Qualification of a Multi-Channel Infrared Laser Absorption Spectrometer for Monitoring CO, HCl, HCN, HF, and CO2 Aboard Manned Spacecraft

摘要

Monitoring of specific combustion products can provide early-warning detectionof accidental fires aboard manned spacecraft and also identify the source andseverity of combustion events. Furthermore, quantitative in situ measurements areimportant for gauging levels of exposure to hazardous gases, particularly on long-duration missions where analysis of returned samples becomes impractical.Absorption spectroscopy using tunable laser sources in the 2 to 5 μm wavelengthrange enables accurate, unambiguous detection of CO, HCl, HCN, HF, and CO2,which are produced in varying amounts through the heating of electricalcomponents and packaging materials commonly used aboard spacecraft. Here, wereport on calibration and testing of a five-channel laser absorption spectrometerdesigned to accurately monitor ambient gas-phase concentrations of these fivecompounds, with low-level detection limits based on the Spacecraft MaximumAllowable Concentrations. The instrument employs a two-pass absorption cell witha total optical pathlength of 50 cm and a dedicated infrared semiconductor lasersource for each target gas. We present results from testing the five-channel sensor inthe presence of trace concentrations of the target compounds that were introducedusing both gas sources and oxidative pyrolysis (non-flaming combustion) of solidmaterial mixtures.