Pictures had shown a three-inch-wide, inch-deep gouge in two heat-shield tiles after launch, and the shuttle's Mission Management Team had debated for nearly a week whether to send astronauts on a space walk to patch it up.
But after a final five-hour meeting, MMT chair John Shannon said he polled the teams of engineers working on the issue--more than 200 people at NASA centers around the country were involved--and they came back with "a unanimous recommendation that the damage was not a threat to crew safety."
Shannon said there was some disagreement, though, over whether to make a repair anyhow; an engineering group in Houston thought it would be, in Shannon's word, "prudent" to send astronauts out to fill the damaged spot with a sealant material.
Such a spacewalk would carry risks of its own--an astronaut might accidentally hit other tiles and do more harm than good--but the dissenters told Shannon "they could not see a reason that that could cause additional damage to the orbiter."
So, Shannon said, "It was not unanimous but it was pretty overwhelming not to do the EVA."
The Endeavour astronauts were told of the decision shortly before they were supposed to go to sleep. "It's great we finally have a decision and we can press forward," said mission control.
"Tell everyone thanks for the hard work," replied the shuttle's commander, Scott Kelly.
One consideration: engineers knew the shape of the existing gouge pretty well, said Shannon, and had tested how it would be affected by heated air rushing past it on re-entry. The same could not have been said for a spot partially filled in by an astronaut with sealant material.
"You have something you know you can live with; why would you take the risk of doing the EVA to change that cavity into what could potentially be an even better situation but also could potentially be a worse situation?" Shannon asked.
"If we had a situation that I thought was a threat to crew safety," he said, "I would go do that EVA and feel good about it."
There will still be a spacewalk on Saturday, according to current plans--but it will be routine work on the space station to get it ready for new parts to be delivered by the next shuttle mission.