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    ESA Science News

    9 Feb 2000

    Eye openers from XMM

    The first pictures from ESA's new X-ray space observatory fully demonstrate the capabilities of the spacecraft's telescopes and its science instruments. The images were officially presented on 9 February at the XMM-Newton Science Operations Centre in Villafranca, Spain.

    Full story, images and 3rd competiton details.

    European Space Agency
    Paris, France

    2 February 2000

    ESA's X-ray space observatory XMM takes first pictures

    The European Space Agency's X-ray space observatory has taken its very first pictures giving new views on the Universe. The commissioning images confirm that the XMM spacecraft, its X-ray telescopes and science instruments are functioning perfectly, to the great satisfaction of all involved.

    Under the aegis of Prof. Roger Bonnet, ESA Director of Science, the mission's Principal Investigators will be presenting these spectacular first images at a press conference to be held on 9 February at the ESA Vilspa facility at Villafranca/Madrid in Spain, where the XMM Science Operations Centre is located. The event will also be the occasion for several major announcements concerning the XMM mission.

    In particular Professor Bonnet will launch the third XMM competition "Stargazing" -- previously announced in September 1999. This will address European youngsters, 16 to 18 years old, who will be offered the unique opportunity of winning observing time using the X-ray telescope.

    Commissioning phase starts

    After a successful launch from Kourou on Ariane 504 on 10 December 1999, XMM was brought to its final operational orbit in the following week. The telescope doors on the X-ray Mirror Modules and on the Optical Monitor telescope were opened on 17/18 December. The Radiation Monitor was activated on 19 December and the spacecraft was put into a quiet mode over the Christmas and New Year period.

    The mission's scientific data is being received, processed and dispatched to astronomers by the XMM Science Operations Centre in Villafranca. Operations with the spacecraft restarted there on 4 January when, as part of the commissioning phase, all the science payloads were switched on one after the other for initial verifications. By the week of 17 January functional tests had begun on the Optical Monitor, the EPIC pn, the two EPIC MOS and the two RGS instruments. The internal doors of the EPIC cameras were opened whilst keeping the camera filter wheels closed.

    Astounding first images

    After a series of engineering exposures, all three EPIC cameras were used in turn, between 19-24 January, to take several views of two different extragalactic regions of the Universe. These views, featuring a variety of extended and X-ray point sources, were chosen to demonstrate the full functioning of the observatory. The Optical Monitor also simultaneously viewed the same regions. One RGS spectrometer obtained its first spectra on 25 January; the other will be commissioned at the start of February.

    This initial series of short and long duration exposures have delighted the Project management team and the scientists even more. First analyses confirm that the spacecraft is extremely stable, the XMM telescopes are focusing perfectly, and the EPIC cameras, Optical Monitor and RGS spectrometers are working exactly as expected. The Science Operations Centre infrastructure, processing and archiving the science data telemetry from the spacecraft, is also performing well.

    Initial inspection of the first commissioning images immediately showed some unique X-ray views of several celestial objects, to be presented on 9 February. The occasion will give Principal Investigators and Project management the opportunity to comment on the pictures and the excellent start of the XMM mission.

    The Calibration and Performance Verification phase for XMM's science instruments is to begin on 3 March, with routine science operations starting in June.

    ESA Science News

    07 Jan 2000

    XMM instrument commissioning

    All of XMM's instruments have been switched ON and their computer software loaded on board. The first task has been to check the health of the instruments repeating the engineering test procedure used on the ground before launch. This has confirmed that all instruments remain in the same condition as before launch. This was also the 'acid test' to verify that the instrument data sent by the spacecraft were reaching Villafranca and were being processed correctly. On 4 January, to everyone's relief, the first data arrived and were processed correctly by the new software installed at the XMM Science Observations Centre. Watching this important event, XMM project manager Robert Lainé commented: "I saw big smiles all around when EPIC then later test images appeared on the screen."

    All the data collected are now being processed in detail by the various institutes which contributed to the development of XMM scientific instruments.

    Currently all instruments are in the 'shut' position (i.e. not looking at the sky) and will remain this way until all parameters of the instruments have been analysed and understood.

    Later this month one by one the X-ray cameras will be opened briefly to have a peek at the real sky. Again the data collected will be analysed before the start of routine operations. The reason for this careful step-by-step deployment of the instruments is to make ensure that there is no surprise degradation of the detectors, for example due to a sudden solar flare sending a heavy dose of high energy radiation and increasing the altitude of the earth radiation belts. In such a case the protective shutters of the cameras would be shut; but of course the operators have first to gain experience in controlling the delicate instruments of XMM before exposing them to the harsh 'space weather'.


  • XMM science instruments
  • ESA Bulletin XMM special
  • XMM science operations centre


    Image 1:
    A simulated EPIC p-n camera deep-field exposure.

    Image 2:
    Simulation of an XMM RGS observation of Capella.


    Paris, 20 December 1999

    XMM flying beautifully

    The European Space Agency's new X-ray space telescope has reached its operational orbit less than a week after being launched from Kourou on 10 December. The XMM spacecraft, which is being controlled by teams at the ESA's Space Operations Centre, ESOC in Darmstadt Germany, is functioning admirably.

    The early orbit phase came to an end on 16 December after XMM had been manoeuvred to its final orbit. This required four firings of its thrusters, on successive passages at apogee, in order to increase XMM's velocity, thus elongating its orbit and raising the perigee from 826 km to 7,365 km. One burn was then made to fine tune the apogee to around 114,000km. The spacecraft, being tracked by ground stations in Perth, Kourou and Villafranca, is now circling the Earth in this highly elliptical orbit once every 48 hours.

    The XMM flight operations staff have found themselves controlling a spacecraft that responds exceptionally well. During these first orbits, the satellite has been oriented several times with razor-sharp precision. On board systems have responded without incident to several thousand instructions sent by controllers. "XMM is flying so beautifully" says Dietmar Heger, XMM Spacecraft Operations Manager. "The satellite is behaving better in space than all our pre-launch simulations and we have been able to adjust our shifts to this more relaxed situation".

    On his return from French Guiana, Robert Lainé, XMM Project Manager immediately visited the Darmstadt Mission Control Centre, at ESOC. "The perfect behaviour of XMM at this early stage reflects the constructive cooperation of European industrial companies and top scientists. Spacecraft operations are in the hands of professionals who will endeavour to fulfill the expectations of the astronomers and astrophysicists of the world. I am very happy that ESA could provide them with such a wonderful precision tool".

