Analysis of a Cold Trap as a Purification Step for Lunar Water Processing

In-situ resource utilization (ISRU) has been proposed for processing the regolith-bound water-ice to provide fresh water, breathable oxygen, and rocket propellant for exploration missions beyond cis-lunar space due to direct evidence of water-ice in the persistently shadowed regions (PSR) on the lunar surface. One possible method of extraction is the sublimation and vapor transport of the water from regolith to a collection and processing system, minimizing mechanized mining. However, the water-ice is found concurrently with other volatile species that can sublimate with water vapor, potentially contaminating and degrading downstream processing systems. Paragon Space Development Corporation® and Giner Inc. are currently developing the ISRU-derived water purification and Hydrogen Oxygen Production (IHOP) system in order 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 water vapor stream while rejecting the majority of the contaminant volatiles. This paper presents an analysis of the possible modes of contaminant retention in the Cold Trap, as well as quantitative, bounding case estimates of the contaminants that could be retained. Results of this analysis indicate the need for further water purification steps prior to generating potable water, breathable oxygen, and rocket propellants.