NASA canceled Thursday's spacewalk to inspect a snarled joint for a set of solar panels and instead instructed its orbiting astronauts to go out a day later to try to fix a torn solar wing.
The newly ripped wing is now the more pressing of the two problems at the international space station, both of which involve the crucial power system and threaten to disrupt future construction work.
NASA fears the damage could worsen and the wing could lose all power-collecting capability and become unstable. If that happened, the wing would have to be junked, said NASA's space station program manager, Mike Suffredini.
"We've made it a priority to go repair it," Suffredini said Wednesday.
Engineers scrambled to put together a plan for a spacewalk as early as Friday to tackle the wing, which remains partially deployed. It ripped in two places as it was being unfurled by astronauts aboard the linked shuttle-station complex Tuesday, and a hinge may have been yanked and partially ripped.
Suffredini said engineers suspect the wing became snagged on a support for one of the wing's guide wires. They do not want to reel it in to make it easier to access for spacewalkers, for fear it could be further damaged.
The torn section of the wing cannot be reached with the space station's 58-foot (18-meter) robot arm. So NASA plans to attach the shuttle inspection boom to the station's robot arm, and put Scott Parazynski on the boom to free the snagged part of the wing.
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Month in Space: January 2014
It helps that Parazynski is tall — 6-foot-2 (188 centimeters) — and has long arms. NASA does not want him bumping the wing or touching its sunlight-collecting blankets. There would be no need to mend the tears.
"It's not really very far outside of our scope of experience, and I'm comfortable that it's something we're going to be able to put together," said flight director Derek Hassmann.
He added: "It's going to be fast and furious over the next couple of days."
If more time is needed to prepare, the spacewalk will be deferred until Saturday. But NASA would prefer to attempt it on Friday in case something goes wrong and another spacewalk is needed to finish the job.
Meanwhile, on the opposite side of the space station from the torn wing, a rotary joint that controls the solar wings over there is out of action. A spacewalking astronaut discovered steel shavings in the right joint last weekend, the apparent result of grinding parts.
Suffredini said he and others will figure out what to do about the joint once Discovery undocks from the space station.
The space station can live with the reduced power caused by the two problems for now. But it poses huge challenges for NASA's plans to deliver European and Japanese laboratories on back-to-back shuttle missions beginning in December.
Suffredini said at least one of the problems will need to be resolved before shuttle Atlantis can lift off with Europe's lab. That launch is currently scheduled for Dec. 6.
NASA is under presidential orders to complete space station construction and retire its space shuttles by 2010, to make way for new rocketships that will aim for the moon.
Discovery's commander, Pamela Melroy, acknowledged the emotional roller coaster of the past few days.
"What's holding us up together and keeping us all upbeat is that we're all doing something that we believe in so strongly and that we love, and we're having a ton of fun together doing it," Melroy said at a news conference.
Halloween, for instance, did not go unnoticed in orbit.
Clay Anderson, who’s winding up a five-month space station stay, wore a black cape as he went about his work. Daniel Tani, his replacement, wore a black eyepatch.