Author Topic: SCRUB: SpaceX Falcon 9/Dragon COTS Demo (C2+) LAUNCH ATTEMPT 1 UPDATES  (Read 192616 times)

Offline wolfpack

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I understood Ms. Shotwell to say that Flight 1 engine 5 was trending high, just not as dramatically or as much as this one because the abort limit was much tighter.

The point though, is that it was trending. That makes twice that engine 5 has shown a high pressure trending problem on start-up, that we know of. How many times have all nine engines been integrated with the fuel tanks and fuel feeds then all nine fired simultaneously?

Fool me once, shame on you, fool me twice, shame on me.



My guess would be 5 is in the center position, so its plume is impinged by the surrounding 8 other Merlins, which lessens the nozzle expansion ratio, and this would make it more likely to run higher Pc. Maybe I've got the physics backwards on that one, I'm an EE not an ME. Anyone?

Offline Avron

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I understood Ms. Shotwell to say that Flight 1 engine 5 was trending high, just not as dramatically or as much as this one because the abort limit was much tighter.

The point though, is that it was trending. That makes twice that engine 5 has shown a high pressure trending problem on start-up, that we know of. How many times have all nine engines been integrated with the fuel tanks and fuel feeds then all nine fired simultaneously?

Fool me once, shame on you, fool me twice, shame on me.



My guess would be 5 is in the center position, so its plume is impinged by the surrounding 8 other Merlins, which lessens the nozzle expansion ratio, and this would make it more likely to run higher Pc. Maybe I've got the physics backwards on that one, I'm an EE not an ME. Anyone?

Thats how I see it,, when have they done a test all up at this time of day with higher density air.. etc.. there must be a backpressure..

Online ugordan

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Err, the plumes don't interact at sea level.

The way I see it, these engines have been through something like 7 ignitions by now - at least - and it's always possible the previous shutdown transients induced some change that didn't register during the actual burn.
« Last Edit: 05/19/2012 04:08 pm by ugordan »

Online Robotbeat

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Each stage has undergone multiple firings in Texas. Also,it's not terribly uncommon to have the same engine give you grief both times. Assuming you have a random engine problem to different launches, the probability of it being the same engine position both times is still one ninth (~11%).
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7 pages late to the party.

Bummed about the abort.

Many thanks to Chris for the forum and the coverage.

Looking forward to May 22.

Rah rah ree SpaceX!
Sometimes I just flat out don't get it.

Offline aero

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Can outside pressure propogate back through the shock at the throat to affect chamber pressure? I don't think so.
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High pressure could be high temps/low fuel in combustion. Prevalve was fully open (nominal). Need to look at the data.


Prevalve, yes, but aren't there are other valves, like the main valves, bleed valves, etc.?

 - Ed Kyle

But watch the presser for that question and that answer. I don't think Ms Shotwell would omit mentioning a problematic valve in relation to the engine by hiding with "Oh, but the prevalve was ok".

The common sense approach on interpretation is sometimes the best approach.

(You watch, they'll find a faulty valve now I've said that! :D)
« Last Edit: 05/19/2012 04:22 pm by Chris Bergin »
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Offline renclod

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Each stage has undergone multiple firings in Texas. Also,it's not terribly uncommon to have the same engine give you grief both times. Assuming you have a random engine problem to different launches, the probability of it being the same engine position both times is still one ninth (~11%).

Combinations of 18 taken 2 at a time =
18! / (2! x 16!) =
18 x 17 / 2 =
153

1 in 153 = 0.0065 = 0.65%


Offline aero

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Question regarding fuel consumption with one or two failed engines. Would an engine out (after launch) have caused the other engines to consume enough extra fuel getting to orbit to spoil the demonstrations planned for today's mission? Or is the first stage fuel not related to the extra fuel needed for the demo?
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Offline aero

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Each stage has undergone multiple firings in Texas. Also,it's not terribly uncommon to have the same engine give you grief both times. Assuming you have a random engine problem to different launches, the probability of it being the same engine position both times is still one ninth (~11%).

Combinations of 18 taken 2 at a time =
18! / (2! x 16!) =
18 x 17 / 2 =
153

1 in 153 = 0.0065 = 0.65%


Exactly. It's not the engines or the turbopumps or the valves, it's the engine location relative to the fuel feed.
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Online arkaska

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Question regarding fuel consumption with one or two failed engines. Would an engine out (after launch) have caused the other engines to consume enough extra fuel getting to orbit to spoil the demonstrations planned for today's mission? Or is the first stage fuel not related to the extra fuel needed for the demo?

