Miniaturized Multi-Analyte Sensor for Monitoring Major Atmospheric Constituents in Space Cabin Air

The Major Constituent Analyzer (MCA) is a mass spectrometer-based instrument that is currently used to continuously monitor the partial pressure of six major atmospheric constituents (MACs), namely, nitrogen (N2), oxygen (O2), hydrogen (H2), carbon dioxide (CO2), methane and water vapor on-board the International Space Station (ISS). The operating life of the mass spectrometer is limited by the operating life of the ion pump and ion source filaments to about 1 to 2 years. Water absorption/desorption in the lines renders reliable measurement of water vapor a challenge. This system is accurate for MACs, but its mass and bulk may not be conducive for next generation spacecrafts sought by the National Aeronautics and Space Administration (NASA) agency. To meet this need, a multi-analyte optical sensor array (MOSA) has been constructed and its performance evaluated to monitor MACs. The MOSA design utilizes organically modified silicates and polymer materials to immobilize chemical indicators onto glass substrates. The chemical indicators are sensitive, selective, and respond to the presence of analytes through luminescence- or absorbance-based pathways. Changes in the luminescence/absorbance properties of the coated substrates are directly related to changes in the analytes of interest. The sensor demonstrates a wide dynamic detection range for each analyte (0–40% O2, 0.01–3% CO2, 20–80% relative humidity (RH)) and is able to resolve changes of ±0.1% O2, ±10 ppm CO2, and ± 5% RH. The optoelectronic design includes a feedback loop circuitry for selfreferencing and drift-free sensor performance. The development of this sensor has broad implications for use in monitoring the air quality of enclosed environments such as aircraft, buildings, submarines and automobiles.