Electro emissive (Esther) devices are thin sheets, whose infrared emissivity can be varied reversibly 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. Due to the very low mass and power consumption of that novel component for space craft thermal control, considerable cost savings in development and operation can be achieved.In the current phase of the development the performance of the Esther devices, achieved in the laboratory, is optimised (where necessary) and consolidated. The applied processes of the thin film technology and the internal structure and materials of the different layers have been optimised w.r.t. reproducibility and stable performance. The manufacturing and the functional test of the Esther devices has been standardised and a number of prototypes were produced (about 200).In parallel to this work a radiator for about 100 elements was designed with all necessary equipment (controller, sensors, data acquisition) and equipped with Esther devices, which shall be space qualified in the second half of 1995. The aim of the development is a flight experiment with the Esther radiator as a demonstrator on a spacecraft. It is planned to fly the demonstrator with the German ASTRO-SPAS on its mission CRISTA-SPAS II in early 1997.