LUNAR SILICON

Silicon is one of the many commodities that can be mined from space materials, along with rocket propellants and other metals like aluminum and iron. But lunar silicon deserves special attention because it can be used to start a flywheel of space-based economic growth: the extracted silicon is used to make thin-film solar cells, whose power is then used to extract yet more silicon from lunar materials.

Silicon is the second most abundant element in the lunar regolith and rocks. It can be extracted from bulk regolith at any landing site, but there are also promising siliconrich volcanic constructs identified from orbit on both the lunar nearside and farside. These are believed to be enriched in quartz, which could be separated to form a concentrate and lower the energy cost to make silicon metal. After excavating raw regolith, multiple techniques can be used to produce silicon-rich alloys and oxygen gas. Currently the most promising are molten regolith electrolysis, molten salt electrolysis, and carbothermal reduction. Chemical-free purification steps can then get to 99.9999% (6N) purity silicon metal, sufficient for solar cells. The estimated energy costs for producing lunar silicon are 55–90 kWh/kg, overlapping terrestrial values of 45–110 kWh/kg. These numbers imply a strongly positive Energy Return on Energy Invested.

The technology stack for an end-to-end lunar regolith to solar cell process has already been demonstrated at the benchtop scale in the lab, and current research is integrating these steps into a single automated package. No new technologies are needed to mine lunar silicon and unlock energy abundance in space.