocket propellant (e.g., Crawford, 2015). A future mission to a PSR would primarily address goals 4a, 4d, 7b, 7c, and 7d These objectives pertain to the presence and behavior of volatiles on the Moon and the qualities of the regolith in which they reside. A robotic or human mission taking in situ measurements will be required to confirm volatile concentrations in the PSRs and assess the utility of any deposits for ISRU

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Conclusion