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| N° 40-1993: OLYMPUS: End of mission 26 August 1993 As indicated in the press release of 17 August, 1993, service from the Agency's experimental OLYMPUS satellite was interrupted during the night of 11/12 August when, for reasons which are not yet understood, the satellite lost earth pointing attitude and began spinning. This event, and the subsequent recovery actions, used the last few kilograms of fuel remaining on the satellite. An assessment of the situation indicated that it would be impossible to re-establish service. It has therefore been decided that the Olympus mission should be terminated and the satellite removed from the geostationary orbital ring. Olympus entered its fifth year of operations in July of this year. Throughout its mission, the satellite payloads were used by a wide range of European and Canadian Organisations to develop and test advanced satellite communications technologies and provide new services. The results of these were the subject of an international Conference held in April 1993, in Seville, Spain, which brought together 300 scientists, engineers, educators and broadcasters, who reported on their achievements using the satellite. The proceedings of this conference, which contain the approximately 130 papers which were presented, are now being distributed. Olympus carried four separate payloads, a two channel high power direct broadcasting payload operating at 18/12 GHz, a four channel 12/14 GHz Specialized Services Payload, a 20/30 GHz payload for advanced communications experiments, and a 12/20/30 GHz beacon package for propagation experiments. The Ka band (20/30 GHz) transponders have been exploited extensively by numerous organisations to demonstrate the use of small terminal networks and for video conferencing and satellite news gathering applications including daily transatlantic transmissions. These have shown a high degree of service availability at these new frequencies. In addition, this payload was used to constitute the geostationary end of a data relay link between the Inter- Orbit Communications (IOC) terminal mounted on the Agency's EURECA spacecraft and ground controllers and experimenters during that highly successful recently completed mission. Olympus has also been instrumental in the development of new applications, such as distance learning, data distribution and new commercial services. In the distance learning field alone, over 100 organisations, in 12 countries have used Olympus to develop training courses which are now part of the established satellite based educational infrastructure. Several of these operations have now been transferred to the EUTELSAT space segment. In the broadcast field, Olympus was the initial test bed for a number of satellite broadcast programmes, which are now running on a commercial basis, including RAISAT and the BBC World Service. It was also used for experimental high definition TV broadcasts, to assist in the development of that new technology. Olympus provided valuable opportunities to collect propagation data for hundreds of scientists across Europe and North America. The 20/30 GHz data, in particular, forms a major part of the statistical information available globally.
It will be remembered that control of OLYMPUS was
accidentally lost in the summer of 1991 and, following an
uncontrolled orbital drift around the world, in a frozen
state at temperatures of some minus 60 degree Celsius, the
satellite was the subject of a spectacular recovery action
which allowed it to be put back into service again. The
recovery at that time, however, used a large amount of
fuel, and little was left on-board to complete the intended
five year mission. By instituting new procedures to
conserve fuel, it was nevertheless hoped that OLYMPUS could
complete its nominal five year mission in early 1994 and
then still have a reserve amount of fuel that could be used
to re-orbit the satellite, i.e. remove it several hundred
kilometres from the geostationary orbital ring. This re-
orbiting at the end of a geostationary satellite mission
is ESA policy in order to eliminate the probability that
a satellite left to drift in that orbit could later strike
or interfere with another satellite.
The re-orbiting process has been initiated and is being
carried out several hours per day. The satellite is now in
an orbit with respectively an apogee some 195 km, and a
perigee some 390 km below geostationary. It was decided to
re-orbit to a lower rather than higher altitude due to the
fact that the incident itself caused an orbital
perturbation in this direction, and, consequently, there
would not have been sufficient fuel to retransfer the
spacecraft to a higher orbit. This activity will continue
for several more days, in order to reach the lowest
possible orbit. Several end-of life tests will then be
conducted with the satellite, after which steps will be
taken to deplete the pressurant remaining in its tanks.
Once the satellite is in this "safe" configuration, it will
be turned off and its mission will have come to an end.
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