Thermo-optical modelling of transparent multilayer panels for space applications in low Earth orbit

Space windows require transparent materials with superior mechanical, thermal and optical properties. While fused silica has been the traditional choice, acrylic glass is now favored in spacecraft for its cost-effectiveness and radiation shielding capacity, achieved due to radiation absorption. However, this can cause heating, with risks for material integrity especially in space stations at low Earth orbit (LEO), where radiation exposure is more severe than in spacecraft. We investigate the thermal and optical performance of multilayer panels operating in LEO, comparing packages with fused silica, acrylic glass or a combination of both. Using established material properties and a detailed energy transfer model, we calculate temperature distribution under extreme orbital conditions, similar to those on the Cupola of the International Space Station. Two key scenarios are analyzed, considering variations in solar, albedo, and Earth infrared radiation, as well as internal temperature control. The window transmissivity, when calculated within the visible spectrum of sunlight, determines the optical transparency. Our findings identify potential issues with acrylic glass when used in LEO, caused by high radiation absorption. More broadly, our methods permit the evaluation of alternative transparent materials for future applications, contributing to the development of space windows for long-term missions.