XMM-Newton ObservatoryAn important X-ray astronomy satellite launched on top of an Ariane 5 rocket by the European Space Agency (ESA) in Dec. 1999 from Kourou, French Guiana. Named officially the High-Throughput X-ray Spectroscopy Mission, it became better known as XMM-Newton from the facts that it is an X-ray multi-mirror (XMM) space observatory and it commemorates the great English physicist Sir Isaac Newton, the ‘father’ of spectroscopy. Its mission was nominally to last two years but it was designed to function for a decade and was still operating smoothly at the end of 2004.
Launched less than six months after NASA's Chandra X-Ray Observatory, XMM-Newton rivals Chandra in technological sophistication. At the time of its launch, the 10-meter-long, 3.8-tonne XMM-Newton was the largest science satellite ever built by ESA. Like Chandra, it observes the hot, high-energy phenomena of the Universe with unprecedented sensitivity, revealing thousands of hitherto unknown X-ray sources. Its observing program is set to include monitoring of the hot regions surrounding black holes and the centers of galaxies, examining the X-ray output of supernova remnants, investigating the X-ray component of the cosmic background radiation, and analyzing the results of gamma-ray bursts. It is also seeking to discover the true nature of the matter making up an ultradense neutron star.
As its official name suggests, X-ray spectroscopy is a central element in XMM-Newton's mission program, and it carries scientific instruments designed to reveal the chemical makeup, temperature and velocity of the new X-ray sources it discovers. Its high-technology design consists of three huge coaligned X-ray telescope barrels made of nickel, each holding 58 wafer-thin cylindrical grazing-incidence mirrors nested inside each other, occupying an area the size of a tennis court. Each mirror has a coating of gold less than a millimeter thick to reflect X-rays that would normally pass right through. In the focal plane of each of the three X-ray telescopes lies a CCD camera providing imaging spectroscopy at a resolution of E/δE ≊ 100 at 6 keV over a 30 arc-minute-diameter field of view. Two of the telescopes also carry reflection-grating spectrometers delivering a resolution of between 100 and 600 in the energy range 0.35–2.5 keV. XMM-Newton also carries a small optical and ultraviolet telescope. Four small thrusters using hydrazine gas and four momentum wheels mounted on the spacecraft allow its attitude to be altered when aiming at a source. XMM-Newton's highly elliptical orbital path around the Earth (apogee 114 000 km, perigee 7000 km) takes it almost a third of the way to the Moon, and one orbit takes 48 hours to complete, so that astronomers can enjoy long, uninterrupted views of celestial objects and long exposure times unhindered by Earth shadowing.