    During the early orbit phase, controllers have activated part of XMM's science payload. The three EPIC X-ray cameras have been switched on and vented. On 17 December the telescope doors were opened allowing the spacecraft's golden X-ray Multi Mirror modules to see the sky. The Optical Monitor telescope door was opened on 18 December. During this last weekend, XMM's Radiation Monitor which records the flux of cosmic particles and radiations was switched on.

    Mission controllers have now placed XMM in a quiescent mode for the Christmas and New Year period. Full operations will resume on 4 January with the start of the spacecraft commissioning phase due to last until 15 February. ESA's XMM Science Operations Centre at Villafranca will be brought online early January allowing the start of the exhaustive calibration and performance verification phase of XMM's science instruments. Progress on this calibration should allow the telescope to target and take "firstlight pictures" of its first X-ray sources next March.

    Further information on XMM and the ESA Science Programme can be found on the Worldwide Web at: http://www.sci.esa.int/.

    ESA Science News

    13 Dec 1999

    XMM into operational orbit

    Over the weekend, the extreme tension of the launch itself disappeared. The XMM satellite is now in the safe hands of the ESOC control teams. In their Main Control Room, XMM has yet to be chalked up on the record board. It is the 42nd mission to be handled by ESOC since 1968.

    Since first acquisition of the spacecraft telemetry, XMM is being gradually manoeuvred to reach its definitive operational orbit. Saturday midday, 24 hours after liftoff, the satellite was at its first apogee, the furthest point from Earth.

    The large display screens on the wall indicate the precise distance, 113,850 km. A planisphere indicates where the satellite's position in space relative to Earth and the visibility for each ground station. The display shows that Perth is being used and that the satellite is high in the night sky over Australia.

    The atmosphere is calm in the Darmstadt control centre. Some operators appear to be so relaxed than an observer might get the impression that nothing is really happening. But no, with a clockwork rigour following their pre-established flight plan, the ESOC flight control teams are preparing for the second of two perigee boost manoeuvres on this first orbit. The first took place two hours earlier.

    The spacecraft is behaving perfectly. As an illustration, during its first 24 hours in space XMM had received some 1240 tele-commands and none had been rejected on-board. Amongst these commands were the activation of the small Visual Monitoring Cameras (VMC). Their pictures created great excitement when they were displayed for the first time after being sent back by the spacecraft.

    The perigee boosts are crucial if XMM is to reach its definitive orbit. Each time the operation consists in activating the spacecraft thrusters in order to increase the spacecraft's velocity. This additional speed elongates the orbit so that at its closest point to Earth, XMM will pass at a higher altitude. After launch, XMM had been released by Ariane 5 at 826 km. The first boosts raised the perigee to 4900 km.

    Three perigee boosts (the first in two parts) are required to raise XMM's perigee to the nominal 7000 km of its operational orbit. A final manoeuvre will then adjust the apogee to precisely 114,000 km.

    Brightly coloured schematics and graphs are displayed on the consoles of the Flight Operations Director, and those of the XMM Project team representatives. On these, can read the temperature and pressure throughout the propulsion system, for example for each of the thrusters as they are firing and the four hydrazine propellant tanks.

    Controllers can also obtain a graphic view of what the spacecraft's star trackers are seeing. For example, on this apogee passage, five stars are represented. It is to these points in space that XMM's Attitude and Orbit Control system has locked-on to maintain the spacecraft attitude.

    XMM has eight main thrusters in two redundant sets. For each perigee boost, one set is activated, the other remain as a backup. All four thrusters work at the same time, providing not only the increase in velocity but also maintaining XMM's orientation.

    The thruster firings last quite long. 53 and 98 minutes on the first orbit, 40 minutes on the second orbit, 55 minutes for the final manoeuvre. Each time the spacecraft's velocity is increased, for example by 87 m/sec on the longest burn. During these manoeuvres, the greater part of XMM's 530 kg of hydrazine will be consumed. For instance 276 kg were used on the first orbit burns.

    When XMM is at its furthest distance from Earth, it is travelling at some 670 m/sec, 2400 km/hour. Certainly very fast in human terms, but when it returns at its perigee passage, it whizzes past Earth nine times faster!

    By Thursday 16 December, after fine tuning the apogee on orbit 4, the spacecraft will have been placed in its operational orbit. The Launch and Early Operations Phase of the mission will be over. XMM will then have a few days of relative calm whilst the ESOC teams enjoy a well-deserved Xmas and New Year holiday.

    Images supporting this release.

    ESA Science News

    13 Dec 1999

    ESOC and XMM teams celebrate Santa Lucia

    Some very special "rocket fuel" was awaiting the B-team XMM flight controllers when they came off shift, midday on December 13. Swedish staff had organised a gathering to celebrate Santa Lucia, Sweden's traditional remembrance of the Sicilian saint.

    XMM's Anders Elfving (Attitude and Orbit systems engineer) and Anders Karlsson (TTC & software engineer) had prepared the potent beverage, called "gl=F6gg", a mixture of wine, spices and a dash of vodka. They were assisted by Swedish colleagues from ESOC Mats Rosengren and Boris Smeds, Tommy Strandberg from Dornier and Andreas Hedqvist from XMM contractor VEGA.

    Whilst the XMM spacecraft continued on its second orbit, the corridor outside the Main Control room resounded to the strains of a violin and the song of Santa Lucia. Everyone heartily enjoyed the gl=F6gg and gingerbread cookies. The Swedish nationals of the XMM project team have always celebrated Santa Lucia at ESTEC, during the development phase of the project. But it was the first time that the feast was celebrated at ESOC.

    XMM was a few hours away from another boost of its thrusters, to again raise its perigee. People at the small party joked about the effects the beverage might have on the increase in speed, but Flight Operations management assured everyone that there was no gl=F6gg on board the spacecraft -- and that the A-team about to take responsibility for XMM were following a dry path into the control room!

    Images supporting this release

    ESA Science News

    11 Dec 1999

    XMM takes pictures of itself!

    The XMM spacecraft, launched on 10 December from Kourou, has sent back pictures of itself in space.

    The photographs were taken by two micro-cameras placed on the exterior of the spacecraft's focal plane assembly. Provided by OIP, subsidiary of Delft Sensor Systems, Antwerp, Belgium, the two cameras (10 x 6 x 6cm) each weigh but 430 grams.

    The cameras are of two types: the FUGA camera has a logarithmic response, with a high dynamic range, providing a black and white picture. The exposure time of the second IRIS camera with a colour filter, can be modified. The field of view of both cameras is fixed (approx. 40 deg x 40 deg), giving a view along the telescope tube towards the service platform and the solar arrays.

    These pictures were taken just under five hours after liftoff, at 19:25 UT (20:25 CET). XMM was then at an altitude of 55,300 km above the Earth's surface. Because of constraints due to the spacecraft's orientation at this time, the cameras could not have a view showing our planet.


