At the time of construction, the XMM-Newton observatory was the biggest science satellite ever built in Europe, and is ESA's second cornerstone of its Horizon 2000 program. Its name derives from its three X-ray telescopes, each containing 58 high-precision concentric mirrors.
The spacecraft consists of three main sections:
- a seven meter long black telescope tube;
- a squarish service module also carrying three "mirror modules" at its forward broader end;
- the focal plane assembly housing the X-ray cameras and detectors at its other extremity.
The XMM spacecraft standing upside down in the clean room at ESA's ESTEC facility. Its front end, where the mirror modules of the X-ray telescopes pass through the satellite's service module, is closest to the ground. At the top is the section containing detectors at the focus of the X-ray telescopes. XMM will be protected from unequal heting on the sunny and shaded sides by the black thermal blanket. (Credit: ESA)
This 'tri-clops' with its golden eyes is more than 10 meters long, just able to fit into the payload bay of the Ariane-5 rocket. XMM-Newton receives power through its pair of solar panels, giving it a 16 meter "wing" span.
The spacecraft's design features extremely high mechanical stability. Its position and control systems allow it to point at targets in the sky over long periods with a remarkable pointing accuracy of 0.25 arcsec over a ten second interval. This is about 1/8000th the diameter of the Moon in the sky, or equivalent to using a hand-held telescope and clearly seeing a melon placed 180 km away!
The space observatory was built in conditions of exceptional cleanliness to preserve its ultra-polished mirrors. Another requirement was its light-tightness to avoid extraneous light. The XMM-Newton program, with the parallel construction of two models and the manufacture of the proto-flight model, was conducted in the space of just less than three years. Most of the testing was done on a modular basis, and the calibration of its mirror modules required a custom-built vertical test facility.
XMM-Newton weighed 3.8 tons on the launch pad. It was designed to operate for at least two years in orbit, and it has already exceeded this specification. It is expected to be operational for many more years; the hydrazine propellant aboard its service module could be enough for a total lifetime of ten years.