NASA will decide Wednesday whether Canadian astronaut Dave Williams or another member of the Endeavour crew will need to make a spacewalk to repair a deep gash on the space shuttle's belly.

This close-up view of damaged tile on the underside of the Endeavour was photographed during a focused inspection of the shuttle's heat shield while docked with the International Space Station.
(NASA/Associated Press)

The chairman of NASA's mission management team, John Shannon, said Monday a specialized NASA team is developing new models to analyze the "fairly deep gouge," on the shuttle, but also assured reporters "we're not talking about catastrophic damage."

The unevenly shaped gouge, discovered on Sunday using the Canadian-made robotic arm, showed the damage went through the 2.5-centimetre-thick tiles, exposing the felt material sandwiched between the tiles and the shuttle's aluminum frame.

Williams and fellow astronaut Rick Mastracchio have already completed two spacewalks since the space shuttle arrived at the space station on a mission to assemble key components of the orbiting platform.

On Saturday the pair successfully installed a roughly two-tonne beam to the backbone of the space station during a spacewalk of more than six hours, and on Monday they replaced a faulty gyroscope to maintain the station's orientation in space.

A third spacewalk is planned for Wednesday, with Mastracchio and space station crew member Clayton Anderson assigned to prepare a segment of the station for relocation during the next mission.

A fourth spacewalk has been scheduled for Friday, with Saskatoon-born Williams the likely candidate.

To patch the gouge, astronauts would have to perch on the end of the Canadarm and apply a protective paint and caulk-like filling.

Canadian astronaut Steve MacLean told CBC News the task would be a difficult one, both because of the inherent risks of spacewalks and the precision required to fix the tiles.

"Any time you put an astronaut on a boom, you have the risk that you might hit the tile and cause more damage," MacLean told CBC News.

NASA has already extended the mission from its original 11 days to 14 days in order to give them time to assess whether a repair is necessary, and said Monday they are considering extending the mission further if more time is needed.

With files from the Associated Press