    XMM launch clips and more images


    Image 1:
    Picture taken by XMM's FUGA camera showing the telescope tube and one solar array on the left. At the top of the picture, one sees the edges of the now deployed telescope sunshield. What appears as a white boom in centre is in fact one of the fixed lateral sunshield panels, seen side-on. 10 December 1999, 5 hours after launch.

    Image 2:
    Picture taken by XMM's IRIS camera show the other solar array on right. At the bottom of the photograph (below the ESA flags) is the MLI thermal insulation just under the lens of the camera.

    ESA Science News

    11 Dec 1999

    XMM in safe hands

    During the first hours after XMM's acquisition by the Perth ground station, the spacecraft control teams at ESOC nursed their baby through its initial in-orbit sequences. Triggered by the onboard timer, the two wings of the solar array opened faultlessly, the telescope sunshield equally well. The star trackers were switched on and the spacecraft's reaction wheels were spun up.

    On a large screen in the Main Control Room, an animation showed XMM's position in space, moving away from Earth on its first orbit. Dietmar Heger, spacecraft controller commented: "It's going very, very nicely. Almost better than the simulations we have been through before launch".

    To reach its definitive orbit, commands will be sent to the satellite to fire its onboard motors several times. On the first orbit, in two burns some 22 and 24 hours after liftoff, the velocity of the spacecraft will be increased so as to start raising the perigee. A second perigee raising manoeuvre will take place at +69 hours and a third at +117 hours. At the start of orbit 4 another manoeuvre will fine-tune the apogee, before XMM is configured for its definitive operational orbit (114,000 x 7,000km)

    During the early orbit phase, part of XMM science payload (notably the three EPIC cameras) are to be switched on, in order to vent the instruments of any residual air. On orbit 5, the radiation monitor will be switched on (to start collecting data on the passages through the Earth's radiation belts) and on the sixth orbit, the door to the Optical Monitor will be opened.

    XMM will be placed in a "sleep mode", pointing at a bright star that will not be occulted during this period over the Xmas and New Year holidays. Operations will resume on 4 January. A long phase of commissioning the spacecraft in orbit and calibration of the instruments will precede the start of the first science observations, scheduled next spring.


  • More news and video clip
  • ESOC homepage


    Image 1:
    Dietmar Heger (XMM spacecraft controller) and his "baby in space". "It's going better than the simulations". ESOC main control room, 10 December 1999.

    Image 2:
    Alan Smith, flight operations manager (on right) explaining XMM first sequences to Jocelyne Landeau (ESOC PR) and Martin Huber. Mission control room at ESOC, 10 December 1999.

    ESA Science News

    10 Dec 1999

    Europe's latest space telescope is off to a good start

    The world's most powerful observatory for X-ray astronomy, the European Space Agency's XMM satellite, set off into space from Kourou, French Guiana, at 15:32 Paris time on 10 December. The mighty Ariane 5 launcher, making its very first commercial launch, hurled the 3.9-tonne spacecraft into a far-ranging orbit. Within one hour of lift-off the European Space Operations Centre at Darmstadt, Germany, confirmed XMM was under control with electrical power available from the solar arrays.

    "XMM is the biggest and most innovative scientific spacecraft developed by ESA so far," said Roger Bonnet, ESA's Director of Science. "The world's space agencies now want the new technology that ESA and Europe's industries have put into XMM's amazingly sensitive X-ray telescopes. And the world's astronomers are queuing up to use XMM to explore the hottest places in the universe. We must ask them to be patient while we get XMM fully commissioned."

    XMM's initial orbit carries it far into space, to 114,000 kilometres from the Earth at its most distant point. On its return the satellite's closest approach, or perigee, will be at 850 kilometres.

    The next phase of the operation, expected to take about a week, will raise that perigee to 7000 kilometres by repeated firing of XMM's own thrusters. The spacecraft will then be on its intended path, spending 40 hours out of every 48-hour orbit clear of the radiation belts which spoil the view of the X-ray universe. Technical commissioning and verification of the performance of the telescopes and scientific instruments will then follow. XMM should be fully operational for astronomy in the spring of 2000.

    All of ESA's science missions present fresh technological challenges to Europe's aerospace industries. In building XMM, the prime contractor Dornier Satellitensysteme in Friedrichshafen in Germany (part of DaimlerChrysler Aerospace) has led an industrial consortium involving 46 companies from 14 European countries and one in the United States.

    XMM stands for X-ray Multi-Mirror Mission. Its main telescopes will gather X-rays from the cosmos with 120 square metres of gold-coated surfaces, in 174 mirrors fashioned, smoothed and nested together with high precision by contractors in Germany and Italy.

    With XMM, Europe has taken the lead in X-ray missions and X-ray detectors: the most sensitive and largest ever made. The four complex scientific instruments on XMM have been developed and led by European scientists with participation from institutes worldwide.

    Compared with NASA's Chandra X-ray telescope launched earlier this year, XMM is at least 5 times more sensitive. The gain in sensitivity is 15-fold, at high X-ray energies. But Chandra has a sharper view, so the two missions are complementary and there is close transatlantic collaboration among the scientists involved.

    Prime scientific objectives for XMM are to find out exactly what goes on in the vicinity of black holes, and to help to clear up the mystery of the stupendous explosions called gamma-ray bursts. Other hot topics for investigation include cannibalism among the stars, the release of newly made chemical elements from stellar explosions, and the origin of the cosmic rays that rain on the Earth.

    XMM is one of a carefully-planned series of scientific satellites built in Europe by which ESA has established a pioneering role in space astronomy. Recently completed missions include the very successful star-mapping satellite Hipparcos, and the Infrared Space Observatory which revolutionized astronomers' knowledge of the cool parts of the universe. Coming along after XMM are Integral for gamma-ray astronomy, FIRST for the far-infrared, and Planck for examining the entire cosmic microwave background far more accurately than ever before.

    Images supporting this release.

    Satellites Business Unit
    DaimlerChrysler Aerospace AG
    Munich, Germany

    December 10, 1999

    Europe's Biggest Space Observatory, XMM, in Orbit: Ariane 5 Successfully Deploys Supertelescope, DSS Bolsters Lead in Science Satellites

    Darmstadt -- Europe's largest research satellite, the X-ray observatory, XMM, is in space. Today, Friday, December 10, 1999, at 3:52 pm (CET), an Ariane 5 launch vehicle injected the spacecraft into a transfer orbit. 29 minutes after lift-off, XMM was released from the upper stage of Ariane 5 in a height of 2350 kilometers. Only one minute later, the communications signal of XMM was received. The supertelescope was developed and built under the industrial lead of Dornier Satellitensysteme GmbH (DSS, Friedrichshafen), a member of DaimlerChrysler Aerospace AG (Dasa, Munich).

