Rosetta, the £600m comet-chasing probe, lifted off at the third attempt from its launchpad in French Guiana this morning at 08:17 CET.

Following a standard ascent - lift-off, booster separation and burn-out of the central core stage of the Ariane 5 rocket - the upper stage entered a prolonged ballistic phase. This was followed by a delayed ignition of almost 17 minutes, two hours after take off.

Two launches were aborted last week, firstly because of concerns over the weather, and then for urgent repairs to the rocket's fuel tank insulation.

Rosetta will soon release four main attachment points securing its payload - the probe Philae. During its 10-year cruise through the solar system, the washing-machine-sized lander will be connected to the spacecraft by a central motor alone.

For most of its journey, Rosetta will simply be coasting. Then, in 2011, a last burn will direct it towards its final rendezvous.

When it arrives at Churyumov-Gerasimenko three years later, Rosetta will finally release the lander about a kilometer from the comet. Philae then faces a 30-minute trip to the surface.

The gravitational field of the comet is very weak, so Philae will touch down at walking pace. Even so, it is equipped with harpoons to secure it to the comet and prevent it bouncing back into space.

The experiments will begin almost immediately after landing. The primary phase, which needs battery power, will last for about 60 hours. The secondary phase, powered by solar cells, will continue for approximately three months. ®

Related stories
Rosetta still earthbound
Comet-chasing Rosetta still on launchpad
Comet chasers seek secret of life