Cosmonauts aboard the international space station struggled for a second day Friday to try to reboot failed computers that control the orbiting outpost’s orientation.

The Russians worked on the system through the night but only succeeded in getting one of three power channels to the station’s computers operating before flight controllers told them to get some sleep, NASA flight director Holly Ridings said.

Valery Lyndin, spokesman for Russia’s Mission Control outside Moscow, said Friday that support staff on the ground had so far been unable to pinpoint the source of the computer failure.

“The lives of the crew are not in danger,” Lyndin stressed.

He said there were no plans to evacuate the space station. A NASA official also said the chance of abandoning the space station was remote.

The station’s oxygen-regeneration and all basic life-support systems are functioning properly, but the orientation system was affected by the computer problems, Lyndin said.

The troubled computers, in the Russian segment, control thrusters that are fired to orient the station and its solar panels toward the sun for maximum energy production. Gyroscopes on the station’s American segments are functioning, and the station is in a more-or-less proper position, he said.

“We’ve had computer failures before, and we have coped with the problem, but now the situation is much more complicated,” cosmonaut Pavel Vinogradov said on NTV television. “We have the shuttle docked to the station, and active work is going on at the station — the Americans’ space walk. We must maintain the station’s orientation.”

While space shuttle Atlantis is still docked, its thrusters can help, if needed, to maintain the station’s position.

NASA said the engineers tried turning off and on the power between the U.S. and Russian sections before rebooting the computers to test if perhaps a bad connection between the Russian side and a pair of new solar arrays might be the problem. They were still testing that theory Friday morning.

“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.”

The new solar arrays were connected by the Atlantis crew Monday. If the power feed from those arrays turns out to be the problem, the Russian section can still 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.

NASA has said that in a worst-case scenario, the space station’s three crew members might have to return to Earth early if the computers can’t be fixed.

Bill Gerstenmaier, NASA’s associate administrator for space operations, called the chances of abandoning the space station because of the computer problem “remote.”

“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.”

Friday afternoon, astronauts James Reilly and Danny Olivas planned to climb out of the space station to staple down a thermal blanket that peeled back during Atlantis’ launch.

The blanket, covering an engine pod, protects part of the shuttle from the blazing heat of re-entry. While engineers don’t believe it would endanger the spacecraft during landing, it could cause enough damage to require repairs on the ground.

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.

The computer problems also created a small inconvenience for the shuttle astronauts: Because the routine dumping of the astronauts’ waste from the space shuttle requires a change in orientation, the Atlantis crew was told to use the toilet in the Russian section of the space station so that the shuttle’s doesn’t overflow.

On the Net:

Shuttle mission: http://www.nasa.gov/mission—pages/shuttle/main/index.html