Optimization and Thermal Vacuum Testing of Variable Emissivity Coatings for Radiators

Abstract

The objective for the development of variable emissivity coatings is to handle the variation of heat loads during the mission, by maximizing the heat rejection capacity and minimizing the heating power demand. The most promising of these coatings are based on Thermochromic (TCH) and Electrochromic (ECH) materials. Thermochromic materials can be adjusted to behave as poor emitters at low temperature, and good emitters at high temperature without the need of any electronic feedback or electromechanical actuation, and therefore at zero power costs. The advantage of ECH for space application is achieved by adapting the infrared emissivity of a surface by application of a low power electrical potential. For the last 3 years an R&D activity co-funded by ESA, CNES and Thales Alenia Space, aimed at the development of thermochromic tiles based on VO2 thin film material and of ECH devices based on conducting polymers. A previous paper described the design, the manufacturing process and the tests of TCH and ECH materials. In this paper we present the continuation in the form of the thermal-vacuum testing of TCH and ECH radiator breadboard. Furthermore, the optimized performances of TCH tiles will be described in detail. We report as well on optical modeling showing the feasibility to lower the solar absorptivity for TCH tiles. The TCH and ECH breadboards were successfully assembled and tested in a vacuum chamber. Their emissivity contrast between cold and hot case was validated to be 0.3 with a hot case emissivity being 0.8. The further optimization of TCH full stack led to the reduction down to [10°C, 40°C] of the switching temperature range within which the emissivity change from low to high, due to the doping of the VO2 layer with tungsten. Concerning the optical modeling of the TCH, the main functions have all been successfully simulated.

Description

Jean-Paul Dudon, Thales Alenia Space, FR
Laurent Dubost, HEF-IREIS, FR
Philipp Hager, European Space Agency, NL
Stephanie Remaury, CNES, FR
Frederic Vidal, Université de Cergy-Pontoise, FR
Alice Ravaux, HEF-IREIS, FR
Bérangère Doll, Thales Alenia Space, FR
Bruno Bras, ESA-ESTEC, NL
Sophie Cantin, LPPI, FR
ICES104: Advances in Thermal Control Technology
The 51st International Conference on Environmental Systems was held in Saint Paul, Minnesota, US, on 10 July 2022 through 14 July 2022.

Keywords

advanced thermal control technologies, variable emissivity coating, smart material for space, thermal testing, thermochromic, electrochromic

Citation