According to the presser Falcon 9 have 2 engine out capability after liftoff but need all 9 for liftoff. Either the other engines burn more fuel or they just burn longer, I would guess the later but am no expert.

And regarding the extra fuel for the demo, it is extra fuel for Dragon which is not used for launch but only in-orbit ops.
« Last Edit: 05/19/2012 04:58 pm by arkaska »

Offline Space Pete

Well, I'm only half-bummed about the scrub.

You see, I set my alarm for 9:00 AM this morning British time (with launch being at 9:55), and sure enough it went off on time. So, I got up, turned the alarm off (I put the alarm down the other end of the room so that I'd have to get up), then lay back down for "just a few more minutes", just to wake up properly.

Bad idea. Next thing I know, it's 10:07 on the clock. So I thought to myself a word I won't repeat here, raced to my computer, and checked in here to see a scrub.

So, scrub = bad, but not missing launch = good. :D
« Last Edit: 05/19/2012 05:01 pm by Space Pete »
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Online ugordan

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Combinations of 18 taken 2 at a time =
18! / (2! x 16!) =
18 x 17 / 2 =
153

1 in 153 = 0.0065 = 0.65%

I don't think that's quite right. If your starting point is that you have two launches with an engine problem, pick any engine out from the 1st launch and there's a 11% chance that's the same engine as on the 2nd launch as it can be any of the 9 engines.

Online edkyle99

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


Prevalve, yes, but aren't there are other valves, like the main valves, bleed valves, etc.?

 - Ed Kyle

But watch the presser for that question and that answer. I don't think Ms Shotwell would omit mentioning a problematic valve in relation to the engine by hiding with "Oh, but the prevalve was ok".

The common sense approach on interpretation is sometimes the best approach.

(You watch, they'll find a faulty valve now I've said that! :D)

If it isn't a valve, I can't think of many very "nice" explanations for what happened.  I'm figuring that I'll be sleeping in on Tuesday...

 - Ed Kyle

Offline Dappa

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Each stage has undergone multiple firings in Texas. Also,it's not terribly uncommon to have the same engine give you grief both times. Assuming you have a random engine problem to different launches, the probability of it being the same engine position both times is still one ninth (~11%).

Combinations of 18 taken 2 at a time =
18! / (2! x 16!) =
18 x 17 / 2 =
153

1 in 153 = 0.0065 = 0.65%

No. Once the first engine has failed, the chance of that first failure happening is 1 (100%), no matter which position it is in. The chance of the next failure being the same engine position is simply 1/9, as Robobeat said.

Offline renclod

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... If your starting point is that you have two launches with an engine problem,

Per Robotbeat' s post, the starting point is (correctly IMO):
two launch attempts
two engine problems
random engine failure

« Last Edit: 05/19/2012 05:14 pm by renclod »

Offline brihath

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


Prevalve, yes, but aren't there are other valves, like the main valves, bleed valves, etc.?

 - Ed Kyle

But watch the presser for that question and that answer. I don't think Ms Shotwell would omit mentioning a problematic valve in relation to the engine by hiding with "Oh, but the prevalve was ok".

The common sense approach on interpretation is sometimes the best approach.

(You watch, they'll find a faulty valve now I've said that! :D)

If it isn't a valve, I can't think of many very "nice" explanations for what happened.  I'm figuring that I'll be sleeping in on Tuesday...

 - Ed Kyle

Yeah...all speculation aside, I hope they find something simple with a readily identifiable root cause.  A long delay has a lot of ISS scheduling issues with other visiting vehicles.  One article in AW&ST that was addressing all the ISS scheduling constraints saw this flight pushing out to September if it had a significant delay in May, and that was before the delay caused by software validation.

Offline Avron

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... If your starting point is that you have two launches with an engine problem,

Per Robotbeat' s post, the starting point is (correctly IMO):
two launch attempts
two engine problems
random engine failure




question to the stats folks, is it significant that a similar problem seems to be happening to as engine is position 5, i.e. is position 5 a bad palace for an engine ? is the sample size too small? and if so how many more firings until its significant?

Offline Carreidas 160

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... If your starting point is that you have two launches with an engine problem,

Per Robotbeat' s post, the starting point is (correctly IMO):
two launch attempts
two engine problems
random engine failure



You method allows for two engines failing on one flight. There are 81 possibilities of two failing engines, e.g. (1, 1), (1, 2), (1, 3), ... etc. where (x, y) stands for "engine x fails on flight 1, engine y fails on flight
2).

There are 9 combinations (1, 1), (2, 2), ... , (9, 9) where the same engine fails on both flights. So 9 / 81 = 1/9 ~ 11%.

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