Heading toward its first target-asteroid, (2867) Steins, ESA's Rosetta spacecraft has started using its cameras to visually track the asteroid and eventually determine its orbit with more accuracy.
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Rosetta started the optical navigation campaign on 4 August 2008, at a distance of about 24 million km from Steins; the campaign will continue until 4 September, when the spacecraft will be approximately 950 000 km from the asteroid.
"The orbit of Steins, with which Rosetta will rendezvous on 5 September, closing to a distance of 800 km, is only known thanks to ground observations, but not yet with the accuracy we would like for the close fly-by," said Gerhard Schwehm, Rosetta Mission Manager based at ESA's European Space Astronomy Centre (ESAC), near Madrid, Spain.
"We will be able to use the first data set for the trajectory correction manoeuvre planned for mid-August."
Comment: The threat to Earth by asteroids and comet fragments has been increasing dramatically, please see our 'must-read' Comet Series for more information.