XMM preparation

XMM during testing at ESA/ESTEC's facilities. The scientific objectives of the XMM mission, for high-through put X-ray spectroscopy, call for a powerfull imaging instrument with the largest possible collecting area, for high-quality spectral measurements of faint sources down to 2x10 -15 erg/cm2/s, together with fast low -and medium- resolution spectroscopy of brighter objects. An assembly of 51 mirrors, carefully sized, formed and nested one inside another, makes the most sensitive X-ray telescope ever built. XMM will carry three identical telescopes of this kind. This astrophysics mission is a "Cornerstone" in ESA's long-term Space Science Programme "Horizon-2000" and the launch took place on December 10th, 1999.