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NASA Glenn Research Center, Cleveland, OH

Bill Sheredy
Fire is deadly and unpredictable on Earth; in an enclosed space vehicle in orbit, its presence takes on even more serious implications. To prevent the threat of smoke and fire on missions, NASA conducted the Smoke Aerosol Measurement Experiment (SAME), designed to create devices that will adequately detect combustion in a zero-gravity environment. Heading SAME is NASA researcher Bill Sheredy.

NASA Tech Briefs: Describe SAME and its purpose.

Bill Sheredy: It's an on-going microgravity investigation, which is designed and built for operation aboard the International Space Station. It was designed and developed by NASA at Glenn Research Center, along with ZIN Technologies, the National Center for Space Exploration Research, and the National Institute for Standards and Technology. Right now, SAME is manifested to launch aboard STS 118, or shuttle flight 13A.1, and it will be assembled and operated in the Microgravity Science Box, or MSG. It is a follow-on to the Comparative Soot Diagnostics (CSD) experiment, which flew on STS 75; its objective is to improve the reliability of future spacecraft smoke detectors by making measurements of the smoke particulate size distributions of common spacecraft materials when they burn.

The result from this experiment will enable the rational design of smoke detectors for NASA's future exploration missions. To that end, when the SAME experiment generates smoke particulates, three diagnostic measurements are taken to determine the particle size distribution for each of these smokes. The instruments used to obtain these measurements are industry standard for monitoring atmospheric particulates, but they have been modified for use in microgravity. Response data from the ISS and shuttle smoke detectors is also gathered for these sample smokes. The results of SAME provide statistics of the smoke particulate size distributions for a range of conditions and measurement of a readily modeled reference for validation of smoke growth models. The experiment design and practical applications of the data is enhanced by the development of a numerical code to predict the smoke droplet growth as a function of the fuel pyrolysis rate - the chemical change brought about by the action of heat - the thermodynamic properties of pyrolysis vapor, and the flow environment. SAME also has the capability to evaluate other fire detection/particulate devices for the test materials at NASA's request.

NTB: Why is SAME being conducted?

Sheredy: The CSD experiment found a significant difference in the smoke detector response for overheated spacecraft materials in one-g versus microgravity. The SAME experiment will enhance the CSD with additional diagnostics to better quantify the characteristics of the low-gravity smoke. The particulate pre-fire signatures obtained from this experiment will be used to design fire detectors for future space exploration systems - a pre-fire state, for clarification, is one in which a material becomes overheated and it begins to produce smoke, but it hasn't reached the state of steady burning. The smoke itself could consist of liquid droplets or solid particulates depending on the source material; to the layperson, these two smokes look essentially the same.


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