    The XMM telescope (X-ray Multi Mirror) is almost eleven meters high and has a mass of nearly four tons. Over a period of ten years it will explore the universe for X-rays emitted by spectacular celestial sources such as exploding stars, pulsars and black holes.

    Astronomers hope that XMM will detect over one million unknown X-ray sources. Under DSS' industrial lead, over 35 companies were involved in building the space telescope with an order volume of 230 million euros, on behalf of the European Space Agency ESA.

    In ESA's satellite control center (ESOC) in Darmstadt, nearly three hundred visitors from politics, industry and science witnessed on video the event at the launch center in Kourou, French Guyana.

    "The successful launch of the XMM telescope substantiates Dornier Satellitensysteme GmbH's lead role in Europe in the field of science satellites", stated a happy Alfred Setzer of the DSS board of management. In the presence of journalists in Darmstadt he continued that Dornier Satellitensysteme GmbH was also the contractor for two other extremely challenging science missions of ESA, namely the Cluster II satellite fleet for the exploration of solar influences on the Earth's magnetosphere, and the cometary explorer Rosetta.

    "We hope that XMM will achieve the same success for the astronomers' community as did the German X-ray satellite Rosat." Rosat, too had been built under the industrial lead of DSS and had been operational for over eight years. Over 100,000 new X-ray sources were discovered in that mission and recorded on an X-ray map of the universe.

    Within the next hours, the XMM ground crew will unfold the spacecraft's solar array with a 16.1-meter span and deploy the sunshield. Within approximately 24 hours, and after three orbital correction maneuvers, they will move the observatory from its transfer orbit to its final high eccentric orbit (7,000 km perigee / 114,000 km apogee).


    Dec. 10, 1999


    American scientists are anxiously awaiting the launch of the European Space Agency's X-Ray Multi Mirror (XMM) spacecraft, set to lift off Dec. 10 from French Guyana on an Ariane 5 launch vehicle.

    The XMM spacecraft, an X-ray satellite designed to provide high quality X-ray spectra of X-ray sources from black holes to very hot objects created when the Universe was very young, is a European Space Agency project with contributions from NASA. NASA's involvement in the mission includes provision of critical components for two of the spacecraft's three science instruments and participation in the science-observing program. Based upon the initial competition for observing time, U.S. scientists will receive about one fifth of the observing time on the spacecraft during its first two years in orbit.

    NASA's Goddard Space Flight Center (Greenbelt, Md.) provided technical oversight of the U.S. provided hardware that is flying aboard the spacecraft. Goddard also will oversee the U.S. guest observer program wherein selected scientists are awarded observing time on the new observatory to gather science data. Goddard will provide support to U.S. guest scientists in the form of data archives, technical guidance and software support.

    "Goddard will be providing support for U.S. scientists using this world class observatory and we are extremely optimistic that this will result in first class science," said Goddard scientist Dr. Richard Mushotzky who is part of the XMM science team.

    U.S. hardware co-investigator, Dr. France Cordova from the University of California at Santa Barbara, contributed to the construction of two of the European instruments. Cordova and co-workers provided the data processing unit, the digital electronics modules, software and science support for the Optical Monitor (OM) instrument. Another U.S. co-investigator, Dr. Steve Kahn from Columbia University in New York City, provided two reflection grating assemblies for the Reflection Grating Spectrometer, data analysis software and science support.

    "Both of these instruments are state-of-the-art and the Reflection Grating Spectrometer in particular has advanced new technology," said Mushotzky.

    The third instrument comprising the science payload, the European Photon Imaging Camera (EPIC), has silicon chips that can obtain medium spectral resolution x-ray spectra from sources much fainter than ever before. The RGS will analyze the spectra in more detail and with greater resolution. The Optical Monitor will observe the same part of the sky as the x-ray telescopes but in the ultraviolet and optical wavelengths. This will give astronomers complementary data on the X-ray sources observed with the EPIC and RGS instruments.

    The spacecraft has four telescopes. Three of them are X-ray telescopes with the combined surface area of a tennis field, 120 square meters. However, due to the fact that the x-rays are focussed via reflection at very shallow angles, the effective collecting area for x-rays is 100 times less. In addition to the large collecting area afforded by XMM, the spacecraft will operate in an orbit that will allow it to take long and uninterrupted observations. The fourth telescope is a 30-centimeter optical telescope, which, by virtue of its operation above the atmosphere, is much more sensitive than a similar telescope on the ground.

    The name of XMM stems from its multiple mirrors. XMM, with the largest x-ray collecting area flown to date, will allow astronomers to gather and analyze more

    X-ray sources quicker than with previous space observatories. Scientists expect XMM will explain a number of cosmic mysteries, ranging from black holes to the origin of the universe. XMM will investigate supernova remnants, black holes, magnetically active flare stars and more.

    XMM, a world-class observatory, is the second cornerstone mission of ESA's Horizon 2000 program. Its large effective area and soft x-ray spectroscopic capabilities very nicely complement the high angular-resolution and higher energy x-ray spectroscopic capabilities of NASA's recently launched Great Observatory for x-ray astronomy, the Chandra X-ray Observatory. The minimum mission life of the spacecraft is two years but it is expected to last much longer.


    23 november 1999

    Lancering van Europese röntgentelescoop

    Op 10 december 1999 zal in Frans Guyana een Ariane 5 gelanceerd worden met aan boord de XMM (X-ray Multi Mirror) satelliet. De telescopen van XMM gaan kijken naar röntgenstraling afkomstig uit het heelal. Voor de röntgenastronomie breken nu dan ook spannende tijden aan. Drie grote observatoria zullen namelijk vanaf begin volgend jaar gegevens verzamelen: XMM, als één van de grote 'corner stone' missies van de Europese Ruimtevaart Organisatie (ESA), Chandra van NASA (met ook een belangrijke Nederlandse bijdrage) en Astro-E van Japan. De drie satellieten vullen elkaar aan en iedere satelliet heeft zijn eigen sterke punten. Voor XMM is dat zijn grote gevoeligheid. Hierdoor kunnen sterrenkundigen voor het eerst in groot detail fysische karakteristieken van hete kosmische gassen bepalen.

    XMM is letterlijk een "multi mirror". Niet alleen heeft de satelliet drie spiegeltelescopen om de röntgenstraling waar te nemen, maar elke telescoop bestaat uit 58 spiegels. De spiegels passen in elkaar zoals een set met steeds kleinere pannen. De telescopen zijn door een koolstof-fiber buis van 7 meter verbonden met de röntgendetectoren. De detectoren worden met hoge precisie, d.w.z. met een afwijking van minder dan 0.1 mm, op hun plaats gehouden ten opzichte van de spiegels. Dit ondanks de extreme temperaturen waaraan de tussenliggende buis wordt blootgesteld.

