A lunar soil classification system for space resource utilization

Abstract

Lunar soils will be an important feedstock for multiple space resource utilization applications including preparing sites for infrastructure, extracting metals, and manufacturing products. On Earth, soil classification systems provide a logical way to categorize different soils and are applied in soil surveys for development projects. However, these systems and others used for soil science are not appropriate to translate to the Moon because of fundamental differences in soil properties, especially clay and moisture content. Here, I propose a lunar soil classification system based on practical space resource use cases. The system includes bulk elemental composition and particle size distribution as its main variables to form 9 soil groups and can be extended with tags that represent additional properties like glass content or other mineral/elemental components. The system is designed to be simple to apply: classification criteria can be measured with in-situ instruments as well as remote sensing. Proof of concept maps are developed globally, and the Apollo 17 sample collection is used as ground truth for orbital-derived classifications over the Taurus-Littrow valley. The different soil groups are expected to perform better or poorer for specific use cases. For example, coarse grained soils will have higher flowability and higher compressibility that are important for excavation and conveyance. Mare composition soils will have lower melting points and are enriched in FeO and TiO2 as sources of iron and titanium. Adopting a simple, standardized classification scheme will improve communication between different players for assessing resources, developing and testing hardware, and eventually selling raw and refined lunar materials.