Combined STS-123, ISS Crew Prepares For Last Spacewalk

The verdict is still out on whether a new heat-shield tile repair method will prove to be the kind of solution NASA has been looking for... but early results are very promising.

As ANN reported, Mission Specialists Michael Foreman and Robert Behnken tested the new procedure Thursday, during the fourth of five planned spacewalks during the shuttle Endeavour's extended stay at the ISS. As part of the 6 1/2-hour excursion, the two men used a device similar to a high-tech caulk gun to insert ablative putty into cracks on a sample tile, then using a brush to smooth the material out.

The 'goo' later solidifies into a plastic-like material, reports The Associated Press, which NASA hopes will prove to be able to withstand the heat generated during reentry. "We are absolutely captivated by what you guys are doing here," Mission Control radioed the spacewalkers during Thursday's test. "You're like brain surgeons up there."

While the new method is similar to previous repair attempts -- which have yielded mixed results -- NASA hopes the new material will be resistant to what the agency dubs the 'rising bread-loaf' effect... in which bubbles form in the material, causing it to swell out from the repair site. STS-123 lead spacewalk officer Zebulon Scoville says so far, the results are encouraging.

"We're just thrilled with the way it turned out," he said, adding final results must wait until the sample is tested on Earth.

Even if the material proves successful, however, it will fall short of being a silver-bullet solution for the kind of damage that led to the 2003 loss of Columbia on reentry. Currently, the repair material is only intended for the silica tiles on the shuttle's underside, and other surfaces exposed to lower heat levels than the reinforced carbon panels lining the leading edges of the shuttle's wings... where damage doomed Columbia.

In related news, on Friday the crew checked Endeavour's wings and nose for signs of micrometeorite damage that may have occurred during the orbiter's stay at the station. That test is usually done after a shuttle undocks from the ISS, but the 100-foot Orbiter Boom Sensor System (OBSS) mounted to Endeavour's robotic arm will have to be left behind at the station, for the crew of STS-124 to use later this year... as every nook and cranny in Discovery's cargo bay will be occupied by the second segment of the Japanese Kibo module.

The Expedition 16 and STS-123 crews spent the remainder of Friday configuring tools and reviewing procedures for the flight’s final spacewalk. This includes the standard "camp out" in the station’s Quest airlock, during which the nitrogen is purged from the bodies of spacewalkers before they enter the void of space.

Behnken and Foreman will begin that spacewalk at 1723 EDT Saturday. Their tasks include stowing the OBSS on the station’s S1 Truss, where it will be picked up by the STS-124 crew aboard space shuttle Discovery, set to launch in May.

Endeavour is scheduled to undock from the station Monday, and return to earth at 2035 EDT March 26.

FMI: www.nasa.gov