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Advanced environmental monitoring and control technologies are required for future human exploration of the solar system, where the spacecraft air supply must be recycled for continuous use over a period of months to years. Primary target compounds and 180-day Spacecraft Maximum Acceptable Concentration (SMAC's) limits have been identified for several classes of contaminants. For the identified major species, O2, CO, CO2 and CH4, room-temperature, near-IR tunable diode laser absorption sensors have already been demonstrated with ∼1 ppm-meter detection limits (at or below many of the current SMAC limits) and continuous response band widths on the order of 1 Hz. Additional sensitivity can be achieved using compact long pathlength multipass optical cells. These new generation diode laser sensors use communications-type diode lasers in compact, fiber-coupled packages ideal for remote and autonomous sensor applications.

Room-temperature, tunable diode lasers operating in the visible and near-IR spectral region have been shown to meet detection sensitivity and time response requirements for most major species and rapid-response pyrolysis product measurements identified for spacecraft environmental monitoring applications. Multi-laser sensors with multiplexed fiber-delivery systems appear to be feasible for simultaneous monitoring of several individual contaminants. Work is underway to extend this approach to a number of volatile organic compounds using overtone and combination band absorption in the 1.5 to 2.0 μm wavelength region. The first quantitative measurements of these absorption bands have been obtained in pure vapors using a sensitive, near-IR FTIR spectrometer. These results are being used to guide the selection of custom-fabricated diode lasers for sensitive and rapid detection of trace contaminant levels.