Astronauts test repair methods
2006-07-12 14:22
Houston - Two Discovery astronauts started a final spacewalk on Wednesday to test shuttle repair material created after the Columbia disaster as part of Nasa's efforts to prevent another tragedy.
Astronauts Piers Sellers and Mike Fossum ventured out of the International Space Station to see if a sealant produced to fix potential cracks on a shuttle's heat shield works in zero gravity.
Columbia's thermal protection was cracked by a piece of foam insulation that peeled off its external fuel tank during lift-off, causing the shuttle to break into a ball of fire as it returned to Earth in February 2003.
Since then, Nasa has made modifications to the massive orange fuel tank to reduce the amount of debris it loses during launch and has tested in-orbit repair techniques in the two shuttle missions since the Columbia accident.
After examining hundreds of images of Discovery's heat shield, the US space agency declared the shuttle free of damage that could endanger its return to Earth on Monday.
Nasa extended the mission by a day, to 13 days, in order to squeeze in the third spacewalk.
Adding to Nasa's tool box
Although the sealant being tried out on Wednesday was tested in a laboratory, officials said they need to see how it reacts in space.
Fossum had said he was "pumped" and "anxious" to test the sealant on pre-damaged samples of a shuttle's reinforced carbon-carbon (RCC) shield.
Being able to "prove that we can repair RCC in flight is pretty valuable to the programme", he said in a US radio interview last week.
In their first excursion, the duo tested the stability of a boom extension on the shuttle's robotic arm for possible future repairs in hard-to-reach areas. Nasa found that the boom showed promise as a possible work platform.
The 30-metre-long platform, combined with a successful test of the sealant on Wednesday, would add to Nasa's "tool box" in the event of damage during future shuttle missions, lead flight director Tony Ceccacci said.
"I don't think that we can say that, 'Hey, that's going to repair every piece of damage or everything that we would see on the vehicle,'" he said. "But it kind of gives us an idea that, 'at least I have something in my tool box that I can use."
While Nasa wants to give astronauts the ability to fix their vessel in orbit, the US space agency has worked intensely over the past three years to protect the shuttle from being damaged during lift-off.
The focus before last week's launch had been on the shuttle's troublesome external fuel tank, which has perplexed Nasa since the Columbia accident.
- SAPA