Atlantis heading home – ISS troubleshooting latest

by Chris Bergin

Atlantis’ ride home on top of NASA Shuttle Carrier Aircraft (SCA) has finally begun at 6am Sunday morning Californian time, taking off from Edwards Air Force Base, with arrival back in Florida due for noon Monday.

Meanwhile, Russian technicians are still unsure as to the exact cause of the computer failure onboard the International Space Station (ISS), but believe they are closing in on the issue – as on orbit testing continues.

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Atlantis was due to leave the Dryden Flight Research Center (DFRC) at Edwards Air Force Base in California around 8am local time Saturday, following overnight mating operations, which started around midnight last night.

It is not known what the exact nature of the technical issue relates to, apart from being associated to the completion of mating operations.

USA (United Space Alliance) information at 8am Eastern then claimed the departure was reset to Sunday, with Dryden later confirming.

‘Turnaround ops at DFRF remain in work. Scheduled departure 1st shift Sunday,’ noted USA information. ‘Scheduled arrival at KSC 1st shift Monday.’

The duo eventually took off at 9am Eastern, heading to Texas for a fuel stop.

Atlantis was originally set to leave on Friday, but issues with the retraction of Atlantis’ landing gear hydraulics and a damaged left hand ‘salad bowl’ joint delayed the continuation of mating operations by 24 hours, before the extra wait until Sunday. These issues were classed as resolved in later information.

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Meanwhile, on the ISS, Expedition 15 commander Fyodor Yurchikhin and engineer Oleg Kotov have been carrying out instructions by Russian engineers on the ground, as they try to find out what caused the computer malfunctions during STS-117.

So far a root cause has not been found, although the Russians believe they are starting to isolate the issue to computer circuitry resistance (impedance) – which is the focus of their current troubleshooting.

‘Yurchikhin and Kotov, with ground support, continued the extensive troubleshooting of the TVM (Terminal) and TsVM (Central) computers of the RS (Russian Segment),’ noted a latest On Orbit Status report.

‘They focused on the cables in the SM associated with the TVM/TsVM operation, testing their shielding capability both for the ‘Start’ and ‘Stop’ circuits, and on the connectors in the associated multi-contact sockets for TVM1, TVM3, TsVM2 and TsVM3, using resistance (impedance) measurements to look for disconnected connectors.

‘Yesterday’s resistance/continuity tests on the TVM2 data processing lane’s ‘start/stop’ control circuitry had indicated all measurements to be nominal except those across the contacts of the ‘stop’ relays which should have indicated completely open but showed partially closed contacts on at least two ‘stop’ relays.

‘This could be a possible explanation of the failure of the TVM2 start-up attempt on 6/21. The search for the root cause is continuing.’

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