STS-117 spacewalkers Patrick Forrester (left, partially obscured) and Steven Swanson helped partially stow a starboard-reaching solar array on the International Space Station's P6 truss on June 13, 2007.
Credit: NASA TV.
HOUSTON -- The loss of vital computers governing Russian systems aboard the International Space Station (ISS) has left the orbital laboratory dependent on U.S. gyroscopes and NASA?s visiting Atlantis shuttle, and may lengthen the orbiter?s already extended flight, mission managers said late Wednesday.
The computers, which control the space station?s Russian-built navigation and command and control systems, shut down early Wednesday as shuttle astronauts began retracting a solar array outside the ISS.
?For reasons that are unknown to us at this time, we lost both of those computers and currently we?re in that configuration,? said Mike Suffredini, NASA?s ISS program manager, during a briefing here at the space agency?s Johnson Space Center.
The computer failures have left the station without the use of its Russian attitude control thrusters, Elektron oxygen generator and other support equipment, though the ISS has plenty of oxygen supplies and U.S.-built redundancy to make up for the loss for the time being, Suffredini said.
The station?s three-astronaut crew and seven visiting shuttle astronauts are not at risk, and have not lost all vital systems, he added.
?The lights, the fans and, thank God, the potty, all those things are working,? Suffredini said.
Shuttle mission extension possible
The ISS is currently relying on its four U.S. control moment gyroscopes to maintain its orientation in space, then shifting to thrusters aboard NASA?s shuttle Atlantis when the gyroscopes are overwhelmed, or saturated.
That dependency is leading mission managers to discuss the possibility of extending Atlantis? 13-day mission by a day or so and conserving its supplies where possible, Suffredini said. Atlantis? mission was already extended two days to allow an added spacewalk and the repair of a torn shuttle blanket.
In a worst-case scenario, in which the issue runs beyond current shuttle mission and exceeds the capabilities of the station?s ?U.S. system ability to control the ISS, its three-astronaut crew could return to Earth.
?If we are in that position, we do have the option to depart,? Suffredini said, stressing that he believes the computer issue will be solved in the next few days. ?I?m not thinking is something that we will not recover from.?
The station?s Russian segment has a network of six primary computers, three for guidance and navigation and three for command and control, any one of which can handle the duties of its counterparts, Suffredini said, adding that only two were online early Wednesday.
While the computers have experienced hiccups in the past, a system-wide reboot typically solved the problem, mission managers said.
?Of course, what?s unique is that when the system went to reboot itself, it wasn?t able to do that,? Suffredini said.
On Tuesday, an unexplained glitch hung up the station?s Russian navigation computers as astronauts deployed two starboard solar arrays from the end of the station?s new Starboard 3/Starboard 4 (S3/S4) truss segments. The glitch kicked off a series of computer errors that included a false fire alarm that sent the ISS crew into emergency procedures for a brief time.
ISS engineers are studying a number of possible explanations for the computer issues, ranging from electromagnetic interference to the added mass and power supply delivered in the new S3/S4 trusses and solar arrays, mission managers said.
Russian flight controllers plan to dedicate much of Thursday morning, when the ISS flies over Russian ground stations, to working through the computer issues.
Of primary concern for ISS flight controllers is the recovery of the Russian attitude control system, which orients the station using thrusters when the outpost?s U.S. gyroscopes are overwhelmed.
The system, Suffredini said, is typically used just after a shuttle docks or undocks from the ISS to dampen out the change in momentum. It is also used to move the ISS out of the way of orbital debris, he added.
Kelly Beck, NASA?s lead ISS flight controller for Atlantis? STS-117 mission, said the station?s Expedition 15 crew worked closely with Russian flight controllers to work through the computer glitch.
Russian ISS flight controllers assured the station?s Expedition 15 that everything was being done to root out the issue.
?Definitely, we are going to do everything possible to resolve it,? Russia?s Mission Control told the ISS crew.
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- Complete Shuttle Mission Coverage