High-altitude winds prompted mission controllers to scrub the launch 20 minutes and 40 seconds before the Ariane 5 rocket was due to lift off from the European Space Agency (ESA) base here, they said.

"We will make a second attempt tomorrow provided the weather is good," said Jean-Yves Le Gall, director-general of Arianespace, the ESA-affiliated company that is in charge of the launch.

In a five-billion-kilometer (three-billion-mile) odyssey, Rosetta will rendezvous in deep space with Comet Churyumov-Gerasimenko in 2014 and follow it closely on its path around the Sun.

The orbiter will scan the comet with its remote sensors and then send down a miniature laboratory, Philae, to assess the surface chemistry and geology.

Thursday's problem lay with winds at altitudes of between 10 and 15 kilometers (six and nine miles), Le Gall told reporters.

The winds did not pose a problem for the rocket itself but if for any reason the launcher exploded or was ordered destroyed at this height, the debris could have scattered outside the launch area's safety zone, Le Gall said.

"We are all dressed up and nowhere to go," said David Southwood, ESA's director of science, putting a brave face on the setback.

"But if you come to the tropics, it rains and you get winds."

He added: "The spacecraft is in good shape... we'll try again tomorrow."

The launch is ESA's second stab to get Rosetta into space.

A launch a year ago was cancelled because of reliability fears about the Ariane 5, and that target, Comet Wirtanen, was substituted by Churyumov-Gerasimenko.

Ten years of scientific and technical prowess have been thrown into the project.

The reason for the mission is belief that comets may contain vital clues as to how the Solar System was formed and, maybe, how life itself began on Earth.

Comets are believed to be orbiting clusters of frozen gas and dust -- the primitive material from which the planets accumulated, more than four and a half billion years ago.

As comets near the Sun, the solar heat warms up their frigid outer layer, which strips away in gassy outgushes and a wake of dust that the sunlight spectacularly reflects as a long "tail."

Some astrophysicists contend that comets are rich in complex, volatile moleculates which seeded Earth with the chemical means for life when the planet was in its infancy and under bombardment by space rubble.

To get Rosetta and Philae to the meeting point will need what ESA engineers dub a "billiard-ball journey."

The mission will use three flybys of Earth and one from Mars, exploiting the gravitational pull each time as a slingshot to reach more than 100,000 kilometers (60,000 miles) per hour to match the comet's speed.

The minutest error in navigation will send the three-tonne craft hurtling out of the Solar System, for Rosetta has to meet up with an object just four kilometers (2.5 miles across), 675 million kilometers (420 million miles) from the Sun.

Rosetta can be launched on any day during the next three weeks.

But the navigational task is so complex that it has to be launched at an exact second on that day. That means mission bosses cannot wait for a few hours to see if winds abate, which is the usual case with satellite blastoffs.

"We do not have a launch window, we have a launch instant," a visibly disappointed Le Gall said.

Rosetta is named after the stone that explained Egyptian hieroglyphics, thus laying bare the culture of the Pharoahs to modern eyes. Philae is so called after an obelisk that itself provided a key to understanding Rosetta.

SPACE.WIRE