Browsing by Author "Williams, E. Spencer"

Now showing 1 - 3 of 3

Analysis of Volatile Compounds from CO2 Removal Systems
(2024 International Conference on Environmnetal Systems, 2024-07-21) Muko, Cristina M.; King, William M.; Hudson, Edgar K. Jr.; Wallace, William T.; Williams, E. Spencer; Gazda, Daniel B.
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 their 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.
Development of a Photoacoustic Formaldehyde Monitor
(2024 International Conference on Environmnetal Systems, 2024-07-21) Mudgett, Paul; Williams, E. Spencer; Beck, Steve; Pilgrim, Jeffrey
Key indoor air quality pollutant formaldehyde (H2CO) is tracked on International Space Station (ISS) using passive badges returned to the ground periodically for analysis. The process is time-consuming in preparation and analysis upon return 6-12 months later. Badges require precious crew time for deploy, retrieval and stow. As NASA's focus in space exploration shifts to the Moon and Mars, archival sample return becomes increasingly impractical. The aim of this project is to develop a highly reliable real-time analyzer for H2CO at low concentrations with data downlinked. Potential sources of H2CO include materials off-gassing, use of formalin as a tissue fixative in biological payloads and overheating of acetal polymers. The Spacecraft Maximum Allowable Concentration (SMAC) for H2CO is 100 ppb for exposures of 7 days or longer. ISS concentrations recently run only 10 - 30 ppb but have spiked as high as 60 ppb in the past. Gateway real time monitoring requirements for H2CO call for a range of 8 - 140 ppb. For this project, a concentration range of 5 - 500 ppb H2CO is targeted. The core tunable diode laser spectroscopy (TDLS) technology was developed by Vista Photonics through the NASA and US Navy Small Business Innovation Research (SBIR) programs. Monitors based on this technology have been demonstrated on ISS, trialed on a nuclear submarine and are in production as Anomaly Gas Analyzers for ISS and Orion. Initially, direct absorption TDLS was used exclusively in these monitors. The H2CO target concentration, however, is much lower, and a longer wavelength required, so a photoacoustic spectroscopy (PAS) technique was adapted, where the laser excitation is detected by a sensitive microphone vs. a conventional photodetector. This paper will discuss the results of NASA-JSC laboratory testing of a prototype PAS based formaldehyde monitor and explore potential adaptations for Gateway missions and beyond.
The Air Quality Monitor “Benzene” Anomaly: Ground Testing and On-going Effects
(2024 International Conference on Environmnetal Systems, 2024-07-21) Wallace, William T.; Limero, Thomas F.; Clark, Kenneth W. Jr.; Hudson, Edgar K. Jr.; Williams, E. Spencer; Gazda, Daniel B.
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 covering 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 investigation by the AQM team, potential causes of the interference, and subsequent reporting of AQM1 results.