HOUSTON -- Two Russian cosmonauts and engineers on Earth have made more progress to revive critical computers aboard the International Space Station (ISS), NASA said Saturday.
NASA ISS program manager Michael Suffredini said all six computers governing command and navigation systems for Russian segments of the station are back up and running, including two that were previously thought failed. A test to check whether they can take control of the space station?s attitude control when needed is forthcoming.
?So when that test is complete, we will consider that the computers are up and healthy,? Suffredini said during a mission update here at NASA?s Johnson Space Center.
That test of the station?s navigation system, Suffredini said, is expected to be performed in the next day or so. If successful, ISS flight controllers would not ask to extend the mission of NASA?s space shuttle Atlantis currently docked at the station, he added.
Atlantis? STS-117 astronaut crew is scheduled to depart the ISS on Tuesday, June 19. But after a meticulous power conservation effort, the astronauts have extended the shuttle?s supplies to offer an extra docked day at the ISS if needed.
?Things are looking up as if Tuesday could be a good day for the shuttle to leave,? Suffredini said.
The space station?s Russian-build segments rely on two computer systems, command and navigation, each consisting of three computers though only one machine, or lane, for each group can provide necessary control over the station?s Russian systems.
All six of the redundant systems shut down earlier this week, prompting overnight scrambling in Russian Mission Control and long hours for Expedition 15 cosmonauts Fyodor Yurchikhin and Oleg Kotov aboard the ISS to track the glitch.
The failure left the ISS without its Russian thrusters, dependent on U.S. control moment gyroscopes to maintain its orientation in space. An oxygen generator, carbon dioxide scrubber and other environmental control systems were also offline and temperatures rose inside the station?s Russian-built Zvezda service module where the computers are located.
?I think we got a little over 80 degrees at one point in the service module,? Suffredini said. ?
U.S.-built systems compensated for the loss of some Russian counterparts, though the station did not lose any lights, fans or communications during the shutdown. With the computers? recovery, vital systems were brought back online beginning with the cooling system, mission managers said.
At fault were overcurrent protection circuits designed to safeguard each computer from power spikes, Suffredini said.
ISS cosmonauts set up shunts for each unit to bypass the circuit, reviving all six to life over the last two days. The bypassed circuits are redundant due to other overcurrent protection systems already in place, Suffredini said.
?Oleg and Fyodor will get to sleep through the night,? Suffredini said of the hard-working ISS crew. ?That?s actually very significant.?
Engineers believe the circuits were tripped due to increased interference, or ?noise,? from the station?s plasma environment related to the addition of massive new starboard trusses and solar arrays.
?The leading theory today is that it?s from noise caused by the growth of the station and how the potential changes as we continue to do that,? Suffredini said, adding that Russian engineers will determine whether other systems are at risk as the station?s construction continues.
Several troubleshooting teams are now standing down, including one eyeing how long the station could support a three-astronaut crew without the Russian computer systems, Suffredini said. But two will continue to root out a specific cause for the computer glitch and draw up new alternatives to maintain ISS attitude control without the Russian computers online, he added.
Meanwhile, aboard Atlantis and the ISS, astronauts spent the day transferring supplies and equipment between the ISS and Atlantis. The shuttle astronauts are gearing up to perform the fourth spacewalk of their planned 13-day mission Sunday.
Commanded by veteran shuttle flyer Rick Sturckow, Atlantis? STS-117 mission delivered a new crewmember and a pair of massive starboard truss and solar arrays while at the ISS. The shuttle?s seven-astronaut crew is due to land at NASA?s Kennedy Space Center in Florida on June 21.
NASA is broadcasting the space shuttle Atlantis' STS-117 mission live on NASA TV. Click here for mission updates and SPACE.com's video feed.
- SPACE.com Video Interplayer: Space Station Power Up with STS-117
- Complete Shuttle Mission Coverage
- All About the International Space Station