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.
- SPACE.com Video Interplayer: STS-120 Mission Profile
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