The space shuttle Endeavour lifts off from the Kennedy Space Center in Cape Canaveral, Florida, May 16, 2011. Endeavour carries a crew of six astronauts on a mission to the International Space Station. [Photo/Agencies]

People watch as the space shuttle Endeavour lifts off from the Kennedy Space Center in Cape Canaveral, Florida, May 16, 2011.[Photo/Agencies]

CAPE CANAVERAL, Fla. - US space shuttle Endeavour blasted off on Monday to deliver a potentially revolutionary physics experiment to the International Space Station on the next-to-last flight in NASA's shuttle program.

Spacecraft Endeavour's 25th and final voyage 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 phasing out the shuttle program this summer.

With six veteran astronauts strapped inside, Endeavour roared off its seaside launch pad at 8:56 a.m. (1256 GMT) when Earth rotated into position to optimally align the shuttle with the space station flying 220 miles (354 kms) above the planet.

The Endeavour mission is being led by Mark Kelly, a four-time shuttle veteran who is married to convalescent US Representative Gabrielle Giffords.

The Arizona Democrat is recovering from a Jan. 8 assassination attempt that killed six people and injured 12 others. She was at Kennedy Space Center to watch Endeavour's launch.

The shuttle carries the $2 billion Alpha Magnetic Spectrometer particle detector, which is designed to analyze cosmic rays for fingerprints of dark matter, antimatter and other phenomena undetectable by traditional telescopes.

The instrument, built by a consortium of 60 research agencies in 16 countries, is expected to sift through 25,000 cosmic ray hits a second and operate for at least the next 10 years while attached to the outside of the space station.

The shuttle also carries a pallet of spare parts to tide over the station after the shuttle program ends this summer.

The last shuttle flight by Atlantis, slated to launch in July, will deliver a year's worth of supplies to the station.

Endeavour is due back on June 1.

Here are highlights of Endeavour's mission, which is scheduled to last 16 days:

* Endeavour is carrying a new type of science instrument, called the Alpha Magnetic Spectrometer, or AMS, which will make detailed studies of high-energy cosmic rays. The device, built by an international consortium of 60 research agencies, will be mounted outside the space station.

* Also aboard Endeavour are spare parts, including 10 circuit breakers, two communications antennas, a tank of ammonia coolant, a high-pressure oxygen tank for the station's airlock and a spare arm for the station's robotic crane.

* Endeavour's astronauts will conduct four spacewalks to install a materials science experiment, refill an ammonia coolant reservoir and conduct other station maintenance.

* A 50-foot (15-metre) extension for the shuttle's robot arm, developed for in-flight inspections after the 2003 Columbia accident, will be left behind at the station for use by its robotic crane.

* The crew also will test sensors being developed for NASA's new deep-space exploration vehicle called Orion.

* Endeavour will be the second of NASA's three space shuttles to be retired this year. After its mission, Endeavour will go on display at the California Science Center in Los Angeles.