Author Topic: SCRUB: SpaceX Falcon 9/Dragon COTS Demo (C2+) LAUNCH ATTEMPT 1 UPDATES  (Read 192572 times)

Offline jongoff

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I take it back, the limits are set right to catch a true hardware failure.

But to what degree did the valve fail?  Would 5 have produced no thrust, partial thrust, exploded?  Or could it have sub optimal but stable?

They can't lose an engine at liftoff but can they have a weak one and still get off the pad?  What's the margin?

Well, the typical failure of a check valve is to leak backwards. But a turbopump-fed rocket engine is a complicated enough beast that without knowing a lot about the Merlin's particular design it'd be hard to tell if this would've been benign or something that would've killed the engine.

I just hope they can find a way to design this problem out so it doesn't crop up again.

~Jon

Offline robertross

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I take it back, the limits are set right to catch a true hardware failure.

But to what degree did the valve fail?  Would 5 have produced no thrust, partial thrust, exploded?  Or could it have sub optimal but stable?

They can't lose an engine at liftoff but can they have a weak one and still get off the pad?  What's the margin?

Check valves 'usually' have a spring (or similar device) in them to keep the seated closed, so as to ensure a positive seal, or to create a specific amount of pressure drop as a fluid passes through it.

If the spring mechanism failed, it could have restricted the check valve by preventing it from fully opening, creating the issue of a lean mixture (oxygen rich, assuming it was the fuel check, which corrolates with the issues they have presented).

Offline edkyle99

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They can't lose an engine at liftoff but can they have a weak one and still get off the pad?  What's the margin?

They're at only a 1.2+ish thrust to weight ratio at T-0, so one lost engine would essentially make the rocket too heavy to efficiently lift off.  It would burn a lot of propellant and hardly go anywhere.

Falcon 9 v1.0 burns about 1.45 tonnes of propellant per second.  After about 30 seconds, it has burned enough propellant to offset the loss thrust provided by one Merlin 1C.  And so on.

 - Ed Kyle
« Last Edit: 05/19/2012 11:38 pm by edkyle99 »

Offline edkyle99

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Check valves 'usually' have a spring (or similar device) in them to keep the seated closed, so as to ensure a positive seal, or to create a specific amount of pressure drop as a fluid passes through it.

If the spring mechanism failed, it could have restricted the check valve by preventing it from fully opening, creating the issue of a lean mixture (oxygen rich, assuming it was the fuel check, which corrolates with the issues they have presented).

I wonder if not seating correctly at the last shutdown could also be a possible failure mode.

 - Ed Kyle

Offline Antares

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Hard to say if this would have caused LOM without seeing the data and knowing the engine pretty intimately.  If the engine was trending toward high power, it could've been a runaway condition on the turbopump, which would either cause an immediate rotor RUD or it could settle into an out-of-power condition where some point of flow on the engine chokes and cannot physically increase any more.  That's something that can either be flown through or an eventual RUD due to high stress and fatigue.
« Last Edit: 05/20/2012 08:32 am by Antares »
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Offline spacetraveler

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So it seems that the parameter ranges weren't overly conservative. That's good news imo as it indicates they didn't have a repeat issue of what occurred previously and it shows that their current ranges are effective in discovering actual issues with the engines as it seems this was.

Offline jongoff

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Check valves 'usually' have a spring (or similar device) in them to keep the seated closed, so as to ensure a positive seal, or to create a specific amount of pressure drop as a fluid passes through it.

If the spring mechanism failed, it could have restricted the check valve by preventing it from fully opening, creating the issue of a lean mixture (oxygen rich, assuming it was the fuel check, which corrolates with the issues they have presented).

I wonder if not seating correctly at the last shutdown could also be a possible failure mode.

Depending on the size of check valve, some sort of debris could also cause the valve to not seat properly, which can cause backward leaks. Debris was by far the most common cause of check valve issues at Masten, but there are probably other ways to get a check valve to jam part way open.

~Jon

Offline Thunderbird5

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Hard to say if this would have caused LOM without seeing the data and knowing the engine pretty intimately.  If the engine was trending toward high power, it could've been a runaway condition on the turbopump, which would either cause a immediate rotor RUD or it could settle into an out-of-power condition where some point of flow on the engine chokes and cannot physically increase any more.  That's something that can either be flown through or an eventual RUD due to high stress and fatigue.

Pardon the ignorance, I get 'LoM', but what is 'RUD'?

Offline arnezami

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I was wondering. At some point in the falcon 1 development (I believe it was after the first flight) they extended their parameters (of the engine) that are checked just before launch. Since, if they had done that, they would have detected (and aborted) a corroded nut issue (I believe).

