SCRUB: SpaceX Falcon 9/Dragon COTS Demo (C2+) LAUNCH ATTEMPT 1 UPDATES

[Lee Jay]

Where did you get this "SpaceX quote stating LOM" from? That never happened. Moving on.

4:08 into the post-abort briefing, it was stated that they need all 9 engines to liftoff, and that's why they aborted.  The implication is that losing one at or soon after liftoff results in LOM.  Of course, now Elon is saying they would have completed the mission with the bad valve.

[DaveH62]

Is Elon saying it would have made it with 8 engines? Sounds like he is implying the engine wouldn't have failed, in spite of the issue.
Is it possible the engine would have functioned in spite of the check valve issue? Early conjecture was that it would not. Is there any reason to now think the engine would have worked?

[Robotbeat]

Where did you get this "SpaceX quote stating LOM" from? That never happened. Moving on.

4:08 into the post-abort briefing, it was stated that they need all 9 engines to liftoff, and that's why they aborted.  The implication is that losing one at or soon after liftoff results in LOM.  Of course, now Elon is saying they would have completed the mission with the bad valve.

I think that meant they could've lasted with the bad valve until they could afford to shut off the engine. Nothing even close to an ideal scenario (and that is just a prediction, who knows what would've happened if it had actually flew), and it may have meant Dragon would've needed more propellant.

The good thing is that no vehicle was lost here, but they still have learned a great deal. Learning about a failure mode without losing a vehicle is a big plus compared to not learning about it or learning about it after losing a vehicle. Probably also means they'll take engine-out capability seriously and test it more thoroughly than they otherwise would've.

[ugordan]

Keep in mind that redlines for launch commit are likely not the actual physical limits of the engine (otherwise they wouldn't have been tweaking them in previous attempts) and it's possible that the engine would have settled into a different regime than nominal, but still operating OK. After all it is a gas generator cycle with reportedly good margins, it's not running on the bleeding edge of performance.

Still, simulation is one thing, test stand run is another. A moot point now, anyway.

[ugordan]

Florida Today has some details on the valve:

SpaceX spokeswoman Kirstin Grantham said a valve on a nitrogen gas line used to purge the Merlin engine before ignition remained stuck open.

Tests performed Sunday appeared to show the new valve working properly and no evidence of similar problems on the eight surrounding engines.

[Garrett]

Florida Today has some details on the valve:

SpaceX spokeswoman Kirstin Grantham said a valve on a nitrogen gas line used to purge the Merlin engine before ignition remained stuck open.

Tests performed Sunday appeared to show the new valve working properly and no evidence of similar problems on the eight surrounding engines.

Ok, so the extra N₂ flow resulted in the higher pressure readings, right?
I presume the only effect of an open N₂ purge would have been a (slightly) lower engine performance during the initial seconds of launch? I'm assuming that the N₂ supply would have been close to empty at T-0.

Question: does the N₂ for purging the pumps come from onboard tanks or from an umbilical link to the pad?

[Jim]

Question: does the N₂ for purging the pumps come from onboard tanks or from an umbilical link to the pad?

pad

[jongoff]

Florida Today has some details on the valve:

SpaceX spokeswoman Kirstin Grantham said a valve on a nitrogen gas line used to purge the Merlin engine before ignition remained stuck open.

Tests performed Sunday appeared to show the new valve working properly and no evidence of similar problems on the eight surrounding engines.

Wow, I guessed it pretty well. Now my only question is if it was a purge going into the Gas Generator fuel feed (my guess) or the main propellant injector.

~Jon

[Rocket Science]

Any history on that valve, was it made in house or vender supplied?

[Garrett]

Question: does the N₂ for purging the pumps come from onboard tanks or from an umbilical link to the pad?

pad

thought so, thanks.
Don't know why I said "pumps" above. I somehow got it into my head that it was the turbopump purge. Did I just imagine that I saw "pump" mentioned somewhere? Do the turbopumps have a purge line?
(Jon Goff only mentioned a gas generator fuel feed or the main propellant injector in his post above)

[Garrett]

Question: does the N₂ for purging the pumps come from onboard tanks or from an umbilical link to the pad?

pad

also, a follow up question:
when the umbilicals are released, I presume another valve on the purge line closes at the attachment point? If that's the case, then would I be right in assuming that any problems caused by the faulty check valve would cease to exist after umbilical detachment?

