Rosetta starts tracking asteroid Steins.

[Notebook]

4 August 2008
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.

http://www.esa.int/esaCP/SEMF0B8N9JF_index_0.html

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[Notebook]

Rosetta's first major correction manoeuvre in the approach phase took place while the spacecraft was just less than 17 million km from Steins. The spacecraft’s thrusters burned continuously for approximately 2 minutes, starting at 13:42 CEST (Central European Summer Time). This achieved a change in Rosetta’s speed with respect to Steins of 12.8 cm/sec.

This tiny change in speed, though, will be enough to correct the spacecraft's 5 September Steins fly-by distance by 250 km. Prior to this manoeuvre, the spacecraft’s trajectory would have led it too close to the asteroid at the time of closest approach; to be compatible with spacecraft performance, Rosetta must be no closer than 800 km from Steins.

http://www.esa.int/esaCP/SEMC9R6UWJF_index_0.html

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