The space shuttle Atlantis has been successfully launched from the Kennedy Space Center in Florida.
The orbiter is taking Europe's Columbus science laboratory to the International Space Station (ISS).
Despite concern throughout the day that cloud, showers and winds might scrub the launch, the weather cleared at the right time to allow a smooth lift-off.
The Columbus module is Europe's major contribution to the science endeavours on the orbiting platform.
A delighted European Space Agency (Esa) chief, Jean Jacques Dordain, was present to see the launch.
"It's a great day for Esa," he said. "Columbus discovered a new world, and I think that with Columbus we are discovering a totally new world," he added.
"From now on, Esa becomes a visible and concrete partner of the space station."
Columbus is the first segment of the ISS that Europe will control, through a ground station in Germany. Its installation will mean Esa becomes a full member of the orbital project and gains "rights" to positions on the platform for European astronauts.
In the short term that means one six-month residency every two years.
Once the 1.3bn-euro ($1.8bn; £0.9bn) lab is in place, an intensive programme of research in weightless surroundings will begin.
The scientific studies will impact diverse fields, from crop breeding to the development of advanced alloys.
The experiments will also help researchers better understand the physiological demands of long-duration spaceflight, something that will be important if humans are ever to colonise the Moon or travel to Mars.
Columbus will be installed on Day Four of the mission.
The 7m-long (24ft), 4.5m-wide (14ft), 12.8-tonne laboratory will be manoeuvred into position by the shuttle's robotic arm, and docked to the station's Harmony Node 2 connector.
Hans Schlegel, the German Esa astronaut on the flight, will play a key role in this process, carrying out two spacewalks to get the job done.
Esa colleague Leopold Eyharts will be staying on the station to commission Columbus, a process that should take a few weeks to complete fully.
The launch proved to be an extremely satisfying day for the US space agency (Nasa), which saw a faulty fuel sensor system on the orbiter thwart its attempts to launch Columbus in December.
And stormy weather to the northwest of Kennedy on Thursday threatened to spoil the latest campaign, with, at one point, meteorologists reporting a 70% probability that conditions would lead to another "no go".
But with under 15 minutes to the scheduled launch time of 1445 EST (1945 GMT), winds that for much of the day had been outside the permitted strength in the flight regulations suddenly relented.
Nasa will confirm that Atlantis made a truly flawless ascent only after engineers have had time to check imagery of the lift-off.
An initial examination of pictures showed at least three pieces of foam falling off the shuttle's external tank, but it is not thought these damaged the ship in anyway.
Atlantis astronauts will also conduct their own survey of the shuttle's external surfaces to confirm the vehicle's integrity.
Nasa is confident it now has the shuttle system working well after encountering no major technical issues with the vehicle during Thursday's launch campaign.
The agency hopes to fly another five missions this year - four more to the space station and one to service the Hubble telescope.
Beyond Columbus, 11 flights in total are required to finish the ISS - a target Nasa believes is achievable by its deadline to retire the shuttles at the end of 2010.
"We just take each flight at a time and see what we get from the hardware and the vehicle," said Bill Gerstenmaier, Nasa's spaceflight chief.
"We've got margin in the overall schedule, but we'll do the right thing."
Atlantis is due to dock with the ISS on Saturday. Its return to Earth is planned for Monday, 18 February.
The orbiter will be bringing back US astronaut and long-stay ISS resident Dan Tani in Leopold Eyharts' seat.