Measurement of Trace Water Vapor in a Carbon Dioxide Removal Assembly Product Stream

The International Space Station Carbon Dioxide Removal Assembly (CDRA) uses regenerable adsorption technology to remove carbon dioxide (CO₂) from cabin air. CO₂ product water vapor measurements from a CDRA test bed unit at the NASA Marshall Space Flight Center were made using a tunable infrared diode laser differential absorption spectrometer (TILDAS) provided by NASA Glenn Research Center. The TILDAS instrument exceeded all the test specifications, including sensitivity, dynamic range, time response, and unattended operation. During the CO₂ desorption phase, water vapor concentrations as low as 5 ppmv were observed near the peak of CO₂ evolution, rising to levels of ∼40 ppmv at the end of a cycle. Periods of high water concentration (>100 ppmv) were detected and shown to be caused by an experimental artifact.