Thin film coatings with variable emittance

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Thin film coatings with variable emittance

Larsson, A.L. / Niklasson, G. / Stenmark, L.

The temperature of a nanosatellite in orbit varies strongly as it goes into Earth shadow or solar radiation. A variable emittance panel built with an electrochromic material, could improve the temperature control by providing an adaptive thermal control. The active function is due to an electrochromic layer, WO₃, deposited by sputtering. Intercalation of Li⁺ leads to a change in the electron configuration, which modulates the radiation properties. Thin WO₃ films were deposited onto indium tin oxide (ITO) coated glass by reactive DC sputtering. IR measurements were done in a Perkin-Elmer 983 spectrophotometer. The IR emittance modulation, Delta epsilon of WO₃ films, deposited on ITO coated glass, has been investigated. The emittance, epsilon , is computed from the reflectance, at 25 degrees C. Initial results show emittances in the range from 0.2 to 0.5. A crystalline film has Delta epsilon =0.12, and the amorphous film has Delta epsilon =0.3. IR properties of WO₃ need to be further investigated as well as the construction of a whole device.