The United States space shuttle Endeavour has blasted off toward the International Space Station (ISS) on the penultimate flight for the US shuttle programme.

The six-member crew, comprising five Americans and one Italian, is delivering a $2bn physics experiment to probe the origins of the universe during its 16-day mission, which will include four spacewalks.

Endeavour, which launched from the Kennedy Space Center (KSC) in Florida, was expected to reach the orbital outpost on Wednesday.

NASA plans one more mission to the station - using the sister shuttle Atlantis - in July, before ending the shuttle programme.

The STS-134 mission, which launched on Monday, had initially been set to begin on April 29.

However, the mission was postponed last month after technicians discovered a power failure in a heating line that served to prevent fuel from freezing in orbit.

NASA completed exhaustive repairs last week.

As many as 500,000 onlookers crowded into coastal viewing spots on Monday in Brevard County, the area around the KSC.

"This mission represents the power of teamwork, commitment and exploration," shuttle commander Mark Kelly said shortly before lift off at 8:56am (1256 GMT).

Kelly's wife, Gabrielle Giffords, the US congresswoman who is recovering from a January 8 assassination attempt, watched the launch from KSC.

'Routine' takeoff

Mission control in Houston described the take off as "a fairly routine ascent" and added "there were no anomalies discussed whatsoever on the way uphill for today's launch".

The shuttle is set to dock at the ISS on Wednesday at 6:15am (1015GMT), and will stay there until May 30, returning to the US on June 1, NASA said.

The Alpha Magnetic Spectrometer-2 (AMS-02), a $2bn 7,000kg particle detector, will be left behind to scour the universe for hints of dark matter and antimatter over the next decade.

"It's a bit like searching for a needle in a haystack," said French scientist Jean-Pierre Vialle, part of the international team that worked on the AMS-02 project.

"But if we find it, it will show beyond a doubt that stars made of antimatter exist in some part of the universe. That would be a major revelation."

After the final shuttle missions, the three spacecraft in the flying fleet and the prototype Enterprise will be sent to different museums across the country.

Discovery, the oldest in the group, was the first shuttle to retire after its final journey to the ISS ended in March.

Endeavour is the youngest, and flew its first space mission in 1991. STS-134 marks its 25th and final mission.