ISS Spacewalk completed – SARJ results show promise following STS-126 work

by Chris Bergin
Expedition 18 crewmembers Yury Lonchakov and Michael Fincke have performed a Russian spacewalk (ISS RS EVA-21), which has included the installation of a probe to aid the on-going investigation into the off-nominal re-entries of two Soyuz vehicles. Meanwhile, the continued assessments into work conducted during STS-126’s EVAs on the Solar Alpha Rotary Joints (SARJs) are showing positive results.
The Expedition 18 spacewalk was conducted in Orlan-M spacesuits, as the duo egressed from the Pirs airlock early on Tuesday morning (UTC).

Their tasks included the installation of the Langmuir Probe on the DC1 Docking Compartment, which will be used to measure plasma fields close to Soyuz, in support of the ongoing pyro bolt anomaly investigation.

The issue centers around the problematic pyrotechnic bolts that separate the crew Descent Module from the Service Module, with the latest thinking surrounding potential issues between the hardware and the long-term exposure to electromagnetic emissions on-orbit, which may be responsible for the issues that were most recently suffered by Soyuz TMA-11.

Back in September, Sergei Volkov and Oleg Kononenko conducted EVA 20A, which included the removal of one of 10 pyrotechnic bolts from the docked Soyuz TMA-12. That vehicle re-entered without issue.

The Langmuir Probe will be able to take specific measurements of the electromagnetic environment from its location just above the Soyuz docking port. The probe’s resulting data will be added to the investigation findings, though no date has been given for the conclusion of the assessments.

Other tasks conducted during the EVA involved scientific equipment being installed on the outside of the International Space Station (ISS), including EXPOSE-R and IPI-SM scientific equipment (Impuls experiment) taking up residence on the Zvezda module. However, issues with the connectors meant EXPOSE-R had to be returned to the airlock, with two get-ahead tasks being lost due to the amount of lost time durng initial troubleshooting.

Meanwhile, NASA managers are continuing to receive positive results from STS-126’s clean and lube work during its four EVAs on Station.

Tests continue to take place on the ISS’ starboard SARJ, which underwent an autotrack test of two full orbits shortly after STS-126’s spacewalk work, which also including the changeout of its Trundle Bearing Assemblies (TBAs).

The latest information on the status of the repair was noted in a recent 8th Floor News internal update.

“Starboard SARJ TBA replacement and grease results: Status briefing on the initial quick look results of the Starboard SARJ rotations and disturbances seen after the ring was lubricated and the TBA’s were changed out,” noted the information on L2.

“The disturbances seen by starboard SARJ motion have greatly decreased based on the two orbits of autotrack that were performed immediately post R&R. The team requested an extended autotrack to obtain more data and determine if the disturbances drop even lower after a long period of operation and distribution of the grease due to rotation.”

These results are vital for the forward plan on ensuring the rotation of the giant Solar Arrays can be carried out without the situation worsening, but also on the required maintenance of the SARJ, which will require lubrication ahead of the current plan to install a replacement race ring called SARJ XL.

However, the results are so positive, SARJ XL may not even be required, as noted via the 8th Floor News information.

“Team is developing a lube rig design that will be used to evaluate the life of a greased ring to determine how long it will be until team is concerned with roller tipping and when the ring should be relubricated,” added the 8th Floor.

“The Board also tasked the SARJ team with identifying a test or series of tests that will identify if the program can live with the existing degraded joint vs having to invest in the SARJ XL modification – which inserts a third race ring into the joint as a replacement for the currently spalled race ring.”

SARJ XL has already been checked over on the ground and is deemed good to fly if required. Should it take a ride to the ISS, it will fly on one of the final missions on the ‘current’ shuttle manifest, in 2010.

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