The in situ production of vital gases and raw materials on the lunar surface is an integral part of NASA’s exploration vision. Development of processes for extraction of oxygen and metallics from the lunar regolith will be vital not only for life support on the lunar surface, but also for spacecraft propulsion to travel further beyond low Earth orbit. This will have a direct impact on cost reduction associated with minimizing the raw material mass from Earth. Aside from utilization of in situ resources, one of the significant limitations of current simulant is the lack of constituents, such as agglutinates. These agglutinates are typically mineral fragments of the lunar regolith that are held together by glass and, depending on location, may constitute 60% to 70% of the lunar regolith.
The glassy phase in the agglutinate is formed when a small, localized area of lunar regolith is rapidly cooled after being melted by high-velocity micrometeoroid impacts. The distinguishing features of the agglutinitic glass are that it is vesicular and contains nanophase elemental iron. The airless or reducing atmosphere on the Moon is believed to be instrumental in precipitating the nanophase iron. The presence of the glassy phase and nanophase iron to a great extent dictates the abrasive and magnetic properties of the lunar regolith. Since the unique lunar environment is instrumental in formation of agglutinates, such phases are not found on Earth. Consequently, lunar simulants, such as JSC-1A, developed from terrestrial resources, although containing an appreciable percentage of amorphous phases, are devoid of the unique agglutinates found in lunar regolith.
Trials were conducted to evaluate production of a high-fidelity simulant. Scanning electron microscopy indicated plasma processing of JSC-1A effectively produced agglutinate and glassy spherules — analog particles similar to those found on the lunar surface. Furthermore, transmission electron microscopy confirmed that these particles contained nanophase iron, which was precipitated directly from the original feedstock of JSC-1A. Therefore, it can be inferred that the plasma processing technique closely duplicates glass formation mechanisms on the lunar surface.
Plasma spraying has been used since the mid-1950s to form metallic alloy, ceramic, and cermet coatings on a wide variety of substrates. These coatings are used for a remarkable number of applications: wear/erosion resistance, oxidation and corrosion resistance, electrical isolation, and thermal protection. Plasma spraying in a vacuum eliminates oxidizing of the feedstock and substrate material.