The XMM-Newton (X-ray Multi-Mirror Mission - Newton) is an orbiting X-ray observatory, named in honor of Sir Isaac Newton.

Originally known as the High Throughput X-ray Spectroscopy Mission, it was launched by the European Space Agency from the Guiana Space Centre at Kourou on 10 December 1999 by an Ariane 5 rocket. It was placed in a very eccentric 48 hour elliptical orbit at 40°; at its apogee it is nearly 114,000 km from Earth, while the perigee is only 7,000 km.

The satellite weighs 3800 kg, is 10 m long and 16 m in span with its solar arrays deployed. It holds three X-ray telescopes, developed by Media Lario of Italy, each of which contains 58 Wolter-type concentric mirrors. The combined collecting area is 4,300 cm². The three European Photon Imaging Cameras (EPIC) are sensitive over the energy range 0.2 keV to 12 keV. Other instruments onboard are two reflection grating spectrometers which are sensitive below ~2 keV, and a 30 cm diameter Ritchey-Chretien optical/UV telescope.

The mission was proposed in 1984 and approved in 1985; a project team was formed in 1993 and development work began in 1996. The satellite was constructed and tested from March 1997 to September 1999. The original mission lifetime was two years, it has now been extended for further observations until at least 2010. These observations are managed and archived at the European Space Astronomy Centre (formerly known as VILSPA) at Villafranca, Spain. The information is also processed and archived at the XMM-Newton Survey Science Centre at the University of Leicester, England.

For more information about XMM-Newton, read the full article at Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.