SpaceX Falcon I Launch III - Build-up Thread

[jongoff]

The core issue here is that our civilization  does not yet have a Theory of Turbulence, so its pretty much Garbage in Garbage Out for computer simulations in this field. Same for some rocket engine simulations. The most famous example of CFD failing was the X-30 simulation work, which was very computation intensive and pretty much useless.

It's been a while since I took my fluids class on turbulence (the only PhD level class I've ever taken), but let's see how much I can recall.  Basically, it's a little more complicated then that.  There are plenty of theories and modeling approaches for turbulence--some of which are extremely good for specific applications, but the fundamental problem is that you have more variables in the Reynolds Averaged Navier-Stokes than you have equations...Which means that on some level you have a problem of actually closing the equations.  There are lots of ways of working around this, k-epsilon models, k-omega models, 0-equation models, etc, etc.  And some of them work pretty well.

But I do agree that generally speaking, I never trust CFD code very much for something new.  Especially for turbulent free-surface flows (slosh), and two-phase turbulent reacting flows (rocket combustion). 

Part of the challenge though is that you really do need to do some sort of modeling and analysis during the design phase for a vehicle.  Just putting in slosh baffles is not enough--you need to have a good idea if they will work, you probably want to know if your FOS is greater than 1 on the baffle structure, you probably care how it impacts your control system, and a bunch of other things--you need at least something better than a SWAG to get the first-pass design done.  After that you can start getting empirical data that can hopefully help you refine your design and your models.  Once you have enough data, doing similar analyses become a lot more reliable. 

...I'm rambling again

~Jon

[Antares]

a Falcon 9 can lift about 9900 kg = 22,000 pounds to low earth orbit.

Depends upon which LEO we're talking about , though I agree 7700 pounds is way too low.  9900kg is probably to 28.5, 100nmi, e=0.

[JonSBerndt]

Also second stage slosh baffles were not "reconfigured" after Flight 2.  They were added.  There were none.  Another case of SpaceX experimenting with which standard practices they can do without.

While it's obvious in hind-sight that they should've had baffles, there are upper stages that don't have slosh baffles (Centaur being a good example).  Another interesting piece of data I heard recently from someone who has worked on several GN&C projects for rocket vehicles: he mentioned that it is typically quite difficult to get slosh going in CFD, but as he put it "it's much easier to get slosh going in reality".  They had done the analyses, and with the expected range of inputs the analysis showed they didn't need it.  Between the issues with CFD for this type of problem that my acquaintance mentioned, and the unexpectedly large disturbance input, I think that cutting them a little slack on this one is perfectly fair.

That said *it is* a good warning for those of us working on rocket vehicles.

~Jon

There is at least one very serious paper I've seen on modeling slosh in tanks - the STS ET in particular.  At its lowest level, the model is a sort of spring-mass-damper setup. NTRS might reference the paper. If I find it, I'll post the link. Interesting stuff.

Edit: Wow. Go here and search on "slosh":

http://ntrs.larc.nasa.gov

Jon

[Chris-A]

http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/SpaceX072308.xml&headline=SpaceX%20Prepares%20For%20Third%20Launch

Larry Williams says: we have no firm date, but in the coming weeks.

[kevin-rf]

http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/SpaceX072308.xml&headline=SpaceX%20Prepares%20For%20Third%20Launch

Larry Williams says: we have no firm date, but in the coming weeks.

More interesting is a 9 engine test planned for august

You know, Elon should put some bleachers up with a good view of the test stand ...

[Comga]

Larry Williams says: we have no firm date, but in the coming weeks.

The FAA page says July 26.
Geoffrey Little was told a nine day launch window opens on July 29.
SpaceX says that "Diane Murphy has joined the company as Vice President of Marketing and Communications" with one of her duties being to meet the "... tremendous demand for updates on the upcoming launch of our Falcon  1, ..."
Why is Mr. Williams saying "no firm date" to Av Week, regardless of how one defines "firm"?

