Daniel B Gazda’s research while affiliated with Georgia Institute of Technology and other places

One of the primary concerns when designing CO2 scrubber systems that will be integrated with a Sabatier reactor to produce water and methane is the amount of water released from the scrubber. Because the gas stream entering a Sabatier reactor must be compressed, water entering the reactor can condense and compromise the integrity of the system, thus rendering its valuable conversion capability useless. When the Johnson Space Center Environmental Chemistry Laboratory was tasked to develop an assay to quantify the water concentration in air samples from CO2 scrubbers, additional testing was also performed to see if any other compounds were being concentrated on the scrubbers. It was thought that the efficiency of the scrubber systems could be quantified by comparing the differences in samples from the ambient air on the International Space Station (ISS) to the exit gas of the scrubber. As this analysis was carried out, it became evident that the concentrations of certain volatile compounds were higher in the samples from the scrubbers than they were in nominal environmental samples. This meant these compounds were being retained and concentrated on the scrubber beds. Based on this finding, concerns were raised about the potential for these compounds to poison the Sabatier reactor. Further investigation was required to identify these compounds due to their high concentrations and unique matrix of the CO2 scrubber exhaust. This paper describes these events as well as the process that was developed to identify the volatile compounds that increased. An examination of how much the certain compounds can be concentrated by the scrubber systems is also included. Nomenclature CO2 = carbon dioxide DF = dilution factor ECL = Environmental Chemistry Laboratory GC = gas chromatography GC/FID = gas chromatography/flame ionization detector GC/MS = gas chromatography/mass spectrometry GC/TGA = gas chromatography/trace gas analyzer GSC = grab sample container ISS = International Space Station JPM = Japanese Pressurized Module JSC = Johnson Space Center OFP = octafluoropropane ppb = parts per billion ppm = parts per million psi = pounds per square inch SM = Russian Service Module tech demo = technical demonstrations

The International Space Station (ISS) Air Quality Monitors (AQMs) have provided targeted in-flight analysis of volatile organic compounds (VOCs) in the ISS atmosphere since early 2013. During their initial half decade of use (which included multiple sets of units), the AQMs performed well, meeting their validation criteria and showing excellent accuracy compared to archival samples. In addition to routine environmental monitoring, the AQMs have also been used during a number of contingency situations and investigations related to Environmental Control and Life Support Systems (ECLSS). These include a potential ammonia leak, increases in atmospheric ethanol, and efforts to locate potential sources of polydimethylsiloxanes that lead to the production of dimethylsilanediol (DMSD) in the US Water Processor Assembly (WPA). As the fleet of AQMs has aged, several issues have arisen. These have ranged from pervasive problems on electronics boards to loss of sensitivity due to operating in an elevated CO2 environment. The most notable issue encountered during on-orbit operations was incorrect identification of compounds. This initially occurred in mid-2020, when AQM1 reported the presence of benzene. While the AQM team questioned the validity of these results, the concentration of the "benzene" continued to increase and eventually exceeded the 30-and 180-day Spacecraft Maximum Allowable Concentration (SMAC). This led to wide-ranging efforts by a number of groups aimed at understanding the situation and identifying the source of the "benzene." AQM1 failed after being relocated to the Russian Segment as part of the investigation, and the unit was returned for evaluation. When archive samples collected while the AQM was measuring elevated benzene showed no detectable benzene, the focus of the investigation shifted to determining the cause of the false positive readings. Here, we will discuss the results of this nvestigation by the AQM team, potential causes of the interference, and subsequent reporting of AQM1 results. Nomenclature AQM = Air Quality Monitor BFE = Bacteria Filter Element CV = Compensation Voltage

