Lunar Geotechnical Properties – In Situ Evaluation for Human Exploration Activities

Paper number

IAC-08.A3.2.INT4

Author

Dr. Jeffrey Plescia, Johns Hopkins University Applied Physics Laboratory, United States

Year

2008

Abstract

The surface of the Moon is covered with a layer of fragmental debris referred to as the regolith.  Unlike terrestrial soils, the lunar regolith is formed primarily by the process of impact-induced mechanical degradation with additional modification due to space weathering.  Chemical and mineralogic alterations also occur due to micrometeorite impact events.  While a general understanding of the geotechnical properties of the regolith were obtained from images and other data from the Apollo and US and Soviet robotic missions, a great deal remains uncertain because direct geotechnical experiments were few and analysis of returned material can not provide appropriate in situ parameters.

The Soviet Lunokhod mission carried a cone penetrometer and shear vane and hundreds of measurements were made.  The Apollo 15 and 16 missions carried a penetrometer that used by the astronauts (Self Recording Cone Penetrometer).  These experiments, supplemented by the active and passive seismic experiments, provide the basic in situ data.  Analysis of returned regolith samples provides information on the of the size-frequency distribution of the particles as well as their chemistry and mineralogy.  Trenching experiments were conducted on several missions to understand physical properties but only qualitative descriptions and pictures are available from which to make assessments.  Images of boot prints and wheel tracks and qualitative data from drilling provide additional insight.  A key problem however is that the in situ regolith has a significantly higher density than can be achieved by recompacting returned regolith samples, and the returned regolith cores lack any particles larger than ~2-3 cm.  Thus, Earth-based experiments conducted on the lunar regolith provide only bounds on the in situ properties.  However, it is the in situ properties that are relevant to surface operations such as mining, site preparation and ISRU.

A series of focused in situ experiments need to be conducted in a variety of terrain types (e.g., intercrater plains, crater rims, crater interiors, slopes) that can provide the necessary geotechnical properties.  In addition to mechanical parameters (e.g., density, cohesion, porosity), electrical properties also need to be determined.  The electrical properties are critical to understanding the potential for charging and charge transfer and for possible dust mobility.  Because measurements need to be made in different terrain types, mobility of the scale of km is required.  Longer distances ( 10s to 100s km) is not needed as the variability within any site is similar to the difference between sites.

Abstract document

IAC-08.A3.2.INT4.pdf

Manuscript document

IAC-08.A3.2.INT4.pdf (🔒 authorized access only).

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