LIVE: STS-120 Flight Day 14 - Undocking - Flyaround - Late Inspections

[ChrisC]

Lee Jay - 5/11/2007  7:49 PM
I think the repair looks surprisingly good from a distance, and more importantly it's functional.  I *think* this one is a post-tensioning closeup.
http://spaceflight1.nasa.gov/gallery/images/shuttle/sts-120/hires/iss016e009201.jpg

I think you think wrong.  The cufflinks aren't taught, certainly not as flat against the blanket as in this flyaround shot:
http://spaceflight.nasa.gov/gallery/images/shuttle/sts-120/hires/s120e008602.jpg
I think your shot was taken from inside the station.

Seconding the hope for a shot of the backside of the repair!

[Avron]

Chris Bergin - 5/11/2007  1:19 PM

SARJ inspection may be in a stage, or later flight, unlikely to be STS-122.

Wonder how long it will take to determine the issue using the tests on the metal partials returning  on 120.. they must be able to get close. Then based on that its either a long hunt (inspection of bearings) or a R&R of one of the two drives..( my money is on the drives - me thinks a small miss-alignment  - I know that bearing have had more press but thats an easy route)   the cleanup plan is something that I look forward to reading more on.

[MKremer]

Avron - 5/11/2007  8:27 PM

Chris Bergin - 5/11/2007  1:19 PM

SARJ inspection may be in a stage, or later flight, unlikely to be STS-122.

Wonder how long it will take to determine the issue using the tests on the metal partials returning  on 120.. they must be able to get close. Then based on that its either a long hunt (inspection of bearings) or a R&R of one of the two drives..( my money is on the drives - me thinks a small miss-alignment  - I know that bearing have had more press but thats an easy route)   the cleanup plan is something that I look forward to reading more on.

My money's on a bad bearing and the metallic residue is from the worn rollers and race within it.

Regardless, once they open the panel to the location of the bad assembly in question there'll be no mistaking the culprit because of the large amount of metallic detritus around and in it.

How they plan to clean up the outer races (and with what) will be interesting to find out.
IMO, they also have to plan for replacing some of the thrust bearings and maybe even a DLA to ensure any metallic residue within them could cause a failure of bearings or gears by gradual wear from any existing metal 'dust' that migrated into internal parts.

[daveglo]

I'd agree with the bad bearing call.  A failed DLA would show damage on the gear teeth, not the bearing surface.  One bad bearing is all it takes.  Of course, the question is, why did the bearing fail?  And, what does that failure mode lead to on the other 23 bearings (12 per SARJ)?

Assuming the vast majority of the detritus is ferrous (based on the on-orbit testing), a good magnet should be able to retrieve most of the filings.  But only most, not all.  The remaining life of the exposed bearings is seriously in question.  In my mind, I think the proper solution will be to identify the failed bearing, R&R it, clean the SARJ (as much as possible), flip the DLAs, and run on the inboard race.  This assumes the failure is a one-off, and not a generic bearing problem.

[ETEE]

I'd be surprised if NASA considers they can actually clean up a SARJ on orbit.  As has been said already, one particle left inside the mechanism would be another potential failure.  I suspect the best solution will be to R&R the joint, bring the old one back to checkout thoroughly and refurbish as a spare.

[DaveS]

ETEE - 6/11/2007  1:04 PM

I'd be surprised if NASA considers they can actually clean up a SARJ on orbit.  As has been said already, one particle left inside the mechanism would be another potential failure.  I suspect the best solution will be to R&R the joint, bring the old one back to checkout thoroughly and refurbish as a spare.

That will not be an easy task both in terms of disassenbling it during many many EVAs and finding space on a shuttle mission.

[hutchel]

DaveS - 6/11/2007  7:09 AM

ETEE - 6/11/2007  1:04 PM

I'd be surprised if NASA considers they can actually clean up a SARJ on orbit.  As has been said already, one particle left inside the mechanism would be another potential failure.  I suspect the best solution will be to R&R the joint, bring the old one back to checkout thoroughly and refurbish as a spare.

That will not be an easy task both in terms of disassenbling it during many many EVAs and finding space on a shuttle mission.

If I've understood everything said about it so far, the only parts that can be replaced are the bearings and the motors - the race/gear teeth are PERMANENT - that's why they built it with 2 sets.  Can't bring the whole thing back - that would mean bringing S2/3 home.  That would pose some problems I would think - I guess S4 could go on Z1 for a while but I don't think it was ever envisioned that it could go there - I will leave it to more knowledgable folks to clarify all of the issues involved.

Lee