Shuttle Tile Damage: Fix It or Leave It?

Aug. 14, 2007 — -- It was another routine day in space.

Astronaut Tracy Caldwell celebrated her 38th birthday in orbit. Teacher-astronaut Barbara Morgan and several crewmates answered questions submitted by Idaho schoolchildren.

And meanwhile, on the ground, engineers were hard at work, still trying to decide what they have to do to get the shuttle home.

NASA has taken pains to say that it does not think the astronauts are endangered by the inch-deep gouge in a tile on Endeavour's underside. But, severely chastened by the loss of Columbia in 2003, they are taking no chances.

"It's not very big, but it's something that — I don't want it to impact the turnaround of the vehicle," said John Shannon, head of the mission management team at the Johnson Space Center in Houston. "So I'm going to go and address it."

Shannon said NASA was balancing conflicting concerns. First, it wanted to assess whether the heated air that surrounds a shuttle on re-entry might damage aluminum struts, normally completely protected by the heat-shield tiles, in Endeavour's underside. Lengthy repairs might delay future flights and NASA has a mandate from the White House to finish the International Space Station in 2010 and retire the space shuttle fleet.

A spacewalking astronaut, riding on a small platform on the end of the shuttle's robot arm, might be able to fill in the damaged spot with sealant material. Several techniques were devised after the Columbia accident and tested by astronauts on a shuttle flight last year.

But engineers are concerned that an astronaut in a clumsy pressure suit might bang against other heat-shield tiles and end up doing more harm than good.

"I do not know that I have to fix this at all," Shannon said. "This is not a catastrophic loss-of-vehicle case."

Nevertheless, teams at NASA are now doing two opposite things:

One team, using 3-D models of the gouge in the tile, is doing tests — roughly the equivalent of firing a welder's torch at the spot in a wind tunnel — to determine what might happen if they leave it as is, and come home as planned.