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Interplanetary spacecraft which are operating in the outer solar system are normally powered by Radioisotopic Thermoelectric Generators. The European (ESA) scientific spacecraft Rosetta however, which shall explore the comet „Wirtanen” begining in the year 2011, shall be powered by low-intensity, low-temperature solar cells even for Sun distances of up to 5.25 AU. To keep the solar array area within feasible sizes, strict power saving is mandatory. Heater power is saved by mitigating the large solar flux differences between hot and cold cases by the thermal design. The resulting thermal design features are louver radiators, superior performance insulation, two stage radiant cooler and electrical heaters. Heater power is saved by reducing the difference between the external heat load in the hot and cold cases by the configuration and the attitudes of the spacecraft which shadow louver radiators and payload from direct sun radiation.

Electro emissive devices, called ESTHER, are thin sheets - similar to solar cells - whose infrared emissivity can be varied reversibely by electrical charging. Bonded to external surfaces of spacecraft radiators, they allow active control of the heat radiated to space while consuming negligible electrical energy. Applying this novel component for spacecraft thermal control, considerable cost savings in spacecraft development and operation can be achieved. Progress in the design and manufacturing process has been made since the first puplication in July '92 /1/ revealing an increased variability of emissivity and an increased duty cycle stability. The material selection process was facilitated by the exposure of material samples to the space environment during two spaceflight missions and the subsequent material analyses.

Electroemissive (ESTHER) devices are thin sheets - similar to solar cells - whose infrared emissivity can be varied reversibly by electrical charging. Bonded to the external surfaces of spacecraft radiators they can be used for the active control of the Irradiated heat by consuming negligible electrical energy. The window to a revolutionary new thermal control design technology for spacecraft may be opened.