The next flight of space shuttle Discovery will be the most closely observed in history. More than 100 cameras will watch the spacecraft lift off the launch pad and shoot into space. The crews of the shuttle and the International Space Station also will take pictures.
Yet NASA hasn't finished the testing needed to guarantee that it will spot tiny but critical cracks along the front of the ship's wings. That's where shuttle Columbia was damaged before it disintegrated on re-entry in 2003.

Shuttle officials concede that if they do spot damage, deciding what to do -- Repair the shuttle? Leave the crew on the space station? Fly home as is? -- will be painful and difficult.

"There is some amount of uncertainty in our ability to evaluate what it is we're looking at," says Stephen Oswald, a former shuttle commander who is now vice president of Boeing's shuttle program. "Until we go fly and demonstrate that to everyone, we're all going to be a little tensed up."

Earlier this year, a NASA committee decreed that engineers must be able to detect cracks in the front edge of the wing that are only 2 inches long and 0.02 inches wide. Wider cracks would lead to catastrophic "burn-through," which is what destroyed Columbia.

To inspect this crucial spot, NASA mounted a laser on the tip of the shuttle's robot arm. Once Discovery is in space, three astronauts will supervise the laser as it scans the front edge of both wings. Discovery could blast off as early as July 13.

NASA's Steven Poulos, manager of the orbiter project office, says the first round of tests shows that the laser can detect 0.02-inch cracks.

However, Poulos concedes that because of incomplete testing:

*NASA doesn't know how often the laser will overlook small cracks.

*NASA can't say with certainty that the laser will even spot damage that small on the next flight.

Testing to nail down the keenness of the laser's vision will start in August and end in December.

"We've got a whole bunch of sensors that we've never used against a shuttle," says John Muratore, manager of shuttle engineering and integration. "We're just going to have to see how well that all works out in real time."

The independent panel that investigated the Columbia accident said NASA should develop a method to inspect the front of the wings before returning the shuttle to space again. Columbia disintegrated, killing the crew of seven, because of damage inflicted by debris to the front edge of one wing.

Poulos and Muratore say Discovery is unlikely to suffer damage, thanks to measures NASA has taken to keep debris from hitting the shuttle. And large debris from the shuttle's fuel tank -- which is what struck Columbia -- would inflict damage much easier to see than a 0.02-inch crack, Poulos says.

But the laser and other sensors are also likely to pick up scuffs and dings on the spacecraft that will be difficult to interpret, says astronaut Andrew Thomas, who heads Discovery's laser-inspection team.

With "all of that information, they're going to see some things that they're not going to quite understand," he says. "So there'll be a lot of head-scratching about what they are and the consequences of that." He adds, however, that whatever damage is seen is likely to be harmless.

Several scientists working with NASA on damage detection say it's not yet clear how quickly the agency will be able to spot and diagnose damage to the shuttle.

"The unknown (is) ... how complex it's going to be," says Sandia National Laboratories' Robert Habbit, a developer of the laser that will inspect the shuttle's wings. "Do you get the answers easy or do you have to dig for them?"

If NASA detected damage to Discovery, managers would have a tough choice to make -- and would need a precise evaluation of the damage to best protect the lives of the astronauts.

Damage such as a short, shallow crack would allow the space shuttle to come home as planned. Extreme damage, such as a gaping hole like the one that doomed Columbia, would require the shuttle's crew to stay on the International Space Station awaiting rescue.

Deputy shuttle program manager Wayne Hale says that is "the last thing we'd like to do."

Damage in a gray area between harmless and catastrophic might prompt officials to tell the crew to repair the shuttle. But repair techniques are unproven.

NASA's computer programs for sizing up damage are good, says Sandia's Basil Hassan, who reviewed the programs. But while some programs do their work in a matter of minutes, the most accurate programs require days to get results, he says.

That means that decisions on responding to certain kinds of damage "are going to be very hard," Hassan says. "It takes time to sift through and look through all that data ... and there's only a certain amount of time the shuttle can stay up there."

The difficulty of making that call even has one member of Discovery's crew sympathizing with the shuttle managers on the ground.

"I do worry and feel for people like Wayne Hale," says James Kelly, Discovery's pilot. "They're going to have to make decisions that we're good to come home. ... It's going to be an incredibly difficult decision to make on our flight."







Publication date: 2005-05-27