Astronauts begin second spacewalk
NASA mulls threat from protrusions
During their spacewalk Monday, Steve Robinson and Soichi Noguchi will replace a faulty gyroscope.
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(CNN) -- Discovery astronauts Steve Robinson and Soichi Noguchi have begun the second spacewalk of the shuttle mission, as NASA officials on Earth debate what to do about two pieces of gap-filling material protruding from the craft's underside.
During Monday's spacewalk, Robinson and Noguchi will replace a faulty gyroscope on the international space station.
On the protrusions issue, NASA officials say they will likely decide Monday what -- if anything -- to do about them.
The belly of the shuttle is lined with thousands of ceramic tiles separated by thousands of ceramic-coated, fabric gap fillers. Their uneven placement can lead to temperature increases upon re-entry into the Earth's atmosphere.
A number of prior flights were found, after they landed, to have had such protrusions.
But this marked the first time engineers have discovered the anomalies during flight -- and the first time they have had an opportunity to consider doing something about it, said Wayne Hale, deputy program manager for the mission.
"They're working to compress a decade's worth of study into two days," Hale told a news conference Sunday.
One possibility would be for astronauts to attempt to repair the gap fillers during a spacewalk, referred to in NASA jargon as an EVA, for extravehicular activity.
"Every EVA is risky business," Hale said. "You need to have a good reason to do it."
It may be best to do nothing, said Steve Poulos, manager of the orbiter project office.
Laser measurements taken Sunday of the affected areas indicate "sufficient safety margins" -- both thermally and structurally -- for the craft to return home unharmed, Poulos said.
The crew members, who trained on Earth to repair the gap fillers and who packed the necessary tools, could simply pull out the gap fillers, he said, since their absence would not appreciably affect the heat shield's thermal characteristics or the integrity of its structure.
It would mark the first in-flight repair of a vehicle in the history of the program, Poulos said.
As NASA aerodynamics experts were crunching the data, Hale outlined the pluses and minuses.
"My immediate, knee-jerk reaction was that we can live with this," Hale said. "On the other hand, this is bigger than we've seen before."
"If it's relatively simple, why worry? Why would you not just go take care of it [with a spacewalk] if you had a simple plan to deal with it?"
He continued, "If aerodynamicists say, 'Lots of margin, don't worry,' I think we're done."
But, he said, if they say "we really don't know ... we really can't guarantee it," then the repairs would be considered.
"Our EVA team, they love a challenge like this," he said. "That's their bread and butter."
The lessons of Columbia
In the prior re-entries of a shuttle where a gap filler was found to be protruding, temperature sensors measured a 15 to 25 percent increase above what had been expected, Poulos said.
Hovering over the discussion of the gap fillers was awareness that apparently minor problems can sometimes become major ones.
In February 2003, the shuttle Columbia broke up over Texas upon re-entry into the atmosphere, killing all seven astronauts aboard.
The craft's loss was blamed on a piece of foam debris that had struck it shortly after its launch, punching a hole in its left wing.
"The Columbia accident made us realize that we had been playing Russian roulette with the shuttle crews -- that we had been very, very fortunate in the past that the foam did not cause critical damage," Hale said.
About this latest concern, Hale added, "The difference between before Columbia and today is night and day."
On this flight and all future shuttle missions, he said, the entire orbiter heat shield would be inspected, something never done before on any flight.
Commander says shuttle safe
Earlier Sunday, the seven-person crew aboard the Discovery, which has been linked up with the international space station since Thursday, did not seem particularly concerned about the dangling filler material.
"I believe the gap fillers are similar to what we had seen in previous flights," Discovery commander Eileen Collins said in a news conference from orbit.
"It's definitely not a big concern for me now. What we looked at during the inspection looked pretty good to us through the camera lenses," she said.
NASA managers on Saturday extended the Discovery's mission by one day, pushing the 21-year-old shuttle's landing to August 8, so astronauts can do more work. (Full story)
Hale also said Saturday that engineers had determined the two dozen dings incurred by the shuttle's thermal tiles during launch don't pose a safety hazard.
NASA has set the possible landing times as 4:37 a.m. ET or at 6:12 a.m. ET.
Having spent more than two years and hundreds of millions of dollars since the Columbia disaster, engineers thought they had solved the problem of falling debris. Its recurrence led NASA last week to ground other planned flights until it is resolved. (Full story)
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