CAPE CANAVERAL, Fla.—Space Shuttle Endeavour blasted off on its final mission today from the Kennedy Space Center, exactly 19 years to the day of the completion of its maiden voyage.

—Click here to see our Space Shuttle Endeavour photo gallery

The shuttle was visible at the NASA press site for only 22 seconds after launch before hitting a very low cloud base. Many experienced shuttle watchers were surprised that the launch was not delayed because of the cloud cover, prompting a flurry of questions from reporters at a post-launch press conference.

“The clouds were where we needed them,” said Mike Moses, launch integration manager for the shuttle program.

The mission will be a complicated one, with spacewalks conducted by shuttle crew while the International Space Station crew sleeps. Shuttle astronauts will install a $2 billion alpha magnetic spectrometer, a sensitive device that will search for the origins of matter in the universe. Midway through the mission a Russian soyuz craft will depart the station, returning three crew members to Earth. This is the first time a craft will depart the station while the shuttle is attached.

Endeavour is slated to return to the Kennedy Space Center on June 1.

Below is a clip from MSNBC’s coverage of the launch, including a few seconds of video from an unusual angle as Endeavour disappears into low cloud cover.

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—Click here to watch the complete story from Brian Williams and to read the story by MSNBC Science Editor Alan Boyle.