HOUSTON - NASA worked feverishly through
the night to finalize the details of a risky spacewalk planned for Friday, only
to delay the extravehicular activity (EVA) until Saturday morning.
The delay
came to buy Mission Control time here at Johnson Space Center (JSC) to refine instructions
to repair a torn
solar array at a far end of the International Space Station (ISS). The
maimed solar power plant can generate electricity, but NASA engineers fear it is
structurally unstable.
Space station and shuttle Discovery crew members,
meanwhile, are biding their extra time today by improvising repair devices from
materials around the laboratory for the spacewalk.
Although
finer details are still in the works, mission managers said
yesterday that a unprecedented robotic arm setup will ferry veteran spacewalker Scott
Parazynski out to the damaged area.
"The
station robotic arm ... doesn't provide enough reach to get the crew outward,"
said Derek Hassmann, lead ISS flight director for the STS-120 mission, of the
57-foot (17-meter) Canadarm2. To get that reach, he said the robotic arm will
pick up the space shuttle Discovery's boom extension, on which Parazynski will
ride to the damaged area.
Astronauts remotely
moved the robotic arm to the center of the space station this morning in
preparation to grab the 50-foot (15-meter) boom extension for this weekend's
EVA. When Parazynski reaches the ripped 4B solar array wing, which is attached
to the Port
6 truss segment, he will untangle a snagged guide wire and stitch in
homemade repair devices. Astronaut Doug Wheelock will accompany Parazynski on the spacewalk.
Mission managers said the operation will be
dangerous, as significant electric power courses through the solar arrays, but
not any more so than general work in the vacuum of space.
"We're
going 24 hours a day, non-stop, with three shifts of folks working,"
Hassmann said of the effort to get the spacewalk plans in line. "When we
go do it, it's not going to be any more risky than what we've done previous to
this. We're not going to do it until we're ready."
Arts and
crafts day
Donning
goggles as they hunched over fresh instructions from Mission Control, ISS commander
Peggy Whitson and space shuttle Discovery pilot George Zamka fashioned the
cufflink-like straps today from materials on board the space station.
"Guys
you're looking great," said Chris Ferguson, spacecraft communicator here
at Johnson Space Center, as Whitson and Zamka performed their handiwork.
The tabbed
ends of the repair devices made from four-inch (10-centimeter) bars of aluminum
wrapped in orange, electricity-proof Kapton tape, followed by thermally protective white tape. Steel cabling runs through
the center of two aluminum bars to create a "cuff link," which
Parazynski will button up the 2.5-foot (0.76-meter) rip in the solar array wing.
Mission managers said the fix should relieve
physical stress yanking on the tear; once the repair is complete, allowing the
arrays to fully deploy from their 80-percent-unfurled state. Should the repair
fail, however, mission managers will use a fifth and final EVA to try again--should
that fail, astronauts might jettison the crippled array into space.
The spacewalk
revision came after a previous change of plans, which had Parazynski and Wheelock
inspecting a troublesome, grit-covered gears at the starboard end of the space station.
Mission controllers awoke the 10 sleeping astronauts
aboard the orbital laboratory to the song "The Lion Sleeps Tonight" by The Tokens
before the crew began their work in the figurative jungle of space. "That
certainly gets you going first thing in the morning," STS-120 commander
Pamela Melroy said as she awoke.
Discovery
is scheduled to undock from the orbital laboratory some time on Nov. 5 and land
Nov. 7 after it careens across the central United States in daylight, but
mission managers hinted yesterday that an extension may be imminent with a delayed
spacewalk that has occurred.
The STS-120
mission
was extended from 14 to 15 days earlier this week and has enough supplies
to remain at the space station for at least two more days.
SPACE.com will
provide live coverage
of the STS-120's fourth spacewalk beginning around 4:30 a.m. ET (0930 GMT)
Saturday morning.
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