eROSITA on SRG

eROSITA (extended Roentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is scheduled for launch in late 2012. eROSITA is fully approved and funded by the German Space Agency DLR and the Max-Planck-Society. The design driving science is the detection of 50-100 thousands Clusters of Galaxies up to redshift z similar to 1.3 in order to study the large scale structure in the Universe and test cosmological models, especially Dark Energy. This will be accomplished by an all-sky survey lasting for four years plus a phase of pointed observations. eROSITA consists of seven Wolter-I telescope modules, each equipped with 54 Wolter-I shells having an outer diameter of 360 mm. This would provide and effective area at 1.5 keV of similar to 1500 cm2 and an on axis PSF HEW of 15' which would provide an effective angular resolution of 25'-30'. In the focus of each mirror module, a fast frame-store pn-CCD will provide a field of view of 1 degree in diameter for an active FOV of similar to 0.83 deg2. At the time of writing the instrument development is currently in phase C/D.