Effects of Thickness and Number of Heat-Insulation Glass Layer on Temperature Distributions of Multi-Layer Optical Windows in Outer Space.

The multi-layer optical windows are usually installed in spacecraft for scientific observation, in which the homogeneity of temperature distribution has effects on image quality. In this paper, considering semitransparent and specularly reflecting interfaces, based on the ray tracing-node analysis method, a multi-layer transient coupled radiative and conductive heat transfer model is used to examine the effects of thickness and the number of heat insulation glass layers on temperature distributions of the multi-layer optical windows. The changes of absorption coefficient and refractive index of the optical window changing with wave length are approximately expressed by using a set of rectangular spectral bands. The study shows that in outer space, thermal radiation plays a very important role in the cooling process of the multi-layer optical window, and in the very thin layer of glass medium very close to the surface of glass layer, the radiative heat flux and the conductive heat flux are coupled with each other intensively. The thinner the insulation glass layer is, the more homogeneous the temperature distribution therein is, thus helpfully improving the image quality. The more the number of insulation glass layers are, the more homogeneous temperature distribution of the multi-layer optical window is, thus also helpfully improving the image quality. Also determination of the optimized number of heat insulation glass layers needs to consider the other factors. [ABSTRACT FROM AUTHOR]