NASA engineers
and their Russian counterparts are closing in on the source of a major computer
glitch that afflicted the International Space Station (ISS) during last month's
shuttle mission to the orbital laboratory.
ISS
engineers are eyeing odd readings in cables, as well as corrosion in an
electronics box, as a potential culprit for last
month's failure of control and navigation computers in the station's
Russian segment during NASA's STS-117
construction mission.
"We know
something is definitely anomalous in these areas," said Kirk Shireman, NASA's
deputy ISS program manager, in a recent mission briefing. "Is that the only
problem? We're still looking at that."
The
targeted cables and electronics box, known as a BOK 3 unit, both feed into the
station's six-computer network governing Russian control and navigation
systems, Shireman said.
The
computers, which oversee the station's Russian-built command systems, vital
life support hardware and attitude control thrusters, failed as the shuttle
Atlantis' astronaut crew installed and activated a new pair of starboard-side
solar arrays at the ISS. The glitch left the orbital laboratory temporarily
dependent on its U.S. segment and Atlantis' thrusters for attitude control. ISS
Expedition 15 commander Fyodor Yurchikhin and flight engineer Oleg Kotov later reactivated
the ailing computers, using jumper cables to bypass faulty surge
protector-like secondary power sources in each of the machines.
Engineers
initially suspected the glitch stemmed in some part from changes to the station's
environment or power grid after Atlantis astronauts installed a new 17.5-ton
pair of starboard trusses and unfurled two new solar wings.
"At this
point in time, it's looking like that was not the cause," Shireman said, adding
that engineers continue to look at all possible sources. "But we haven't
dismissed it."
In its
current configuration, the repaired ISS computer systems are capable of supporting
NASA's planned STS-118 shuttle mission to the station in early August, mission
managers said.
Commanded
by veteran shuttle flyer Scott Kelly, shuttle Endeavour
and its STS-118 crew will deliver more than two tons of cargo to the
station, as well as a new spacer piece of the outpost's starboard-side truss
and a host of spare parts. Endeavour's crew also includes NASA's first educator
astronaut Barbara Morgan, who first joined NASA more than 20 years ago as the
backup flyer for the agency's Teacher in Space program before the 1986
Challenger accident.
ISS engineers,
however, continue to discuss whether to send replacement parts for the
afflicted cables, BOK 3 unit or computers themselves to the ISS aboard the
unmanned Russian cargo ship Progress 26 before Endeavour's crew reaches the
orbital laboratory. The automated supply ship is slated to launch Aug. 2 from
Baikonur Cosmodrome in Kazakhstan and dock at the ISS a few days later.
NASA's
STS-118 crew is set to launch aboard Endeavour on Aug. 7.
"It's
likely that we'll actually perform some of the maintenance activities while we
are docked during STS-118," Shireman said.
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