    Stichting Ruimte Onderzoek Nederland (SRON) heeft een belangrijke wetenschappelijke bijdrage geleverd aan XMM in de vorm van de Reflectie Tralie Spectrometer, oftewel de RGS (tralie=grating). Deze röntgenspectrometer kan het röntgenlicht van sterren en sterstelsels uitéén rafelen in verschillende 'kleuren' net zoals een prisma dat kan met zichtbaar licht. De RGS bestaat uit een traliedeel dat het röntgenlicht in de verschillende golflengtes ontleedt en een cameradeel dat met behulp van speciale detectoren uiteindelijk het röntgenlicht registreert.

    Stichting Ruimte Onderzoek Nederland (SRON) is een instituut van de Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) en initieert, ontwikkelt, bouwt en gebruikt instrumenten voor wetenschappelijk onderzoek in en vanuit de ruimte. Nadere informatie over SRON activiteiten SRON internetsite.

    European Space Agency
    Paris, France

    22 November 1999

    Lifting the veil on the X-ray universe

    X-ray astronomy is a relatively young branch of astrophysics which today is one of the most competitive and popular. In the few decades since the discovery of X-ray radiation from cosmic X-ray sources, this field has grown at an astonishing rate leading to the identification of numerous exciting new phenomena.

    ESA's X-ray Multi Mirror mission -- XMM -- is the second Cornerstone in ESA's Long Term Scientific Programme (*). This new X-ray space telescope promises even more discoveries. With the large collecting area of its mirrors and the high sensitivity of its cameras, XMM is expected to increase radically our understanding of high-energy sources -- clues to a mysterious past, and keys to understanding the future of the Universe.

    174 wafer-thin X-ray mirrors

    X-rays coming from celestial objects are highly energetic and elusive. They can best be measured and studied after focusing a sufficient number upon sensitive detectors. To achieve this, XMM's Mirror Modules have been given a gargantuan appetite for X-rays.

    The space observatory combines three barrel-shaped telescope modules. In each are nested 58 wafer-thin concentric mirror shells highly polished and subtly shaped. Passing through at an extremely shallow angle, the so-called "grazing incidence", the X-rays will be beamed to the science instruments situated on the focal plane at the other extremity of the satellite.

    The three mirror modules have a total mirror surface of over 120m2 -- practically the size of a tennis court. The collecting power of XMM's three telescopes is the greatest ever seen on an X-ray space mission, many times more than the most recently launched X-ray satellite.

    The design and assembly of the mirror modules, their testing for operation in space and their precise calibration constitute one of the greatest achievements of the XMM programme. The flimsy mirror shells, with their gold reflective surface on a nickel backing, were made by replication like carbon copies from master moulds. They were shaped to an accuracy of a thousandth of a millimetre, and then polished to a smoothness a thousand times better than that.

    Packaged one within another like Russian dolls, each mirror was focused and centred with respect to its neighbour to an accuracy of 25 microns -- a quarter of the width of a human hair.

    A multi-spectral space telescope

    The spacecraft carries three sets of science instruments, not only capable of making images of an X-ray source but also able to precisely distinguish the "colour" of the X-rays being viewed.

    At the prime focus of each of the telescopes are three European Photon Imaging Cameras. With silicon chips that can register extremely weak X-ray radiation, these advanced cameras are capable of detecting rapid variations in the intensity of a source.

    Grating structures at the exit of two mirror modules will reflect about half the incoming rays to a secondary focus, with its own cameras. This Reflection Grating Spectrometer will "fan out" the various wavelengths (much like a prism with visible light), and indicate in more detail the presence of individual elements, such as oxygen and iron.

    The third instrument aboard XMM is a conventional but very sensitive optical telescope. It will observe simultaneously the same regions as the X-ray telescopes but in the ultraviolet and visible wavelengths, giving astronomers complementary data about the X-ray sources being studied. In orbit, this 30-cm telescope will be as sensitive as a 4-m instrument on the Earth's surface.

    The mysteries of the X-ray sky

    XMM will explore the hidden depths of the Universe, its violent hotspots where stars and galaxies are formed, and where worlds and matter itself disappear. Much as the colour of a street lamp can indicate which gas it uses, the science instruments on board XMM will reveal the deepest secrets of X-ray objects, their chemical composition and temperatures -- clues to the physical processes that are taking place.

    Astronomers will use XMM to resolve the mysteries of stars that exploded long ago as supernovae and whose remnants, glowing with X-rays, may be supplying material for new planets and stars. They will study regions of supernova remnants that are still hot and may hold the key to understanding the origin of the enigmatic cosmic rays that pervade the Universe.

    The mission will study X-rays that originate from "vampire stars" that feed upon their companions, where intense gravitational fields swirl matter from one sphere to the other in strange and terrifying ballets.

    XMM's high-speed cameras will examine celestial sources whose X-rays pulse rhythmically and mysteriously, and those that flash briefly, pinpointing perhaps gigantic explosions that result from colliding black holes in far off galaxies.

    XMM will delve into enigmatic black holes, cosmic dustbins that consign matter and light to oblivion, where tired X-rays have lost energy and time itself is slowing down.

    The golden X-ray eyes of ESA's observatory will try to make sense of a 'bigger picture', ascertaining how galaxies aggregate millions of stars, how these galaxies themselves form clusters and groups scattered across cosmic space. XMM will also attempt to understand the nature of the invisible dark matter that fills interstellar space.

    A high-flying mission

    The XMM spacecraft, the largest science satellite ever built in Europe, is due to be launched in December 1999 by an Ariane-5 from the European Spaceport in Kourou.

    After being released by the launcher, XMM will be placed in a highly eccentric 48-hour orbit, rising to a distance of 114,000 km from the Earth, then returning to within 7,000 km of our planet.

    This orbit has been chosen for several reasons. It offers an optimal contact between ground tracking stations and the satellite; it will allow the satellite to pass rapidly through the Earth's radiation belts which could harm its delicate science instruments; and above all it will offer astronomers the longest possible observation periods.

    Notes: No X-rays from space can penetrate the Earth's atmosphere so all X-ray astronomy is carried out with instruments on rockets, stratospheric balloons or satellites. X-rays from the Sun were first detected during sounding rocket flights in the 1950s. By 1970, more than forty X-rays sources had been detected during rocket-borne experiments.

    Satellites have since conducted more extensive surveys. The first satellite dedicated to X-ray astronomy was Uhuru. Launched in 1970 it mapped the sky identifying 339 sources. Several others were to follow, including Einstein which carried grazing incidence mirrors and detectors capable of recording images of cosmic X-ray sources. Einstein studied more than ten thousand sources.

    EXOSAT (1983-1986) was the European Space Agency's first X-ray observatory mission. Placed on a highly eccentric orbit reaching out 191,700 km from Earth, it allowed very long observations above the radiation belts and greatly enlarged our understanding of many classes of X-ray sources.

    The German/US/UK ROSAT launched in 1990 was another big step forwards. Until its recent switch off it carried out a complete sky survey identifying 100,000 X-ray sources.

    XMM will be opening up a golden age of X-ray astronomy alongside two other major missions. Launched in July 1999, Chandra is the third of NASA's Great Observatories. It is exploring X-rays from space with images 25 times sharper than previously obtained. ASTRO-E is Japan's fifth X-ray astronomy mission and is due to be launched early in 2000.

    Europe has already begun studying a next generation X-ray astrophysics facility, XEUS. By making use of the International Space Station and by ensuring significant potential for growth and evolution, XEUS will offer vastly expanded capabilities allowing the study of the very first black holes created when the Universe was just a few percent of its present age.

    Further information on XMM and the ESA Science Programme can be found on the Worldwide Web at: http://sci.esa.int/categories/scienceprograms/ and click << Horizon 2000 >> on the left-hand bar.

    ESA Science News

    12 Nov 1999


    Green light for XMM launch on 10 December

    All lights are green to launch ESA's X-ray Space Observatory on 10 December with a launch window starting at 14:32 GMT.

    The ESA Director of Science Roger-Maurice Bonnet has given the green light to Robert Laine, the XMM Project Manager, to proceed to the next phase in preparing XMM for launch. This means that the XMM spacecraft is confirmed for a launch on 10 December 1999.

    M. Lainé, currently in French Guiana overseeing the final operations before launch, is delighted. "All actions on the flight hardware of our spacecraft are closed, the science instruments are in flight configuration, everything is on schedule for the big day."

    The next milestones in the satellite campaign will be the fuelling of the spacecraft, due to start on Monday 15th November, followed on the 19th by the arrival of the Ariane 504 launcher in the Final Assembly building, where the satellite is being prepared.


  • Campaign account


    XMM being prepared for hydrazine loading. In the foreground the (transfert) tank containing the hydrazine.

    Satellites Business Unit
    DaimlerChrysler Aerospace AG

    Munich, Germany


    "Green Light" for Europe's Space Telescope XMM:
    DSS Team Embarking For Launch Campaign in Kourou

    Überlingen -- Europe's largest science satellite, XMM, has received the "green light" for launch. Today, Tuesday, October 5, approximately 120 space experts will convene in Überlingen on Lake Constance for the so-called "Flight Acceptance Review". The prime industrial contractor for the spacecraft, measuring 11 meters, is Dornier Satellitensysteme GmbH (DSS, Friedrichshafen), a member of DaimlerChrysler Aerospace AG (Dasa, Munich). The launch of XMM onboard an Ariane 5 launch vehicle is scheduled for December 8, 1999.

    In Überlingen, DSS submitted the satellite test and analysis results to its customer, the Paris-based space agency ESA. In the last months the spacecraft had undergone a thorough check. A space simulation test (at various temperatures and under vacuum conditions), vibration tests (to simulate the ascent loads during launch) and extensive functional checks were performed.

    "All tests were completed successfully; in part the results are better than the requirements posed by the customer", is the proud statement of the DSS project manager, Uwe Minne. Robert Lainé, the XMM project manager on behalf of ESA, agrees: "I am highly satisfied with the achievements of the industry consortium. On the one hand, the cost target was observed and on the other hand, we are ahead of schedule because according to the original schedule, the launch had been planned for January 21, 2000. On top of this, all system requirements were met. I congratulate DSS on their outstanding team."

    Soon, an approximate fourteen-member team of space engineers and technicians from Dornier Satellitensysteme GmbH will prepare for its journey to South America, for the XXM launch preparations. The spacecraft will be deployed into space with Ariane flight no. 504 from the space center Kourou in French Guiana.

    Among other things, astronomers hope that XMM (X-ray Multi Mirror) will provide conclusive evidence of the existence of black holes.

    Under the leadership of DSS, an industrial consortium of 35 European companies developed and built the 230-million Euros spacecraft. With a length of almost eleven meters, a diameter of four meters and a total mass of nearly four tons, this is the largest satellite ever built under ESA's science program.

    X-rays from space

    X-rays are a result of high-energy processes, for example in supernovas. These are high-density stars which explode in the final stage of their development, releasing clouds of gas at temperatures of many millions of degrees, and generating high-energy X-rays in the process. The centers of galaxies, clusters of galaxies, and quasars -- even normal stars like the Sun -- all emit X-rays. The relatively weak X-rays emitted by the Sun were detected as early as 1948 by an upper atmosphere sounding rocket. These short-wave X-rays from space cannot penetrate the Earth's atmosphere as they are absorbed in high altitudes by air molecules. Therefore, the best approach to detect their cosmic origin is through the use of satellites. A major breakthrough in the generation of a sky map of X-ray sources was achieved nine years ago with the launch of the German X-ray satellite Rosat, also a DSS development. 120,000 cosmic X-rays have been detected so far. After far exceeding its specified life span, Rosat was switched off in December 1998, as the gas supply needed for the detector was depleted.

    Similar to the color of visible light which provides important information on the temperature, composition and dynamics of cosmic objects, X-rays offer a wealth of chemical and physical data over a much wider energy range. XMM, with a far better resolution than its precursors, will substantially advance the "decoding" of X-ray sources. A marked increase in the number of detected sources is also expected. In a single day, XMM will detect more X-rays than the first US X-ray mission did 25 years ago in three years.

    Mapping of X-rays

    Apart from the fact that the X-rays of cosmic objects do not penetrate the Earth's atmosphere, it is very complicated to focus and record them using satellite instruments. X-ray photons can only be focused by optical mirrors on the scientific instruments when they hit the metallic mirrors at a grazing incidence angle. This requires a special design for the X-ray optical system. The barrel-shaped mirror consists of two segments, with the first segment formed according to a paraboloid and the second to a hyperboloid mirror. The effective area of these is only a small, few-millimeter-wide ring. In order to focus as many X-rays as possible, one XMM mirror assembly consists of 58 nested mirror shells. The XMM telescope contains three identical X-ray mirror assemblies with an outer diameter of 70 centimeters each. With a total of 174 mirror shells, this new telescope has an enormous throughput and high sensitivity compared to all previous projects, which is what is primarily required for spectroscopy.

    On account of the high packing density in the mirror assemblies, these mirror shells must be extremely thin and, at the same time, lightweight to ease their transport into space. DSS in Friedrichshafen performed early feasibility studies on how to comply with these exacting structural requirements ten years ago. The studies showed both carbon-fiber reinforced plastics (CFRP) and nickel to be suitable materials. They offer extreme long-term surface accuracy and the mirrors can still be manufactured much thinner than those of Rosat, which were made of glass-ceramics. ESA finally opted for nickel mirrors. A thin gold film is deposited on their internal surface for maximum reflection.

    The mirror assemblies' focal length of 7.5 meters necessitates the spacecraft's uncommonly large dimensions of four by ten meters and a total mass of four tons. In the telescope's focal plane three imaging CCD cameras and, for the first time for X-rays, two high-resolution reflection grating spectrometers are installed. In the X-ray spectrum of 0.35 to 2.5 keV, the latter are to provide data on the composition, temperature, dynamics and other properties of the investigated astronomical objects. Scientists from Europe and the USA, involved in the project, hope to capture approximately 30,000 X-ray spectra in unprecedented detail during the spacecraft's planned ten-year mission life.

    The electronic cameras, too, discriminate X-rays of different energy levels. They can view X-rays between 0.1 and 10 keV (wavelength of 12 to 0.12 nanometers) "in color". Using the so-called spectrophotometry, astronomers will obtain a wealth of information that has been inaccessible so far.

    In addition to those instruments for detection of X-ray photons, an optical camera is being developed for observations in the visible and ultraviolet light. It will allow astronomers to perform simultaneous visual observations of the sources scanned with "X-ray eyes". All three scientific instruments, which are currently under development at various European and American institutes, will be simultaneously operated and will transmit real-time data down to Earth.

    Black holes in focus

    Black holes are the remnants of past explosions of stars. Some scientists presume that black holes also formed shortly after the big bang and are still wandering through the universe. As they emit no radiation at all, these black holes are invisible. It is only their enormous gravitational force that acts on the environment. They continuously absorb gas and dust. Before matter drops into a black hole, where it is lost forever, it revolves around this strange object virtually at the speed of light. The frictional forces among these accelerated gas particles generate temperatures of several million degrees. It is precisely then that this cosmic swirl emits X-rays, which can be detected with special spacecraft telescopes. Astrophysicists hope to examine the physical processes at the "edges" of black holes with the help of XMM. The expected data could provide conclusive evidence of the existence of these "gravitational monsters" which were theoretically calculated by the German physicists Albert Einstein and Karl Schwarzschild.

    The list of observation objects however is not only made up of potential black hole candidates but also includes neutron stars, supernova remnants, the center of the Milky Way and cores of distant galaxies.

    ESA Science News

    27 Sep 1999

    XMM arrives in French Guiana

    As scheduled, the Arianespace MN Toucan berthed at Kourou's Pariacabo harbour on the afternoon of 23 September after a ten-day crossing from Europe. A welcoming party was present as the ship lowered its rear access ramp, revealing its full load: the XMM giant container and eight others with various Ariane-4 and Ariane-5 rocket stages.

    On the quayside were Arianespace Mission Director for the XMM launch, Philippe Rolland; Jean-Yves Trébaol, the Launch Range Manager for the XMM flight from the French Space Agency (CNES); and Robert Lainé and Uwe Minne, XMM Project Managers respectively from ESA and prime-contractor Dornier. They were glad also to see that their two colleagues accompanying the spacecraft appeared to have survived their transatlantic trip!

    The Toucan first unloaded its hazardous items, such as propellant-filled rocket stages, and the XMM trailer was only rolled out at the next high tide the following morning. Local television and press media were there to cover the event.

    The XMM container then led an exceptional convoy of nine vehicles. Escorted by police, it left through the small harbour's industrial estate, rejoining the 'Space Road' which first passes the technical complex of the Guiana Space Centre (where the Jupiter Mission Control is situated) before reaching the launch complex itself a further 13 kilometres along the coast road.

    Upon entering the forward zone of the European spaceport, XMM headed for the largest building, the Ariane-5 Final Assembly Building (BAF). It is an impressive cathedral-like structure, 90m tall, fully air-conditioned with a volume of 123,000 cubic metres! It is from the BAF that the Ariane launch vehicles, ready for lift-off, are taken to their launch site.

    The BAF also accommodates clean rooms where exceptionally sized satellites can be prepared for launch. The XMM trailer reversed into the building's air lock, the protective tarpaulin was removed and an over-head gantry crane transferred the long container.

    The XMM launch campaign starts practically immediately as much work remains before the launch in December. First activities will see the unloading of mechanical and electrical ground support equipment, and removal of the spacecraft from its container. Numerous system checks on the satellite will take place before fuelling in mid-November.

    Eight members of the ESA team and 15 colleagues from Dornier have already arrived for the long campaign in French Guiana. Others are arriving soon. It is all too clear: with their spacecraft now only 5 km away from its launch site, the mood is good and everyone is highly motivated.


    XMM launch preparations
    Ariane homepage

    Images supporting this release.


    [IMAGE 1]
    XMM leads convoy to the Kourou spaceport.

    [IMAGE 2]
    MN Toucan preparing to unload at Pariacabo harbour.

    [IMAGE 3]
    The XMM container arrives at the Ariane 5 Final Assembly Building (BAF).

    [IMAGE 4]
    The Ariane 5 Final Assembly Building, where XMM is being prepared for its launcher.

    ESA Science News

    11 Jun 1999

    XMM ready for launch in December, a month earlier than envisaged!

    The European Space Agency's XMM mission had until very recently been officially set to liftoff on 21 January 2000. Now, with a common accord between the ESA project management and Arianespace, the launch of the X-ray astronomy mission by an Ariane 5 has been rescheduled to mid- December this year.

    Explaining the decision to bring the launch forward, ESA's XMM Project manager Robert Lainé said: "It was a result of the extra capability provided by Ariane 5. A greater knowledge of the launcher after the 502 and 503 qualification missions allowed Arianespace to tell us that the vehicle could carry XMM to a higher altitude before it is released. Our spacecraft is also lighter than originally expected, approximately 100 kg."

    This good news allowed the XMM project team to open the launch window a month earlier. The spacecraft will also be carrying more fuel for its in-orbit life. Another factor allowing the launch to take place sooner, according to Robert Lainé, is an uneventful series of tests upon the spacecraft with no surprises, allowing the team to have XMM ready earlier. But he insisted: "We have cut no corners. All the tests that were planned have been completed successfully."

    The spacecraft, whose two halves were mated on 26 May, will now complete its final tests at ESA's ESTEC technical centre in Noordwijk, including electrical verifications and accoustic tests at the start of July. There will be a solar array deployment test in mid-August. By then a giant satellite container will have been delivered and the spacecraft will be packed for shipping on one of the Arianespace vessels to French Guiana. Departure from Rotterdam is scheduled for mid-September.

    The launch campaign, starting end of September, will take place entirely in the satellite preparation area of the Ariane 5 Final Assembly Building (BAF), leading up to a launch now nominally set for the 15th December.

    The prospect of having XMM in orbit sooner also greatly pleases the scientific community, eagerly waiting to use the space observatory.

    Images supporting this release

    ESA Science News

    01 Apr 1999

    XMM receives its golden eyes!

    ESA's X-ray space observatory XMM, currently being assembled in view of a launch from Kourou next January, has been fitted with its three X-ray telescopes -- the extremely high-precision Mirror Modules, each with its 58 wafer-thin gold-covered mirror shells which will give the mission its unprecedented vision of the X-ray universe.

    The telescopes have now all been fitted to the spacecraft's lower platform, which has completed most of its environmental tests at ESA's ESTEC Technical Centre at Noordwijk in the Netherlands. At the end of February, the three structural and thermal models of the telescopes, used during these tests, were removed to make way for those that will fly on the spacecraft.

    The positioning of the first of XMM's 'golden eyes' began on 24 March. Operations took place in an ultra-clean 'class 100' tent situated in the ESTEC satellite test area. A small team of engineers from prime contractor Daimler-Chrysler Aerospace (Dornier) and from ESA wore special suits to avoid any contamination of the flight hardware as they carefully moved the telescope vertically into the waiting orifice on the satellite. Once slotted in, the first telescope was fixed to its mounting interface by means of six bolts and 3 centring pins around its external circumference.

    These delicate operations were repeated for the second telescope on 26 March, and the third telescope was placed in position on 30 March. After each mounting, precise measurements were taken with micrometer gauges to evaluate any deformation to the satellite platform due to the added mass of the telescopes, weighting in total 1420 kg. When all was finished, engineers were pleased to announce that the deformation of the platform was low, below 10 microns, and they confirmed that there were no undue loads on the spacecraft.

    Before the lower half of XMM is mated to the focal plane assembly, scheduled at the end of May, one further XMM 'eye' will be added: the Optical Monitor. This telescope which will observe the heavens in the visible and ultraviolet, is due to be fitted in the third week of April.

    Images supporting this article

    Testing XMM (ESA Bulletin 94, pdf-format)


    Paris, 10 February 1998

    ESA unveils its big XMM spacecraft

    Looking like a black pillar more than 10 metres tall, Europe's largest scientific spacecraft now stands in a test bay at ESTEC, ESA's space and technology centre at Noordwijk in the Netherlands.

    XMM, the X-ray Multi-Mirror mission, is due to be launched in 1999. It is a European conception with innovative telescopes. XMM will revolutionize the study of X-rays coming from the Universe, by harvesting far more X-rays per hour than any previous mission. Its enormous capacity will enable astronomers to analyse many strong sources of cosmic X-rays very quickly, and to discover and characterize many faint sources previously beyond their reach.

    As the most popular and competitive branch of space astronomy, X-ray astronomy reveals special places in the Universe where very high temperatures or violent forces generate energetic radiation. These sources include black holes, exploding stars, pairs of stars orbiting very close together, and the central regions of clusters of galaxies.

    XMM's optical monitor, viewing the scenes by visible light, will help in the interpretations. The combination of X-ray telescopes and optical monitoring should be well-suited to tracking down gamma-ray bursters -- extraordinary explosions in space that mystify the astronomers.

    Full descriptions of the X-ray sources will depend on precise spectral analysis of the relative intensities of X-rays of different energies, including the signatures of identifiable chemical elements. Such spectral analysis is XMM's task, using instruments of the highest quality fed by the remarkable telescopes.

    As seen at ESTEC today, the spacecraft stands upside down. 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.

    Surmounting the assembly, a pair of cones will carry heat away from the detectors. XMM's appearance is, though, dominated by the long tube that spans the telescopes' focal length, and by the black thermal blanket that will protect the spacecraft from unequal heating on the sunny and shaded sides.

    A miracle of telescope engineering

    "You have to imagine the big tube of XMM filled with focused X-rays en route to the detectors," says Robert Laine ESA's project manager for XMM. "That's the whole purpose of the mission, and our chief preoccupation has been with the three multi-mirror modules that accomplish it. Critics thought we were too ambitious, trying to nest 58 precisely formed mirrors together in each module. No one had ever attempted such a feat before. It wasn't easy, but thanks to excellent innovative work by European industry, XMM's telescopes are even better than we hoped."

    X-rays are focused by glancing them off a carefully shaped mirror, like a bucket without a bottom. In a single-mirror telescope, most of the incoming X-rays miss the mirror. To catch more of them, designers nest multiple mirrors inside one another. Before XMM, astronomers had to choose between many mirrors with relatively poor focusing, or a very few mirrors with a sharp focus. With 58 precision-made mirrors in each of its three X-ray telescopes, XMM combines enormous gathering power with accurate focusing.

    Carl Zeiss in Germany made shaped and polished mandrels (moulds) for mirrors of 58 different diameters, up to 70 cm for the widest. Media Lario in Italy made the mirrors by electrodeposition of nickel on the mandrels, coated their inner surfaces with gold, and carefully assembled them in their nested configuration, in a high accuracy structure fabricated by APCO in Switzerland.

    The performance of each XMM mirror module has been verified in special facilities of the Centre Spatiale de Liege in Belgium and the Max-Planck-Institut fur extraterrestriche Physik in Germany. The first flight model conformed with the specification, and the second and third were even better.

    Some facts about XMM

    The total surface area of the extremely thin mirror that gathers X-rays in XMM's three multi-mirror telescopes (taken together) is larger than 120m2.

    Two of the three X-ray telescopes are fitted with reflection grating spectrometers for the most detailed analysis of the X-ray energies.

    XMM is designed to fit in the fairing of Europe's new Ariane 5 launcher.

    Some 46 companies in 14 European countries (and 1 in the USA) have contributed to XMM's construction. The investigators responsible for the instruments in XMM come from the Netherlands and the UK, with investigators in Belgium, France, Germany, Italy, Switzerland and the USA.

    XMM will spend most of its time south of the Earth, travelling quite slowly out to distances of more than 100,000 kilometres, well clear of the Earth's radiation belts.

    XMM will be controlled by ESA's satellite operations centre (ESOC) from Darmstadt (Germany) and Villafranca (Spain) via ground stations in Perth (Australia) and Kourou (French Guiana).

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