HOUSTON -- Atense day in orbit ended with some relief for astronauts aboard theInternational Space Station (ISS) and their Mission Control teams Friday, closingwith two critical Russian computer systems back in action.
Four of sixcontrol 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?sExpedition 15 crew bypassed a faulty circuit switch inside them, missionmanagers said Friday.
?It was avery simple shunt,? NASA ISS program manager Mike Suffredini said of the fixduring a briefing here at the Johnson Space Center.
The shuntallowed two computers governing the station?s Russian control system, as wellas a separate pair overseeing Russian guidance, navigation and attitude control,to power up and perform as expected following a grim morning that beganwithout any systems online. By the end of the day, not only were thestation?s Russian computers running, but Atlantis shuttle astronauts had successfullyfurled a stubborn solar array and repaired a torn shuttle blanket duringthe third spacewalk of NASA?s STS-117 mission.
?Our colleagueswere very excited about the events,? Suffredini said, adding that seeing thecomputers restart together as designed marked a milestone. ?When we all sawthat, it was kind of an indication that things have changed, and changed forthe better.?
Thecomputers 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-builtZvezda service module.
?It hadwarmed up a bit,? Suffredini said of the Zvezda while the computers wereshutdown.
Moretesting ahead
Engineerswill track the station?s Russian control and navigation systems for up to 48hours to determine if they?ve made a full recovery, mission managers said.Early Saturday, flight controllers will check the health of the computers anddecide whether to restart other ISS systems, likely one at a time, later in theday.
Kelly Beck,NASA?s lead ISS flight director for the STS-117 mission, said flightcontrollers are taking measures to lighten the duties for Expedition 15commander Fyodor Yurchikhin and flight engineer Oleg Kotov. Both Russiancosmonauts, thetwo spaceflyers have rearranged their sleep schedule to accommodate late-nighttroubleshooting efforts when the ISS is in communications range of Russianground stations on Earth.
Russian ISSmanagers plan to launch spare parts or replacement computers for the afflictedsystems aboard an upcoming Progress cargo ship later this year. Initiallyslated to launch in August, Russian space officials are targeting an earlierliftoff on July 23, Suffredini said.
Computerglitch
Each of thespace station?s Russian-built primary systems has three computers, or lanes,for redundancy but can operate with only one machine running. Of the six forboth systems, the power sources for two are believed to be failed, renderingthem unavailable.
Thecomputers failedearlier this week as NASA astronauts installed two massive newstarboard-side girders to the ISS and unfurled a pairof expansive solar arrays from their tip. By Wednesday all six computershad failed, leaving the ISS without access to its Russian attitude controlsystem that uses thrusters to orient the orbital laboratory.
Instead,the station relied on its U.S.-built control moment gyroscopes and used theAtlantis shuttle?s thrusters as a backup. But the Russian attitude controlsystem is expected to be required once Atlantis undocks next week, since theactivity typically overwhelms the capacity of the U.S. gyroscopes, NASA hassaid.
Astronautsaboard the space shuttle Atlantis continue to conserve their spacecraft?s powersupplies in case their mission is extended one day to help support ISS attitudecontrol, NASA said.
Meanwhile,engineers at NASA and their Russian counterparts have been hard at work onalternative attitude control methods, such as using docked Russian crew andcargo ships. While efforts will not stand down until ISS managers confirm theRussian computers are fully functional, there is some ease of tension in theranks, Suffredini said.
?I thinkthat there?re a lot of folks that are working on the teams?that feel a certain amountof relief that they won?t have to implement some of the things they?re lookingat,? he added.
NASA isbroadcasting the space shuttle Atlantis' STS-117 mission live on NASA TV. Click here for mission updates andSPACE.com'svideo feed.
- SPACE.com Video Interplayer: Space Station Power Up with STS-117
- Complete Shuttle Mission Coverage
- All About the International Space Station
