This story was updated at 3:49 p.m. EDT.
HOUSTON -- Russian and U.S. engineers are drawing up plans to work around the failure of critical computers aboard the International Space Station (ISS) in time for the departure of the shuttle Atlantis next week.
NASA?s ISS program manager Mike Suffredini said engineers are studying alternatives to help maintain control of the space station?s orientation, including using rockets aboard docked Russian spacecraft, once Atlantis? STS-117 crew casts off from the orbital laboratory on June 19.
?The highest priority would be maintaining attitude once the shuttle has departed,? Suffredini said Friday.
The space station?s six Russian computers governing control and navigation systems went offline Wednesday, leaving the outpost unable to use Russian-built thrusters to maintain its orientation as it flies through space.
The station is currently relying on U.S.-built control moment gyroscopes, with thrusters aboard NASA?s visiting shuttle Atlantis as backup. After the shuttle undocks, however, the station?s gyroscopes are expected to be overwhelmed, or saturated, and have typically used Russian-built rockets to compensate.
Suffredini said that engineers are studying options to use thrusters aboard the Russian-built Soyuz spacecraft or two Progress cargo ships to dampen the station?s momentum after Atlantis undocks in case the computer issue is not resolved by then. The computer issue is not one which threatens the station or its crew, he stressed.
?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, adding that there are no plans in work to for the station?s Expedition 15 crew abandon the outpost. ?I fully expect us to repair this problem.?
Mission managers are also considering moving up the launch of the next Russian Progress ship from August to July 23 to deliver spare parts for the computers, some of which appear to have failed secondary power supplies.
Some causes ruled out
Mission managers have ruled out interference from power lines between the station?s new starboard solar arrays and the station?s Zvezda service module, which houses the computers.
On Friday, ISS flight controllers also ordered a spacewalking Atlantis astronaut Jim Reilly to disconnect an unused power cable on the station?s new Starboard 3/Starboard 4 truss segment - which he connected during a June 11 spacewalk. The Russian computer systems appeared to begin experiencing difficulties when the cable was first attached, Suffredini said.
?This is a case where it?s circumstantial,? he added. ?We don?t know if that?s the cause."
The computer failure has also left the station?s primary oxygen generator, the Russian-built Elektron, offline since it requires computer control, Suffredini said. But a new U.S oxygen generator is expected to be activated following a spacewalk today to install a hydrogen vent valve, and the station has a sufficient supply of stored oxygen aboard to maintain its three-man crew, he added.
When Atlantis launched towards the ISS on June 8, the station carried enough oxygen supplies to support 10 astronauts for 56 days, mission managers said, adding that those supplies would support three astronauts for a longer period.
Overnight efforts to recover six computers failed to return them to full operations, though power was restored to one command computer before troubleshooting efforts stood down.
?We ended up in the configuration that we started out the day in, which is unfortunately not having a central computer or a terminal computer,? said NASA ISS flight director Holly Ridings early Friday.
Late Thursday, ISS astronauts scanned power lines to the Russian segment from the space station?s U.S.-built solar arrays for any signs of interference, and ultimately disconnected cables transporting power from the newly installed starboard solar arrays to the orbital laboratory?s Russian modules. Engineers hoped the work would help determine if electromagnetic interference or possible ?noise? in the power feed from new starboard solar arrays were a contributor to the station?s computer woes.
?The engineers looked at that data and they did not find anything that was grossly off-nominal,? Ridings said. ?It would have been nice to find a smoking gun, but that?s usually not how these things work.?
Engineers restored power to one of the balky computers and briefly found a 'heartbeat' signaling its availability before standing down on troubleshooting efforts for the day, Ridings said.
NASA hopes to resolve or workaround the computer issue by the time Atlantis undocks from the ISS on June 19, though mission managers are studying the possibility of keeping the shuttle at the ISS for an extra if needed.
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