NASA is "cautiously optimistic" that astronauts will not have to undertake repairs of a damaged area on the Endeavour shuttle's heat shield, an official said on Tuesday.
"We are still looking at the tile damage," mission chief John Shannon told a news conference, referring to the 8.75 by 5.0 centimeter (3.5 by 2.0 inch) gouge near a landing gear's hatch.
"We are cautiously optimistic that we can fly as it is," he said after seeing the results of aerodynamic and thermal assessments of the damaged area.
Officials at the National Aeronautic and Space Administration will continue to analyze data and recheck calculations regarding the vulnerability of the ship upon reentry.
They expect to announce a decision late on Wednesday on whether or not to send astronauts on a space walk to mend the problem.
The concern is that the gash could result in excess friction as the shuttle hurtles into the Earth's atmosphere at high speeds, though NASA has said the problem "poses no threat to crew safety or mission operations."
Shannon said there was little doubt that an in-space repair job could be done.
"We are following two parallel paths, one the thermal assessment, and the potential repair options," he said.
"I feel comfortable we can execute the repair if required."
If a repair job is required, NASA will have three astronauts on Earth undertake the operation in a mockup of the shuttle to sort out the logistics and possible problems.
NASA officials said the gouge was likely caused by a 100 gram (3.5 ounce) piece of foam, or foam with ice, that broke from the external fuel tank 58 seconds into the shuttle's launch on August 8. Earlier reports characterized the debris as just ice.
The damage to the heat shield has evoked the February 2003 Columbia disaster, when broken tiles on that shuttle's heat shield led to its disintegration upon its return from space, killing the seven astronauts aboard and putting in limbo the shuttle program for nearly 18 months.