Shuttle May Get Repair in Space
HOUSTON — Concern over two protruding pieces of heatresistant fabric on the underside of Discovery prompted NASA on Sunday to consider a first-ever in-flight shuttle repair that would require a spacewalk.
Paul Hill, flight director for the 114th shuttle mission, said an engineering team of aeroheating specialists expected to have a recommendation today on whether an astronaut would be sent out with a hacksaw to trim off the pieces of fabric, known as “gap fillers.â€
“We have viewed the options from pulling the gap fillers out to trimming the gap fillers to putting [them] back down into the gap,†Hill said.
Thousands of gap fillers -- made of a flexible, ceramic-coated material about as thick as a credit card -- are placed between the heat-resistant tiles covering the shuttle.
Two of them near the front landing-gear door are sticking out as much as 1.1 inches, well beyond the quarter-inch allowed by engineers.
The concern is that even a small protrusion could disrupt airflow under the extreme conditions of reentry, increasing the heating just behind the protrusions by nearly 600 degrees Fahrenheit. That could render the surface hot enough to threaten the integrity of tiles protecting the spacecraft.
Protruding gap fillers have been observed on previous flights, but always after the shuttle has landed. This time, dozens of new sensors and cameras installed after the destruction of the shuttle Columbia on reentry 2 1/2 years ago have allowed engineers to see damage while the craft is in orbit.
If NASA managers decide to fix the problem, an astronaut will have to be carried on Discovery’s or the space station’s robotic arm to the underside of the shuttle.
The repair itself would not be difficult. Since the gap fillers are bonded to the vehicle with glue, they could be pulled out.
The problem is that no spacewalk procedure is completely safe. One to perform this kind of repair was not practiced during the years that the crew trained for the mission, although Discovery does carry “EVA scissors,†a special hacksaw-like device provided for this eventuality.
Engineers and aerodynamicists are working overtime to come up with a recommendation. “They’re pressing decades of study into two days,†said N. Wayne Hale Jr., deputy shuttle program manager.
He said engineers were keeping in mind the famous remark by former astronaut John Young: “There’s not anything that happens to the shuttle that you can’t make worse by trying.â€
The protruding gap fillers are in a particularly sensitive area. Temperatures can reach 2,300 degrees in that area as the craft uses the Earth’s atmosphere to brake from 17,500 mph to a safe landing speed.
The silica tiles that cover most of the aircraft are not designed to withstand the most extreme heating, which is why the nose and leading edges of the wings are covered with expensive reinforced carbon panels.
The engineers could well decide to leave the craft as it is. “My immediate reaction is we can live with this,†Hale said.
But if the engineers are unable to assure him that there will be no dangerous excess heating, the management team might decide to err on the side of caution and fix the problem. “Why should I lose sleep over gap fillers?†Hale said.
Hill said an unplanned fourth spacewalk to fix the gap fillers was a possibility, but he added, “I think that’s a very low-likelihood case.â€
The more likely scenario, he said, was to repair the damage during the third spacewalk, scheduled for Wednesday. The principal job scheduled on that walk is installing a stowage platform, a kind of heated toolshed, on the space station.
There is one historical precedent for the gap filler problem on Discovery: On the STS 73 mission in 1995, a gap filler in the same general area on Columbia bulged out about 1.4 inches.
“There was some noticeable additional heating, but nothing that ultimately became a concern,†said Steve Poulos, manager of the orbiter project office.
Discovery’s flight has been dogged by problems, beginning the day of launch when a large piece of foam fell off the external fuel tank. Even though the foam did not hit Discovery, NASA quickly grounded the shuttle fleet pending resolution of the problem.
In succeeding days, one problem after another -- from tile damage to blemishes on the reinforced carbon panels -- have raised concerns. Each one, until now, was ultimately found not to be a threat to the vehicle.
The new sensors and imagers on Discovery have “literally put the orbiter thermal protection system under a microscope,†Hale said.
While space agency managers on the ground debated Sunday what to do about the gap fillers, the crew had its lightest day of work so far.
The astronauts continued moving food and water to the space station in anticipation of what could be a long time before the next visit from the shuttle fleet.
Discovery’s seven crew members had enough spare time to make the rounds of the morning television talk shows, where they defended the space program but also voiced concern about NASA’s engineering decisions.
Some of the astronauts said they were disappointed and surprised to learn that a 3-foot piece of foam, weighing about 1 pound, had broken away from the fuel tank during liftoff.
Crew member Andrew Thomas said the engineering decisions approving liftoff must now be questioned.
“The area where the foam came up is an area that was not examined, or decisions were made not to look at it and not to test the foam there,†Thomas, 53, said during an interview with NBC’s “Meet the Press.â€
“I think we do need to address why that decision was made,†added Thomas, who holds a doctorate in mechanical engineering and has been a part of three previous space missions. “Was there some technical reason why they made that decision -- or was it subject to cost pressures and schedule pressures?â€
The commander of Discovery, Eileen Collins, said she was aware before launch that NASA officials had decided not to retrofit the surface area from which the foam broke loose.
Both Collins and NASA Administrator Michael D. Griffin said the decision not to retrofit the area was based on X-ray and other noninvasive testing that found nothing suspicious.
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Times staff writer David Willman contributed to this report.
