"ARIANE-504 DELIVERS XMM-TELESCOPE INTO SPACE"
A
faultless launch of the Ariane-504 rocket, carrying ESA's XMM (X-ray Multi
Mirror) space telescope, on December
10, 1999, was a text-book flight. It was the last launch of a major ESA project
of the millennium. This was the fourth flight of the Ariane-5 and the first
commercial flight of Europe's most powerful rocket. The first two flights of
the Ariane-5 did not go as expected, and this successful launch confirms Europe
as the leader in the lucrative satellite launching business.
A faultless, uninterrupted countdown allowed
the Ariane-5 to lift off precisely as scheduled, at 15:32 CET from Kourou, French Guiana. A billowing trail of smoke
in a clear blue sky, and XMM was in orbit 29 minutes after lift-off, the
satellite was released into space with an exceptional accuracy. The mighty
Ariane 5 launcher, making its very first commercial launch, hurled the
3.9-tonne spacecraft into a far-ranging orbit. Post launch data showed that it
had been injected to within 1.5 km of its target, on an orbit with a perigee of
825.6km and an apogee of 113 946km. 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.
Being the world's most powerful observatory for
X-ray astronomy, the XMM is the biggest science satellite ever built in Europe.
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.
The XMM is 10 meters high, 4 meters width, and
it's span in orbit is 16 meters. The total mass of the telescope at lift-off
was 3764 kg., and it's expected that the life time of XMM will be about 10 years.
Its main telescopes will gather X-rays from the cosmos with 120 square metres
of gold-coated
Surfaces. The telescope consists of three
barrel-shaped Mirror Modules, each containing 58 wafer-thin concentric mirrors.
The focal distance of the telescope is 7,5 m
Some twenty seconds after XMM's release, its
first telemetry was received by the ESA/ESOC Mission Control Centre in
Darmstadt Germany. The Villafranca ground station had locked on to the
launcher's own telemetry, and so immediately picked up the satellite's signals
when it was released as it passed over the Middle East. During the 3 minutes
passage within visibility of the Villafranca antenna, before XMM passed below
the horizon, the ESOC teams were able to confirm that everying was operating
as planned onboard the satellite.
About 30 minutes after separation from the
Ariane-5 rocket the first of the two solar array's was deployed. The deployment
took about four minutes and 10 minutes later the second solar array was
deployed. The two solar array's of the XMM telescope were built by Fokker Space
BV in the Netherlands. Each solar array consist of three panels, each panel is
1.81 by 1.94 meter and has 1240 solarcels on it. These solarcels will power the XMM with at least 1600 W at
the end of it's ten year life.
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. Coming along after XMM are Integral for gamma-ray
astronomy, due for launch in October 2001. FIRST for the far-infrared, and
Planck for examining the entire cosmic microwave background far more accurately
than ever before.
Tekst: Jacques van Oene, Published in Spaceflight Magazine February 2000.