The scientific objectives of this mission,for high-throughput X-ray spectroscopy,call for a powerful 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