Smoke Particle Sizes in Low-Gravity and Implications for Spacecraft Smoke Detector Design

This paper presents results from a smoke detection experiment entitled Smoke Aerosol Measurement Experiment (SAME) which was conducted in the Microgravity Science Glovebox on the International Space Station (ISS) during Expedition 15. Five different materials representative of those found in spacecraft were pyrolyzed at temperatures below the ignition point with conditions controlled to provide repeatable sample surface temperatures and air flow conditions. The sample materials were Teflon®, Kapton®, cellulose, silicone rubber and dibutylphthalate. The transport time from the smoke source to the detector was simulated by holding the smoke in an aging chamber for times ranging from 10 to1800 seconds. Smoke particle samples were collected on Transmission Electron Microscope (TEM) grids for post-flight analysis. The smoke particle size distributions were measured using three particulate aerosol diagnostics that measure different moments of the size distribution and smoke detectors from the ISS and the space shuttle, These diagnostics were used to estimate the particle number concentration (zeroth moment), the diameter concentration (first moment) and the mass concentration (third moment), These values were combined to estimate the diameter of average mass, the count mean diameter, the geometric mean diameter and the geometric standard deviation. Even though the analysis of these data is ongoing, information from the various instruments and the calculated mean particle sizes has important implications for the design of spacecraft smoke detectors. These implications are reviewed in this paper relative to the operating principles of existing smoke detection technology, These results can be used to establish design requirements for smoke detectors for future spacecraft.