ESA's X-ray space observatory is unique. XMM-Newton is the biggest science satellite ever built in Europe. Its telescope mirrors are the most powerful ever developed in the world, and with its sensitive detectors, it is capable of seeing more than any previous X-ray satellite.
The spacecraft consists of several main sections:
- A nearly seven metre long black telescope tube
- A squarish service module, located at the spacecraft's forward broader end, also carrying the three 'mirror modules' and the deployable solar arrays
- The focal plane assembly housing the X-ray cameras and detectors at the spacecraft's other extremity.
This 'tri-clops', with its golden eyes is more than 10 metres long, just fitting under the Ariane 5 fairing for its launch. Its pair of solar panels has a 16-metre span.
One of XMM-Newton's three golden eyes with its 58 wafer-thin mirrors
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. In terrestrial terms, this is equivalent to using a hand-held telescope and seeing without any jitter a melon placed 180 km away!
Because of their high energy and their interaction with matter, X-rays are difficult to focus. When using mirrors, like XMM-Newton, the mirror surface has to be made of a material that does not readily absorb the X-rays, and the design has to ensure that the incoming rays hit the mirror surface at a shallow angle (grazing). Only in this way can the X-rays be efficiently reflected and directed to a focus point.
XMM-Newton uses barrel-shaped mirrors angled along their length to focus the X-rays on the detectors. The three 'mirror modules' each have 58 wafer-thin nickel mirrors, which are gold-plated and nested in each other just a few millimetres apart. The total mirror surface area of the three mirror modules together exceeds 120 m², rivalling the size of a tennis court. Constructing the mirror modules to such a level of perfection is one of the programme's greatest achievements.
XMM-Newton also carries the Optical Monitor, a 30-cm diameter telescope which observes the same region of the sky as the targeted X-ray sources, but at optical and ultraviolet wavelengths.
Realizing the XMM-Newton mission has been challenging in many respects. The space observatory was built in conditions of exceptional cleanliness to preserve its ultra-polished mirrors. Another requirement was light-tightness to prevent extraneous light entering the detector arrays.
The programme, with the parallel construction of two spacecraft models and the manufacture of the proto-flight model, was conducted in just under three years. Most of the testing was done on a modular basis, and the calibration of the mirror modules required intensive testing and calibration at different sites and facilities in Europe. The satellite was assembled in facilities of unusual dimensions.
Last Update: 19 Sep 2011