The Technology Transfer and Partnerships Office
Carbothermic Reduction of Regolith
Regolith and Environment Science and Oxygen and Lunar Volatile Extraction

The carbothermic reduction process is a mature terrestrial technology using carbon to reduce metal oxides (ores) to produce metals such as iron in blast furnaces and metallurgical grade silicon. The same process can be used to reduce minerals containing various metallic oxides in the lunar and other planetary regolith to produce oxygen. Orbitec Inc. partnered with Physical Sciences Inc. and Kennedy Space Center to develop the technology for ISRU demonstrations.


Goal

Extract oxygen from regolith by high-temperature reaction of oxides with a carbon source and recover oxygen in multi-step process.



Principle of operation

The baseline carbothermal reduction process has three basic steps
— Step 1.Carbothermic Reduction of Metallic Oxides
Minerals containing metallic oxides (e.g., ferrous, silicon, titanium, etc.) are reduced by reaction with a carbonaceous source (e.g., methane) to form carbon monoxide and hydrogen.
— Step 2. Methane Reformation
Carbon monoxide produced in Step 1 is reduced by reaction with hydrogen to form methane and water. The methane product is cycled back to use in Step 1.
— Step 3. Water Electrolysis
Water formed in Step 2 is electrolyzed to form oxygen and hydrogen. The hydrogen is then cycled back to use in Step 2.
The hydrogen formed in Steps 1 and 3 is consumed in Step 2. The methane formed in Step 2 is reused in Step 1. This closed cyclic process does not depend upon the presence of water or water precursors in the lunar materials. It will produce oxygen from ilmenite and silicate minerals in the lunar regolith regardless of their precise composition and fine structure.
While the composition of the Moon is not homogeneous, analyses of the Apollo samples indicate that minerals containing SiO2 (silicates) comprise 40-50% by weight of the total oxide mixture. Since silicates are so abundant in the lunar regolith, the carbothermal reduction process can be operated at virtually any location on the Moon with approximately the same efficiency.

Technology Features

  • The regolith is exposed to a laser beam or concentrated solar energy to heat and melt a localized region, surrounded by unmelted regolith. The containment of molten regolith in this configuration is possible due to the very low thermal conductivity of 0.0172 – 0.0295 W/mK of lunar regolith in its granular form. This avoids thermal compatibility issues that typically plague the use of crucible-type containers.
  • Methane gas filling the chamber only pyrolyzes on and near the surface of the molten regolith.

regolith is exposed to a laser beam Spheroids of molten regolith simulant material JSC1-A formed during a 40-minute heating test (Credit: Orbitec Inc.)
(Image credit: Orbitec Inc.) Spheroids of molten regolith simulant material JSC1–A formed during a 40-minute heating test.(Credit: Orbitec Inc.)

Results and Performance

  • ORBITEC has conducted carbothermal experiments using a 440 W CO2 laser
  • Equivalent oxygen yields up to 28 wt% have been produced
    — Yields >15-20 wt% are only produced in a carbon rich processing environment where the carbon losses in the system may be significant
  • Carbon loss in the processed regolith with oxygen yields <15% is typically very low
    — Measured values range from 0 – 0.03%wt per ASTM E1019 (1.7 kg of carbon lost per 1,000 kg of oxygen produced)
regolith machine
Schematic of Integrated Carbothermic Reduction of Regolith system for field tests (Image credit: Orbitec Inc.)

References:

Demonstrating the Solar Carbothermal Reduction of Lunar Regolith to Produce Oxygen, R.J. Gustafson, B.C. White, M.J. Fidler, A.C. Muscatello, AIAA 2010-1163, 48th AIAA Aerospace Sciences Meeting, 4-7 January 2010, Orlando, FL.


2010 Field Demonstration of the Solar Carbothermal Regolith Reduction Process to Produce Oxygen, R.J. Gustafson, B.C. White, M.J. Fidler, AIAA 2011-434, 49th AIAA Aerospace Sciences Meeting, 4-7 January 2011, Orlando, FL.