Following a confirmed combustion event onboard the International Space Station (ISS), crew members will don Emergency Masks, each fitted with 2 ISS fire cartridge filters. As the crew member breathes through the filters, combustion products in the cabin air are either filtered or catalyzed by the fire cartridge media to minimize crew exposure to harmful levels of contaminants. Rigorous certification, acceptance, and surveillance programs for the fire cartridges ensure that each lot meets stringent performance requirements throughout the service life of the cartridges. In accordance with the Quality/Acceptance Test Plan, multiple fire cartridges from each lot undergo chemical challenge tests involving one or more chemicals at specified concentrations. These tests are conducted at specific temperatures, humidity levels, and gas flow rates intended to mimic the worst-case conditions for fire cartridge performance. These challenge tests are conducted by the Environmental Chemistry Laboratory at the NASA Lyndon B. Johnson Space Center. Many of the challenge tests focus on carbon monoxide (CO), but other gases include hydrogen cyanide (HCN), hydrogen chloride (HCl), cyclohexane, acrolein, ammonia (NH3), and acetaldehyde. A fire cartridge is exposed to the test gas in a chamber at the specified conditions, and the outlet is monitored for breakthrough during the 2.5-hour test. This paper will briefly introduce fire cartridges and how they work and will then discuss details of the challenge gas delivery and exposure system, breakthrough monitoring methods, and discussion of issues that have arisen during the course of the test program. Although the focus of this paper will be on the challenge tests, a general summary of the performance of the fire cartridges will also be provided. Nomenclature CO = carbon monoxide CO2 = carbon dioxide CSA-CP = Compound Specific Analyzer-Combustion Products ∆P = pressure drop EC = Crew and Thermal Systems Division ECL = Environmental Chemistry Laboratory GC/FID = gas chromatography/flame ionization detector GC/MS = gas chromatography/mass spectrometry HCl = hydrochloric acid HCN = hydrogen cyanide HM = Humidification Module 1 ISS = International Space Station LPM = liters per minute mGSC = miniature grab sample container N2 = nitrogen gas NH3 = ammonia PSMO = pressure systems management office ppm = parts per million RH = relative humidity SMAC = Spaceflight Maximum Allowable Concentration TPS = task performance sheet VOC = volatile organic compound ZA = zero air

Monitoring of the spacecraft environment is required to ensure the health of the crew and the vehicle systems. For the ISS atmosphere, routine volatile organic compound (VOC) monitoring has been performed for almost a decade by Air Quality Monitors (AQMs). The target compounds measured by the AQMs include three types of chemicals: 1) those compounds that would be harmful to crew, 2) those compounds that have been detected regularly in archival samples, and 3) compounds that, while not necessarily harmful to crew health, could present problems for Environmental Control and Life Support Systems (ECLSS). Following the docking of SpaceX-Demo1 (SpX-DM1), the AQMs began to report high levels of isopropanol (IPA). While elevated IPA is routinely observed with visiting vehicles, the level measured by the AQM, and its continued presence following multiple days of scrubbing, caused concerns regarding the U.S. Water Recovery System. Following the departure of SpX-DM1, the IPA levels decreased to nominal levels, allowing the team to investigate the cause of the elevated measurements. Based on the changes in the shape of the gas chromatograph (GC) traces in the IPA region during docked operations, it appeared that an unknown coeluting species was causing problems with quantification. However, with the docking of Northrup-Grumman-11 (NG-11), the elevated IPA returned, as well as the changes in GC traces. In contrast to the SpX-DM1 results, the AQM IPA results did not return to nominal levels following the departure of NG-11, suggesting that the changes could not be tied directly to the visiting vehicle. In this paper, we will discuss a number of potential causes for both the genuine (measured in archival samples) increases in IPA as well as the much higher levels measured by the AQM. Additionally, we will discuss methods being explored to decrease the potential for a reoccurrence in the future.

