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NASA managers 'thrilled' with heat shield repair test BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: March 21, 2008 Astronaut Bob "Bam Bam" Behnken and Michael "Dr. Goo" Foreman wrapped up a six-hour 24-minutes spacewalk early today, successfully replacing a faulty circuit breaker and testing a promising heat-shield repair technique, one of the final steps in NASA's recovery from the Columbia disaster. The tile repair demonstration went smoothly and while a complete assessment will require detailed post-landing analysis, the astronauts and NASA managers were pleased with the results. "This was a huge success for a lot of people on the ground, a lot of people on the space station," said Zeb Scoville, lead spacewalk officer at the Johnson Space Center in Houston. "We're just thrilled with the way it turned out." Efforts to develop viable heat shield repair options in the wake of the 2003 Columbia disaster were "a monumental effort that has been going on for years by hundreds of people, literally, to develop the tools and the techniques to be able to pull off this tile repair test," Scoville said. "I remember in 2003, shortly after the ‚olumbia accident, they hadn't really figured out what the root cause was of the accident. And there was an EVA officer at the time who leaned over to me and said, 'Zeb, regardless of what happens, we're going to have to figure out a way to repair tiles.' And now this person is the ISS lead flight director sitting right next to me." He was referring to Dana Weigel, lead space station flight director during Endeavour's mission. "For many years she worked as one of the lead operations officers trying to develop this technique and the tools and the repair capability, along with just hundreds of people in engineering and the contractor world, developing the materials and making sure the material's properties were correct," Scoville said. "So I really salute everyone involved. I feel it's a little unfair for me to sit up and talk about what a great success it was without really giving them as much credit as I possibly can. I congratulate them all on a huge success." Behnken and Foreman tested a pressure-driven gun-like applicator and a heat-resistant two-compound material known as STA-54, squirting the pink goo into deliberately damaged or scooped-out heat shield tiles mounted on a sample board. On Earth, bubbles that form when the compounds mix and flow out of the applicator rise to the surface. Engineers worried that in the space environment, the bubbles would be more evenly distributed, causing the STA-54 to swell like a rising loaf of bread. That could cause problems if the repair material bulged out beyond the surface of surrounding tiles because it could disrupt airflow during re-entry and cause extreme downstream heating. But the material proved relatively easy for the spacewalkers to manage and swelling, while present, was not extreme. "I'm thrilled with what we saw today," Weigel said. "In fact, I actually thought the material would swell quite a bit more than it did. It behaved very similar to what we've seen on the ground. That gives me a lot of comfort. We've done a lot of testing in the vacuum chamber, so we do have a lot of experience with the off gassing and what that looks like, both while we're manipulating the material and also post repair. "My expectation is when we get this material to the ground and cross section it, we'll find that everything with the material's performance is very much in family with all the testing that we've done. We learned a lot in terms of validating what we've done on the ground. But we really didn't have any big surprises. So I'm confident that it performed very well and as we expected it to." Behnken and Foreman also completed two get-ahead tasks, freeing launch locks on two Harmony module ports and removing a thermal cover from the Canadian Space Agency's Dextre maintenance robot. Foreman also inspected one of the robot's joints that did not operate properly after power was turned off and back on. Engineers don't yet know what the problem is, but Weigel said they are working to resolve the issue. The spacewalkers were unable to unplug a stuck electrical connector from a patch panel in the station's Z1 truss that would have re-routed power to one of four control moment gyroscopes. CMG-2 and CMG-3 were wired into the same circuit in the wake of an earlier failure and the cable change today was needed to hook CMG-2 back up to its own power supply, restoring lost redundancy. As it now stands, a single failure could take out both CMGs, a situation NASA wanted to correct. The astronauts made two attempts to free the connector. Working in the so-called "rat's nest" where dozens of cables are routed to various station systems, Foreman made an initial attempt early in the spacewalk and Behnken had another go at it toward the end of the excursion. But the connector refused to budge. Weigel said the CMGs were left in the same state they've been in for several years and that there was no pressing urgency to rectify the situation. This was the 108th spacewalk devoted to station assembly and maintenance since construction began in 1998 and the fourth of five planned for Endeavour's mission. The crew's cumulative EVA time now stands at 27 hours and 26 minutes. Total station EVA time through all 108 spacewalks is 681 hours and nine minutes. Behnken and Foreman plan a fifth and final spacewalk - the third for each astronaut - Saturday evening.
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VIDEO:
TILE REPAIR DEMONSTRATION PREVIEW 