Thermochromic Variable Emissivity Material Thermal Modeling and Test Correlation

In the future, spacecraft thermal engineers could greatly benefit from thermochromic variable emissivity materials (VEMs). VEM optical properties (i.e., emissivity and absorptivity) vary in response to material temperature. As a result, VEMs provide passive and adaptable heat rejection and temperature regulation for spacecraft thermal engineers. These qualities are extremely attractive to spacecraft designers but will present challenges to their acceptance within the spacecraft community. First, thermal analysis tools (e.g., Thermal Desktop) are not inherently well-suited for modeling these unique surfaces. In this paper, we will detail several methods for capturing VEM properties within traditional thermal modeling tools. We will describe the advantages and disadvantages of each approach. Second, correlating a thermal model to ground test results requires careful planning to accommodate changing surface properties. In this work, we will focus on considerations when modeling and correlating VEMs to test data. To help illustrate these modeling and correlation methods, we will leverage our recent experience with SPIRRAL (Space Power InfraRed Regulation and Analysis of Lifetime). SPIRRAL is an International Space Station (ISS) maturation experiment measuring both ground and on-orbit performance of VEMs. The SPIRRAL thermal vacuum test campaign will be detailed including a description of instrumentation and ground testing methodology. The goal of this work is to help spacecraft engineers develop modeling and test correlation methods for future VEM missions.