Laser Spectroscopy Multi-Gas Monitor: Results of a Year Long Technology Demonstration on ISS

Tunable diode laser spectroscopy (TDLS) is an advanced trace and major gas monitoring technology with unmatched selectivity, range and stability. The technology demonstration of the TDLS based Multi-Gas Monitor (MGM), initially reported at the 2014 ICES conference, has been operating continuously on the International Space Station (ISS) for over 15 months as of this writing. The MGM is designed to measure oxygen, carbon dioxide, ammonia and water vapor in ambient cabin air in a low power, relatively compact device. While on board, the MGM experienced a number of challenges, planned and unplanned, including a test of the ammonia channel using a commercial medical ammonia inhalant and carbon dioxide spikes from thruster firings from another payload. Data from the unit was downlinked once per week and compared with other analytical resources on board, notably the Major Constituent Analyzer (MCA), a magnetic sector mass spectrometer. MGM spent the majority of the time installed in the Nanoracks Frame 2 payload facility in front breathing mode, sampling the ambient environment of the Japanese Experiment Module (JEM), but was also used to analyze recirculated rack cooling air. MGM can be operated in portable mode (via internal rechargeable lithium ion polymer batteries or by plugging into any Express Rack 28VDC connector). Results show excellent stability and agreement with MCA data for oxygen and carbon dioxide. The ammonia challenge (~ 75 ppm) was successful as well, showing very rapid response time in both directions. Water vapor results showed weekly spikes corresponding to dry out cycling of JEM condensing heat exchangers and good agreement with dew point measurements in Columbus module. None of the 4 sensor channels has degraded perceptibly to date. Work on expanding the capability in next generation devices has just begun. Target gases include combustion products, formaldehyde and hydrazine. Various hand-held and integrated laser spectroscopy based monitors are envisioned for use on ISS, Orion and Exploration missions.