Shuttle’s shield tiles are nicked
NASA officials said Friday that the space shuttle Endeavour sustained damage to its protective tiles during this week’s launch, but they won’t know until Sunday at the earliest whether the damage will require an in-space repair job.
Mission Management Team Chairman John Shannon said several heat-resistant tiles on the orbiter’s underside were nicked.
The most serious divot was a 3-inch-square gap near the landing gear door that might reach down to Endeavour’s thin aluminum skin, he said.
If so, that could necessitate a spacewalk by members of the shuttle’s seven-person crew to make repairs.
“The concern is the depth,” Shannon said during a briefing at Johnson Space Center in Houston. That’s because the outside of the orbiter is exposed to temperatures above 2,500 degrees during reentry and landing.
Shannon said NASA engineers were not certain what caused the damage to Endeavour, but they suspected that shards of ice could have flown off from the external fuel tank during Wednesday’s launch.
Although the weather in Florida has been hot, ice forms on the fuel tank because it’s filled with liquid oxygen and hydrogen chilled to minus 427 degrees.
Shannon said radar images of the launch showed a spray of particles that appeared to strike the orbiter about 58 seconds after launch, when the shuttle was accelerating to its 17,500 mph orbital velocity.
Ice is more dangerous to the shuttle, because it’s sharp and can cut into the tiles, thermal blankets and reinforced carbon-carbon panels that cover the shuttle’s body.
On Sunday, the Endeavour crew will use a boom with a camera and laser attachment to scrutinize the damaged tile.
Shannon said the crew was informed of the issue Friday afternoon. Among the seven astronauts is former teacher Barbara Morgan, the backup for Christa McAuliffe, who died when the Challenger blew up on launch in 1986.
Shannon insisted there was no cause for alarm, at least for now. “We have a rich history of tile damage” on previous shuttle flights, he said, “some of which is more significant-looking than what we have here.”
Before the addition of a suite of new cameras and radar to analyze launches, NASA was rarely even aware of tile damage until a flight was over. Now engineers take every incident seriously and conduct studies to see whether the nicks and divots that occur on almost every flight need to be addressed.
The monitoring equipment was added after the Columbia was lost in 2003. Investigators later determined that Colum- bia had been damaged during launch by foam that flaked off the shuttle’s giant external tank.
The first on-orbit repair occurred last year, when an astronaut was sent to the underside of the Discovery to remove a protruding gap filler, a kind of plastic spacer between the tiles. Engineering analyses showed the protrusion could have caused unacceptable heating behind the spacer during reentry.
If a repair is ordered in this latest incident, the astronauts would use one of three re- pair kits: an emissivity wash to paint the surface; a protective plate that could by screwed in- to the body over the hole; or “the goo,” a putty-like sub- stance that would be applied by hand.
NASA also revealed that Endeavour came within a mile of a piece of floating space junk during the launch. The garbage was an old Delta rocket body that has been orbiting for years, NASA said.
Space junk has been an increasing concern for the space agency, especially since the Chinese blew up one of their satellites several months ago, adding hundreds of new pieces to the dump orbiting Earth.
Despite the glitches, the crew is on schedule to install a new truss segment to the International Space Station’s backbone. It also will replace one of the four gyroscopes that keeps the station oriented in space.
NASA has not made a decision whether to extend the 11-day mission to 14 days, which would allow time for a fourth spacewalk to continue construction work at the station.
NASA has said it will finish work on the station and retire the aging, problem-plagued shuttle in 2010.