Building the XMM-Newton Spacecraft and Payload - A picture gallery
IntroductionAn description of the (expected) science performance of XMM and its instruments is provided in our XMM Users' Handbook. Here we describe the process of building the XMM spacecraft and its payload, with a lot of photos showing the satellite hardware. The accompanying text sets the background for the picture gallery presented here, but is not meant to be an extensive satellite description.
Various parties require acknowledgement for the photo material, and where possible are noted for each image. Particular thanks are due to the XMM Project team at ESTEC, Centre Spatial de Liege, Medialario, Dornier, Max-Planck-Institut für extraterrestrische Physik (MPE) and the Space Research Organization of the Netherlands (SRON), Utrecht.
- note that most photos have been scanned at high resolution. The file sizes are of order 200 to 500 kB. Depending on the speed of your connection to the outside world, these might take some time to download (but we think it's worth the wait)!
The presentation of the hardware construction of XMM is structured into several sections. In order to go to one directly, please click on the component you want to read about. If you want to follow this document step by step, just proceed from here.
The different constituents of XMM are presented in the following order:
The XMM spacecraftIn order to provide an overview of the satellite first, artist's impressions of XMM in orbit are shown below.
The different components of the XMM spacecraft and its payload are visible in sketches in which XMM has been "disected", as shown in the following images.
A series of photos shows how the XMM spacecraft, which had been taken apart for transport, is re-assembled at the ESTEC testing site. The first part of the spacecraft with the focal instruments is lifted by a crane and placed ontop of the second part of the tube holding the so-called "service module".
In the following, we will present the XMM mirror modules. More information on the instruments onboard XMM is provided further below. To go there directly, please click either here or on the instrument name.
The XMM payloadXMM's payload consists of three X-ray telescopes, the science instruments on these, a parallel-mounted optical/UV telescope and two star trackers. Before going on to the science instruments, we will first describe the construction of XMM's mirror systems.
The mirror modulesThe above two sketches show that XMM, unlike previous generations of X-ray telescopes (e.g. Einstein and ROSAT) will not employ massive, highly polished glass mirrors. Instead, in order to obtain very high collecting area, a mirror replication technique is used. In this process, thin nickel shells are electroformed onto highly polished mandrels. Each mirror shell is made of a parabolic and a hyperbolic section. This combination constitutes the Wolter design. 58 concentric shells are co-aligned in each of the threee mirror modules. The use of two mirrors each shortens the focal length of the telescopes from ca. 30 m (top) to 7.5 m (bottom). At the same time, the two mirrors minimize astigmatism. The Wolter design is the X-ray equivalent to the optical Cassegrain design. The mirror shells are being produced in Italy by the company Media Lario/Kayser Threde.
The scope of this ambitious programme is to build the largest collecting area of focusing optics deployed for X-ray astronomy. No previous satellite could focus even approximately as much radiation as XMM. At the same time, the XMM mirrors still maintain an excellent angular resolution with a resolving power (Full Width at Half Maximum) of ca. 6 arcseconds and a Half Energy Width of its point-spread function of ca. 15 arcsec. Some photographic examples of the mirror mandrels achieving these tasks are provided below. The first set of photos shown below displays one of the flight modules (FM), namely the FMx mirror module, at Centre Spatial de Liege (CSL) in Belgium. As ordered below, the images show:
From early testing to flight modelsIn the following, we provide some historic background information on the mirror development. The mirror assembly is performed at the Medialario facility.
First, test mirrors were produced, leading to the assembly of a "Qualification Model", QM. The production process involves several steps.
The XMM science instrumentsThe light paths in XMM's three Wolter 1 telescopes are fixed. Except for a minimum of moveable parts within the detectors (see below), there are no moveable parts in the light path in front of them. The mirrors thus focus X-ray photons in the way illustrated in the two sketches above onto a suite of focal instruments, which are built by several teams all over Europe. The three basic types of detectors onboard XMM are:
European Photon Imaging Camera (EPIC)These are XMM's prime focus CCD cameras. The whole camera system production is coordinated by the CNR IFCTR group in Milano. They are also responsible for fabrication of the digital electronics which interfaces to the XMM spacecraft.
p-n cameraThe p-n camera CCDs are new technology X-ray CCDs, with 6x2 chips on a single wafer. Thus, they are produced as one array and not assembled later, as in the case of the MOS camera. With 64x200 pixels per chip, the p-n camera offers a square field of view with a size similar to that of the 7 MOS chips. The chip array itself is embedded in an electronics board carrying the camera electronics. The EPIC p-n camera as a whole is shown here.
