The Thermal Control System of the X-Ray Telescope Erosita on Spektrum-Roentgen-Gamma

The X-ray telescope eROSITA is the main instrument besides the Russian ART-XC on the Spektrum-Rontgen-Gamma mission. Starting from 2014, an all-sky survey will be performed in the range between 0.3-10 keV, followed by pointed observations. The main objective of this mission is the detection of 100 000 galaxy clusters in order to constrain cosmological parameters, amongst others the density distribution and evolution of dark energy.Due to the minimum lifetime of seven years the thermal control system has to be completely passive without any consumables. With the ideal operational temperature of the CCD cameras being between 173K and 183K, this requires a very effective heat rejection system, consisting of a complex heat pipe system and a good thermal insulation. Simultaneously, a very sensitive temperature control via variable conductance heat pipes is implemented. For special outgassing requirements at the beginning of the mission these heat pipes are not working after launch but can be switched on any time.On the other hand the mirror modules have to be tempered at room temperature and more than 200W of the electronics have to be dissipated without affecting the surrounding components or the satellite structure.The thermal control system has to be able to keep up the required temperature range and has to guarantee the optimum working conditions for all parts of the instrument. Calculations and verification tests validated the thermal concept.