To reach its target, Rosetta will complete several revolutions of the Sun, using the gravitational pull of other planets to "bounce off" and modify its trajectory while consuming a minimum of fuel. In all, it will require four fuel-saving gravity assists. 

The first was round the Earth in March 2005, one year after launch. On 25 February 2007, the probe made a close approach to Mars, acquiring remarkable pictures of the planet’s surface.

The second Earth swing-by took place on 13 November 2007.

On 5 September 2008, Rosetta encountered asteroid Steins, approaching to within 802.6 km. The data from its instruments allowed scientists to precisely determine the asteroid’s composition. An Earth flyby is then scheduled in November 2009. Lastly, a close flyby of asteroid Lutetia is planned in July 2010.

This strategy involves a long cruise phase lasting 10 years. Outside a so-called hibernation period when the probe is at its furthest point from the Sun, and remains out of contact with Earth to save power, mission controllers will be continuously uplinking commands during the planned planetary flybys and 2 asteriod flybys to calibrate its instruments and acquire the first science data.

Rosetta will begin observing the comet in mid-2014 for about 18 months, until it passes perihelion. It will drop the lander onto the comet’s surface after a few months in orbit. The Philae lander will conduct measurements for at least five days, then will embark on an extended, higher-risk mission.

Rosetta initially planned to encounter comet 46/P Wirtanen in 2011, landing on its surface in 2012. When the launch had to be postponed in January 2003, a new comet was sought. In May 2003, ESA’s Science Programme Committee selected Churyumov-Gerasimenko as the new target.