NASA worries about loose ends on shuttle

A couple of short strips of material dangling from Discovery’s belly may require an unprecedented repair by spacewalking astronauts, if engineers determine there’s even a possibility that the problem could endanger the shuttle during descent, NASA said Sunday.

Teams of experts at NASA's Johnson Space Center in Texas scrambled to understand just how serious the problem was, even as astronauts transferred tons of supplies from the shuttle to the international space station and prepared for the 13-day mission's second spacewalk.

The latest concern has nothing to do with foam or other launch debris, but rather the accidental slippage of ceramic-fiber fabric used to fill the thin gaps between thermal tiles. It will be Monday before the analysis is complete and mission managers decide whether to have the crew’s two spacewalkers cut or pull the hanging material.

Such a spacewalking feat would be a first: In 24 years of shuttle flight, astronauts have never ventured beneath their spacecraft in orbit and have made few repairs to their ship — certainly none of this magnitude.

Although he did not refer specifically to the concern over the filler material, NASA Administrator Mike Griffin predicted on NBC's "Meet the Press" that Discovery would be given the all-clear for next week's scheduled return to Earth.

"We're working a couple of issues on Discovery right now," he said. "But we think
we have work-arounds. We think Discovery is safe to bring home."

However, Griffin cautioned that no one could be absolutely confident about Discovery's safety until the shuttle is "stopped on the runway and is ready to be towed off."

In Houston, flight director Paul Hill said two engineering teams were working "aggressively" on the concerns over the gap fillers, with heated discussions raging over what to do, if anything. Discovery and its crew of seven may be perfectly safe to fly back with the two drooping pieces, Hill stressed, as space shuttles have done many times before, although not necessarily with dangling pieces as large.

One piece is sticking out an 1.1 inches (2.8 centimeters) between thermal tiles. The other protrudes at an angle from six-tenths to nine-tenths of an inch (1.5 to 2.3 centimeters). For those areas, far forward near the nose, the general wisdom and flight history indicate that the limit should be a quarter-inch (6 millimeters), Hill said.

Hill noted, however, that the quarter-inch measurement was taken following previous re-entries, and the intense heat could have burned some of the material off. Discovery’s flaws were spotted in orbit — a first — because of all the photography and laser imaging being aimed at normally hard-to-see spots.

On a flight by Columbia in 1995, the shuttle returned with a gap filler that protruded 0.6 inches (1.5 centimeters), but it was rolled up and located farther back on the belly, in an area less likely to overheat, said Steve Poulos, manager of the orbiter project office. When unrolled, the strip of material stretched 1.4 inches (3.6 centimeters) long. The only overheating effect was to nearby damaged tiles.

The extremely thin gap fillers are held in place with glue and by the tight fit of the thermal tiles; thousands cover the shuttle. Poulos speculated that the glue may have come loose.

Pros and cons for spacewalk
Any repair, if deemed necessary, would most likely be performed during the third and final spacewalk of the mission on Wednesday, although a fourth unplanned spacewalk might be required, he said. The second spacewalk, for space station repairs, is set for Monday.

The astronaut would have to stand on either the shuttle or station’s 50-foot (15-meter) robotic arm in order to reach the two hanging strips of filler. There are drawbacks to using either arm — namely, clearance and time constraints.

There’s also the possibility, however remote, that the spacewalker or the arm might damage something.

"There are pretty strong arguments for and against most of the options," Hill said.

NASA / AP This NASA image pinpoints a protruding gap filler as well as damage to a tile on the shuttle Discovery's nose landing gear door.

One extreme option would be to put an astronaut on the end of the brand new 100-foot (30-meter) inspection crane assembly, but it would likely be a bouncy ride — and that makes spacewalk and robotic specialists nervous. Poulos said Sunday evening that that option was considered but ruled out.

Anything dangling from the normally smooth bottom of the shuttle will overheat the area and downstream locations during re-entry; as it is, temperatures there typically hit 2,300 degrees Fahrenheit (1,260 degrees Celsius).

A hole in Columbia’s left wing, carved out by a large chunk of flyaway fuel-tank foam, led to the spacecraft’s destruction during re-entry on Feb. 1, 2003. All seven astronauts were killed.

After days of inspections, NASA has cleared Discovery's thermal protection tiles for landing on Aug. 8. Although engineers are still studying data about the reinforced carbon-carbon panels that line the shuttle's wings and nose cap, the question about the gap fillers is the only significant issue that needs to be addressed, Poulos said.

Spacewalk may be safest course
Deputy shuttle program manager Wayne Hale, who heads Discovery's mission management team, said his first instinct was to clear the shuttle for landing without trying to repair the gap fillers. But as he heard more about the situation, he came to see more value in making the repair — particularly if the engineers could not guarantee that the shuttle would make a safe landing as is, and the spacewalk experts came up with a simple fix.

"You begin to say, 'Why should I lose some sleep over these gap fillers if I can take care of it that easily?'" he said during an afternoon news conference. "But we'll wait and get the technical answer from the technical folks."

He said the engineers were working overtime to compress "a decade's worth of study into two days."

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