Author Topic: Investigation called after STS-127 SSME 1 found to have 100s of leaks (Read 21583 times)

Chris Bergin · « **on:** 09/05/2009 05:22 am »

http://www.nasaspaceflight.com/2009/09/investigation-sts-127-ssme-1-found-340-leaks/

Not good, even had one usually undramatic engineer using phrases such as "we dodged a bullet". If anything it shows these beasts can still perform nominally despite the post flight observations with this SSME.

They'll gain lessons learned and this engine will get a new nozzle ahead of STS-131, providing the investigation doesn't find something wrong in-family.

See next article, link posted on page 2, for update:
http://forum.nasaspaceflight.com/index.php?topic=18669.msg482723#msg482723

Obvious reference back to the Columbia STS-93 event, so the often used clips from the full video on L2 are attached as reference:

Orbiter · « **Reply #1 on:** 09/05/2009 02:05 pm »

Thanks Chris!

If the leaks were more severe, wouldn't Endeavour either lost an engine during the ride up hill (RTLS, TAL, ect) or and RSLS abort on the pad or could it have preformed nominally still?

robertross · « **Reply #2 on:** 09/05/2009 02:23 pm »

Great article Chris.

I hope they can clear the latest engines to fly. This could have a siginificant impact on flow if they can't get this sorted out.

I thought about additonal nickel plating on the nozzle at this late stage to help reduce the chance of corrosion, but obviously a schedule impact since it would require removing the nozzles from each engine. Would probably require re-testing too.

ChrisGebhardt · « **Reply #3 on:** 09/05/2009 02:43 pm »

Quote from: Orbiter on 09/05/2009 02:05 pm

Thanks Chris!

If the leaks were more severe, wouldn't Endeavour either lost an engine during the ride up hill (RTLS, TAL, ect) or and RSLS abort on the pad or could it have preformed nominally still?

Absolutely no way of knowing. It would have completed depended on what time in the flight the engine shut down. However, RTLS and TAL were not the only two aborts modes available to Endeavour. She also had AOA and ATO.

Chris Bergin · « **Reply #4 on:** 09/05/2009 06:02 pm »

Thanks Orbiter and Robert.

collectSPACE · « **Reply #5 on:** 09/05/2009 06:10 pm »

Good article Chris, though I am left wondering about the undramatic engineer.

Quote from: Chris Bergin on 09/05/2009 05:22 am

Not good, even had one usually undramatic engineer using phrases such as "we dodged a bullet".

Jerry Cook, SSME project manager, "characterized the issue as relatively minor" in an interview with Bill Harwood.

Quote

"As a matter of fact, the total leak rate on the nozzle from all these leaks is so small that it's not even the equivalent of one ruptured tube. They are tiny. The total leak rate in the 340 hot wall leaks that we have is 0.6592 pounds per second. So it's not even equivalent of one tube rupture, nothing you could see in the ascent performance going up hill at all."

Chris Bergin · « **Reply #6 on:** 09/05/2009 06:17 pm »

Which is why I didn't use his comments in the article. However, there are a number of engineers who deem this as not being minor, and a failure investigation team suggests this is not minor.

collectSPACE · « **Reply #7 on:** 09/05/2009 06:23 pm »

NASA practically convenes an investigation anytime they cannot immediately explain something happening (as they should), regardless of how minor it may be. This topic deserves attention (hence the "good article") but the anonymous engineer's comment seemed out of place with Cook's account.

Chris Bergin · « **Reply #8 on:** 09/05/2009 07:05 pm »

Quote from: collectSPACE on 09/05/2009 06:23 pm

...the anonymous engineer's comment seemed out of place with Cook's account.

Totally, and it doesn't seem out of place, it is out of place with Cook's comment (which is good!), but one could probably say a few other comments I received, which note the obvious - that leaks on a engine nozzle are never great (added to the removed contamination that "surprised" them when the engine came back with leaks) - are out of place with the characterization of "minor"....as much as the context is minor from a flight safety aspect, so "dodging the bullet" is an incorrect representation by the engineer I mentioned, based on Cook's comments. That's obvious.

However, I have to be open with the readership and mention that one engineer (who I know and trust) actually said that to me (as much as it shocked me). Wrong or right, I'll at least note it, and we are going to follow this up based on the results of the failure investigation team findings.

Would have been irresponsible if I had used that in the article - but I didn't (and wouldn't).

collectSPACE · « **Reply #9 on:** 09/05/2009 07:10 pm »

To be clear Chris, I'm not criticizing you or your including the comment in the thread (and I would commend you for keeping the comment out of the article but that would suggest that you made anything but the obvious choice).

