Important Considerations for Lunar Soil Simulants

Abstract

Lunar samples are not readily available for In-Situ Resource Utilization (ISRU) studies, necessary for preparations for a return to the Moon with landers, robots, and astronauts. Lunar soil simulants have been produced as substitutes for the real thing; BUT how good are they? JSC-1 and 1A were produced only to approximate the geotechnical properties of lunar soil, with its natural glassy component. This welded volcanic tuff is neither highlands- or maria-like in composition, being at best only half-way between in FeO content, and is only typical of a 2-3 % by area of the lunar surface. Indeed, JSC-1A has the wrong mineralogy [e.g., it has no ilmenite, yet has been used for hydrogen reduction of ilmenite, as well as for as feedstock for several other oxygen-production and ISRU processes.] And largely because of the blessings of NASA in the production of JSC-1, similar lunar simulants have been effectively duplicated by other nations (e.g., China, Japan). The Minnesota Lunar Simulant (MLS-1) was a reasonable hi-Ti mare soil simulant in composition, yet has been abandoned by NASA. When NASA MSFC got into the lunar simulant business, lunar soil experts repeatedly advised that “one size does not fit all”, meaning that each lunar soil simulant should only be used for very specific purposes. But the education of the engineering community has not been sufficient such that “high-quality studies are still being performed on the wrong simulants”. Also, lunar soil simulants are being produced supposedly with certain properties, which are in reality definitely not proper lunar simulants For example, simulants with nanophase metallic Fe are far from being similar to lunar soils; JSC-1A made with nanophase Fe has an order of magnitude more nanophase magnetite than metallic Fe, so what good is this product? Indeed, most people questioned are not really sure what or why they are trying to simulate nanophase Fe: magnetic susceptibility? Dielectric properties? Toxicity? A review of the unique properties of lunar samples required for studies in engineering and applied sciences (exclusive of biology) is conducted here. This naturally leads to an evaluation of current simulants and the requirements for simulants that must accurately reflect all properties of lunar soils. If not possible to synthesize suitable materials, it may be necessary to use the soils from the Apollo lunar sample collection.