Author Topic: SCRUB: SpaceX Falcon 9/Dragon COTS Demo (C2+) LAUNCH ATTEMPT 1 UPDATES  (Read 192624 times)

Offline sdsds

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If it were me, I wouldn't just say a check valve 'failed' even if I saw a broken spring as the cause, because then I'd be concerned on the whole batch

Maybe the quick fix is because they have seen this failure mode before? If they have an estimate of its frequency of occurrence they could be confident with a same-batch replacement.
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Offline FinalFrontier

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Elon just tweeted: 

Engine pressure anomaly traced to turbopump valve. Replacing on engine 5 and verifying no common mode.




Well that's unfortunate. That's really unfortunate.

Swapping is fine but that doesn't explain why the valve failed or what precisely went wrong with it. And that's not exactly a small or non critical valve, its a critical component.


Going to have to see where this leads. Agree with edkyle that I will also be sleeping in on Tuesday. I don't see them making the 22nd.


Just got back from work (additional day today, wonderful I know  :P ) and figured I would chime in.


Really not happy to see that the issue was with a component like that, but I am still glad the vehicle and team preformed as planned and the vehicle remained safe.
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Offline FinalFrontier

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If it were me, I wouldn't just say a check valve 'failed' even if I saw a broken spring as the cause, because then I'd be concerned on the whole batch

Maybe the quick fix is because they have seen this failure mode before? If they have an estimate of its frequency of occurrence they could be confident with a same-batch replacement.


Personally, I would be concerned about other failures as a result. For example, what if there is an unknown risk of pieces of the valve/spring/(ect) breaking off and entering the pump if the same failure mode occurs? What if the batch is bad, we swap, and then that happens?

You do have a point but there are risks to that approach. Anytime something like this fails (my personal opinion) would be that its best to determine why rather then just swapping parts. But that's just me, can't speak to what SpaceX will do or has done in the past.
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Offline kevin-rf

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Well that's unfortunate. That's really unfortunate.

Swapping is fine but that doesn't explain why the valve failed or what precisely went wrong with it. And that's not exactly a small or non critical valve, its a critical component.
 

I would like to make a few points on that.

1. They have not replaced the valve yet, so they have not done an analysis and learned why it "failed". Until that part has been removed and the analysis is done, everything is an educated guess. So there is no reason to be disappointed in them for this scrub.

2. They do not have to fully share the failure mode with us, only give a satisfactory answer to NASA on why they scrubbed.

3. Was the quote from SpaceX that it would have been a LOM if they had not scrubbed even accurate? That originally came very soon after the scrub from a SpaceX employee who's job it was to interface with the press and public. They are repeating what they have been told by other members of the team one would assume the managers pressed for answers on what just went wrong. It makes a nice quote, but did they at that point even know enough to make that statement?
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Offline Ronsmytheiii

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SpaceX statement:

Today’s launch was aborted when the flight computer detected slightly high pressure in the engine 5 combustion chamber. We have discovered root cause and repairs are underway.

During rigorous inspections of the engine, SpaceX engineers discovered a faulty check valve on the Merlin engine.  We are now in the process of replacing the failed valve.  Those repairs should be complete tonight.  We will continue to review data on Sunday.  If things look good, we will be ready to attempt to launch on Tuesday, May 22nd at 3:44 AM Eastern.

The real question is whether SpaceX will investigate all of the similar check valves on the rest of the engines on this vehicle, as well as the rest of the MErlin Engines produced and valves procured.  THat was definitely something we would see on shuttle, but then again it is a commercial venture.

Would love to see a report on the issue just like shuttle, but that would probably be proprietary.

Offline Antares

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SpaceX won't.  Others would.  Goodness of either approach depends on what is important to the observer.
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Offline pippin

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Well, as long as you don't know exactly what was the fault in the valve and don't have a better design to replace it there is little sense in changing all of them, isn't there? After all, the ones in the engines right now are tested and why would a new one be any better as long as it's the same design/production run?
If you can identify a systematic issue you can mitigate it makes sense to change all valves, and given the fact that it seems to be something you can do in a day I would guess SpaceX would do that, they don' want to lose missions or launch opportunities, too, but if you can't, there's no sense in changing something that has worked so far for something you don't know whether it's better or not.
« Last Edit: 05/20/2012 09:18 am by pippin »

Offline manboy

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There is a discussion thread, please take this there.
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Offline MP99

There is a discussion thread, please take this there.

