On Friday, NASA officials announced the successful docking of the US Space Shuttle with the International Space Station. "It was a flawless rendezvous," said NASA Flight Director Matt Abbott at a press conference in Houston, Texas. "Everything was from the book."

But before docking the astronauts detected damage to Endeavour’s heat shield that it may have sustained during take off.

After the analysis of the images taken during the docking and sent by Endeavour back to Earth it appears the damage was about 7.5 by 7.5 centimeters in diameter on a tile on the underbelly of the space craft.

The damage was likely caused when a piece of ice struck the tile during Wednesday's launch, according to NASA Programme Manager John Shannon.

The spot is to be examined more closely on Sunday to help decide what repairs might be needed. During their first spacewalk shuttle astronauts Rick Mastracchio and Dave Williams will inspect the gouged area more closely using the shuttle's robotic arm and laser-tipped extension boom.

"It's way too early now to determine whether any repairs are required," added John Shannon.

He said that such repairs were a new phenomenon. "We have a rich flight history of tile damage." Shannon said. "In the past we didn't even know we had damage and we flew back home."

Damage to the heat shield - much larger than that discovered on Endeavour - was what led to the Columbia shuttle disaster in 2003, in which seven astronauts were killed.

There won’t be a problem even if the damage is important and the shuttle crew would have to abandon Endeavour. According to NASA officials there are enough supplies to last to the end of October, whereas another shuttle could be launched as early as Oct. 5.

Also during the first spacewalk the astronauts will install a new truss segment to the International Space Station's backbone. The new segment, known as the S5, is relatively small and weighs about 5,000 pounds. The piece provides clearance between sets of solar arrays on the truss structure.

Mastracchio and Williams will provide on-the-scene guidance while astronauts inside the space station use a crane-like robotic arm to maneuver the 2-ton, $11 million segment into place. Mastracchio and Williams will then work on removing launch restraints and bolting the segment into place.