Energy Absorption Through Radiation in Multilayer Windows for Spacecrafts

The overall heating of satellites operating in low Earth orbit, essentially due to direct radiation from the Sun, terrestrial albedo, and planetary radiation, is well studied, but little is found specifically on transparent plates used for windowing spacecrafts. The most historic material of choice is fused silica; more recently, acrylic glass is being used, but its refractive properties are poorly documented. The effects of electromagnetic waves incident on multilayer windows composed of panes of fused silica or acrylic glass, or a combination of these, are analyzed. Using data of refractive index from the literature, which, however, have been found incomplete and sometimes contradictory, the problem is addressed by accounting for the dependence of transmissivity and absorptivity of each material on the energy spectrum, which is different for solar and planetary radiation. Worked examples show that fused silica allows most radiation to pass directly through, while acrylic glass is characterized by absorption depending on the thickness; this can potentially increase its temperature, posing a problem since the mechanical properties decay at temperatures near 100 degrees C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$100 <^>{\circ }\textrm{C}$$\end{document}. This study contributes to the analysis of thermal problems for space windows, of considerable interest since glazing can fail due to thermal shocks, constrained thermal variations, or temperature concentrations.