Electrets Used in Measuring Rocket Exhaust Effluents from a Space Shuttle Model

Abstract

The purpose of this experimental research was to investigate the use of electrets as a measuring device to measure the hydrogen chloride concentrations of rocket exhaust effluents. The word electret was derived by Heaveside (1892) to describe a permanently polarized dielectric, which is the electrical equivalent of a permanent magnet. A Japanese physicist, Eguchi, prepared the first electret in 1919 from carnauba wax (Eguchi, 1919). In assessing the effectiveness of electrets, comparisons were made with hydrogen chloride measuring devices from chamber and field tests and computed results from the NASA/MSFC multilayer diffusion model. The experimental data used in this investigation were obtained from 18 static test firings at Marshall Space Flight Center, Huntsville, Alabama, and chamber tests at Arnold Engineering Development Center, Tullahoma, Tennessee. The results show that electrets have multi-pollutant measuring capabilities, simplicity of deployment and speed of assessment. Electrets are desirable because of their small size, light weight, long life and low cost of manufacturing. The electrets compared favorably with other HCl measuring devices. The summary of the measured data from the electrets and the HCl detectors is within the upper and lower bounds of the computed HCl concentrations from the NASA/MSFC multilayer diffusion model.