This
story was updated at 3:49 p.m. EDT.
HOUSTON --
Russian and U.S. engineers are drawing up plans to work around the failure of
critical computers aboard the International Space Station (ISS) in time for the
departure of the shuttle Atlantis next week.
NASA's ISS
program manager Mike Suffredini said engineers are studying alternatives to
help maintain control of the space station's orientation, including using
rockets aboard docked Russian spacecraft, once Atlantis' STS-117 crew casts off
from the orbital laboratory on June 19.
"The
highest priority would be maintaining attitude once the shuttle has departed,"
Suffredini said Friday.
The space
station's six Russian computers governing control and navigation systems went
offline Wednesday, leaving the outpost unable to use Russian-built
thrusters to maintain its orientation as it flies through space.
The station
is currently relying on U.S.-built control moment gyroscopes, with thrusters
aboard NASA's visiting shuttle Atlantis as backup. After the shuttle undocks,
however, the station's gyroscopes are expected to be overwhelmed, or saturated,
and have typically used Russian-built rockets to compensate.
Suffredini
said that engineers are studying options to use thrusters aboard the
Russian-built Soyuz spacecraft or two Progress cargo ships to dampen the
station's momentum after Atlantis undocks in case the computer issue is not
resolved by then. The computer issue is not one which threatens the station or
its crew, he stressed.
"There is
nobody in this agency and, as far as I know in the Russian agency, that thinks
that this vehicle is at risk of being lost," Suffredini said, adding that there
are no plans in work to for the station's Expedition 15 crew abandon the
outpost. "I fully expect us to repair this problem."
Mission
managers are also considering moving up the launch of the next Russian Progress
ship from August to July 23 to deliver spare parts for the computers, some of
which appear to have failed secondary power supplies.
Some
causes ruled out
Mission
managers have ruled out interference from power lines between the station's new
starboard solar arrays and the station's Zvezda service module, which houses
the computers.
On Friday,
ISS flight controllers also ordered a spacewalking Atlantis astronaut Jim
Reilly to disconnect an unused power cable on the station's new Starboard
3/Starboard 4 truss segment - which he connected during a June 11 spacewalk.
The Russian computer systems appeared to begin experiencing difficulties when
the cable was first attached, Suffredini said.
"This is a
case where it's circumstantial," he added. "We don't know if that's the
cause."
The
computer failure has also left the station's primary oxygen generator, the
Russian-built Elektron, offline since it requires computer control, Suffredini
said. But a new U.S oxygen generator is expected to be activated following a
spacewalk today to install a hydrogen vent valve, and the station has a
sufficient supply of stored oxygen aboard to maintain its three-man crew, he
added.
When
Atlantis launched towards the ISS on June 8, the station carried enough oxygen
supplies to support 10 astronauts for 56 days, mission managers said, adding
that those supplies would support three astronauts for a longer period.
Overnight
trials
Overnight
efforts to recover six computers failed to return them to full operations,
though power was restored to one command computer before troubleshooting
efforts stood down.
"We ended
up in the configuration that we started out the day in, which is unfortunately
not having a central computer or a terminal computer," said NASA ISS flight
director Holly Ridings early Friday.
Late
Thursday, ISS astronauts scanned power lines to the Russian segment from the
space station's U.S.-built solar arrays for any signs of interference, and ultimately
disconnected cables transporting power from the newly
installed starboard solar arrays to the orbital laboratory's Russian
modules. Engineers hoped the work would help determine if electromagnetic
interference or possible "noise" in the power feed from new starboard solar
arrays were a contributor to the station's computer woes.
"The
engineers looked at that data and they did not find anything that was grossly
off-nominal," Ridings said. "It would have been nice to find a smoking gun, but
that's usually not how these things work."
Engineers
restored power to one of the balky computers and briefly found a 'heartbeat'
signaling its availability before standing down on troubleshooting efforts for
the day, Ridings said.
NASA hopes
to resolve or workaround the computer issue by the time Atlantis undocks from
the ISS on June 19, though mission managers are studying the possibility of
keeping the shuttle at the ISS for an extra if needed.
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