The space shuttle Endeavour has docked with the International Space Station, after a two-day trip to reach the orbiting outpost.

With the docking, the station's population grew to 13, the highest number in the outpost's history.  The Endeavour crew is to spend 11 days at the station working on a Japanese lab and doing other maintenance tasks.  Incoming  U.S. astronaut Timothy Kopra is taking the place of Japan's Koichi Wakata, who has been on the space station since March.

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.  He said officials are not worried about the current flight, but need to understand what such a loss of debris means for future missions.

The debris could be seen hitting the spacecraft about two minutes after Wednesday's blast off 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.