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.

Others are laying out plans for a spacewalk, which could happen Friday or Saturday. It might be an added job on a spacewalk that was already planned.

Shannon said he did not think there would be a decision on the course of action before Wednesday.

The wait may seem hard on the nerves, but Morgan's husband, Clay, insisted he was doing fine.

"Everyone feels that the risk is more to, damage to the shuttle, rather than danger to the crew," said Morgan, an author who has experience as a smoke jumper fighting forest fires.

In an interview with ABC News, he said, "I don't want them going out there, going on a dangerous spacewalk underneath the shuttle, just to make the show of doing something."

Fifty-eight seconds after launch last week, engineers noticed a piece of debris breaking off Endeavour's orange external fuel tank, bouncing against a support strut and hitting the underside of the orbiter.

Shannon initially said the video of the debris — either foam or ice — breaking up in a spray was "underwhelming."

But Friday, as a matter of course since the loss of the Shuttle Columbia in 2003, astronauts did a photo survey of Endeavour as it approached the International Space Station for docking. Those pictures showed a 3-inch spot on the bottom of the shuttle's right wing.

More precise readings came Sunday from cameras and a laser range finder on the shuttle's robot arm. They showed the debris had cut more than an inch through one of the heat-shield tiles — almost all the way to the aluminum skin the tiles are meant to protect.

Shuttles have safely landed with worse damage before — but that was before the Columbia accident. Since then, NASA has been very sensitive about any damage to a shuttle's outside surfaces.

"This is something we would rather not deal with, but we have really prepared for exactly this case," Shannon said Sunday. "So I feel very comfortable that whatever is required, we can go do, and do successfully."

Meanwhile, Endeavour's seven astronauts, working with the three men on the space station, went on about their business. Astronauts Rick Mastracchio and Dave Williams went on the mission's second spacewalk Monday afternoon, and two more are planned.

Barbara Morgan has become the media darling of Endeavour's crew, having been the backup for the first teacher in space, Christa McAuliffe, one of the seven astronauts killed onboard the Shuttle Challenger back in 1986.

It has been 21 years since then, and students of the space program say the shuttles have continued to remind their makers what delicate machines they are.

"What they have done is mitigate the problem. They have worked around it as a way of managing the risk," said Howard McCurdy, a former space reporter who now teaches at American University, "but the risk is still there, and you can't make it go away unless you stop flying the shuttle."