Astronauts from the U.S. space shuttle Endeavour have set out on the first spacewalk of their mission at the International Space Station.

Veteran spacewalker Dave Wolf and newcomer Tim Kopra floated out of the hatch Saturday to help the crew install an external platform on the massive Japanese lab at the station.

The six-and-a-half hour operation will require a hands-on effort by the spacewalkers, in addition to using the shuttle's and station's robotic arms.

The platform will complete the lab and allow scientists to conduct experiments in the vacuum of space.

In order to cut down preparation time, Wolf and Kopra "camped out" in the space station's airlock entrance Friday night.

Theirs is the first of five planned spacewalks during Endeavour's 11-day mission.

The shuttle docked with the Space Station earlier Friday, after a two-day trip from Earth.

With the shuttle crew, the station's population grew to 13, the highest number in the outpost's history.  

Kopra is taking the place of Japan's Koichi Wakata, who has been on the space station since March.

On Thursday, the U.S. space agency said foam insulation that broke off Endeavour's external fuel tank shortly after liftoff is no cause for concern.

NASA's shuttle program manager, John Shannon, said the loss of the foam insulation did not hurt the Endeavour because it occurred "so late" after takeoff.  

The debris could be seen hitting the spacecraft about two minutes after Wednesday's liftoff from the Kennedy Space Center in the southeastern state of Florida.

NASA has been concerned about debris from the external fuel tanks since the shuttle Columbia disaster in 2003.  Foam insulation damaged the shuttle's heat tiles during launch, which led to Columbia breaking apart upon re-entry.  All seven astronauts aboard the flight were killed.

Some information for this report was provided by AP.