With the comet approaching the Sun, the spacecraft will begin making observations that could give clues to the origins of the solar system and possibly how life began on Earth.
Comets are balls of frozen ice and dust, usually left over from the formation of the solar system about five billion years ago, although some are also thought to be interstellar travellers. Scientists have suggested that prebiotic life forms could have been carried between stars on comets, and then "seeded" life on newly-formed planets.
The climax of the mission will come when a lander will drop on to the comet's surface to carry out experiments to find out more about its composition.
The spacecraft will measure almost 100ft - as wide as a football pitch - across its solar panels, though the main body will be much smaller.
Rosetta is the latest mission in the comet exploration programme being conducted by the European Space Agency (ESA). British scientists have developed instruments for the orbiter and lander, and are contributing to a study of the comet's nucleus, inner structure, and"tail" created as the Sun heats and boils gases and liquids that comprise the comet.
"This is a tremendously exciting mission with extremely demanding technical and scientific requirements, and reflects the key role UK scientists are making to ESA's science programme," said Professor Ian Halliday, chief executive of the Particle Physics and Astronomy Research Council.
More details of the mission will be revealed next Thursday at the Royal Society in London, where a model of the Rosetta orbiter and lander will be unveiled.
t The Cassini spacecraft, launched in October 1997 on a mission to Saturn, has passed around Venus as part of a "slingshot" journey to gain speed on the way through the solar system. It passed about 390 miles above Venus's surface on Thursday, collecting data which British scientists will analyse in the coming months.
Cassini will pass the Earth at an altitude of 725 miles as part of its acceleration phase on 18 August.
Anti-nuclear protesters have warned that if it hits the Earth, radioactive material from its on-board power supply would be showered into the atmosphere. Mission controllers have argued that the risk is infinitesimal.Reuse content