[Herb Schaltegger]

Any history on that valve, was it made in house or vender supplied?

Someone posted a link (in this thread or one of the others - can't recall) to a page for a component manufacturer that seems to indicate these valves are made by vendors. Probably a good call - flow control valves, check valves, transducers, couplings . . . all these things are semi-standardized, in that there are a several aerospace industry stalwarts who have a long history of manufacturing parts like that, are all familiar with the industry and government/NASA/milspec standards, are all familiar with the certification processes and procedures, etc.  They also all have in-house testing facilities for development and acceptance testing if required. No need to reinvent the wheel for every single component.

[Rocket Science]

Any history on that valve, was it made in house or vender supplied?

Someone posted a link (in this thread or one of the others - can't recall) to a page for a component manufacturer that seems to indicate these valves are made by vendors. Probably a good call - flow control valves, check valves, transducers, couplings . . . all these things are semi-standardized, in that there are a several aerospace industry stalwarts who have a long history of manufacturing parts like that, are all familiar with the industry and government/NASA/milspec standards, are all familiar with the certification processes and procedures, etc.  They also all have in-house testing facilities for development and acceptance testing if required. No need to reinvent the wheel for every single component.

Thanks Herb, I found this in a search, but it speaks about SpaceX making valves their selves. In this case I can’t locate any hard info.

http://forum.nasaspaceflight.com/index.php?topic=27858.msg857256#msg857256

http://www.airspacemag.com/space-exploration/Visionary-Launchers-Employees.html?c=y&page=2

I’m not on a witch hunt, just curious…


~Robert

[corrodedNut]

Question: does the N₂ for purging the pumps come from onboard tanks or from an umbilical link to the pad?

I case you're wondering, IIRC the red bottles attached to the bottom of the second stage perform this function for Merlin Vac.

[Garrett]

Question: does the N₂ for purging the pumps come from onboard tanks or from an umbilical link to the pad?

I case you're wondering, IIRC the red bottles attached to the bottom of the second stage perform this function for Merlin Vac.

I wasn't wondering, but thanks all the same
For some reason I didn't think the second stage engines needed purging, but that's because I don't fully understand all the reasons for purging in the first place. Of course, if they do need purging, then on board tanks make sense, at least for the ascent phase.

[MarekCyzio]

Wow, I guessed it pretty well. Now my only question is if it was a purge going into the Gas Generator fuel feed (my guess) or the main propellant injector.

~Jon

I am not a rocket expert but I bet for gas generator. Why? Low pressure = a broken check valve's leak would not be catastrophic as there is one more valve down the line. If this was a propellant injector purge check valve, pressure in the N2 purge system would probably rip it apart. And Elon said the rocket would fly with the broken valve.

[ugordan]

I case you're wondering, IIRC the red bottles attached to the bottom of the second stage perform this function for Merlin Vac.

I'd think the primary function of those is nitrogen storage for cold gas RCS?

[corrodedNut]

I'd think the primary function of those is nitrogen storage for cold gas RCS?

I thought they used helium for that, Falcon 1 did. But I'm not terribly confident that F9 does. F9 user's guide just says Dracos.

[kkattula]

I wasn't wondering, but thanks all the same
For some reason I didn't think the second stage engines needed purging, but that's because I don't fully understand all the reasons for purging in the first place. Of course, if they do need purging, then on board tanks make sense, at least for the ascent phase.

IANARS, but in case you've got a slow leak through one of your main propellant feeds, purging with inert gas a few seconds before ignition will prevent a hard start, or propellants mixing in places they shouldn't like the pumps, regen passages or injectors.

Also, IIRC, they do a cryo chill down of Merlin before ignition. If that's with LOX, some of it's going to flow back through the RP-1 injector. So you really want to purge the engine after that.

[Norm38]

Also, don't know where your getting the idea that there was a SpaceX quote stating it would be an LOM,  thats totally ridiculous they never said any such thing.

I think it was this quote from Ms. Shotwell during the post-scrub presser:

This is not a failure, this is aborted with purpose, it would have been a failure if we lifted off with this issue.

I took that as LOM when I first heard it.  It's clear now she meant a failure of the launch procedure, not a LOM itself.