This computer-generated image shows how astronaut Stephen Robinson will be positioned beneath Discovery's heat shield. Image
HOUSTON--While STS-114 spacewalker Stephen Robinson will be working alone during a one-man repair job underneath the shuttle Discovery Wednesday, he will not be out of sight or the minds of his fellow crewmates and flight controllers, the astronauts and shuttle officials said today.
As part of a planned extravehicular activity (EVA) tomorrow, Robinson is expected to board the end of a long robotic arm and remove two strips of ceramic fiber cloth--known as gap-filler--jutting out from between the fragile heat-resistant tiles along Discovery's belly. The repair is scheduled to take place at about 7:30 a.m. EDT (1130 GMT), three hours and 20 minutes into the early morning spacewalk, shuttle officials said.
"At the highlight of the EVA, when Steve is removing the gap-filler, we're all going to be listening very intently," STS-114 commander Eileen Collins told reporters vie video downlink earlier today.
During the fix, Robinson's fellow Discovery astronauts will track his movements via robot-arm mounted cameras radio while his spacewalking partner Soichi Noguchi, of the Japanese Aerospace Exploration Agency (JAXA), will keep close watch on the operation from a vantage point outside the ISS.
"He's there to give us another set of eyes and also serve as relay [for communications] if needed," said Kelly Beck, flight director of NASA's Tiger Team assigned to hammer out procedures for changes in Discovery's flight plan, during a mission status report here at Johnson Space Center (JSC).
Shuttle officials decided Monday to press forward with the spacewalk repair to clear any concerns with Discovery's vital heat shield. The protruding gap-fillers could disrupt the aerodynamics of Discovery's reentry planned for Aug. 8, forcing the air around the orbiter to shift from the smooth laminar flow into a turbulent mix a bit earlier in the descent, while it flies at Mach 21 as opposed to Mach 18 or so, that could cause increase heating to its tile surface and wing leading edges, they said then.
During the repair, Robinson will stand atop the robotic arm attached to the International Space Station (ISS), while Discovery's crew maneuvers the shuttle's robotic arm - capped with an orbital boom extension to make a 100-foot crane - to watch with its own camera.
"They're not used to reaching down around the bottom of the orbiter," said Paul Hill, STS-114's lead shuttle flight director, of ISS arm controllers for the first-time repair job. "That's a little bit of a new touch."
Spacewalk planners are unsure whether Robinson helmet mounted camera will be able to broadcast images of the fix as the astronaut first uses his right hand to pull out the gap-fillers, and then a saw to cut them off if they don't budge.
Discovery astronauts and flight controllers agree that the removal technique for the gap-fillers, a simple tugging motion by hand, is relatively simple, but they are concerned about potentially damaging the shuttle's tile-lined belly.
"We may get a little closer than a foot [from the tile], but when we do we'll have very good visibility and we'll be moving very slowly," said astronaut David Wolf, head of the EVA branch of NASA's Astronaut Office. "We don't like getting close to the tile, [it] is a delicate instrument of the shuttle."
Robinson will take care not to bump his helmet, the most probably point of impact, on the shuttle's vulnerable tiles, Wolf added.
Spacewalk officials are confident that should a gentle touch or slip from Robinson's secondary tool - the modified hack saw - does cause tile damage, it will be relatively minor. But just in case, Robinson and Noguchi will preposition a tile repair method they tested in an earlier spacewalk - an emittance wash applicator that coats chipped tiles to increase heat shedding - just outside the shuttle airlock, which could be applied to any damage caused, shuttle officials said.
"When we went to look at this, we had difficulty even inducing intentional tile damage with the saw," Wolf said. "And you'd be able to detect when you're hitting the orbiter will before you do a critical damage."
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