Author Topic: SCRUB: SpaceX Falcon 9/Dragon COTS Demo (C2+) LAUNCH ATTEMPT 1 UPDATES  (Read 192620 times)

Offline 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%).

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.
Didn't read what I said, did you? If you have 9 engines, and fail one randomly then another randomly, there's a one out of nine chance that it'll be the same engine.
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Online Ronsmytheiii

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Taken by Andre Kuipers as ISS passed overhead a few minutes before the T-0

http://www.flickr.com/photos/astro_andre/

Offline wintermuted

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Can outside pressure propogate back through the shock at the throat to affect chamber pressure? I don't think so.

That's correct, in supersonic flow anything that happens downstream of the choke point cannot communicate upstream.

Offline aero

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If all the fuel constraints were on Dragon because of the demo, why were we thinking that the launch window was only one second wide because of fuel constraints? Does Dragon do the "cross range" burns and not the boosters?
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Offline renclod

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You method allows for two engines failing on one flight.
If random engine failures occuring, yes it should be allowed in considerations.

« Last Edit: 05/19/2012 05:34 pm by renclod »

Offline Robotbeat

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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?

I don't think you can say yet with confidence with just statistics that it's engine placement. Of course, later analysis may show that engine placement matters, but you can't say that (yet) just because it happened to the same engine position twice. Of course, if it happens three or four times... You have a pretty strong hint.
« Last Edit: 05/19/2012 05:34 pm by Robotbeat »
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Offline arkaska

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If all the fuel constraints were on Dragon because of the demo, why were we thinking that the launch window was only one second wide because of fuel constraints? Does Dragon do the "cross range" burns and not the boosters?

Dragon is so heavy because of the fuel load that Falcon have no fuel margin, it needs all the fuel to reach orbit without flying cross range.

If Dragon would have needed less fuel it would weight less meaning Falcon would have margin to fly cross range as shuttle could. I guess that technically they could load more payload on shuttle and then loose the cross-range capability.
« Last Edit: 05/19/2012 05:37 pm by arkaska »

Offline Space Pete

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.

Correct - there are some windows in May and June, after which the ISS schedules and beta angles likely push the flight into September.

Are you sure it was AW&ST? I never saw that. Here's the one I wrote from two weeks ago:
http://www.nasaspaceflight.com/2012/05/iss-schedule-dragon-launch-19-may-future-manifest-outlook/
« Last Edit: 05/19/2012 05:36 pm by Space Pete »
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Offline wolfpack

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That's correct, in supersonic flow anything that happens downstream of the choke point cannot communicate upstream.

I stand corrected.

"The choked flow of gases is useful in many engineering applications because the mass flow rate is independent of the downstream pressure, depending only on the temperature and pressure on the upstream side of the restriction. Under choked conditions, valves and calibrated orifice plates can be used to produce a desired mass flow rate."

Told you, we never covered this in Circuits 101.  :P

Back on topic, given when Ms. Shotwell said, must be something with the fuel flow. My guess is maybe the injector (pintle?) could have been damaged during shutdown transients after the hot-fire test? Plausible?

Offline Antares

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Can outside pressure propogate back through the shock at the throat to affect chamber pressure? I don't think so.

Small point of emphasis: there's no shock at the throat.  If there were, everything downstream would be subsonic.
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Offline Antares

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This whole fuel margin thing is an integrated problem between Falcon and Dragon.  Falcon *could* yaw steer or Dragon could plane change or an optimized combination of both to get back into the plane of Station.  However, SpaceX *chooses* not to use any propellant on either vehicle to do that.  This maximizes the amount of propellant remaining on Dragon for prox ops in case a re-rendezvous needs to occur.  Tis better to have a spacecraft holding on orbit waiting for repaired software than having it safely back floating in the Pacific wishing it hadn't spent those hypergols getting into the plane or altitude of Station.
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Offline ChrisC

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Thanks Antares for the explanation on margin.  Sadly I expect you (and others) will be answering the exact same question in three days, because that's what's been happening here for months now.  FAQ #1: why the instantaneous / 1sec launch window?  Shuttle, cross range, Soyuz, over and over and over.

Also, can you guys who are arguing about the statistics just agree to disagree and stop cluttering this update thread, especially as many of us are checking this thread (and L2) frequently throughout the weekend to see what SpaceX finds out and decides?
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Offline psloss

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Also, can you guys who are arguing about the statistics just agree to disagree and stop cluttering this update thread, especially as many of us are checking this thread (and L2) frequently throughout the weekend to see what SpaceX finds out and decides?
Agreed -- can we have a thread for updates?  Please?  There's a general discussion thread that would work for the armchair problem solving:
http://forum.nasaspaceflight.com/index.php?topic=28486.0

Online Chris Bergin

Taken by Andre Kuipers as ISS passed overhead a few minutes before the T-0

http://www.flickr.com/photos/astro_andre/

Wow. That's all types of epic!
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Offline brihath

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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.

Correct - there are some windows in May and June, after which the ISS schedules and beta angles likely push the flight into September.

Are you sure it was AW&ST? I never saw that. Here's the one I wrote from two weeks ago:
http://www.nasaspaceflight.com/2012/05/iss-schedule-dragon-launch-19-may-future-manifest-outlook/

My apologies!  I thought it was in the commercial space articles from an April issue, but I reviewed them and it wasn't.  That information was presented in your article, and it was excellent. 

That is why I come here FIRST for authoritative spaceflight reporting!

Offline Space Pete

My apologies!  I thought it was in the commercial space articles from an April issue, but I reviewed them and it wasn't.  That information was presented in your article, and it was excellent. 

That is why I come here FIRST for authoritative spaceflight reporting!

No worries, thanks. You just got me worried that AW&ST had nicked our content! ;)
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Offline Chris-A

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The webcast was archived by YouTube. (we got lucky)


Edit: I don't care for embedded youtube videos. Interesting, a section of the livestream feed was archived.
« Last Edit: 05/19/2012 08:25 pm by Chris-A »

Online ugordan

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Meh, that's a crappy quality version of the source webcast available here: http://new.livestream.com/spacex/Launch

Online Chris Bergin

All very quiet at the moment. Nothing from all sides at this time (of course, a lot will be sleeping during the day). We know via L2 they got through detanking and were going to pad open, but no reports back on any status of the investigation yet.
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Offline JNobles

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Elon just tweeted: 

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

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