| CAPE CANAVERAL, Florida
CAPE CANAVERAL, Florida Russian flight controllers successfully restored two of the International Space Station's main computers on Friday, as spacewalking U.S. astronauts fixed insulation damage on the visiting space shuttle Atlantis.
A third system remained shut down and the cause of the failure remained a mystery. Friday's progress was the most encouraging since the computers crashed on Wednesday.
The computers control the station's positioning in space so that it can draw power from the sun, maintain proper temperatures and position antennas for communicating with ground controllers.
The German-built computers also command critical life-support equipment, such as the oxygen generators and scrubbers that remove deadly carbon dioxide. Those machines can be manually controlled as well.
Russian engineers have determined that one or two of the systems' backup power supplies have failed, prompting flight controllers to move up by two weeks the launch of a resupply ship with spare parts, said NASA space station program manager Mike Suffredini.
The computer crash was not considered life-threatening to either the station or shuttle crews.
The most pressing problem, Suffredini said, is to recover some ability to steer the station, which is vulnerable to bumps and vibrations from departing and arriving spaceships.
The shuttle is scheduled to leave the outpost on Tuesday, but NASA is considering leaving it for another day or two to help with recovery efforts.
LINK TO SOLAR WING?
During Friday's spacewalk, the third since the shuttle's arrival last Sunday, astronauts James Reilly and John "Danny" Olivas may be asked to disconnect a cable they installed on Monday as part of hooking up a new solar power wing.
Problems with the station's computers occurred when that connection was made.
The new panel is generating electricity that is being used by other parts of the station. The Russian computers, however, seem to be picking up some interference from the wing or related equipment.
At some point, the station's computers must be repaired or the $100 billion outpost will have to be abandoned.
The station maintains a three-person escape capsule to evacuate the crew. Astronauts and cosmonauts could return when the problem was resolved.
"There is nobody in this agency and as far as I know in the Russian agency that thinks that this vehicle is at risk of being lost," Suffredini said.
A more immediate issue for NASA was the repair of space shuttle Atlantis, which originally was scheduled for a weeklong construction mission.
Flight controllers added two days and another spacewalk so the astronauts would have enough time to tuck a protruding piece of insulation into an engine pod near the rear of the spaceship.
The corner flap of a blanket tore loose during Atlantis' climb to orbit last Friday.
Fixing the insulation was the first task of a spacewalk by Reilly and Olivas, which began shortly after 12:30 p.m. EDT (1630 GMT) and was expected to last 6 1/2 hours.
While the exposed gap is not believed to pose a Columbia-like heat shield breach, managers said repairing the damage would protect the shuttle's underlying structure from weakening during the scorching plunge through the atmosphere.
A breach in shuttle Columbia's wing, caused by a debris impact during launch, triggered the spaceship's breakup over Texas on February 1, 2003. All seven astronauts aboard died.
After the repair, Reilly and Olivas will help guide a balky solar wing back into its storage box.
The shuttle is due back at the Kennedy Space Center in Florida on Thursday.