( AP )- Two astronauts planned to climb out of the international space station to staple down a thermal blanket that peeled back during the launch of space shuttle Atlantis.
James Reilly and Danny Olivas were expected to emerge into the void of space shortly before 1:40 p.m. EDT Friday on the mission's third spacewalk.
Meanwhile, engineers continued testing whether a bad power feed going into the Russian side of the international space station was causing failures in computers that control the outpost's orientation and produce oxygen.
The power feed hooks up the Russian side to a pair of new solar arrays that were delivered to the space station by the shuttle and connected to the orbiting outpost by two of Atlantis' crew members during a spacewalk Monday.
"A power line has a certain magnetic field around it, and that can affect systems near it," said Mike Suffredini, NASA's space station program manager. "This is the leading theory today."
In an effort to fix the problem, flight controllers planned to disconnect the power feed between the U.S. and Russian sections of the space station and then reboot the computers in the morning as the station passes over Russian tracking centers 220 miles below.
If the power feed from the new arrays turns out to be the problem, the Russian section can get power from other solar arrays.
Cameras, computer laptops and some lights on Atlantis were turned off Thursday to save energy in case it needs to stay an extra day at the station to help maintain the outpost's orientation while the problem with the Russian computers is addressed. The mission had already been extended from 11 to 13 days to repair the thermal blanket.
While Atlantis is still docked, its thrusters can help, if needed, to maintain the station's position. Gyroscopes on the U.S. side of the space station also were helping maintain orientation, but they can't do the job full time.
Bill Gerstenmaier, NASA's associate administrator for space operations, called the chances of abandoning the space station because of the computer problem "remote." Seven visiting shuttle astronauts and three crew members are currently living at the orbiting outpost.
"We're still a long way from where we would have to de-man the space station," Gerstenmaier said.
This type of massive computer failure had never been seen before on the space station, although individual computers do fail periodically.
"These sorts of things happen," said astronaut Ed Lu, who lived at the space station for six months in 2003. "I don't think it's that serious."
During the spacewalk, the shuttle's robotic arm will move Olivas to the tail of Atlantis where the thermal blanket covers an engine pod.
Engineers don't think the damaged section of the thermal blanket, which protects part of the shuttle from the blazing heat of re-entry, would endanger the spacecraft during landing. But it could cause enough damage to require schedule-busting repairs.
"This will be a great repair that brings Atlantis home safely," said Atlantis crew member Patrick Forrester, who will coordinate the spacewalk from inside the space station.
NASA has focused intensely on any problems that could jeopardize a shuttle's re-entry into Earth's atmosphere since shuttle damage resulted in the 2003 Columbia disaster that killed seven astronauts.
Training for spacewalk tasks can take months, but Olivas only has had a day to prepare for the repair job. Mission Control had only a few days to develop the procedures, which will use a medical stapler and loop-headed pins to secure the blanket corners in place against protective tile.
While Olivas repairs the blanket, Reilly will install on the outside of the station's U.S. section a valve that will be used for its oxygen-generating machine. Once both tasks are done, the astronauts will help retract a 115-foot solar wing that NASA wants folded up into a storage box so it can be moved later.
The array is now only halfway folded up after two days of efforts by Mission Control and astronauts at the space station. Mission Control hopes the spacewalking astronauts can help shake loose some stuck wires on the solar wing.