PREDICTION OF PARTICULATE CONTAMINATION ON AN APERTURE WINDOW

This paper presents an analysis of light scattering by surface particl es on the sensor window of a missile during ascent flight. The particu late contaminant distribution on the window is calculated by tallying the number of particles in a set of size ranges. The particulate conta mination at the end of the mission is predicted by adding the contribu tions from the events of ground and flight operations. The surface par ticle redistribution caused by vibroacoustic-induced surface accelerat ion was found to contribute the most to particulate surface contaminat ion. The analytical surface obscuration calculation with a set of part icle counts was compared with the results of the image analyzer measur ement. The analytical results, which were calculated with a given func tion of particle shape depending on size, were more conservative than the measurement. A scattering calculation using a verified BSDF model showed that the scattering was less than 0.001 at 20 deg off the direc tion of the incident light in the mid IR wavelength when the surfaces were at Level 300 initially.