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The long trek 
The three-tonne spacecraft was first inserted into a parking orbit, before being sent on its way towards the outer Solar System. Unfortunately, no existing rocket, not even the powerful European-built Ariane-5, has the capability to send such a large spacecraft directly to Comet 67P/Churyumov-Gerasimenko. Instead, Rosetta will bounce around the inner Solar System like a ‘cosmic billiard ball’, circling the Sun almost four times during its ten-year trek to Comet 67P/Churyumov-Gerasimenko.
Along this roundabout route, Rosetta will enter the asteroid belt twice and gain velocity from gravitational ‘kicks’ provided by close fly-bys of Mars (2007) and Earth (2005, 2007 and 2009).
Rosetta first travels away from its home planet and then encounters Earth again, a year after launch, in March 2005. Rosetta remains active during the cruise to Earth. The fly-by distance is between 300 and 14 000 kilometres. Operations mainly involve tracking, orbit determination and payload check-out. Orbit correction manoeuvres take place before and after each fly-by.
After the first fly-by of Earth in March 2005, Rosetta heads to Mars and then returns to Earth twice in November 2007 and November 2009 for its second and third fly-bys of our planet.
Rosetta flies past Mars in February 2007 at a distance of about 200 kilometres, obtaining some science observations. An eclipse of Earth by Mars lasts for about 37 minutes, causing a communication black-out.
The spacecraft goes into passive cruise mode on the way to the asteroid belt. Rosetta observes the asteroids from a distance of a few thousand kilometres. Science data recorded on board are transmitted to Earth after the fly-by.
After a large deep-space manoeuvre, the spacecraft goes into hibernation. During this period, Rosetta records its maximum distances from the Sun (about 800 million kilometres) and Earth (about 1000 million kilometres).
The spacecraft will eventually arrive in the comet’s vicinity in May 2014. Rosetta’s thrusters will then brake the spacecraft, so that it can match Comet 67P/Churyumov-Gerasimenko’s orbit.
Over the next six months, it will edge closer to the black, dormant nucleus until it is only a few dozen kilometres away. The way will then be clear for the exciting transition to global mapping, lander deployment and the comet chase towards the Sun. Last update: 1 November 2004
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