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FW: Press Release N44-2001 - Artemis recovery operation continuing successfully





-----Original Message-----
From: ESA Media Relations [mailto:ContactESA@esa.int]
Sent: Wednesday, July 25, 2001 9:28 AM
To: Paul Willmott
Subject: Press Release N°44-2001 - Artemis recovery operation continuing
successfully


Paris, 25 July 2001
Press Release
N°44-2001

Artemis recovery operation continuing successfully 

Ground control in Fucino, Italy - the operations team and system engineers
of the Altel (Alenia Spazio-Telespazio) consortium, supported by ESA
specialists - reports that since last night  (Tuesday 24 July) ESA's
Artemis satellite has been successfully positioned in its circular parking
orbit at about 31000 km.

The satellite, launched from Kourou by an Ariane 5 on Thursday 12 July,
had been put into the wrong orbit due to a malfunction on the launcher's
upper stage. The injection orbit had a perigee of 590 km, an apogee of
17487 km and an inclination of 2.94°, compared to expected values of 858
km, 35853 km and 2° respectively.

Since injection into orbit, the spacecraft's behaviour has been nominal,
allowing ESA to rapidly adopt a recovery strategy that aims to take the
satellite to a nominal geostationary position of  approximately 36000 km,
maximising the lifetime of the spacecraft originally planned to last ten
years.

The strategy consists of four steps, the first two of which have been
successfully completed.

Under step 1 (18 to 20 July), the apogee boost motor (chemical propulsion)
was fired during five perigee (shortest distance from Earth) passes to
increase the apogee (maximum distance) to about 31000 km, without 
significant changes to the perigee.

Under step 2 (22 to 24 July), the elliptical orbit was circularised by
three consecutive motor burns. This resulted in a circular parking orbit
with the satellite at approximately 31000 km, an orbit duration of about
20 hours and an inclination of 0.8°. On completion of this step, the solar
arrays were fully deployed, as were the two antenna reflectors.

As of today, the satellite is operating  in quasi-nominal mode fully under
the control of the ESA/Alenia Spazio-Telespazio team, pointing at the
Earth and with the solar panels tracking the sun, while not yet in
geostationary orbit. Under current step 3 with the satellite in parking
orbit, new unforeseen but now required control modes for orbit-raising
using ion engine propulsion will have to be patched (by software uploads)
and commissioned. The ion engines themselves will then be initialised and
checked out.

Under step 4 (expected to start late September and last several months),
the satellite will be "spiralled" from parking to nominal geostationary
orbit using its novel electrical ion-propulsion system. Spacecraft
commissioning (activation and checking that all items are operating
correctly) will proceed subsequently. These operations, which are common
to all satellites at the beginning of their lifetime, will last a further
couple of months.

The recovery operation involves a certain number of unusual activities
which could not all be planned for in advance. In particular, the ion
propulsion system - originally to be used only for controlling the
inclination of the spacecraft throughout its lifetime - will be operated
in a new mode.

The on-board supply of propellant remaining after the orbit raising
manoeuvres, i.e. chemical and xenon (the gas used for the electrical
ion-propulsion system), should make possible a meaningful technology
mission in geostationary orbit, assuming proper operation in new modes
both in parking orbit and during ion-engine orbit-raising manoeuvres.

The next progress update will be released with the start of step 4
operations, presently scheduled for late September.

For further information contact:
ESA Media Relations
Franco Bonacina
Tel:+33.(0)1.5369.7713






 


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