A Real-time Sensor for Hydrogen Cyanide in Spacecraft Atmospheres

A need exists for continuous monitoring of hydrogen cyanide (HCN) in spacecraft/habitat air. HCN, a highly toxic gas generated by burning or smoldering plastics, can provide early warning of spacecraft fires. NASA has established a Spacecraft Maximum Allowable Concentration (SMAC) of 1 ppm for manned missions exceeding one week. Useful space-borne instruments must satisfy stringent requirements unique to manned missions in space: low power draw, low weight, fully automated operation, self-calibrating, self-checking, and long term, maintenance free operation. The sensors also require an exceptional combination of sensitivity and selectivity: a 1 ppm alarm point requires a detection sensitivity of 100 parts per billion, yet the system must be free of false alarms despite by large concentrations of other species. Southwest Sciences proposes the development of a sensor for hydrogen cyanide based on optical absorption spectroscopy using diode lasers. This approach will meet all of the requirements identified above for space-borne sensors. Two types of diode lasers could be used. Each has a different set of advantages and disadvantages, and the Phase I effort will determine which of the two is best suited to NASA's needs.