Tense Day Ends in Some Relief for Space Station

HOUSTON -- A tense day in orbit ended with some relief for astronauts aboard the International Space Station (ISS) and their Mission Control teams Friday, closing with two critical Russian computer systems back in action.

Four of six control and navigation computers in charge of the Russian-built attitude control, life support and other critical systems aboard the ISS were restored after the station?s Expedition 15 crew bypassed a faulty circuit switch inside them, mission managers said Friday.

?It was a very simple shunt,? NASA ISS program manager Mike Suffredini said of the fix during a briefing here at the Johnson Space Center.

The shunt allowed two computers governing the station?s Russian control system, as well as a separate pair overseeing Russian guidance, navigation and attitude control, to power up and perform as expected following a grim morning that began without any systems online. By the end of the day, not only were the station?s Russian computers running, but Atlantis shuttle astronauts had successfully furled a stubborn solar array and repaired a torn shuttle blanket during the third spacewalk of NASA?s STS-117 mission.

?Our colleagues were very excited about the events,? Suffredini said, adding that seeing the computers restart together as designed marked a milestone. ?When we all saw that, it was kind of an indication that things have changed, and changed for the better.?

The computers resumed operations around 4:30 p.m. EDT (2030 GMT), Suffredini said, with the command system reactivating the station?s cooling system in its Russian-built Zvezda service module.

?It had warmed up a bit,? Suffredini said of the Zvezda while the computers were shutdown.

More testing ahead

Engineers will track the station?s Russian control and navigation systems for up to 48 hours to determine if they?ve made a full recovery, mission managers said. Early Saturday, flight controllers will check the health of the computers and decide whether to restart other ISS systems, likely one at a time, later in the day.

Kelly Beck, NASA?s lead ISS flight director for the STS-117 mission, said flight controllers are taking measures to lighten the duties for Expedition 15 commander Fyodor Yurchikhin and flight engineer Oleg Kotov. Both Russian cosmonauts, the two spaceflyers have rearranged their sleep schedule to accommodate late-night troubleshooting efforts when the ISS is in communications range of Russian ground stations on Earth.

Russian ISS managers plan to launch spare parts or replacement computers for the afflicted systems aboard an upcoming Progress cargo ship later this year. Initially slated to launch in August, Russian space officials are targeting an earlier liftoff on July 23, Suffredini said.

Computer glitch

Each of the space station?s Russian-built primary systems has three computers, or lanes, for redundancy but can operate with only one machine running. Of the six for both systems, the power sources for two are believed to be failed, rendering them unavailable.

The computers failed earlier this week as NASA astronauts installed two massive new starboard-side girders to the ISS and unfurled a pair of expansive solar arrays from their tip. By Wednesday all six computers had failed, leaving the ISS without access to its Russian attitude control system that uses thrusters to orient the orbital laboratory.

Instead, the station relied on its U.S.-built control moment gyroscopes and used the Atlantis shuttle?s thrusters as a backup. But the Russian attitude control system is expected to be required once Atlantis undocks next week, since the activity typically overwhelms the capacity of the U.S. gyroscopes, NASA has said.

Astronauts aboard the space shuttle Atlantis continue to conserve their spacecraft?s power supplies in case their mission is extended one day to help support ISS attitude control, NASA said.

Meanwhile, engineers at NASA and their Russian counterparts have been hard at work on alternative attitude control methods, such as using docked Russian crew and cargo ships. While efforts will not stand down until ISS managers confirm the Russian computers are fully functional, there is some ease of tension in the ranks, Suffredini said.

?I think that there?re a lot of folks that are working on the teams?that feel a certain amount of relief that they won?t have to implement some of the things they?re looking at,? he added.

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.

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