<P><B style="FONT-SIZE: 14px">JOHNSON SPACE CENTER, Texas (CNN) -- On Earth, it would
be a mundane home improvement project. But in the weightlessness of space and
on the underside of a spacecraft, removing a piece of protruding insulation
takes on several new dimensions.</B></P>
<P>In a history-making repair during Wednesday's spacewalk, Discovery astronaut
Steve Robinson will come within feet of the shuttle's underbelly and gently
pluck filler material sticking out from between heat-resistant tiles in two
places on the orbiter.</P>
<P>"It's conceptually very simple, but has to be done very, very carefully,"
Robinson said.</P>
<P>The astronaut will be dangled from a robotic arm on the international space
station and maneuvered to the bottom of Discovery to remove the gap fillers --
thin fabric stiffened with a ceramic material that is used to plug gaps between
tiles on the orbiter.</P>
<P>At a Tuesday news conference, astronaut David Wolf demonstrated the techniques
Robinson will attempt.</P>
<P>In what Wolf described as a "choreograph of delicate robotics," astronaut
Robinson, with his tether tied behind him to prevent it from hitting the hull,
will approach the orbiter and attempt to free the gap filler material using his
gloved fingers.</P>
<P>"Our expectation is that this is all the task is going to involve," NASA's Kelly
Beck said Tuesday.</P>
<P>"It'll be a gentle pull with my hand," Robinson said of the repair, which will
last approximately 90 minutes. "If that doesn't work I have some forceps, I'll
give a slightly more than a gentle pull." If that doesn't work, he said he will
use a saw to remove the fillers. There will be "no yanking," he said.</P>
<P>During the procedure, Robinson will only be visible to the other members of
Discovery's crew via a camera on the space shuttle's boom. A second astronaut,
Soichi Noguchi, will be spacewalking at the same time, but he will be working
on other tasks.</P>
<P>The removal of the gap fillers is being added to the list of tasks set out for
the spacewalk, during which Robinson and Noguchi will also install an external
storage platform to the space station.</P>
<P>Robinson's assignment will mark the first time NASA has ever tried to repair the
exterior of a shuttle in orbit, a capability developed in the wake of the 2003
Columbia disaster.
</P>
<P>The Columbia shuttle disintegrated over Texas, killing all seven crew members,
as it returned from space.</P>
<A name="1"></A><A name="rv1"></A>
<H3>Risky job</H3>
<P>Andy Thomas, another member of the Discovery crew, acknowledged that the crew
had initial "misgivings" about the repair, scheduled to take place during
Wednesday's scheduled spacewalk.
</P>
<P>"We were concerned about the implications of it and what was motivating it," he
said. "However, it's a lot better...(to) remove this material."</P>
<P>Discovery commander Eileen Collins agreed. "This situation, I believe, will
certainly be safer for entry. I'm actually not that worried about it," she said
when asked how she felt about returning to Earth in a repaired shuttle.</P>
<P>NASA managers decided Monday to attempt the repair after an analysis showed the
protrusions might produce excessive heat during re-entry and threaten the
spacecraft.</P>
<P>"It was prudent to take action so that we wouldn't have to worry about some of
the worst consequences," said Wayne Hale, NASA's deputy shuttle program
manager, at a news conference Monday. "If we can't prove that it's safe, then
we don't want to go there."</P>
<P>President Bush called the crew Tuesday and expressed his support for the mission
and the space program.</P>
<P>He thanked the astronauts for being "risk takers for the sake of exploration."</P>
<P>"We look forward to the successful completion of this mission," he said. (<A href="/2005/US/08/02/bush.discovery.ap/index.html">Full
story</A>)</P>
<P>The protruding gap fillers were discovered during an extensive inspection of
Discovery's exterior, carried out by cameras and lasers on a new boom on the
space shuttle. The crew of the space station also photographed the underbelly
of the shuttle before it docked last Thursday, part of a new inspection regime
put in place after the Columbia disaster.</P>
<P>Hale said NASA managers are satisfied that appropriate safeguards are in place
to prevent Robinson from damaging the tiles during the repair operation, which
could make Discovery's re-entry even more problematic.</P>
<P>Calculations by NASA experts showed that the protrusions could increase the
re-entry temperature by 10 percent to 30 percent, possibly exceeding NASA's
safety guidelines for how much heat the shuttle's thermal protection system
should be allowed to endure, Hale said.</P>
<P>While the protrusions might not pose any threat to Discovery, the "large
uncertainty" about their possible effect on the aerodynamics of the shuttle
convinced NASA officials to try to fix the problem in space, he said.</P>
<P>Hale said there is no data to show whether previous shuttle missions have
managed to return safely with similar protrusions. While extended gap fillers
have been found before, they were only discovered after landing, leaving NASA
experts with no way to know whether the material shifted before or after
re-entry.</P>
<P>Discovery can return safely without either of the gap fillers in place, Hale
said. One of them keeps tiles from vibrating against each other during liftoff
and has no purpose for re-entry; the other is designed to prevent repeated
overheating of a gap between two tiles, but not having it in place during a
single re-entry would still be "well within our safety margins," Hale said.</P>
<P>On Monday, Robinson and Noguchi completed their second spacewalk of the mission,
during which they replaced a faulty gyroscope on the space station.</P>
<DIV class="cnnStoryContrib">
<P>Copyright 2005 CNN. All rights reserved.This material may not be published,
broadcast, rewritten, or redistributed. <A href="/interactive_legal.html#AP">Associated
Press</A> contributed to this report.</P>
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