Development of regolith simulants for lunar South Pole-Aitken Basin based on lunar soil and remote sensing data

Abstract:

The surface of the Moon is generally covered by regolith, which may cause severe problems in landing missions. Specifically, mechanical interactions between regolith and a lander are difficult to theoretically estimate, while their appropriate treatments are essential to minimize risks of landing missions. Ideally, real-scale engineering experiments should be done at an earlier stage of designing a landing system, which requires plenty amount of lunar materials. However, actual lunar soil samples are still too limited for such purpose, simulated regolith material (simulant) becomes essential. Many types of lunar soil simulants (e.g. JSC-1) have been developed most often based on Apollo samples and some are widely used as standard materials for general purposes. Our interests are in some minor-looking factors, which are not fully considered in previous works. For example, the existence of microvesicles can be important for engineering experiments for landers because they may largely affect the overall mechanical properties of regolith soils. We develop several new simulants for Apollo landing sites, specifically focused on (1) particle textures, (2) bulk chemistry, and (3) particle size-distributions. We crashed terrestrial igneous rocks without using mills to keep angular textures of the particles, which are examined under an optical and a scanning electron microscopes. The bulk chemical compositions are adjusted based on the XRF measurements. The particle size distributions are also modified to follow the results of Apollo soil analyses. The composition of our simulant is within 2% difference for major ten elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) when we calculate the mixing ratio of raw material that has similar petrography with lunar pristine rocks using chemical compositions. We successfully developed simulants for Apollo landing sites that have a minimal difference in the term of petrographical texture, particle size distributions and major element compositions. Furthermore, We compile remote sensing data (Clementine’s elemental data) of the South Pole Aitken basin, a landing site candidate, and developed a simulant based only on chemical compositions using the same scheme.