This
story was updated at 4:55 p.m. ET
HOUSTON - With NASA's go-ahead today,
astronauts have geared up for a tricky solar wing repair at a far end of the
International Space Station (ISS) tomorrow morning.
Crewmembers
scrounged around the orbital laboratory yesterday for supplies, gathering tools
and crafting "cuff links" that will
button up two rips in the maimed solar array wing. NASA hopes the efforts
will enable the damaged array to fully and safely deploy--a crucial step to
complete the orbital laboratory by September 2010, when NASA retires its aging
space shuttle fleet.
But damaged
solar blankets are not the only problem facing the power-generating abilities
of the space station. "At this point we have problems on both ends of the
truss, unfortunately," said Derek Hassmann, ISS lead flight director for
the STS-120 mission.
In addition
to damage to the solar wing, which generates electricity but is structurally
unstable, spacewalker Dan Tani discovered unusual
metallic grit in solar-array-orienting gears on Oct. 28. Since the Port 6
(P6) solar wing tore during its deployment on Oct. 30, however, mission
managers shifted their focus to repairing the solar power tower.
"We
need to address one of these two problems before we proceed," Hassmann
said. "The P6 solar array is the ... priority
problem that we can go fix now."
Scramble
for instructions
ISS flight
director Heather Rarick said hammering out detailed spacewalking plans in
little more than two days was no easy task.
'"We've
had at least three or four extra teams running throughout the shifts,"
Rarick said of the last-minute efforts to finish the spacewalk instructions.
"It's just been a fantastic effort." She added that under normal
circumstances, such a procedure would take weeks or months to produce.
Astronauts
took the changes in stride as well, offering up their sparse free time to
outfit the space station's newest room as
well as create the solar wing-saving cuff links. Today, crewmembers prepared
Parazynski's ride--a 90-foot (27.4-meter), extended robotic arm--to the damaged
solar wing.
"We
know and understand how hard you guys are working down there," spacewalker
Doug Wheelock told mission controllers last night. "We're ready to
execute."
Wheelock
will accompany Parazynski during the fourth and now final spacewalk of the
mission. A fifth spacewalk was planned for Sunday, but mission managers
cancelled the operation to focus on hashing out plans to repair the 4B solar
wing, which is attached to the Port 6 truss section of the space station.
Risky
repair?
The entire
solar wing can generate about 110 volts of electricity at 90 amperes in full
sunlight, but mission managers said Parazynski's risk of being electrocuted
will be more than acceptable.
"A
spacewalking astronaut could put his hand on that solar array and there would
be no risk of any shock of any kind," Hassmann said, referring to a
pristine solar array and glove. Although the 4B array is damaged, Hassmann said
engineers saw no live wires exposed at the site where Parazynski will conduct
repairs.
"A
number of different things have to happen all at once for there even to be a
small risk," he said. "We have a number of risk mitigations in place
that are going to protect Scott from any kind of electrical hazard."
The bigger
concern, mission managers noted, is how far Parazynski will be from the safety
of the airlock--about 30 minutes or so in an emergency, said lead STS-120
spacewalk officer Dina Contella.
But David
Wolf said yesterday that the somewhat risky spacewalk is necessary to ensure
the future completion of the space station.
"There
comes a time when the station needs repaired, one-time events where we--with
good mitigation and knowledge--accept high risk," Wolf said. "And
that's one of them. Our job is to think of all those possible ways where a bad
outcome could occur and be sure that every hazard is mitigated and
handled."
Looking
forward
Hassmann
said the astronauts are excited about the coming spacewalk.
"They're
in great spirits," he said, noting that the astronauts studied the
procedures since they received them Friday morning. "They have a lot of
confidence that they're ready to go do what we've asked them to do."
The space
shuttle Discovery and its seven-astronaut crew are slated to leave the orbital
laboratory on Nov. 5 and land at Kennedy Space Center on Nov. 7, weather
permitting. NASA officials said that the crew has enough supplies to stay
docked for the ISS for two more days beyond Monday, should the need arise.
And it might.
Mission managers said that if Saturday's
spacewalk effort fails to repair the solar wing, mission managers said they
will resurrect the fifth spacewalk for a second try on Sunday or Monday.
SPACE.com's
live coverage of
the spacewalk begins Saturday morning at 5:30 a.m. EDT (0900 GMT).
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