NASA hopes to duplicate the success it had with rewiring the international space station earlier this week so it can continue tackling a problem that has vexed it for days.

Spacewalking astronauts rewired half of the orbiting lab on Thursday and were set to rewire the other half on Saturday. The task went so flawlessly last time that U.S. astronaut Robert Curbeam and Swedish astronaut Christer Fuglesang were ready to go back into the space shuttle Discovery an hour ahead of schedule.

This time, Curbeam, a veteran spacewalker, and Sunita Williams, a rookie, will venture out to complete the rewiring task. If they have time to spare, they plan to make their way over to a halfway retracted solar panel, which so far has refused to fold properly.

The solar wing is part of the space station's temporary power system. A primary goal of Discovery's seven-day mission was to rewire the lab and hook a new set of solar wings onto the permanent electricity grid. To do that, NASA needed to retract the old solar panel so that the new ones had room to rotate with the movement of the sun to maximize the amount of electricity generated.

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The old solar panel retracted enough to give the new ones clearance, but it did not fold all the way as NASA wanted. A guidewire stuck in grommets on the panel seems to be the problem. Multiple attempts by the space agency on Friday to shake the array and help free the wire were unsuccessful.

NASA has asked Curbeam and Williams to venture over to a box into which the accordion-like array is folding and to pat it, in the hopes that movement will unsnag the wire.

The space agency has kept the option open to schedule a fourth spacewalk if necessary, in which astronauts — likely Curbeam and Fuglesang — would manually help the 115-foot (35-meter) array fold. That foray would take place no earlier than Monday.

"We're excited about the possibility of helping out and helping make the house up here a little better by fixing that solar array," Curbeam said Friday at a news conference from space.

He cautioned that the solar wing was composed of delicate pieces, so it would be a challenge to make sure the astronauts don't inadvertently damage the hardware.

During the first spacewalk, a 1.8 metric tons, US$11 million (euro8.4 million) addition was installed to the space station. The rewiring represents a milestone for the orbiting space outpost, graduating it from its infancy stage and getting it to ready to receive additional laboratories from Europe and Japan in the next few years.

"Even though we're having some problems, we're still making very good progress on the activities for this flight and we're very pleased about that," Kirk Shireman, NASA's deputy space station program manager, said at a briefing late Friday.

Discovery is due to return to Earth on Thursday, though it could be delayed if a fourth spacewalk is squeezed in.