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.
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