Titanium-aluminum-nitride coatings for satellite temperature control

Intense solar irradiation, radiative cooling to outer space, and internal h eat generation determine the equilibrium temperature of a spacecraft. The b alance between the solar absorption and thermal emittance of the surface is therefore crucial, in particular for autonomous parts directly exposed to the solar radiation and thermally insulated from the main thermal mass of t he spacecraft. The material composition but also the coating thickness are found to influence the equilibrium temperature of an object in space. In th is paper we report on a systematic search for a suitable composition and th ickness of TixAlyNz alloy coatings prepared by reactive, unbalanced magnetr on sputtering from targets consisting of differently sized titanium and alu minum sectors. The films were deposited on glass, glassy carbon, aluminum s heet metal, and on sputtered aluminum and TixAl(1-x) films on glass. The st oichiometry and sheet resistance of the films was determined with Rutherfor d backscattering and four-point probe measurements respectively. Reflectanc e spectra for the visible and infrared spectral ranges were used to obtain average solar absorptance and thermal emittance values used in model calcul ations of the equilibrium temperature. Neglecting internal heat contributio ns, the lowest calculated equilibrium temperature in orbit around the Earth , 32.5 degrees C, was obtained for a 505-nm-thick Ti0.14Al0.47N0.40-film. ( C) 2000 Elsevier Science S.A. All rights reserved.