Assessment of Geo-mechanical properties of lunar simulants
Abstract
Abstract
Sophisticated manned and unmanned lunar missions are being developed by international collaborations of the USA, Canada, EU, India, China, Japan etc. for a long-term human presence on the moon. These lunar missions require prototype testing of rovers and other hardware on the earth to successfully interact with the lunar surface. This laboratory testing requires various simulant (terrestrial soil mimicking one or more lunar regolith characteristics) testbeds. Actual lunar soil is too pristine and scarce to be used for destructive testing. Hence, simulants have been developed by research institutions, space research organizations, or commercial manufacturers to cater to a wide range of applications. The geotechnical engineering applications of simulants are of paramount importance for the testing of in-situ hardware prototypes and lunar rovers. Although there has been significant development of different forms of simulants, in general, the lunar simulants developed in the last few years are under characterized or uncharacterized from a geotechnical engineering perspective. This research study aims to reduce the gap with the effective geotechnical characterization of seven lunar simulants interpreted with up-to-date soil mechanics theory. Additionally, benchmark terrestrial soils and a Martian simulant (MMS-1) were also tested and a comparison between the lunar simulants and these soils was done to evaluate the possible use of abundantly available soils, as a potential feedstock or raw material to develop lunar simulants.
The selected lunar simulants include a mix of lunar mare and lunar highland simulants (CAS-1, EAC-1, OPRL2N, LMS-1, LHS-1, OPRH2N, OB-1A) and they were tested for basic geotechnical properties, stress-strain relationships, and dynamic properties. Resonant column testing of lunar simulants is not known to have been performed before. The experimental regime consisted of tests at relatively low pressures, different relative densities, and with 100% dry conditions. The lunar simulants are finer compared to terrestrial soils. Several properties (PSD, shear strength, Cc) of tested lunar simulants fall within the range of the values of lunar regolith. The mineralogy, particle size distribution, and particle shapes of the materials were found to have a considerable influence on the geotechnical properties of the lunar simulants. The general trends of stress-strain relationships and dynamic properties follow those of terrestrial soils. However, the unique mineralogical components of basalt, anorthosites, plagioclase feldspar etc. in the lunar simulants compared to terrestrial soils tend to give higher values of several parameters (peak friction angle, shear wave velocity, etc.) compared to terrestrial soils. The results when viewed alongside the data of terrestrial soils suggest that a judicious choice of benchmark terrestrial soils might allow the development of lunar simulants with an enhanced fidelity to lunar regolith. In addition, the crushed nature of many of these lunar simulants needs to be investigated in further detail given how significantly the geotechnical properties seem to be influenced by this aspect of the simulants.