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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