HOUSTON - The
Discovery astronaut tapped to pluck out two strips of filler material jutting from
the orbiter's heat shield said Tuesday that the first-time repair
appears simple, but that great care must be taken to avoid damaging the
shuttle.
Shuttle
astronaut Stephen Robinson, a mission specialist and spacewalker for Discovery's
STS-114 flight, said he is confident in NASA's plan
to send him under the orbiter Wednesday to remove two strips wedged between the
heat-resistant tiles as part of third extravehicular activity (EVA) of the
mission. That spacewalk will begin at 3:14 a.m. EDT (0714 GMT) on Aug. 3.
"Like most
repairs, its conceptually simple but it has to be done very, very carefully,"
said Robinson, speaking via video downlink from the International Space Station
(ISS) where he and other Discovery and ISS astronauts spoke to reporters. "The
tiles, as we know, are fragile and an EVA crewmember has a lot of mass, so we'll
have to be very careful."
Robinson
will be the first astronaut to be sent beneath a NASA space shuttle, let alone
to repair its ceramic tile heat shield in orbit, when he rides the ISS robotic
arm under the forward section of Discovery Wednesday. Taking care not to bump
his helmet or any other part of his spacesuit against the fragile black tiles
along Discovery's belly, he will pluck his targets - two pieces of stiff ceramic
fiber cloth used to fill excess space and prevent tiles from shaking against
one another during launch.
"The main
tools I plan to use are right here," Robinson said, pinching the thumb and
forefinger of his right hand together. "It'll be a gentle pull with my hand and
if that doesn't work I have some forceps and will give it a stronger pull. If that
doesn't work, I saw it off with a hacksaw."
Known to
NASA as gap-fillers,
the small strips have been seen jutting from between tiles on orbiters in the
past and are not caused by impact or foam debris damage, shuttle officials
said, adding that they likely became unglued from their bases during launch.
Shuttle
officials are concerned that the two gap-fillers, which jut out 1.1 inches (2.7
centimeters) and up to nine-tenths (2.3 centimeters) respectively, could cause higher
than normal heating to downstream tiles and the wing leading edges during
reentry. They decided
Monday to press ahead with the repair.
Some members
of Discovery's seven-astronaut crew were concerned about the added risk of the
gap-filler repair, but conceded that the straightforwardness of the task and
from flight controllers on the ground justified the action.
"When we
first heard about it I think a number of us did have misgivings, we were concerned
about it," said STS-114 mission specialist Andrew Thomas, who will choreograph
the spacewalk repair from inside Discovery. "However, it's a lot better for a number
of performance reasons to remove the material, and that justifies doing it
since the removal should be pretty straightforward and pretty easy."
Discovery's
STS-114 commander, veteran astronaut Eileen Collins, said she is confident that
the repair plan drawn up by flight controllers will be effective and safe for
her crew and spacecraft.
"This
situation, I believe, will certainly be safe for us for reentry," Collins said,
adding that NASA engineers have made progress in orbiter progress and repair methods.
"We are able to repair small types of damage...we have come to a point where we know
what is safe to come home with."
Collins
said that while the gap-filler repair is a departure from the training
Robinson and his spacewalking partner Soichi Noguchi, of the Japanese Aerospace
Exploration Agency (JAXA), received before launch, can be folded in line with the
astronaut's experience.
"It's important
to do the gap-filler task...I think we have the flexibility to do that," Collins
said, adding that she and her crew have been reviewing the new EVA operations
today. "We're starting to get comfortable with it."
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