Infrared Fiber-Optic Fire Sensors: Concepts And Designs For Space Station Applications

Abstract

Concepts of infrared fiber -optic (IFO) sensors were investigated for application as distributed fire sensors for Space Station Freedom. Testing of breadboard configurations (based on those concepts) showed that IFO fire -sensors will be able to detect fires in complex spacecraft with a network of lightweight fibers interfaced to a central detector. Fiber-multiplex configurations are preferred for large areas or modules, while small spacecraft compartments can be monitored with fiber configurations that are not location -sensitive with respect to individual fibers. Single -fiber (250 to 300 -gm diameter) responsivity measurements conducted with reflective and refractive optical configurations for the central detector system indicated background -limited-ranges (BLR) of 2 to 3 m for early sensing of hydrocarbon and hydrogen flames (area of approximately 3 cm2).Signal processing techniques were also investigated, and the results showed significant differences in the fire sensor performance depending on the method of optically chopping the radiation signals. The single fiber BLR could be extended to 8 m by optically chopping the signals at the fiber input (as opposed to 2 to 3 m when chopping at the fiber output) for the flames tested. The results of the research work showed that IFO fire -sensors are feasible for application on Space Station Freedom; however, additional development work will be required to eliminate false alarms caused by high temperature objects if the sensors are to be used in other applications.Technology associated with acoustic-optic -tunablefilter (AOTF) spectrometers offers a potential method of solving this problem.