Is it possible SpaceX is now greatly benefiting from that decision, after learning it the hard way?
« Last Edit: 05/20/2012 12:10 am by arnezami »

Offline SpacexULA

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Pardon the ignorance, I get 'LoM', but what is 'RUD'?

Rapid Unscheduled Disassembly
No Bucks no Buck Rogers, but at least Flexible path gets you Twiki.

Offline jabe

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I think RUD is something like rapid undesirable disassembly
Jb
Edit:I was close:)
« Last Edit: 05/20/2012 12:11 am by jabe »

Offline jongoff

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Hard to say if this would have caused LOM without seeing the data and knowing the engine pretty intimately.  If the engine was trending toward high power, it could've been a runaway condition on the turbopump, which would either cause a immediate rotor RUD or it could settle into an out-of-power condition where some point of flow on the engine chokes and cannot physically increase any more.  That's something that can either be flown through or an eventual RUD due to high stress and fatigue.

Pardon the ignorance, I get 'LoM', but what is 'RUD'?

Rapid Unplanned Disassembly

aka Engine Self-Cannibalization
aka Baysplosions

Anyone else have any fun euphemisms for an energetic engine failures?

~Jon

Offline spacetraveler

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Offline Lee Jay

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Anyone else have any fun euphemisms for an energetic engine failures?

At some point, the engine was an assemblage of parts waiting to be put together, i.e. a "kit", much like an R/C airplane kit.  In R/C aircraft, we generally call this "rekitting".

Offline deltaV

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Doesn't the last page of posts belong in the discussion thread?

Anyone else have any fun euphemisms for an energetic engine failures?

I seem to recall reading "engine-rich combustion" or something like that for certain engine failures.

Offline Rocket Science

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“A collection of parts flying in loose formation”… ;D

And now back to our regular un-scheduled updates…
« Last Edit: 05/20/2012 12:40 am by Rocket Science »
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator

Offline robertross

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Check valves 'usually' have a spring (or similar device) in them to keep the seated closed, so as to ensure a positive seal, or to create a specific amount of pressure drop as a fluid passes through it.

If the spring mechanism failed, it could have restricted the check valve by preventing it from fully opening, creating the issue of a lean mixture (oxygen rich, assuming it was the fuel check, which corrolates with the issues they have presented).

I wonder if not seating correctly at the last shutdown could also be a possible failure mode.

Depending on the size of check valve, some sort of debris could also cause the valve to not seat properly, which can cause backward leaks. Debris was by far the most common cause of check valve issues at Masten, but there are probably other ways to get a check valve to jam part way open.

~Jon

Well you would think that the fuel (RP-1) would be filtered via a transfer system prior to entering the rocket, and a coarse screen used at the tank outlet pipe on the off chance the tank wasn't 100% clean or something got past the transfer filter. To me, this seems like an unlikely source, though possible.

Sometimes there are finer screens ahead of critical components in case a component (or part of one) fails. In an engine that has previously fired, something might have dislodged creating this scenario. One would have to believe if these was an issue that cropped up during the last static test, at any point during the firing, they would have noticed something significant in the dta. As it seems likely they didn't, I'm thinking it could have occurred during movement from vertical to horizontal, or back to vertical again, or something failed at the latest engine firing as it started up.

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 (in all engines). If it were debris, where did it come from, and what else could it have affected, and is there more upstream, and is anything now downstream.

I imagine long hours of borescoping just to be sure (but that's just me).

Offline Swatch

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Doesn't the last page of posts belong in the discussion thread?

Anyone else have any fun euphemisms for an energetic engine failures?

I seem to recall reading "engine-rich combustion" or something like that for certain engine failures.

We like to call it HRC... Hardware Rich Combustion.   Gives you GREAT ISP......for about 1 second.

Also, I'm partial to 'punted' pintles...
« Last Edit: 05/20/2012 12:58 am by Swatch »
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Offline dunderwood

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Also, I'm partial to 'punted' pintles...

Occasionally referred to as 'puntles.'

Offline jongoff

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Doesn't the last page of posts belong in the discussion thread?

Anyone else have any fun euphemisms for an energetic engine failures?

I seem to recall reading "engine-rich combustion" or something like that for certain engine failures.

We like to call it HRC... Hardware Rich Combustion.   Gives you GREAT ISP......for about 1 second.

Also, I'm partial to 'punted' pintles...

We once had a punted pintle on an engine where the pintle diameter was bigger than the throat diameter...

...but we probably ought to get back to updates before the moderators take us out behind the woodshed.

~Jon

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