Analysis of archive water samples from the International Space Station (ISS) provides important insight into the performance of the U.S. Water Processor Assembly (WPA). Ensuring the results from ground analysis of these samples accurately represent the chemical composition of the samples at the time of collection on-orbit is essential, as this data is used to make operational decisions regarding the use of limited on-orbit replacements for WPA components. Recently, samples of effluent from the Multifiltration (MF) beds were collected to determine if the expected breakthrough products (acetate and bicarbonate) were responsible for increased conductivity measured by in-line conductivity sensors. Initial results showed the presence of acetate, but the bicarbonate concentration was lower than expected based on the in-line sensor readings, suggesting loss of carbon dioxide due to diffusion through the Teflon sample bags. To assess this possibility, a second set of samples were collected in duplicate; aliquots were collected in both the standard archive bags and smaller Teflon bags that were subsequently sealed in Mylar to minimize gas permeation. The aliquots of MF bed 1 effluent collected in the standard bags showed breakthrough of a number of expected species, though many were present at lower than anticipated levels. Analysis of the aliquots that had been sealed in Mylar confirmed that gas diffusion had occurred in the standard bag, as the bicarbonate and conductivity readings were both higher than the level measured in the standard bags. The acetate concentration also was significantly higher in the aliquots that had been sealed in Mylar. Interestingly, a repeat analysis of the same sample aliquot from the bag that was sealed in Mylar showed no carboxylate species. A fresh aliquot obtained from the sample bag that had been refrigerated in the Mylar pouch showed acetate results close to the original concentrations, but repeat analysis of this aliquot 4 days later showed no detectable carboxylates. Here, we will discuss efforts to understand the mechanisms that lead to the compositional changes seen during analysis of the archive samples of MF bed effluent, which appear to be dependent on gas diffusion and temperature. International Conference on Environmental Systems 2 Nomenclature CO2 = Carbon dioxide CFU = Colony forming units DMSD = dimethylsilanediol IC = Ion chromatograph ISS = International Space Station ITCS = Internal thermal control system MF = Multifiltration PWD = Potable water dispenser R2A = Reasoner's 2A S/N = serial number TIC = Total inorganic carbon TOC = Total organic carbon WPA = Water processor assembly

Real-time monitoring of volatile organic compounds (VOCs) on the International Space Station (ISS) is currently performed using a pair of Air Quality Monitors (AQMs), instruments that combine gas chromatography (GC) separation with detection using a differential mobility spectrometer (DMS). Each AQM occupies a volume of approximately 4900 cm 3 and has a mass of 3.7 kg. Each AQM also requires a power supply that is roughly the same size and mass. While these parameters do not present a concern on the ISS, they are too large for future exploration missions. The most obvious avenue for decreasing the size and mass of the AQMs lies in the reduction from 2 instruments and power supplies to a single unit and power supply. As currently configured, the required target VOCs cannot be successfully monitored on a single GC column, as the column cannot be cooled sufficiently to allow separation of early-eluting compounds. Here, we will show how limited method changes and additional cooling of the GC column can minimize the effects of compound coelution and allow all analytes to be monitored on a single AQM. We will also discuss other potential improvements that could increase the sensitivity and further reduce the size of an exploration-ready AQM. Nomenclature AGA = Anomoly gas analyzer AQM = Air quality monitor CSA-CP = compound specific analyzer-combustion products DC = Direct current DMS = Differential mobility spectrometer EA = Ethyl acetate ECLSS = Environmental Control and Life Support Systems GC = Gas chromatography GC-DMS = Gas chromatograph-differential mobility spectrometer IPA = Isopropanol ISS = International Space Station MCA = Major constituent analyzer MEK = Methyl ethyl ketone (2-butanone) MGM = Multi-gas monitor International Conference on Environmental Systems 2 RF = Radio frequency SAM = Spacecraft Atmosphere Monitor TDLS = Tunable diode laser spectroscopy TEC = Thermoelectric cooler Vc = Compensation voltage VOC = Volatile organic compound

Since 2009, gas chromatography-differential mobility spectrometry (GC/DMS) has been used on-board the International Space Station (ISS) to monitor the atmosphere for volatile organic compounds. The technology was originally tested as part of a Station Detailed Test Objective (SDTO) and then transitioned to operational hardware. The operational version of this hardware, the Air Quality Monitor (AQM), currently monitors 22 compounds, though the target list is flexible and can be adjusted depending on changes in materials or the spacecraft environmental control systems. After separation on the GC column, target compounds are ionized via charge transfer from a Reactant Ion (RI). In the positive mode, H + (H2O)n is the RI while O2-(H2O)n acts as the RI in the negative mode. In the early stages of the SDTO, it was discovered that the position of the RI Peak (RIP) in the negative mode was shifting with time on orbit, and the instrument was losing sensitivity to certain compounds. This shift of the RIP appeared to be correlated with increasing concentrations of CO2 in the recirculation system of the instrument. The operational version of the AQM uses larger, replaceable sieve packs to clean the recirculated carrier gas. It was hypothesized that incorporation of the large sieve packs would minimize the effect of CO2 on the position of the RIP. Unfortunately, this phenomenon has also been observed on the first two sets of AQMs operating on the ISS. In this paper, we will discuss the mechanisms behind the shifting RIP as well as the effects on the ionization of selected target compounds. Additionally, we will discuss potential approaches to mitigate the impact of the RIP shift and extend the current 6-month life of sieve packs on-orbit. Nomenclature AQM = Air Quality Monitor AQM-GFE = Air Quality Monitor-Government Furnished Equipment AQM-SDTO = Air Quality Monitor-Station Detailed Test Objective CH4 = Methane CO2 = Carbon dioxide DCE = 1,2-dichloroethane DCM = Dichloromethane EA = Electron Affinity

