The X-Ray Multi-Mirror space telescope, Europe's largest science satellite, is on budget and on schedule for a launch aboard the Ariane 5 on 2 August, 1999, mission managers and scientists reported at a quarterly project review at the Matra Marconi Space (MMS) factory at Filton in Bristol, in the UK.

Meeting the schedule was an achievement in itself, considering that much of "-the technology for the XMM, including the reflection-grating spectrometer, was not available" when the mission was given the go-ahead in 1988, according to ESA project manager Robert Lainé.

The 3,900kg, 10m-long XMM, built by prime contractor Daimler-Benz Aerospace subsidiary Dornier, is the second European Space Agency (ESA) Cornerstone mission. It is equipped with three highly sensitive X-ray-imaging cam- eras, two high-resolution X-ray spectrometers and a 300mm-diameter optical-monitoring telescope which will, for the first time, enable simultaneous observations in the visible and near-infra-red wavelength.

The attitude and orbit-control system - being developed by MMS - will enable the XMM to remain pointing at a specific target for up to 40h, providing images of unparalleled sensitivity of the hottest objects in the universe, with temperatures exceeding 10,000¹C. These are produced by extreme forces powered by intense gravitation and include quasars and black holes in the hearts of distant galaxies. The XMM will be five times more sensitive than NASA's X-Ray Astrophysics Facility (AXAF), which will be deployed by the Space Shuttle in 1998. The AXAF, however, will have optical spatial resolution superior to that of the XMM.

The XMM telescope will be placed into an eccentric, 100,000 x 7,000km orbit, with an orbital period of 48h, enabling the craft to be outside the Earth's interfering radiation belts for as long as possible. The cost of the ten-year XMM mission will be about $800 million.

The selection of the Ariane 506 for the XMM launch in August 1999 indicates the conservative schedule being accorded to the Ariane 5. The 506 will be only the third fully commercial mission operated by Arianespace. The first three launches are development missions. The maiden flight 501 failed, the 502 is scheduled for launch late this year and the 503 - carrying a commercial satellite from Arianespace's manifest - is planned to be launched in 1998.

Source: Flight International