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Last Updated: Friday, 7 March, 2003, 16:29 GMT
Comet chaser has new quarry
By Jonathan Amos
BBC News Online science staff

Rosetta, Esa
There is no time for a major redesign of the mission
Europe's great comet-chasing mission is back on.

The Rosetta probe, which has been more than 10 years in development, will now head for 67P/Churyumov-Gerasimenko in February, 2004.

The remarkable mission, which has so far cost 600m, will pursue the comet at breakneck speed and then attempt to put a lander on its surface.

The first attempt to launch Rosetta in January this year - to Comet Wirtanen - had to be called off when concerns were raised about the reliability of its rocket.

Europe's Ariane 5 vehicle is currently grounded following the loss of a launcher shortly after blast-off late last year.

Long mission

Scientists confess they know relatively little about Churyumov-Gerasimenko and are therefore busy studying the object to learn more about its size, shape and behaviour.

CG, Tim Puckett and Ingrid Siegert, Villa Rica, Georgia, USA
67P/Churyumov-Gerasimenko moves between the Sun and Jupiter
(Image by Tim Puckett and Ingrid Siegert)
Barring any surprising discoveries, the choice of Churyumov-Gerasimenko will be confirmed by the European Space Agency's Science Policy Committee in two month's time.

If any adjustments need to be made to Rosetta, they will have to be minor. There is not enough time between now and the launch window next year in which to make radical changes to the probe.

"It's great to have a new target," Dr Chris Lee, an Imperial College London researcher working on Rosetta, told BBC News Online.

"Because it is such a long mission, there was a fear that if we waited several years before launching, people would start to drift away from the project and the expertise would be lost."

Bigger pull

Just like its first mission plan, Rosetta will get to Churyumov-Gerasimenko via a series of complex space manoeuvres.

These will go out to Mars and back, producing a slingshot that will build Rosetta's speed up to the point where it can catch the comet out near Jupiter and then follow the body in towards the Sun.

The timescales involved are similar, too, with the rendezvous possible in 2014.

The larger size of the comet - it is three or more kilometres in diameter - compared with Wirtanen could pose some problems for the lander part of the mission.

Researchers are concerned that Churyumov-Gerasimenko's gravitational attraction will pull the lander in at a much higher velocity than the craft was designed for.

The landing team are now looking at the possibility of redesigning its legs to help cushion the impact.

Accident investigation

"There really is very little time to change anything on the mission," said Dr Lee. "If you make changes, they have to be re-qualified; you have to do mock-ups and testing."

The decision to postpone Rosetta had come as a bitter blow to the scientists and engineers who had worked on the project for a decade or more.

The mission's problems began in December last year when Europe's new super rocket, the Ariane 5-ECA (ESC-A), exploded over the Atlantic on its maiden flight.

Although Rosetta was scheduled to fly on a standard version of the Ariane 5, the post accident investigation ordered a thorough review of systems on all launchers.

The delay while this was carried out pushed Rosetta beyond the launch window necessary to get it into position to catch Wirtanen.

Rosetta comet chaser on hold
14 Jan 03  |  Science/Nature
Engine glitch brought down rocket
07 Jan 03  |  Science/Nature

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