Spacesuit Monitor

The concentration of carbon dioxide in exhaled breath is 3.8%; a concentration of 2% causes deepened breathing, and 4% causes a marked increase in respiration. These higher concentrations of CO2 also cause drowsiness and can be unsafe. Therefore, it is desirable to monitor the concentration of CO2 in exhaled breath to guarantee the safety of an astronaut in the dangerous extravehicular environment. This Phase I program proposes the use of a miniaturized SAW sensor array coupled with pattern recognition data analysis for the ambient temperature determination of CO2 in exhaled air. The SAW array systems proposed here are in a 1-cm square package containing a minimum of three SAW devices and an integrated circuit package including all driver and RF circuitry required for sensor operation in a direct DC mode. Multiplex circuitry is currently under development that will allow for the application of up to seven SAW sensors in the array. The final operational system can be equipped with either readout devices or alarms, if immediate notification of an unsafe situation is required. Previous work by the Principal Investigator on a related system has shown that response times are fast, on the order of one second; recovery is complete and equally fast. Accurate determinations in the presence of various interfering compounds are accomplished by means of a pattern recognition algorithm, which allows for the differentiation of signals from several devices to provide characteristic signatures for each of the analytes (or interferents) under consideration.