The article review(文章导读):
By David McAlary Washington12 July 2006
Astronaut Mike Fossum (on arm)installs the International Space Station's railcar-like mobile transporter U.S. space shuttle astronauts are on their th
Text(正文):
By David McAlary
Washington
12 July 2006
Astronaut Mike Fossum (on arm)installs the International Space Station's railcar-like mobile transporter
U.S. space shuttle astronauts are on their third spacewalk since Saturday, this time to practice methods of inspecting and repairing the vehicle's fragile shell in orbit.
-------
The spacewalk is part of the U.S. space agency NASA's three-year effort to prevent the loss of another shuttle following the Columbia accident in 2003. It has developed tools astronauts could use in orbit to inspect and fix the ceramic tile and reinforced carbon skin that protects a shuttle against the searing heat of re-entry into Earth's atmosphere.
Columbia burned up when gases superheated by re-entry friction entered a hole in its wing. The puncture occurred at launch when hard foam insulation broke away from the external fuel tank. Columbia's crew had no way of knowing about or filling the hole in space and perished as a result.
On today's spacewalk outside the shuttle Discovery, astronauts Piers Sellers and Mike Fossum are testing two techniques that NASA hopes would avoid such a catastrophe.
"Our number one goal is to never have to use them," Ceccacci says.
Tony Ceccacci is the lead flight director for Discovery, which is docked at the International Space Station on a resupply mission.
He says one new tool the spacewalkers are evaluating is a heat-sensing infrared camera designed to detect invisible damage to the reinforced carbon panels that cover the leading edges of shuttle wings. The camera can record subtle temperature differences that would indicate the presence of a crack.
"Their hope is this is another sensor that will help us detect damage and minimize the impacts that we have to a mission," Ceccacci says.
Astronauts Fossum and Sellers are also testing a way to patch cracks. They are using caulking guns and putty knives to apply a black paste the consistency of peanut butter to samples of damaged wing panels. Ceccacci says it is expected to seal cracks up to 10 centimeters long, but not large holes.
"I do not think that is going to repair every piece of damage or everything that we would see on the vehicle, but it may give us an idea that at least I have something in my toolbox that I can use," Ceccacci says.
NASA has already equipped the robot arms on shuttles with a boom extension that holds a camera and sensors to inspect the underside of the orbiters during a flight. Astronauts Fossum and Sellers bounced around on it during their first spacewalk Saturday and found it stable enough to use as a platform on which to make orbital repairs.
NASA says if Discovery's mission is successful, it will launch another shuttle next month to resume space station construction for the first time since Columbia's demise.
|
