The Technology Transfer and Partnerships Office
Hydrogen Reduction of Regolith

Hydrogen is a strong reducing chemical reagent and like carbon can be used to obtain certain metals from their oxides. Metals that form carbides when reacted with carbon like Tungsten are produced commercially by hydrogen reduction as is pure Molybdenum. The hydrogen reduction process has some appeal in ISRU because hydrogen is available as a gaseous reagent on the Moon and at other destinations that also harbor water. In its first stage of development, the process aims at reducing available minerals such as Ilmenite (FeTiO3) found on the Moon to produce oxygen. The development of the technology has been pursued at different scales: examples are the PILOT project (Precursor In-situ Lunar Oxygen Testbed) by Lockheed Martin Astronautics (LMA) and NASA centers, the ROxygen project by Johnson Space Center (JSC), Glenn Research Center (GRC) and Kennedy Space Center (KSC). All projects used lunar regolith simulant materials and were supported by the NASA ISRU Program.


Goal

Extract oxygen from regolith by high-temperature reaction of iron oxides in the regolith followed by water electrolysis.


Principle of Operation

The baseline hydrogen reduction process for lunar regolith has two basic steps for the extraction of oxygen:


Step 1. Hydrogen Reduction of iron oxides
Minerals containing iron oxides (e.g., Ilmenite FeTiO3) are reduced by reaction with heated pure hydrogen near 900°C to form water vapor.
Step 2. Water Electrolysis
Water formed in Step 1 is electrolyzed after purification to separate oxygen and hydrogen. The hydrogen is then cycled back to use in Step 1.

The reaction is limited to iron oxides, which forces the selection of a soil where these oxides are abundant and/or the use of techniques to beneficiate the regolith to obtain a soil with a larger portion of iron oxides. The simplicity and the relatively low operating temperatures of this technology make it a good candidate for early demonstrations of oxygen extraction on a limited scale during robotic space missions.


PILOT (Precursor In-situ Lunar Oxygen Testbed) (LMA /NASA)

images show sublimation of ice in the trench

PILOT Hydrogen Reduction system during field tests in Hawaii in 2008 (Image credit: Lockheed Martin)

Technology Features

  • The PILOT system was built to scale to achieve production rates equivalent to 1000 kg O2 per year to support a lunar outpost.
  • The regolith is introduced into the reactor by an auger at the bottom of a hopper.
  • The regolith is tumbled in a conical reactor resting at an angle similarly to cement mixers while hot hydrogen fills the space. This fluidization of the soil is important to improve the exposure of all the regolith grains to the gas.
  • The water produced passes through a purification module that removes contaminants (hydrogen sulfide, chloride and fluoride) that hinder the operation of the electrolyzer.
  • Once reacted with the hydrogen, the hot regolith is poured out of the reactor. Its heat content can be recuperated to pre-heat the incoming fresh regolith.

PILOT Results and Performance
  • System integrated with mini rover equipped with bucket drum excavator bringing soil to the reactor. Integrated system was tested during field tests in Hawaii.
  • Processing capacity of ~ 15 kg of regolith per batch yielding 150 g of O2.
  • Produced oxygen yields of 1 wt% of processed regolith.

ROxygen (JSC / GRC / KSC)
Technology features
  • The NASA ROxygen fluidized bed and auger hydrogen reduction reactor makes oxygen at approximately 660 kg/yr, which is about 2/3 of the scale required for the initial stages of a Lunar Outpost being designed for the NASA architecture (1000 kg/year).
  • It consists of a cylindrical reactor that has an internal auger system that stirs (fluidizes) the regolith to enhance heat transfer and prevent regolith sintering.
  • Regolith simulant is delivered from the ground level to the inlet tube of the ROxygen reactor cylinder, which is constrained to a vertical configuration to enable a gravity feed of regolith simulant into and out of the reactor cylinder.

Results and Performance
  • Two large–scale reactors were tested in 2008 at the first ISRU technology field tests.
  • Tests in large reactor provided oxygen yields in the range 0.2% – 0.5% by mass of regolith. The low yields are attributed to the operational limits of a contaminant scrubber.
  • Recirculation of hydrogen was achieved with removal of hydrogen halide contaminants from the produced water.

images show sublimation of ice in the trench

Hot Hawaiian tephra soil used in ROxygen reactor pouring out after reaction with hydrogen. (Image credit: Johnson Space Center/ Kennedy Space Center)


Concentric Hydrogen Reduction Reactor (JSC / GRC)
Technology features
  • Concentric cylindrical chambers allow the exchange of heat from the hot regolith being processed to fresh regolith waiting to be introduced.
  • Maintains regolith in fluid and loose state (fluidization) by hydrogen flow and/or vibration of the reactor – compares efficiencies.

Results and Performance
  • Vibrofluidization and gas fluidization with Helium gas are near equally efficient in heat recuperation. Fluidization with hydrogen is not as effective.
  • Tests in large reactor provided oxygen yields in the range 0.2% – 0.5% by mass of regolith. The low yields are attributed to the operational limits of a contaminant scrubber.
  • Added mass and complexity of a dual chamber reactor is also counterproductive for ISRU usage.

images show sublimation of ice in the trench

ROxygen system in operations during field tests in Wahine Valley on Mauna Kea, HI in 2008. (Image credit: Johnson Space Center / Kennedy Space Center)


















images show sublimation of ice in the trench

Hardware schematic for dual chamber H2 reduction reactor with thermocouple locations (credit: Glenn Research Center).

images show sublimation of ice in the trench

Dual Chamber H2 reduction reactor mounted on flex stand (Credit: Glenn Research Center)





























References:

Field Test Results of the PILOT Hydrogen Reduction Reactor, D. Larry Clark and B.W. Keller, J.A. Kirkland, Lockheed Martin Space Systems Company, Denver, CO, AIAA 2009-6475, AIAA SPACE 2009 Conference & Exposition 14 - 17 September 2009, Pasadena, CA.

Evaluation of Heat Recuperation in a Concentric Hydrogen Reduction Reactor, D. Linne, J. Kleinhenz, U. Hegde, NASA Glenn Research Center, Cleveland, OH, AIAA 2012-0636, 50th AIAA Aerospace Sciences Meeting, 09 - 12 January 2012, Nashville, TN.

Lunar Regolith Simulant Feed System for a Hydrogen Reduction Reactor System, R. P. Mueller and I. Townsend, Kennedy Space Center, FL, AIAA 2009-1658, 47th AIAA Aerospace Sciences Meeting, 5 - 8 January 2009, Orlando, FL.

The ROxygen Project, Outpost Scale Lunar Oxygen Production System Development at Johnson Space Center, K.A. Lee, L. Oryshchyn, A. Paz, M. Reddington, and T.M. Simon, J. of Aerospace Engineering. posted online ahead of print March 17, 2012.