Spacewalk Resolves One Problem; Damaged Blanket Poses Another
The crew of the space shuttle Discovery resolved one problem Wednesday with protruding “gap fillers” during a first-ever spacewalk under the craft, only to face yet another potential danger in a “poofed-out” insulation blanket under a cockpit window.
The same engineering team that spent the previous four days analyzing the gap fillers -- ceramic-coated fabric set between heat-resistant tiles -- is now trying to figure out whether the aerodynamic forces of reentry could cause a piece of the quilted blanket to come off and hit the spacecraft.
So far, analysts think that the biggest chunk that could come off during reentry would weigh 0.05 of a pound. But even that small piece could be trouble.
“In the worst case ... you wouldn’t like the result,” said N. Wayne Hale Jr., deputy manager of the shuttle program.
Some experts are not surprised that the shuttles, which began flying in 1981, are showing signs of age.
“This has been a troubled spacecraft since the day it was built,” said physicist Robert L. Park of the University of Maryland.
“It was built to reduce the cost of flying into space, but it has turned out to be the most expensive way possible.”
The part of the insulating blanket sticking out is about 20 inches long by 4 inches wide.
Early engineering studies showed that if a piece of this section of blanket hit the craft near the tail, there could be structural damage.
Hale could not say whether such damage would be catastrophic. He said wind-tunnel and other tests were to be performed Wednesday night at several NASA centers.
The results will help determine whether NASA orders a fourth spacewalk to fix the problem or decides to leave the blanket alone.
“I am very hopeful we will be able to put this to rest” soon, Hale said.
The mission has already been extended one day. Another spacewalk could add a day to the mission, which began July 26.
Repair options include shredding the blanket so that it comes off in bits too small to damage the craft, or trying to pull it in one piece.
It is glued to the aluminum hull of the spacecraft.
Hale said engineers had assured him that Discovery could land safely without the blanket.
The blanket is one of 32 that cover portions of the shuttle.
Although silica tiles protect most of Discovery, the lightweight blankets are used in places that don’t receive as much heat during reentry.
The bulging blanket is just the latest problem to bedevil Discovery, which is the first shuttle to be launched since the 2003 loss of Columbia, which was damaged by a piece of foam that came off during liftoff and destroyed on reentry.
A large piece of insulating foam fell off Discovery’s external tank during launch from Kennedy Space Center last week, embarrassing the space agency, which had labored for more than two years to prevent recurrence of such a problem.
Although the foam piece did not hit Discovery, NASA immediately grounded the shuttle fleet until it could figure out what went wrong and how to fix it.
Following that problem, engineers studied a piece of damaged tile for several days before deciding that it would not be a threat on reentry.
Then came the gap-filler problem, which was potentially serious because the two protruding pieces were located in an area that gets very hot, above 2,300 degrees during reentry.
The problem was resolved on a Wednesday morning spacewalk when astronaut Stephen Robinson tugged the gap fillers out by hand.
The insulating blanket tear has put a new strain on the shuttle’s engineering team. “The team is getting tired,” Hale said.
NASA is not sure what damaged the blanket.
Some speculate that it could have been caused by striking a bird on liftoff or by thruster covers that flew off and may have hit the craft.
Hale said engineers had never seen anything quite like this on previous flights.
“Mother Nature always hands you something you hadn’t prepared for,” he said. “The only thing we’ve got to worry about is, if that blanket comes off, where would it go and what would it do?”
Asked if Discovery had turned out to be a trouble-plagued flight, Hale said he didn’t think so.
More problems have occurred on other flights, but in those cases, NASA didn’t know about them until after the orbiter landed.
After the Columbia accident, cameras and sensors were installed on Discovery, allowing officials to uncover safety problems in flight.
Those devices detected the foam, gap filler and blanket situations.
Asked whether future flights would require so much in-flight repair work, Hale said no.
He added that the repairs on Discovery have, so far, not thrown off the crew’s schedule to load supplies and repair the International Space Station, where the shuttle is docked.
Removing the gap fillers took 10 minutes, although more time was spent convincing the worried astronauts of the necessity of the repair.
Current plans call for Discovery to undock from the space station Saturday and land Monday at Kennedy Space Center in Florida. The landing is scheduled for 1:46 a.m. PDT.