Only one of XMM's three telescopes, namely that without a grating spectrometer in the light path (see below), is using a p-n camera.
The EPIC p-n camera is built by the Max-Planck-Institut für extraterrestrische Physik (Garching) and Astronomisches Institut Tübingen.
MOS cameraThe MOS camera system is produced by a consortium which includes Leicester University (CCDs and camera head), the University of Birmingham (thermal control system) and CEN Service d'Astrophysique Saclay (control and event recognition electronics). Each camera consists of an array of 7 CCD chips of 600x600 pixels each. The chips are built and wired individually and then arranged into the pattern visible in the photo. This provides a large field of view at the prime focus of XMM. Note that the vertical offset of the chips with respect to each other is exaggerated in the photograph. The central chip does indeed sit farther back than the surrounding six, however by only a few millimetres, following the slight curvature of XMM's focal surface.
More information on EPIC will be added here as soon as more photos become available.
Reflection Grating Spectrometer (RGS)
Reflection Grating Arrays (RGAs)As mentioned above, two of XMM's three X-ray telescopes are equipped with RGS detectors. Dispersive spectroscopy in the X-ray domain is a new technology and XMM is the first satellite to fly with Reflection Grating Arrays (RGAs) onboard.
In the photos above one can see how the RGAs disperse (for illustrative purposes optical) light.
RGS focal cameras (RFCs)The RGAs intercept ca. 50% of the total incoming radiation, reflecting the light onto linear arrays of 9 MOS chips each in two of XMM's X-ray telescopes (cf. EPIC MOS).
The CCD arrays are elongated along the dispersion direction of the RGAs, with a cross-dispersion width of ca. 5' and a length that ensures that no emission of an X-ray source at small off-axis angles (<5') is lost off the edges of the arrays. The arrays are actually so long that one does not only detect light from the -1. grating order, but also the -2., -3., and (depending on the brightness of the source) possibly even higher orders.
Testing of an RGS focal camera (RFC) at the Panter facility test beam facility is displayed in the next set of photos.
The temperature of the RFCs is controlled via a radiator at the end of its mechanical/thermal structure. Note that these radiators are the grey surfaces that are visible in one of the above photos of XMM in the ESTEC testing facility.
A more detailed view of an RFC is provided in the following photo. Here, one can see several components of the RGS hardware, including the radiator with its struts (black) and the camera's metal casing.
Optical Monitor (OM)XMM, although primarily an X-ray observatory, provides an up to now unique opportunity, namely a small but powerful optical/UV 30 cm telescope co-aligned with the X-ray telescopes for contemporaneous observations.
The OM consists of a modified 30 cm Ritchey-Chretien telescope with a focal ratio of f/12.7, i.e. a focal length of ca. 3.8 m. The incoming light is reflected by a mirror inclined at an angle of 45° to one of two redundant detectors. The OM telescope tube with baffle is shown in the following photos.
The OM telescope tube is ca. 2 m long. Incoming light falls onto the primary mirror, which reflects it onto the secondary, from where it goes to the inclined mirror that reflects it onto the detector (see above). Right in front of the detector, a filter wheel is mounted. This does not only contain filters, but also other optical elements, like grisms and a magnifier (i.e. optics for a longer focal length and thus higher resolution on the sky). The mirror, filter wheel and detector are displayed in the following two photos.
A schematic cut through an OM MIC is displayed in the following figure. The light enters from above, passing through an entrance window and hitting a photocathode. From there, the signal is amplified about 100,000 times in total by three consecutive MCPs, before the electrons hit a phosphor layer, from which the resulting photons are imaged onto the CCD (at the bottom).
More information on OM will be added here as soon as more photos become available.
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