The Rosetta lander soared into the skies above South America atop an Ariane-5 rocket from Kourou, French Guiana. About two hours later, a 17-minute engine burn sent the spacecraft out of the earth's gravitational pull and on its way to the comet.
"We received the first communication from the spacecraft, which means the spacecraft is in good shape at the moment. Everything seems to be OK," Gaele Winters, the European Space Agency's director of operational and technical support, said at mission control in Darmstadt after the engine firing.
Rosetta is expected to reach an ice-caked comet called 67P/Churymov-Gerasimenko in May 2014 and go into orbit around it, then release the lander that will try to touch down on the surface. Previous spacecraft have made only brief fly-bys of comets.
A first launch attempt Thursday was scrapped because of high winds in the upper atmosphere. The second attempt was abandoned Friday when a routine inspection found that a piece of insulating foam had fallen off the main booster stage — raising fears that ice could form at the hole and break off after liftoff, possibly damaging the rocket.
A chunk of insulation helped doom the U.S. space shuttle Columbia last year when it broke off after launch and damaged the craft's wing, leading to catastrophic failure during re-entry into the atmosphere and the death of the crew of seven.
European space officials and scientists at mission control toasted their success with champagne after Rosetta was blasted out of its Earth orbit, accelerating to almost 25,000 mph. In another critical step, the probe's solar panels — its electrical power source — unfolded as planned, said flight director Alan Smith.
"The spacecraft is where we wanted it to be," Smith said.
Scientists hope the mission will reveal clues about the birth of the sun and the planets of the solar system, since comets are the system's most primitive objects — formed when it was still very young, more than 4.6 billion years ago.
Comets are believed to hold deep-frozen matter left over from the birth of the sun and planets.
Since comets pelted Earth in the time after the solar system formed, scientists theorize they may have brought some of the building blocks for life, like water and organic materials onto our planet.
67P/Churymov-Gerasimenko, discovered by two Soviet astronomers in 1969, is only 2 to 3 miles in diameter and has gravity so weak that the Rosetta lander will have to use a harpoon and spikes to fasten itself to its surface.
The comet has been studied intensively using the orbiting Hubble Space Telescope in preparation for the mission.
The $1.25 billion mission is more than a year behind schedule. ESA abandoned a January 2003 launch window after another rocket in the Ariane-5 family veered off course the previous month and had to be destroyed. The rocket that now launched the comet probe is a more time-tested version.
Named for the Rosetta Stone tablet that helped historians decipher Egyptian hieroglyphics, the Rosetta lander is to test the comet's composition with nine experiments and a drill to take subsurface samples.
The mission will send Rosetta on two excursions into the solar system's main asteroid belt between Jupiter and Mars. The craft will take a roundabout route, swinging through the gravitational fields of Earth and Mars during several fly-bys, picking up speed before heading into deep space.
French Prime Minister Jean-Pierre Raffarin issued a statement congratulating European space scientists for the launch's "perfect success."