This paper presents and discusses results from chemical analyses performed on archive potable water samples collected in the U.S. Segment of the International Space Station (ISS) during Expeditions 50-53. The sixth increase in the total organic carbon (TOC) concentration of the water produced by the U.S. water processor assembly (WPA) began during Expedition 50. Despite an initially precipitous climb, the TOC trend reversed several times and levels remained well below the potability limit. There have been five prior instances of organic contaminants breaking through the treatment process into the WPA product water since the system became operational in 2008. Contaminant breakthrough was signaled each time by an increase in TOC measured by the onboard TOC analyzer (TOCA). In all previous instances, the WPA multifiltration beds were replaced and the TOC concentration returned to nominal levels. The archival sample results discussed herein indicate that dimethylsilanediol (DMSD) was the primary compound responsible for the latest increase.

Maintaining a safe supply of potable water is of utmost importance when preparing for long-duration spaceflight missions, with the minimization of microbial growth being one major aspect. While biocides, such as ionic silver, historically have been used for microbial control in spaceflight, their effectiveness is sometimes limited due to surface reactions with the materials of the storage containers that reduce their concentrations below the effective range. For the Multi-Purpose Crew Vehicle, the primary wetted materials of the water storage system are stainless steel and a titanium alloy, and ionic silver has been chosen to serve as the biocide. As an attempt to understand what processes might reduce the known losses of silver, different treatment processes were attempted and samples of the wetted materials were tested, individually and together, to determine the relative loss of biocide under representative surface area-to-volume ratios. The results of testing presented here showed that the materials could be treated by a nitric acid rinse or a high-concentration silver spike to reduce the loss of silver and bacterial growth. It was also found that the minimum biocidal concentration could be maintained for over 28 days. These results have pointed to approaches that could be used to successfully maintain silver in spacecraft water systems for long-duration missions.

During the early years of human spaceflight, short duration missions allowed for monitoring of the spacecraft environment to be performed via archival sampling, wherein samples were returned to Earth for analysis. With the construction of the International Space Station (ISS) and the accompanying extended mission durations, the need for enhanced, real-time monitors became apparent. The Volatile Organic Analyzer (VOA) operated on ISS for 7 years, where it assessed trace volatile organic compounds in the cabin air. The large and fixed-position VOA was eventually replaced with the smaller Air Quality Monitor (AQM). Since March 2013, the atmosphere of the U.S. Operating Segment (USOS) has been monitored in near real-time by a pair of AQMs. These devices consist of a gas chromatograph (GC) coupled with a differential mobility spectrometer (DMS) and currently detect a target list of 22 compounds. These targets are of importance to both crew health and the Environmental Control and Life Support Systems (ECLSS) on the ISS. Data is collected autonomously every 73 hours, though the units can be controlled remotely from mission control to collect data more frequently during contingency or troubleshooting operations. Following a nominal 3-year lifetime on-orbit, the initial units were replaced in February 2016. This paper will focus on the preparation and use of the AQMs over the past several years. A description of the technical aspects of the AQM will be followed by lessons learned from the deployment and operation of the first set of AQMs. These lessons were used to improve the already-excellent performance of the instruments before deployment of the replacement units. Data trending over the past several years of operation on ISS will also be discussed, including data obtained during a survey of the USOS modules. Finally, a description of AQM use for contingency and investigative studies will be presented. Nomenclature AQM = Air Quality Monitor DMS = Differential Mobility Spectrometer DMSD = dimethylsilanediol