NASA Details Plans for Potential Fix to Discovery's Heat Shield
HOUSTON - As shuttle managers debate whether an untried repair is needed to pry two space-filling strips from the underside of the Discovery orbiter, spacewalk planners have chosen which astronaut would perform the potential task, the mission's lead spacewalk officer said.
Shuttle astronaut Stephen Robinson, mission specialist and flight engineer for Discovery's STS-114 spaceflight, would perform the repair as part of a planned Aug. 3 spacewalk if mission managers decide it is necessary later today, said Cindy Begley, the flight's lead extravehicular (EVA) officer.
Discovery's mission management team (MMT) convened at 2:00 p.m. EDT (1800 GMT) here at NASA's Johnson Space Center (JSC) to go over final data and decide whether to remove two gap-fillers jutting out from between the heat tiles lining the shuttle's forward section or leave them as is.
"We don't currently have directions to do [the repair] but as always we try to get all our ducks in a row ahead of time," Begley said. "Something we've never been done before is put a crewmember underneath the vehicle."
Shuttle tile gap-fillers are small strips of ceramic fiber cloth glued between the orbiter's heat-resistant tiles to fill excess space. Orbital photographs and a subsequent focused inspection detected two gap-fillers jutting out; one sticking 1.1 inches (2.7 centimeters) out of a region just behind Discovery's nose landing gear doors and the other further back, ranging between six-tenths (1.5 centimeters) to nine-tenths (2.3 centimeters) of an inch above the tile.
Space shuttles have landed safely many times with gap-filler protrusions, and the same may hold true for Discovery, shuttle officials have said.
But mission managers said Sunday that added analysis was warranted since the two seen during the current STS-114 flight stick out further out than those found after past orbiter landings.
Analysts are expected to present data to the MMT today regarding the potential increased local heating effects that could stem from simply leaving the gap-fillers in place during reentry, information which will likely factor into the management team's decision, shuttle officials said.
"No decision has been made yet as to whether, in fact, we're going to down and do this," said Phil Engelauf, STS-114 mission operations representative, said of the potential repair.
A just-in-case plan
Begley said that, should the gap-fillers need to be addressed, Robinson would be placed at the end of the robotic arm attached to the International Space Station (ISS), where Discovery is currently docked.
Whether STS-114 pilot James Kelly or mission specialist Wendy Lawrence would helm the ISS arm - both have done so during the current docked operations - is not yet decided, added Mark Ferring, lead ISS flight director for the STS-114 flight.
Armed with forceps, scissors, a modified hacksaw, and his own two hands, Robinson would then be positioned sideways under the orbiter, spacewalk officials said.
Current plans would call for Robinson to simply pull on the gap-fillers with his spacesuit-clad fingers to remove them or, failing that, he could use forceps to hold protrusions while shearing it off with the hacksaw, Begley explained.
"It's cutting and pulling," Begley said. "It's very simple skills and very simple tools."
The scissors are currently at the bottom of the preferred tool list, since they may not cut as much of the material off and could bring Robinson's gloved hands closer to the shuttle tiles, she added.
Robinson's spacewalking partner, astronaut Soichi Noguchi of the Japanese Aerospace Exploration Agency (JAXA), would not accompany his counterpart beneath the shuttle's belly, Begley said.
"It only takes on crewmember to do it and we'd want to avoid too many tools or other items...at the end of arm to protect the vehicle as much as possible," she added.
Spacewalking tools typically left free-floating during an EVA, such as tethers and other equipment, would be tied close behind Robinson to prevent damaging Discovery's ceramic tile heat shield, Begley said.
While it could take at least 90 minutes to pre-position the ISS arm, then another 45 minutes to transport Robinson to his first gap-filler worksite, the actual repair should go relatively quickly, Begley added. Moving from one gap-filler site to the other could take about 10 minutes, she said.
Robinson and Noguchi would have to give up at least one task on their third EVA - most likely the installation of a camera and lighting package - to wedge in the gap-filler fix, though the astronauts have already racked up enough extra time in two spacewalks for the planned installation of a spare parts platform and the added retrieval of a broken rotary motor along the station's exterior, Begley said.
NASA officials stressed that the plans laid out by Begley are still preliminary since the MMT has not made definitive decision on what, if any, action may be required for the gap-fillers.
A press briefing on the results of today's MMT meeting is slated to begin at 6:00 p.m. EDT (2000 GMT).
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