Technology Readiness of a Modulated Laser Analyzer of Combustion Products for the Manned Spacecraft Environment

This study focuses on a sensitivity analysis of a Modulated Laser Analyzer for Combustion Products (MLA-CP) developed by SouthWest Sciences of Santa Fe, NM. The MLA-CP uses a single telecommunications-grade IR diode laser to scan several wavelengths and, using wavelength modulation spectroscopy (WMS), determine the concentrations of four target gases (CO₂, CO, HCCH, HCN) to a precision of parts per billion for HCN. The sensitivity analysis, conducted at the NASA-Johnson Space Center and the University of Colorado at Boulder, is designed to expose the MLA-CP to temperature and gas concentration conditions likely to be encountered in the spacecraft environment. This analysis will aid a greater trade study of microgravity fire detection systems in cooperation with the Microgravity Combustion Research Group at Glenn Research Center. The initial tests, conducted in July and August 2005, exposed the sample cell to known concentrations of gases, including breathing air, grade B nitrogen, ultra high purity nitrogen, and 1% carbon dioxide in a balance of nitrogen. Trials were conducted increasing the temperature as the gas was flowed through the cell. Additionally, overnight tests were conducted with ambient temperature conditions and environmental flows. Initial findings showed that the MLA-CP is extremely sensitive to temperature, temperature ranges, and rates of temperature change. Significant sources of error were identified as being inherent to the IR diode laser itself, in the form of unwanted optical interference fringes, or etalons.