XMM-Newton ESA's Satellite Observatory is Unique
by European Space Agency
More articles in SatellitesThe XMM-Newton (X-ray Multi-Mirror) is the biggest science satellite ever built in Europe. Its name derives from its three X-ray telescopes, each containing 58 high-precision concentric mirrors. This large number of mirrors was necessary because of the new technique used to focus the X-rays onto the different detectors. The design made it possible to have the largest collecting area of focusing optics deployed for X-ray astronomy. A simple animation from the Astrophysics and Space and Research Group in Birmingham (UK) shows how the mirrors focus the incoming X-ray photons. No previous satellite could focus even approximately as much radiation as XMM-Newton.
telescope schematicThe spacecraft consists of 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.
This 'tri-clops' with its golden eyes is more than 10 meters long, just fitting under the Ariane-5 fairing for its launch. Its pair of solar panels have a 16 meter 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. In terrestrial terms, this is equivalent to using a hand-held telescope and seeing without any jitter a melon placed 180 km away!
The Mirrors and Detectors
xmm's mirrors X-rays can only be focused by changing their course, accomplished by bouncing them off a surface at a shallow angle. XMM-Newton uses barrel-shaped mirrors angled along their length to focus them on the detectors.
There are three main instruments on-board XMM-Newton with very specific tasks: the European Photon Imaging Cameras (EPIC), the Reflection Grating Spectrometer (RGS), and the Optical Monitor (OM).
The EPIC consists of three cameras ( two called MOS and one called p-n) which each cover a diameter of approximately 30 arc minutes with up to 600 x 600 pixels as small as 1.1 x 1.1 arc sec each. The EPIC MOS and p-n are providing excellent X-ray pictures of the sky in energies ranging from 0.2 to 10 keV.
At lower energy and for stronger point-like sources, the RGS can provide very high signal-to-noise dispersive spectroscopy between 0.35-2.5 keV.
A third instrument, the Optical Monitor (OM) adds multiwavelength information (both in optical and Ultra Violet) to the X-ray observations.
Tell Me More About:
The X-ray Mirrors
The European Photon Imaging Camera
The Reflection Grating Spectrometer
The Optical/UV Monitor
XMM-Newton's Challenges
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.
Fully Assembled Satellite
The 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 purpose-built vertical test facility. The satellite was assembled in facilities of unusual dimensions.
XMM-Newton weighed 3.8 tons on the launch pad. It has been designed to operate for two years in orbit; however, the hydrazine propellant aboard its service module could be enough for ten years. Observation data will be sent back to Earth in real time.
Fully assembled, XMM-Newton stands ten meters tall. It is shown here during acoustic testing at ESTEC in July 1999.