The US space agency Nasa has successfully launched the space shuttle Endeavour - at the sixth attempt.
Earlier launches at the Kennedy Space Center in Florida were called off because of bad weather and fuel leaks.
The crew will spend 11 days on the International Space Station, finishing work on a Japanese research laboratory.
If the shuttle had not taken off by Thursday, it would have had to have waited until the end of the month to make way for a Russian cargo ship.
"The weather is finally co-operating so it is now time to fly," said launch director Pete Nickolenko. "Persistence pays off, good luck and God speed."
The seven crew members will spend 11 days on the space station
Mission commander Mark Polansky replied: "We're ready to go, and we're going to take all of you with us on a great mission."
The orbiter is taking a seven-strong crew into space, made up of six Americans and one Canadian - Julie Payette - who will operate the shuttle's robotic arm during the mission.
Their arrival, on Friday, will bring the total crew on the outpost to 13 - a record for the International Space Station (ISS).
On the first of five spacewalks, a platform will be added to the Japanese laboratory complex, Kibo, which can be used for experiments that require materials to be exposed to the harsh environment of space.
The crew will also install new batteries to one of the solar arrays, which provide power to the space station, and perform other maintenance tasks.
Astronaut Julie Payette is to operate the shuttle's robotic arm
In addition, Endeavour will deliver a new long-stay US crew member, Tim Kopra, to the ISS and bring back Japan's Koichi Wakata, who has lived aboard the platform for more than three months.
The $100bn space station, now about the size of a four-bedroom house, has been under construction for more than a decade.
This is the 127th space shuttle flight, the 29th to the station, the 23rd for Endeavour and the third in 2009.
Seven further flights to the platform remain before the shuttles retire in 2010.
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