NASA was leaning against repairing damage to the shuttle Endeavour's heat shield after lab tests and engineering analyses indicated the shuttle could safely fly home next week, officials said Wednesday.
Shuttle deputy program manager John Shannon said mission managers will wait for one last heat test before making a final decision today.
"We're pondering. But my personal feeling is, the data is 80 percent to 90 percent that we can use" the shuttle as is, Shannon said at a briefing Wednesday evening at Johnson Space Center in Houston.
The fear is that in trying to drive the safety margin higher by trying an on-orbit repair, astronauts could make the situation worse. There is also concern that NASA has never attempted such a repair on the underside of the shuttle and much of the work would be done out of sight of ground controllers.
"I am cautiously optimistic that repairs will not be needed," Shannon added.
Endeavour was damaged during last week's launch, when a chunk of foam broke off a bracket on its external fuel tank, ricocheted off a strut and hit the underside of the orbiter near the right main landing-gear door.
The foam tore off a 3-inch-wide portion of two of the silica tiles that protect the shuttle from the 2,300-degree heat of re-entry. The damage extends almost down to the shuttle's aluminum body, which could start melting at 1,200 degrees.
Over the weekend and again Tuesday, space agency engineers conducted exhaustive analyses of the damage to see if temperatures in the tile gash could endanger the shuttle and its seven-person crew.
Every test and analysis, Shannon said, indicated the shuttle could fly home safely without endangering the integrity of the vehicle. Even if, by some chance, the aluminum skin was damaged during re-entry, the damage is not in a sensitive area.
The main concern would be having to spend extra time on the ground repairing the shuttle, he said.