  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 ~
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 ~ 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 deg
in diameter for an active FOV of ~ 0.83 deg^2. At the time of writing the
instrument development is currently in phase C/D.
