Experimental Proof of Concept of a Cold Trap as a Purification Step for Lunar Water Processing

Since the observation of direct evidence of water-ice in the permanently shadowed regions (PSR) on the lunar surface, in-situ resource utilization (ISRU) has been proposed for processing the regolith-bound water-ice to provide fresh water, breathable oxygen, and liquid rocket propellant for lunar exploration missions. One possible method of extraction is the sublimation and vapor transport of the water from the regolith to a collection and processing system. However, the water-ice is found concurrently with other typically volatile species that can sublimate with water vapor and that would contaminate and degrade downstream processing systems. Paragon Space Development Corporation� is developing the ISRU-derived water purification and Hydrogen Oxygen Production (IHOP) system to collect, purify, and process water-ice from PSRs on the lunar surface. A critical component of this system concept is a cold trap that selectively deposits water-ice from a saturated water vapor stream while rejecting the contaminant volatiles.

This paper presents results, analysis, and discussion of an experimental proof of concept demonstration wherein a warm process gas containing water vapor and volatile contaminant components (H2, CO, H2S, NH3, SO2, C2H4, CH4, CO2, and CH3OH) was passed into an evacuated and actively chilled thick-walled glass bottle. Water-ice samples were collected from each of eight test batches with varying contaminant components present at concentrations with respect to water vapor matching their observed proportionality from the LCROSS mission results. Each water sample was analyzed for impurities in both the liquid water and the gaseous headspace of the sample. Results indicate that retained contaminants have concentrations at or below the Henry�s Law estimates made in ICES-2020-71, demonstrating proof of concept of a freeze distillation purification step for lunar water processing by using a cold trap for water collection.