Nasa finally launched the shuttle Endeavour last night on a 6.6 million-mile mission that will set a record for the biggest get-together in space.

After five previous delays — two due to technical problems and three to bad weather — the 17-year-old spaceship blasted off the launch pad at Cape Canaveral, Florida, carrying seven astronauts to the International Space Station 220 miles above Earth.

"The vehicle's ready, our support teams are definitely ready and the weather is finally co-operating, so it's now time to fly," Pete Nickolenko, the launch director, told the crew over the radio after meteorologists and technical directors cleared Endeavour for lift-off with ten minutes to spare.

Pieces of debris peeled off from the shuttle's external fuel tank as it blasted off but a US space agency official downplayed the potential for damage to the craft or danger to the crew.

The debris could be ice or foam, said Bill Gerstenmaier, NASA 's associate administrator for space operations, said.

"We had some foam loss events," he told reporters. "You can clearly see, on the front part of the orbiter, some white indications where the tiles were dinged. We don't consider those an issue for us — those are probably coating losses."

Nasa has been cautious about conditions for the space shuttle's exit and return since the shuttle Columbia blew apart 65,000ft (20,000 metres) above Earth in 2003 as it was returning to Florida after a 16-day mission.

As Endeavour crossed the imaginary line that marks the beginning of space, at an altitude of 62 miles and a speed of more than 8,000mph, rookie pilot Doug Hurley, 42, seated on the forward flight deck, became the 499th person to go into space.

Millionths of a second later, Chris Cassidy, 39, seated behind him, became the 500th. The crew held a vote several months ago to decide who would sit where, determining which of them would claim the accolade, 48 years after Yuri Gagarin, a Russian cosmonaut, became the first man in space.

When they arrive at the $100 billion (£61 billion) space station tomorrow, Endeavour's international crew will be welcomed aboard by the six-strong team already living there, creating the biggest crowd ever assembled off the planet.

They will work together on a gruelling and risky series of tasks that will include installing the final segment of the station's $1 billion Japanese laboratory module — known as Kibo — to create an external platform on which scientific experiments can be conducted in space.

"People think that this is pretty routine ... and we should never have anything bad happen," said Mark Polanksy, the shuttle's commander. "Well you know, I hate to let some folks know this, but this has risk. This is an extremely unforgiving environment and it's amazing technology."

Endeavour has already orbited Earth nearly 4,000 times in its lifetime, covering a distance of 103 million miles during 22 previous expeditions. It will add another 256 laps during its current mission, circling the planet 16 times a day.

It's launch came as America prepared to mark the 40th anniversary today of the lift-off of the Apollo 11 mission, which led to Neil Armstrong and Buzz Aldrin becoming the first humans to walk on the Moon.

The US space agency, which has not been back to the moon since 1972 and has often faced criticism for the resources it has expended on the space station at the cost of more ambitious human exploration, hopes to use the anniversary to reinvigorate public interest in its work. Plans include returning man to the Moon by 2020 and sending the first humans to Mars by 2037. The space station is providing a testing ground for some of the research required for such missions.

"Nasa's a pretty darn cool place and we do pretty amazing things and I know that we have our detractors, but ... it's really exciting to be a part of all this," said Mr Polanksy, 53.

"I would also be less than honest if I didn't say that I would have hoped by the time that I got to be my age — having been 13 years old when we landed on the Moon — that I'd have been doing something similar to that and not just going a couple of hundred miles up. Doesn't mean that I think that the work's not important, or that what we're doing is just trivial. It's just that I think we've been in low Earth orbit long enough so I'm really excited to be a part of this process that gets us out of here, and gets us to more human exploration."

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