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The progress in the development of a sensor for the detection of trace air constituents to monitor spacecraft air quality is reported. A continuous wave, external-cavity tunable diode laser centered at 1.55 μm is used to pump an optical cavity absorption cell in cw-Cavity Ringdown Spectroscopy (cw-CRDS). This technique exploits the sensitivity enhancements provided by the long effective pathlength from the optical cavity created between two highly reflective mirrors (R>0.9999). Preliminary results are presented that demonstrate the sensitivity, selectivity, and reproducibility of this method. Detection limits of 2.0 ppm for CO, 2.5 ppm for CO2, 1.8 ppm for H2O, 19.4 ppb for NH3, 7.9 ppb for HCN, and 4.0 ppb for C2H2 are calculated.

Investigators from three institutions have partnered in a Rapid Technology Development Team whose goal will be the deployment of laser-based sensors for air-constituent measurements on board spacecrafts. The sensors will eventually be based on Type II Interband Cascade (IC) lasers being developed at the Jet Propulsion Laboratory. These lasers will be used in implementations of both photo acoustic spectroscopy based on the use of quartz tuning fork oscillators as a resonant acoustic sensor (QE-PAS) and cavity ring down spectroscopy (CRDS). In the first year of the program, work at Rice and George Washington Universities has focused on the development of both QEPAS and CRDS sensors for ammonia using near infrared lasers. Simultaneously, the JPL portion of the team has fabricated both Fabry Perot and distributed feedback lasers in the mid infrared that can be used for formaldehyde detection.

An extensive reliability and maintenance data base has been compiled for a gas turbine engine used for propulsion of a fleet of military aircraft, covering a full eight years of operational service. Non-parametric statistical tools were applied to analyze the engine flight line removal data set contained in this data base. This analysis was directed towards eliciting information useful in managing maintenance and design change activity directed to enhancing aircraft reliability and availability. Intensive preventive maintenance, high levels of “censoring” due to the phased buildup of the fleet of aircraft and the modular maintenance policy applied to this military engine introduced significant conceptual and practical challenges that required innovations in data treatment and analysis. The resultant analysis toolset is defined and some results described.

An optical sensor for the detection of carbon dioxide concentrations and stable isotope ratios is described. Either a continuous wave, fiber-coupled distributed feedback laser or an external cavity laser is used to pump an optical cavity absorption cell in cw-Cavity Ringdown Spectroscopy (cw-CRDS). This technique exploits the sensitivity enhancements provided by the long effective pathlength from the optical cavity created between two highly reflective mirrors (R>0.9999). The inherently high precision of the technique combined with its rapid data throughput allows for reliable measurements of both concentration and the isotopic composition of the sampled carbon dioxide. Data collected using a prototype of this sensor could be useful for monitoring module occupancy, crew health (through breath tests), and plant growth chambers.