Rather, I was only contrasting the comments by the "undramatic engineer" with Cook's...

Lee Jay · « **Reply #10 on:** 09/05/2009 07:16 pm »

If I understand correctly, this is a zero-fault-tolerant (i.e. safe-life rather than fail-safe) system that does have the capability of causing a loss of vehicle. Said system had an unexpected but non-catastrophic failure. The fact that the experts on the system investigated the corrosion and didn't anticipate this outcome indicates a lack of understanding of the underlying phenomena. That lack of understanding sounds serious to me given the safe-life nature of the system and the fact that the system has the potential to fail in such a way as to lead to a "bad day". I applaud NASA for convening a team to investigate. I hope they can gather sufficient data to drive this one to ground and end the current lack of understanding that led to this result.

Chris Bergin · « **Reply #11 on:** 09/05/2009 07:23 pm »

Quote from: collectSPACE on 09/05/2009 07:10 pm

To be clear Chris, I'm not criticizing you or your including the comment in the thread (and I would commend you for keeping the comment out of the article but that would suggest that you made anything but the obvious choice).

Rather, I was only contrasting the comments by the "undramatic engineer" with Cook's...

No I know, and I appreciate the comments as it gave me a chance to explain to everyone why I posted it....so kinda responding to all.

Plus it's good news per Cook's comments, and that's always going to be welcomed.

dmac · « **Reply #12 on:** 09/05/2009 08:51 pm »

So from what we know could this have caused a LOV going up-hill

Ford Mustang · « **Reply #13 on:** 09/05/2009 10:53 pm »

Highly doubtful. Would have been an engine shutdown first.

kraisee · « **Reply #14 on:** 09/06/2009 04:07 am »

That loss rate would have resulted in somewhere around 300kg of additional LH2 being used during the ~510 seconds flight to orbit, which represents somewhere around 35-40% of typical reserve LH2 on a normal Shuttle flight.

I don't, however, know what the specific margins were for this particular flight though. They might have had greater reserves than normal.

Of course, this is *PRECISELY* the sort of reason why the thing has these reserves in the first place. The overall systems worked as it was supposed to: They experienced a small failure, but the redundancy which is designed into the system allowed the mission to proceed as planned. It did exactly what its supposed to do.

I would have probably phrased it "very glad it wasn't any more serious".

Ross.

sdsds · « **Reply #15 on:** 09/06/2009 04:18 am »

Quote from: kraisee on 09/06/2009 04:07 am

That loss rate would have resulted in somewhere around 300kg of additional LH2 being used during the ~510 seconds flight to orbit, which represents somewhere around 35-40% of typical reserve LH2 on a normal Shuttle flight.

Is there an analysis performed post-flight to estimate how much LH2 and LOX were left in the tank at MECO?

Chris Bergin · « **Reply #16 on:** 09/24/2009 09:18 pm »

Update:

http://www.nasaspaceflight.com/2009/09/adhesive-tape-caused-sts-127-ssme-nozzle-leaks-sts-130-ssme-milestone/

Lee Jay · « **Reply #17 on:** 09/25/2009 02:32 am »

Quote from: Chris Bergin on 09/24/2009 09:18 pm

Update:

http://www.nasaspaceflight.com/2009/09/adhesive-tape-caused-sts-127-ssme-nozzle-leaks-sts-130-ssme-milestone/

So, is this a "shot across the bow" that says any nozzles with a history of this particular adhesive need to be NDE'd very carefully?

William Barton · « **Reply #18 on:** 09/25/2009 12:08 pm »

I'm puzzled that this managed to happen. Sulfur-containing adhesive on a nickle-containing surface. It seems to this non-engineer as the same class of oversight a SpaceX's use of aluminum B-nuts in a salt water rich environment. And it seems likely NASA has a lot more engineers than SpaceX, and a lot more experience with its engines. Is the adhesive new to the program?

Almurray1958 · « **Reply #19 on:** 09/25/2009 01:17 pm »

From the article:NOT new, old. The tape was used in the 1990's. Use was stopped when the risk was determined. A chemical inhibitor was used in 1999 but the nickel was partially compromised. Time and repeated exposure lead to rust and pinholes.

Reminds me of the mid 1990's issue of integrated circuits suddenly failing. Analysis showed it was mild acid, most likely from tiny drops of exhaled spittle from inside the cleanroom that caused the failure. 10 YEARS later.