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 the June

shuttle mission to the orbital laboratory.

ISS engineers are eyeing odd readings in cables and

corrosion in an electronics box


potential culprits 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,”

Kirk Shireman, NASA’s deputy ISS program manager, said 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 BaikonurCosmodrome in Kazakhstan and dock at the ISS a few days later.

NASA’s STS-118 crew is set to launch aboard Endeavour

Aug. 7.

“It’s likely that we’ll actually perform some of the maintenance activities while we are docked during STS-118,” Shireman said.