A couple short strips of fabric 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 (search) said Sunday.
Teams of experts were scrambling to understand just how serious the problem was, with "strong arguments" raging on what to do, if anything.
The trouble has nothing to do with foam or other launch debris, but rather the accidental slippage of ceramic-fiber cloth used to fill the thin gaps between thermal tiles, which some engineers worry could trigger potentially treacherous overheating during re-entry.
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 two hanging strips.
If NASA's spacewalking specialists come up with a relatively easy solution, "Why worry? Why would you not just go take care of it?" deputy shuttle program manager Wayne Hale (search) said Sunday evening. "Why should I lose sleep over these gap fillers if we can take care of them that easy?"
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.
Discovery (search) and its crew of seven may be perfectly safe to fly back in a week with the drooping strips, officials stressed, as space shuttles have done many times before, although not necessarily with pieces that large.
Hale, in fact, did not think it was that big a deal when he first learned of the problem a few days ago.
"My immediate knee-jerk reaction was that we can live with this," he said. "On the other hand, this is bigger than we've seen before."
One piece is sticking out 1.1 inches between the thermal tiles, the other protrudes at an angle from six-tenths to nine-tenths of an inch. For those areas, far forward near the nose, the general wisdom and flight history indicate that the limit should be a quarter-inch, said flight director Paul Hill.
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, an outcome of the 2003 Columbia disaster.
On a flight by Columbia in 1995, the shuttle returned with a gap filler that protruded 0.6 inches, but the material 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, it was 1.4 inches long. The only overheating effect was to nearby damaged tiles.
"Tonight they're working overtime trying to compress, I believe the phrase was, a decade's worth of study into two days," Hale told reporters.
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 on Discovery, the glue may have come loose.
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. 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 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 bang into the shuttle and damage something.
"There are pretty strong arguments for and against most of the options," Hill said.
One extreme option would be to put an astronaut on the end of the brand new 100-foot inspection crane, 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.
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.
NASA has cleared Discovery's thermal tiles for landing on Aug. 8; they constitute the vast majority of the shuttle's exterior. The only remaining issues, before the final go-ahead can be given for descent, are the reinforced carbon panels that line the wings and nose cap, and the two dragging gap fillers.
In a series of TV interviews from space, commander Eileen Collins and her crew said they believe Discovery is safe to come home. She expressed surprise and disappointment that a big piece of foam came off Discovery's redesigned tank during last Tuesday's liftoff, after everyone — including herself — signed off on analysis showing that the specific area did not need to be improved in the wake of the Columbia tragedy.
"Was there a sound technical reason why they made that decision or was it subject to cost pressures or schedule pressures?" said astronaut Andrew Thomas. "I think we do need to address the question of why that area was not examined."