50th International Conference on Environmental Systems ICES-2021-292 12-15 July 2021 Experimental Proof of Concept of a Cold Trap as a Purification Step for Lunar Water Processing Jordan B. Holquist1, Sean Gellenbeck2, Chad E. Bower3, and Philipp Tewes4 Paragon Space Development Corporation, Tucson, AZ 85714, USA 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. Nomenclature B.C. = Best Case H2O = Water CH4 = Methane H2S = Hydrogen sulfide C2H4 = Ethylene ICICLE = ISRU Collector of Ice in a Cold CH3OH = Methanol Environment CO = Carbon monoxide ICPMS = Inductively Coupled Plasma Mass CO2 = Carbon dioxide Spectrometry COTS = Commercial Off-The-Shelf IHOP = ISRU-derived water purification and CTE = Cold Trap Experiment Hydrogen Oxygen Production CTTS = Contaminant Tolerant Test Stand ISRU = In-Situ Resource Utilization DI = De-ionized water IWP = Ionomer-membrane Water Processing GCMS = Gas Chromatography Mass JSC = Johnson Space Center Spectrometry LCROSS = Lunar Crater Observation and Sensing H-L = Henry’s Law Satellite H2 = Hydrogen MFC = Mass Flow Controller Hg = Mercury N2 = Nitrogen HOPA = Hydrogen Oxygen Production NASA = National Aeronautics and Space Assembly Administration 1 Ph.D., Aerospace Engineer, Paragon Space Development Corporation, [email protected] 2 Aerospace Engineer, Paragon Space Development Corporation, [email protected] 3 Thermal Analyst, Paragon Space Development Corporation, [email protected] 4 Ph.D., Aerospace Engineer, Paragon Space Development Corporation, [email protected] Copyright © 2021 Paragon Space Development Corporation NH3 = Ammonia O2 = Oxygen SO4 = Sulfate ppb = Parts per billion (molar basis) TIC = Total Inorganic Carbon ppm = Parts per million (molar basis) TOC = Total Organic Carbon PSR = Permanently Shadowed Region TRL = Technology Readiness Level RH = Relative Humidity W.C. = Worst Case SBIR = Small Business Innovative Research WIPE = Water, ISRU-derived, Purification SO2 = Sulfur dioxide Equipment I. Introduction ASA has identified a critical need for the design, fabrication, and testing of in-situ resource utilization (ISRU) N components to produce purified water, oxygen, and hydrogen on the Moon and/or Mars from regolith-based resources. Extended stays on the Lunar or Martian surface will require a readily available source of purified water. Once the water is purified, it can be used as a source of oxygen, (both as breathable air for habitat crew and as propellant oxidizer), and hydrogen as propellant fuel. In the near term, NASA has specifically identified the need for development and testing of critical components for the extraction and purification of water from ice that exists at the lunar poles in permanently, or near-permanently, shadowed regions (PSRs) on the Moon. Purification and electrolysis of in-situ lunar water has never been done before. It presents unique challenges related to the hazardous, corrosive, toxic, and flammable gases present with the lunar water and the lunar polar environment; as well as the typical constraints of system launched to the lunar surface (mass, volume, power, autonomy, robustness, reliability, and lifetime). This technology development is vital to allow humans to achieve a sustainable presence on the Moon. Paragon Space Development Corporation (Paragon) and our partner Giner, Inc. (Giner) are pursuing development and testing of key components in the ISRU-derived water purification and Hydrogen Oxygen Production (IHOP) subsystem (see Figure 1) as well as advancement of the subsystem architecture. Paragon is developing an innovative, contaminant robust subsystem that removes acidic and water soluble contaminants found within ISRU-derived water on the Moon that could corrode systems, degrade electrolyzer (or other downstream system) performance, or present serious toxicity issues to humans. In the IHOP subsystem shown in Figure 1, an H2O Cold Trap Assembly (Cold Trap) and Paragon’s Nafion-based Ionomer-membrane Water Processing (IWP) technology provide broadband contaminant filtration, while an ammonia (NH3) scrubber and water polisher are optimized for specific contaminant and final trace contaminant removal, respectively. The purified water is then electrolyzed using a static feed water electrolyzer to produce H2 and O2 propellant. This closely-coupled architecture of water purification and propellant production allows NASA maximum flexibility to adapt IHOP to a variety of upstream and downstream ISRU subsystems for applications on either the Moon or Mars. Our technical solution builds on both prior executed contracts as well as internal research and development. Figure 1. IHOP Subsystem Block Diagram with IHOP Contract Development Level-of-Effort Labelling 2 International Conference on Environmental Systems II. Background NASA’s LCROSS mission measured the presence of water-ice in Table 1. “Updated” Lunar Volatiles the PSRs on the Moon’s South Pole at 5.6 wt% ± 2.9 wt% with respect 2,3 to regolith mass. In addition, the LCROSS mission detected the from LCROSS Data presence of other chemical species shown in Table 1. Many extraction methods of the lunar ice have been proposed in recent years and are Conc. (mol% Conc. undergoing active investigation. Cold trapping of water vapor and the relative to (wt% in cleanup of collected water are integral components to these Compound total H2O) regolith) architectures, but the technology to accomplish these tasks in the lunar H2O 100 5.60 PSR environment remains critically under-developed. Current state- H2 225 1.40 of-the-art hardware does not provide the capability to collect and CO 8.09 0.70 purify water from various lunar mining architectures. This research is H2S 7.30 0.77 aimed at closing that capability gap through the development of a Cold NH3 2.66 0.14 Trap to collect volatilized (sublimated) lunar water while purifying it SO2 1.40 0.28 of the co-located contaminants described in Table 1. C H 1.37 0.12 In the course of the execution of the IHOP contract, Paragon 2 4 CO 0.94 0.13 identified the need to define the expected contaminant load being 2 CH OH 0.67 0.07 provided to downstream IHOP assemblies from the H O Cold Trap 3 2 Hg 0.36 0.22 Assembly shown on the left of Figure 1. As part of this definition effort, Paragon developed a contaminant retention model based on CH4 0.28 0.014 Henry’s Law temperature-dependant solubility of gasses in water, NOTE: These values are updated from the original described in Ref. 1. The model predictions of contaminant retention proposal and early reporting values. They are now from Ref. 1 are shown graphically in Figure 2. However, because a referred to as the “Updated” as per discussions with Cold Trap operating on the Moon will collect the water from the NASA customers and the LCROSS Principal process flow via deposition (the phase change of water from vapor to Investigator, Anthony Colaprete (JSC) solid, the opposite of sublimation), the Henry’s Law solubility analysis, while useful as an approximation, does not represent realistic performance. The present article describes the experiments conducted at Paragon with a simulated Cold Trap operated with relevant wall temperatures, flow pressures, water content, and contaminant Figure 2. First order estimate of the lunar water purification concentrations to study contaminant retention performance of the IHOP Cold Trap1 with deposited water vapor. III. Methods & Apparatus A. Test Overview & Description A contaminant tolerant test stand (CTTS) was developed for the IHOP program and configured to initially support the Cold Trap Experiment. The general overview of the test set up and procedures were as follows: