ESA's XMM-Newton space observatory is the flagship of European X-ray astronomy. It is the most powerful X-ray telescope ever placed in orbit and is observing the 'hot' X-ray universe including objects like neutron stars, black holes and active galaxies. Over 300 scientific papers are published annually using data provided by XMM-Newton.
The satellite is detecting more X-ray sources than any previous satellite and is helping solve cosmic mysteries, from what happens in and around black holes to the formation of galaxies in our early Universe. XMM-Newton's high-tech design uses over 170 wafer-thin cylindrical mirrors spread over three telescopes.
Its 48-hour orbit takes it almost a third of the way to the Moon enabling astronomers to obtain long, uninterrupted views of celestial objects. At perigee (closest approach), it passes 21 500 km above Earth at a speed of 24 000 km/hr. XMM-Newton's highly eccentric operational orbit has been chosen so that its instruments can work outside the radiation belts surrounding the Earth.
The XMM Mission Operations Centre (MOC) is located at ESOC, Darmstadt, Germany.
|ROLE||X-ray space observatory|
|LAUNCH DATE||10 Dec 1999/Ariane|
|LAUNCHER/LOCATION||Ariane/Kourou, French Guiana|
|LAUNCH MASS||3800 kg|
|APOGEE/PERIGEE||100 000 km/21 500 km|
|ORBIT||48 hr elliptical|
|NOMINAL MISSION||Two years - extended to 2016|
|+ Europe's largest-ever science satellite +|
The Flight Control Team
The Flight Control Team at ESOC operates from a Dedicated Control Room co-located with the Integral DCR. The Spacecraft Operations Manager, Dr Marcus Kirsch, leads a team of flight control engineers, analysts and spacecraft controllers working full-time on the mission.
"The mission was originally designed for a 10-year life, however, since the satellite and instruments are operating admirably without major degradation, we hope to operate the observatory into the next decade, our only limitation being the hydrazine fuel supply. Our 'baby' has been out there for a long time now and is still providing X-ray astronomers with exiting new science results daily. Having worked previously as an astrophysicist for some time on the science side of XMM, I am now putting my energy into ensuring the safe and efficient continuation of mission operations," says Kirsch.
Flawless mission operations is a key element in achieving a high scientific output. The mission provides the operations team with ongoing demands; XMM-Newton, for example, has no on-board storage so all vital science data must be downloaded via a ground station as soon as it is collected.
Other ESOC teams provide specialised support to XMM-Newton in several areas, including Flight Dynamics, Ground Facilities and Software Support.
Mission operations overview
XMM was launched on Ariane Flight V 119, on board the first Ariane-5 commercial flight (504) on 10 December 1999.
After a perfect injection by Ariane, and having been tracked for the previous ten minutes by the ESA ground station at Villafranca, Spain, the MOC assumed control of the satellite to begin the critical Launch and Early Orbit Phase (LEOP).
Activities conducted in this phase included setting up on-board systems for mission operations, establishing the correct thermal environment, calibrating the attitude and orbit control system and the reaction control system, and bringing the spacecraft into its operational orbit. All operations in this first phase of the mission proceeded according to the flight operations plan, allowing the next phase, the commissioning phase, to start on 4 January 2000.
In this phase, all instruments were carefully exercised in all their modes, while the XMM Science Operations Centre (SOC), located at ESAC, ESA's European Space Astronomy Centre, came on stream to receive and process the science data. The first images of X-ray objects collected by XMM were presented to the public in a press event held at ESAC on 9 February 2000. The spacecraft was also renamed XMM-Newton.
The mission is now in the routine phase and has been extended until 2012.
The ground stations - Perth, Kourou
Contact for continuous real-time interaction with the spacecraft over almost the entire orbit is provided by the ESA ground stations at Perth and Kourou (with Villafranca and Santiago as back-up).
XMM-Newton's operational orbit is highly eccentric and has been chosen for two reasons. First, the XMM-Newton instruments need to work outside the radiation belts surrounding the Earth. Second, a highly eccentric orbit offers the longest possible observation periods - less interrupted by the frequent passages in the Earth's shadow that occur in a low orbit.
In addition, the orbital period of XMM-Newton is exactly two times the Earth rotation period to maintain optimal contact between XMM-Newton and the ground stations tracking the satellite. This allows XMM-Newton data to be received in real-time and for it to be fed to the Mission Control Centres.
XMM-Newton has no inboard data storage capacity, so all data is immediately downloaded to the ground in real time.
Ground segment & mission control system
The XMM-Newton ground segment uses the SCOS-2000 mission control system.
In 2005, the XMM-Newton Flight Control Team completed a first-ever upgrade from an older mission control system to the new SCOS-2000 system while the mission was in full operation. The project was completed without problems, on time and under budget.
The XMM-Newton SOC at ESAC manages science operations in continuous round-the-clock interaction with the MOC. The SOC is responsible for all science aspects of the mission, including relations with the science community, science observation planning, observation monitoring, quick-look analysis, instrument calibration, archiving, and distribution.
The XMM Science Survey Centre (SSC) at Leicester University, United Kingdom, also plays a role. It performs pipeline processing of all XMM science data to identify and categorise all X-ray sources detected by XMM instruments.
The platform and payload
XMM-Newton carries three very advanced X-ray telescopes. They each contain 58 high-precision concentric mirrors, delicately nested to offer the largest collecting area possible to catch the elusive X-rays. These Mirror Modules allow XMM-Newton to detect millions of sources, far more than any previous X-ray mission.
The telescopes work in conjunction with cameras, a spectrometer and an optical/ultraviolet monitor.
European Photon Imaging Cameras (EPIC)
The main mirror modules sends the image beam along the telescope tube to five cameras at the extremity of the spacecraft. At the prime focus of each of the telescopes, behind six-position filters, are three European Photon Imaging Cameras (EPIC). With silicon chips that can register extremely weak X-ray radiation, these advanced charge-coupled device (CCD) cameras are capable of detecting rapid variations in intensity, down to a thousandth of a second and less.
Reflection Grating Spectrometer (RGS)
For a complementary analysis of the spectrum, a grating structure on two mirror modules reflects about half of the incoming rays to a secondary focus, with its own CCD camera. This Reflection Grating Spectrometer (RGS) "fans out" the various wavelengths, thus indicating, in more detail than EPIC, the exact condition of individual elements, such as oxygen and iron.
Optical/UV Monitor (OM)
The third instrument aboard XMM-Newton is a conventional but very sensitive Optical/UV Monitor (OM), which can observe simultaneously the same regions as the X-ray telescopes, but in the ultraviolet and visible wavelengths. This gives astronomers complementary data about the X-ray sources. In orbit, this 30-cm telescope is as sensitive as a 4-metre instrument on the Earth's surface.
For more on XMM-Newton's instruments, follow the links above at right.