Update:

At the Johnson Space Center, engineers are wrapping up analyses of the heat shield gouge and comparing sophisticated computer modeling results with final test runs in a high-temperature furnace to make sure the computer predictions match up with the actual re-entry environment.

Computational fluid dynamics calculations indicate the aluminum skin below the gouge in two tiles on the belly of the shuttle will not exceed NASA's conservative 350-degree design limit. The computer calculations indicated the skin temperature would only rise some 40 degrees above normal and stay below the limit. A mockup of the damage using tiles deliberately carved out to mimic the damage on Endeavour were put in the arc jet facility and subjected to the sort of 2,200-degree wind the shuttle will experience during peak heating. Again, the temperature of the aluminum skin under the tiles did not climb above 350 degrees.

The final tests carried out overnight involved a tile mockup with more idealized damage, a carved pit with the sort of straight lines and angles used in the computational fluid dynamics model. The idea is to make sure the computer models are accurate and do not include any incorrect assumptions. As an additional safety check, the analyses is being independently peer reviewed.

"The primary point of debate (Wednesday) was did we need to run the simplified model in the arc jet facility?" said John Shannon, chairman of the Mission Management Team. "Because a lot of folks thought that we had two fairly independent analyses, one was the thermal analysis done on computer, one is the arc jet that said you don't have a problem here. But just to tie the two together and make sure we didn't make some significant error in either of those, we're going to run this simplified model in the arc jet. That was the primary point of discussion. People thought we had enough data, some people wanted to go get some more data. So we're going to go get some more data."

NASA managers say they do not view Endeavour's gouge as a Columbia-class problem. Shannon said the issue is whether re-entry heating might cause damage to the shuttle's aluminum skin in the immediate area that would require time-consuming post-landing repairs.

But Shannon made it clear he viewed the risk of a spacewalk repair as significant and that such a repair could only be justified if it was necessary to prevent serious damage during re-entry. And based on the testing and analysis through Wednesday, that did not appear to be the case. But, as Shannon cautioned, the analyses is not complete and any major surprise or disagreement between the computer models and the arc jet facility could change that assessment.

NASA's Mission Management Team has finished a five-hour meeting to assess the health of the shuttle Endeavour's heat shield. At 9 p.m., mission control informed the astronauts that a tile repair spacewalk had been ruled out.