Solar-vapor pyrolysis of lunar regolith for oxygen production in high vacuum: An experimental investigation and thermochemical modeling
Year: 2022
Type: dissertation
Abstract: Oxygen is one of the essential consumables in space exploration, being used as an oxidizer in chemical propulsion and for human life support systems. With the planned future long-term human missions to the moon, the need for oxygen delivery to the lunar surface will only increase. The idea of producing oxygen and other consumables from lunar materials has been present in research for some time. Multiple processes have been developed and tested here on Earth. Most processes utilizing oxygen bound in the lunar regolith also require consumables themselves. This thesis investigates the process of solar vapor pyrolysis, which can use unbeneficiated regolith, sunlight, and vacuum to produce oxygen and other byproducts without requiring any consumables.\n\nThermal reduction of metal oxides in lunar regolith is heavily dependent on pressure conditions during the pyrolysis process. Lower pressures decrease the temperature at which oxides present in lunar regolith are dissociated into oxygen, suboxides, and metals. This makes pressure an essential parameter for future design and optimization of reactors for lunar operations. The pyrolysis reactions are studied at lower pressures in the high vacuum regime to determine the ideal conditions for oxygen production. This is done experimentally on a small purpose-built solar-vacuum furnace where partial vaporization of regolith simulant EAC-1A is demonstrated, although no quantitative conclusions on oxygen production can be drawn.\n\nIdeal conditions for pyrolysis in the pressure range of 10−8 mbar to 103 mbar and temperatures range of 289 K to 3773 K are determined through thermochemical equilibrium modeling. The influence of regolith composition on oxygen production is studied through modeling of three representative regolith compositions and the EAC-1A simulant. It is shown that the ideal molecular oxygen yields range from 6.6% to 14.1%, with EAC-1A exhibiting the highest yields, followed by low-Ti Maria, high-Ti Maria, and Highlands regolith.\n\nAdditionally, a model is presented which combines the oxygen yield from the thermochemical model with a solar-thermal simulation of the regolith surface to evaluate oxygen production during solar heating of regolith. The model shows that the experiments were performed nearly at the lowest solar power boundary, where pyrolysis still occurs. An increase in solar power applied to the regolith surface would significantly increase oxygen production. A doubling of the experimental solar power would lead to an up to ten-fold increase in theoretical O2 mass production. Further increases in solar power would lead to progressively lower increases in oxygen production.
Language: English
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7043326269