Spacewalkers to test material for repair

Houston, Jul 12: Space shuttle Discovery's two spacewalkers head back into their ship's open cargo bay today to practice a procedure NASA hopes it never has to use.

As part of the US space agency's response to the 2003 Columbia disaster, engineers developed materials and techniques crewmembers could use to repair the shuttle's heat shield in space.

''Our number one goal is to never have to use them,'' said lead flight director Tony Ceccacci.

But just in case, NASA will always fly repair kits that can be used on the most vulnerable and critical parts of the shuttle's heat shield: the ceramic tiles and the carbon wing panels, which must be able to survive temperatures as high as 3,000 degrees Fahrenheit when the shuttle returns to Earth.

That's hot enough to melt not only the shuttle's aluminum skin, but even steel.

Columbia was destroyed when re-entering the Earth's atmosphere by foam which broke off during its launch 16 days earlier, damaging one of its wings.

Discovery docked with the International Space Station on Thursday. The third and final spacewalk of its planned 13-day mission is devoted to testing a sticky carbon-laced polymer sealant for fixing cracks in wing panels.

The substance, which has the consistency of peanut butter, was tested during the first post-Columbia mission last year.

The follow-up studies planned aboard Discovery will help engineers understand how temperatures affect the material's performance.

Astronauts Piers Sellers and Michael Fossum will make their way to the back of Discovery's cargo bay and open a box containing a pallet of 12 pre-damaged wing panel samples. Some samples have cracks that the astronauts will fill using a caulking tool loaded with the heat-resistance black goop.

The shuttle crew spent more than a day scanning their ship for launch debris impacts. Discovery received a clean bill of health and on Monday was cleared for landing.

The mission, which is only the second since Columbia's disintegration, clears the way for NASA to resume construction on the half-built, 0 billion International Space Station.

The agency is targeting its next shuttle flight for August 28.

REUTERS