  XEUS is under study by ESA as part of the Horizon 2000+ program to utilize
the International Space Station (ISS) for astronomical applications. XEUS will
be a long-term X-ray observatory with an initial mirror area of 6m2 at 1 keV
that will be grown to 30m2 following a visit to the ISS. The 1 keV spatial
resolution is expected to be 2-5'' HEW. XEUS will consist of separate detector
and mirror spacecraft aligned by active control to provide a focal length of
50m. A new detector spacecraft, complete with the next generation of
instruments, will also be added after visiting the ISS. The limiting
sensitivity will then be ~4 10-18 erg/cm2/s - around 250 times better than XMM,
allowing XEUS to study the properties of the hot baryons and dark matter at
high redshift.
