Oxygen produced from lunar resources is a very desirable product to greatly reduce the mass lifted from the Earth’s surface in support of exploration activities. The ability to obtain high yields of oxygen from undifferentiated lunar soils enables planning for near-term piloted missions to the Moon. One technology tested for the production of lunar oxygen has been hydrogen reduction of lunar soils. Oxygen yields from hydrogen reduction are generally between one and four percent of un-beneficiated lunar soil.
The Carbon Monoxide Silicate Reduction System (COSRS) was developed to boost lunar oxygen yields significantly above that obtainable by hydrogen reduction. The carbothermal reduction method employed by COSRS can yield about ten times as much oxygen as hydrogen reduction, resulting in significant reductions of excavation and process equipment size.
The COSRS is a novel technology to achieve oxygen yields of about 20 percent from lunar soil. Ferrosilicon and nearly pure SiO byproducts are also generated. The SiO byproduct can be reduced to make nearly pure silicon metal. Over ten years, launch mass savings equivalent to about 15 heavy-lift launches are attained for a COSRS plant producing 36.5 tonnes per year of oxygen.
The closed-circuit COSRS flow sheet consists of three solids treatment steps: iron oxide reduction by carbon monoxide, in situ deposition of carbon in the soil by carbon monoxide disproportionation, and high-temperature carbothermal reduction of silicates. Most of the oxygen recovered from soil is in the form of carbon monoxide evolved during high-temperature carbothermal reduction of silicates. The evolved carbon monoxide is reacted with feed soil at lower temperature, where it is converted to carbon dioxide by reduction of iron oxides and by disproportionation, which deposits carbon throughout the soil. Carbon dioxide is reacted with hydrogen in a reverse water gas shift (RWGS) system. The RWGS system regenerates carbon monoxide for recycle to the COSRS process and produces water, which is electrolyzed to produce oxygen. Hydrogen from electrolysis is recycled within the COSRS system.
Oxygen from lunar soil at a yield of about 20 percent is the primary product of the COSRS. Nearly pure SiO is also generated at yields up to 5 percent, along with ferrosilicon at yields up to 25 percent. The closed-loop process exhibits high process leverage (mass of oxygen produced divided by total mass of reagents plus consumables) and short break-even time.
This work was done by Mark Berggren, Stacy Carrera, and Robert Zubrin of Pioneer Astronautics for Johnson Space Center. MSC-24696-1