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Paris, 31 January 2003
Press Release
Nĝ 07-2003

Artemis finally reaches operational orbit
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Artemis has finally reached geostationary orbit, some 36 000 km above
the Earth, at 21.5ĝE. This announcement would, if all had gone to
plan, been made just a few days after lift-off on 12 July 2001. Now,
eighteen months and some serious brainstorming further on, the most
advanced ESA telecommunications satellite ever commissioned, is on
station, ready to play its part in the development of new
telecommunications services. 

It will be remembered that Artemis (which stands for Advanced Relay
and Technology Mission) was left in a lower than intended orbit when
the Ariane 5 upper stage malfunctioned. It was even feared at the time 
that the entire mission might be lost. But thanks to creative
thinking, often under severe time pressure, by engineering and other
specialists from the European Space Agency, from prime contractor
Alenia Spazio, from Astrium, which designed the ionic propulsion
system, and from Telespazio, responsible for satellite operations at
the Fucino control centre, satellite and mission have now been
recovered. 

Novel, unplanned use of the ion propulsion technology built into
Artemis was the key to this success.

Initially provided on an experimental basis to correct orbit drift
once Artemis was on station, the ion propulsion system* was used to
raise the satellite's orbit from 31 000 km to 36 000 km.

This is a much slower process than using a conventional apogee boost
motor - a bit like using an outboard motor to drive an ocean liner -
but here it was a case of better late than never!

Before the orbit-raising operations could get underway, a huge
reprogramming effort was required and it even proved necessary to
develop completely new software from scratch, against the clock.
Those operations began with an initial, rapid shift to a safe parking
orbit beyond the upper Van Allen Radiation Belt, the required thrust
coming from the satellite's conventional, chemical-powered apogee
boost motors. The small ionic motors then took over in February 2002
and, at an average of 15 kilometres a day, Artemis rose in spirals
towards geostationary orbit. Needless to say, there were incidents and 
unexpected problems on the way, as engineers strove to make a system 
do a job for which it had not been designed.

Slowly but surely then, Artemis progressed towards its final
destination, demonstrating its intrinsic modernity and illustrating
the merits of a satellite of this kind, designed to test new
technologies and services. 

It should be noted that in the final approach phase the chemical motor 
fired thrice in succession to adjust the satellite's velocity.

Artemis has now taken up its operational station in Earth orbit and
its instruments, placed in hibernation throughout the recovery
campaign, have been reactivated. But while its real job is only just
beginning, Artemis already has a world first to its credit, earned
when its communications payloads were checked out from the ground
while preparations for the orbit-raising operations proceeded. The
highlight of those checks came when a link was established between the 
CNES SPOT-4 Earth observation satellite and Artemis (see ESA press 
release no. 75/2001); imaging data from SPOT-4 was transmitted by 
laser to Artemis and from there by radio waves to the Spot Image
processing centre in Toulouse. An unprecedented link-up between
satellites in space! 

Once all systems are fully active Artemis will be ready to embark on
what may prove to be a ten-year operational career, barely less than
the service life that had been planned before these celestial
gymnastics became necessary - and which have in the end provided a
wealth of information and experience for future missions.

(*) The principle of any kind of thrusters in space is to accelerate
molecules and expel them from the satellite at the highest possible
speed. Conventional thrusters use a chemical reaction between fuel and 
oxidiser to heat a gas and eject the molecules at a speed of typically 
1 km/sec. Electrical propellant systems first ionise (i.e.
electrically charge) the molecules of  a gas (xenon, for instance).
The ionised gas is then accelerated by electrical fields and ejected
from the satellite at a speed of typically 30 km/sec.


For further information, please contact :
ESA Media Relations Service
Tel: +33(0)1.53.69.7155
Fax: +33(0)1.53.69.7690

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