The Discovery astronauts may be asked to collect a sample of the presumed grease seen inside the space station's left-side solar alpha rotary joint. NASA managers have not made a final decision, but engineers would like to get a sample to pin down where the grease might be coming from and astronaut Michael Fossum will be in the area during a third and final spacewalk Sunday.

"There is some discussion about potentially going back and looking at the port SARJ on EVA-3," Flight Director Annette Hasbrook said late today. "Some folks are interested in getting a sample of the grease that was seen. That is still very preliminary and that request will be taken to mission managers tomorrow morning for discussion. We need to be prepared to give the crew a briefing message on that so we are preparing a package for the crew telling them what we'd have to do if that decision is made to go out and re-inspect the port SARJ."

The station has two SARJ mechanisms, one on each side of the main solar power truss, that are designed to rotate outboard solar arrays like giant paddle wheels to track the sun. Each joint features a motor-driven 10-foot-wide gear that is gripped by 12 trundle bearing assemblies. The port SARJ is working normally, but the right-side SARJ has suffered major erosion of its bearing surface that has generated extensive metallic contamination.

During a spacewalk Tuesday, Fossum tested techniques for cleaning up the contamination and carried out a quick inspection of the left SARJ during a spacewalk Thursday. During a previous inspection of the port SARJ, grease was noted on the bearing surface. Engineers believe it may be coming from one or more trundle bearings and that it may be beneficial in slowing or preventing the sort of surface breakdown that has damaged the right-side gear.

In any case, engineers are not sure where the grease is coming from and a sample would help resolve the issue.

The astronauts were also asked to use a digital camera with a telephoto lens to take photographs of two of Discovery's wing leading edge panels. The shuttle's nose cap and wing leading edge panels endure the most extreme heating during re-entry and they are normally scrutinized with a laser scanner and high resolution cameras the day after launch.

But Discovery was launched without its heat shield inspection boom. The Kibo lab module it carried to the station was too big to include the boom and the crew of a shuttle mission in March left theirs behind for Discovery. It was retrieved during Tuesday's spacewalk and it will be used after undocking for a detailed inspection.

In the meantime, engineers are evaluating other photographs and data from sensors mounted behind the leading edge panels. Readings from one sensor showed a "spike" of 1.4 Gs during a flip maneuver during the shuttle's final approach to the space station.

"There's been a request that you take some 800-millimeter photos of the starboard wing RCC panels 15 and 16," mission control radioed. "During your RPM (rendezvous pitch maneuver) on flight day three, we saw some pulses from the wing leading edge sensors, something on the order of about 1.4 Gs. Now that's normally in family, nothing that would cause any alarm all by itself, however we did not have all the wing leading edge sensors turned on. So 1.4 Gs, if that was the panel where the pulse originated, wouldn't be a big deal. But there's a chance that pulse originated from a panel that didn't have a wing leading edge sensor. Given the inverse square law and the damping, we don't have a whole lot of insight into how big that pulse would have been. That's why we want to take the pictures.

"There is not a high level of concern about this, but we do need to run this to ground and this data will help us close this out."

Additional coverage for subscribers:
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VIDEO: RIGHT-HAND BOOSTER CAMERA LOOKING UPWARD PLAY
VIDEO: RIGHT-HAND BOOSTER CAMERA LOOKING DOWNWARD PLAY

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