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Press Release N43-2001 - ESA starts recovery of Artemis



Paris, 19 July 2001
Press Release
N°43-2001

ESA starts recovery of Artemis 

ESA's Artemis telecommunications satellite is fully under the control of
the Altel (Alenia Spazio-Telespazio) operations team and system engineers
in Fucino, Italy, supported by a team of ESA specialists, after a
successful first orbit-raising manoeuvre last night.

The satellite was launched by an Ariane 5 on Thursday 12 July from Kourou
but was left in a degraded orbit due to a malfunction in the launcher's
upper stage. Artemis was injected into an orbit with a perigee of 590 km,
an apogee 17 487 km and inclination of 2.94°, compared to expected values
of 858 perigee, 35 853 apogee, and 2° inclination. Since injection into
orbit the spacecraft's behaviour has been nominal. The solar arrays were
partially deployed, according to plan, some two hours after launch and
started delivering the power required for operation. Several calibrations
and simulated apogee firings have been performed in the last few days to
prepare for the orbit manoeuvres described below.

The recovery strategy adopted aims to bring the satellite to the nominal
geostationary position and to maintain chemical propellant and xenon (the
gas used for the electrical ion-propulsion system) to maximise the
lifetime of the spacecraft, originally planned to last 10 years.

The combined ESA/Alenia Spazio-Telespazio team has jointly selected a
four-step strategy for bringing Artemis from the current non-nominal orbit
to the geostationary orbit, as follows:

Step 1: The apogee boost motor (using chemical propulsion) is operated
during several perigee passes (at the shortest distance from Earth) to
increase the apogee (the maximum distance from Earth) to about 31 000 km.
The perigee will not be raised by very much. Ground stations at Fucino
(Italy), Malindi (Kenya), Perth (Australia), Goldstone (USA) and Kourou
(French Guiana) will monitor the satellite.

Step 2: The elliptical orbit is then  circularised by a number of apogee
and perigee manoeuvres  resulting in a quasi-circular parking orbit with
the satellite at 31 000 km above the Earth and an orbit duration of about
18 hours. On completion of this step, the solar arrays will be fully
deployed, as will the antenna reflectors. The satellite will then be in
nominal mode, while not yet in geostationary orbit.

Step 3: With the satellite in the parking orbit, nominal spacecraft
commissioning (activation and checking that all satellite elements are
operating correctly) will be carried out, as far as is possible, in this
sub-geostationary orbit.

Step 4:	The satellite will then  be "spiralled" from the parking orbit to
the nominal geostationary orbit using the satellite's electrical
ion-propulsion system.

The first apogee boost motor burn at perigee was successfully accomplished
yesterday evening (18  July) between 17:19 and 17:39 CEST. Ground
controllers reported that all went well and that the satellite has now
been raised to an apogee altitude of 19 164 km  (the perigee moving to 609
km, with no change in the inclination of 2.9°).

The end of step 2, i.e. arrival at the parking orbit, is planned for the
next few days. Step 3 will last about 2 months, during which the
commissioning tests will be performed and preparations will be made for
raising the orbit. Step 4 is expected to start at end of September and
will last  several months.

This recovery scenario is the one which offers the best chances of
bringing the satellite from the degraded injection orbit to the nominal
geostationary position and saving enough chemical fuel and xenon to
support some years of nominal operation. The amount of fuel and the
resulting remaining lifetime can be predicted only after completion of
step 2, albeit with some uncertainty.

The recovery activities involve a number of unusual operations which could
not be planned for in advance. A particular case in point is the use of
the electrical ion-propulsion system, for which a new mode of operation
has to be defined.

The next progress report will be published on completion of step 2.

For further information:
ESA Media Relations Office
Franco Bonacina
Tel: +33.(0)1.5369. 7713
Fax: +33.(0)1.5369.7690

See also http://www.esa.int

Note to broadcasters:
A Video News Release for TV Broadcasters will be available on Friday 20
July from 04:30-04:45 GMT on Eutelsat W1. For more information on the TV
transmission consult http://www.television.esa.int or contact Medialink:
+44.207.554.2704

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