For years the use of variable emissivity devices and coatings has been envisaged by the academic and industrials space actors. The aim is to overcome the drawback specific to constant thermo-optical coatings with regard to the variation of heat load during the mission and so to maximize the heat rejection capacity and to minimize the heating power budget. 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. As such, they are proposed as smart elements capable of supporting thermal control on board of spacecraft, without the need of any electronic feedback or electromechanical actuation, and, therefore, at zero power costs. The solutions proposed for TCH smart radiators are pretty heterogeneous, and range from sintered tiles, to sol-gel paints, to vacuum thin-films.
Another promising approach is based on electrochromic devices. Common ECHs work in the visible spectrum and modulate transmitted or reflected light intensities upon application of voltage. 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.
In an ongoing R&D activity funded by ESA and CNES the TCH multilayer tiles are based on VO2 technology developed with industrial means and ECH devices are based on encapsulated conducting polymers. In this presentation the various approaches in order to design, manufacture and test TCH and ECH materials as well as variable emissivity radiator breadboards will be discussed. Some coupons and materials issued from this activity will also be presented.