I've responsed in the discussion thread.

http://forum.nasaspaceflight.com/index.php?topic=28486.msg900578#msg900578

cheers, Martin
« Last Edit: 05/20/2012 10:45 am by MP99 »

Offline MP99

Normal ignition for all nine engines. 5 started fine then started trending high.

Vehicle was held down at all times.

High pressure could be high temps/low fuel in combustion. Prevalve was fully open (nominal). Need to look at the data.


SpaceX statement:

Today’s launch was aborted when the flight computer detected slightly high pressure in the engine 5 combustion chamber. We have discovered root cause and repairs are underway.

During rigorous inspections of the engine, SpaceX engineers discovered a faulty check valve on the Merlin engine.

Are prevalve & check valve the same thing?

cheers, Martin

Offline JayP

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Normal ignition for all nine engines. 5 started fine then started trending high.

Vehicle was held down at all times.

High pressure could be high temps/low fuel in combustion. Prevalve was fully open (nominal). Need to look at the data.


SpaceX statement:

Today’s launch was aborted when the flight computer detected slightly high pressure in the engine 5 combustion chamber. We have discovered root cause and repairs are underway.

During rigorous inspections of the engine, SpaceX engineers discovered a faulty check valve on the Merlin engine.

Are prevalve & check valve the same thing?

cheers, Martin

No. The pre-valve is an actuated valve upstream of the engine that opens to allow fuel to flow to the engine itself. A check valve is a passive, one way device that does not allow the fluid flow to reverse. There are a few common ways to design a chck valve, so no telling exactly what went wrong with it, but it sounds like something prvented it from fully opening which led to a low flow rate.

Offline clongton

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My biggest concern is that there are 8 other identical check valves in the vehicle. I hope they plan to borescope all of them.
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Offline Zed_Noir

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Just out curiosity. How much does it cost for one of these check valve in the Merlin engine? Is it tens, hundreds or thousands of dollars per valve.

Offline Lee Jay

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My biggest concern is that there are 8 other identical check valves in the vehicle. I hope they plan to borescope all of them.

Aren't there 9 more?  Isn't the upper stage engine identical except for the nozzle?

Offline robertross

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Just out curiosity. How much does it cost for one of these check valve in the Merlin engine? Is it tens, hundreds or thousands of dollars per valve.

Probably in the range of $200 to $600 each, more for any documentation & testing you would want done to them (before installation). Lots of variables though: materials of construction, connection method, whether it has soft seals or metal seats...

It matters not. It could just be a one of situation. And you could pay $1, $10,000 or $1M and it could still fail.

Considering how far SpaceX have come, so quickly, is a testament to the knowledge & experience of the people they have. I'm sure they will do what they feel is best to move forward.

Offline Nickolai

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My biggest concern is that there are 8 other identical check valves in the vehicle. I hope they plan to borescope all of them.

Aren't there 9 more?  Isn't the upper stage engine identical except for the nozzle?

There are other differences in the upper stage engine, most notably I believe it is capable of throttling. Since throttling involves lowering the flow rate of all components (including and especially the turbopump), it's hard to say how similar the plumbing of the two engines really is.

Offline JohnFornaro

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Swapping is fine but that doesn't explain why the valve failed or what precisely went wrong with it.

FWIW, swapping "on the pad" is something that I think is pretty cool and quite an accomplishment.  I don't know the particular risk statistics whatsoever, but if there is confidence in the utility of the replaced part, it could be swapped, and the reason for the failure studied at a later time.

I think I'm saying more or less the same thing as sdsds:

Quote from: sdsds
Maybe the quick fix is because they have seen this failure mode before? If they have an estimate of its frequency of occurrence they could be confident with a same-batch replacement.
Sometimes I just flat out don't get it.

Offline Jim

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FWIW, swapping "on the pad" is something that I think is pretty cool and quite an accomplishment. 


It is actually done in the hangar.

Offline oiorionsbelt

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Have they rolled back?

Offline ugordan

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The SFN feed still shows it vertical at the pad.

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