NASA officials say a chunk of ice may have cut a gouge on the underside of Endeavour during launch. The damage was seen in photographs taken from the International Space Station before the shuttle docked Friday.

Officials have not said whether the damage is critical. But while NASA has been concerned with shuttles getting hit by foam during launches, ice is far more dense and could therefore cause much more damage.

Endeavour's fuel tank was filled with super-cold fuel before lift-off, so large pieces of ice may have formed on the outside.

The gouge appears to be 7.6 centimetres in length. If it's deep enough, astronauts will have to perform a spacewalk to patch it, said John Shannon, chairman of the mission management team.

The Endeavour crew -- including Canadian astronaut Dave Williams -- could repair the damage using several methods. They can either fill up the gouge with a paste, apply black paint, or attach a protective plate.

If the damage is so severe that it can't be fixed, the astronauts will be stranded at the space station. But they have enough supplies to last two months, and a rescue shuttle could reach them by October.

The crew will get a closer look at the damage on Sunday, using lasers at the end of the Canadarm to measure the exact size of the cut. The damage is metres away from the starboard main landing gear door.

Images taken during the launch show white particles falling from the shuttle after 58 seconds, suggesting ice may have hit a tile and scratched Endeavour's underside.

"It looks like it was an ice impact to me," said Shannon.

Pictures of Endeavour's underside were taken moments before docking, as Commander Scott Kelly steered the shuttle through a "backflip."

Officials also wanted to look at damage caused by pieces of foam insulation that struck the shuttle's exterior during launch. But NASA has said that damage does not appear to be critical.

Foam has been a concern to NASA since 2003, when the shuttle Columbia disintegrated upon re-entry to the atmosphere, killing seven astronauts.

A piece of falling foam insulation had knocked a hole in Columbia's protective heat shield during the launch, unbeknown to the astronauts and NASA. The disaster put a halt to the shuttle program for more than two years.

Dave Williams will be part of the Endeavour crew that conducts a spacewalk Saturday, when the shuttle will be checked more thoroughly.

This is Williams' second space flight, but his first visit to the space station and his first spacewalk. He is scheduled to go outside the station three times in all, to transfer payloads and carry out the construction of the station elements during the mission.

If all walks are completed, Williams will have set a Canadian record for the number of spacewalks and hours spent outside the ISS.

After Endeavour docked Friday, cameras flashed as teacher-turned-astronaut Barbara Morgan made her way into the International Space Station.

Morgan was a possible replacement for astronaut Christa McAuliffe on the ill-fated 1986 Challenger mission, and watched from the ground as that shuttle disintegrated, killing everyone on board.

A former Idaho schoolteacher, Morgan's presence on the station is proof of NASA's renewed commitment to bringing educators into space. It's also made her something of a celebrity to her crewmates, who snapped pictures as she came threw the airlock.

Endeavour is delivering supplies to the crew of the space station, and is bringing along a new segment of the Integrated Truss Structure.

This new structure is relatively small and weighs about 2,200 kilograms. When installed, it will provide clearance between sets of solar arrays on the truss structure.

Canadarm and Canadarm2 will play important roles in the construction during the spacewalks. The truss segment will be moved into position using the Canadarm2 before the astronauts secure it to the station.

With files from The Associated Press