[Comga]

....  Between the issues with CFD for this type of problem that my acquaintance mentioned, and the unexpectedly large disturbance input, I think that cutting them a little slack on this one is perfectly fair.

~Jon

Oh, I was not being harsh, certainly not impugning anyones abilities, and hindsight is 20-20, as you say.  It was just a statement of fact that there were no slosh baffles in the second stage for Flight 2.

FWIW, I wish them luck and look forward to watching the video feed next week.

[iamlucky13]

Paypal sold for 1.1 billion, but if I recall correctly Musk did not own a 100% share of the company.

No. He had a start-up partner, and there were other investors. The wikipedia article references an SEC document and says he held 11.7% at time of sale, and a sale value of $1.5 billion ($175.5 million). However, that wasn't his sole investment. Further down, it claims his worth at $328 million. The discrepancies seem large, but not unbelievable.

At around the time they unveiled Dragon, Musk said either that he'd invested about $100 million in SpaceX, or that SpaceX had spent about $100 million so far...I don't remember which. That was shortly before they started getting COTS money. I'd imagine his investment has stabilized since then, as the government money is contract payment and doesn't dilute his value the way taking on additional partners would.

[Cretan126]

Paypal sold for 1.1 billion, but if I recall correctly Musk did not own a 100% share of the company.

No. He had a start-up partner, and there were other investors. The wikipedia article references an SEC document and says he held 11.7% at time of sale, and a sale value of $1.5 billion ($175.5 million). However, that wasn't his sole investment. Further down, it claims his worth at $328 million. The discrepancies seem large, but not unbelievable.

Paypal was actually NOT founded by Elon.  He started X.com, which early-on competed with Paypal and ultimately the two merged.  He was CEO of the combined company until being ousted in a coups resulting from his stubborness in perpetuating the X.com brand and technology.  There's a good book chronicaling this called "The Paypal Wars."  Note that he did propogate his fascination with "Brand X" into the "SpaceX" name.

The EBay-Paypal deal was a stock deal, so Elon ended up with stock in Ebay.  At the time the deal was completed in Oct 2002, Ebay was around $14-15/share, adjusted for splits since then. At the end of 2004, it had almost quadrupled.  So, turning $1.75M into $700M was as easy as holding onto Ebay stock for two years.  Therefore, given timely selling and reinvesting, assuming that his net worth is (was?) closer to $1B is by no means a stretch.

[Cretan126]

Let me know any comments or crits.

Three nits:
Flight 1 did not explode.  That is one of the dangers it demonstrated.  It fell more or less intact and fueled onto the reef.

Actually, Flight 1 DID explode on its way down, well above the reef.  I have that on eyewitness accounts, both live and on video.  However, no video or photos were ever released to reinforce the very impression you have cited.

[Comga]

Actually, Flight 1 DID explode on its way down, well above the reef.  I have that on eyewitness accounts, both live and on video.  However, no video or photos were ever released to reinforce the very impression you have cited.

Once again my statements turn out to be what was said, not what I saw.
Any idea what caused the rocket to explode?  Did it just break apart from  aerodynamic forces?
I always wondered how the payload fell back on the island if the rocket hit the water intact.

[zappafrank]

Let me know any comments or crits.

Three nits:
Flight 1 did not explode.  That is one of the dangers it demonstrated.  It fell more or less intact and fueled onto the reef.

Actually, Flight 1 DID explode on its way down, well above the reef.  I have that on eyewitness accounts, both live and on video.  However, no video or photos were ever released to reinforce the very impression you have cited.

The fact that SpaceX never released a video of the first launch failing is very troubling.  What do they have to gain by censoring that?

Sure have a lot to lose.

Until they can actually put stuff into orbit and do it reliably, I don't trust them.

[Patchouli]

On the first Falcon 1 test they probably blew it up on purpose when it was evident the launch went wrong .

The same thing had to be done with the first Ariane V test vs allow it to become a land shark.

It's best to blow up a vehicle while it's still in the air vs allow it to crash intact just ask the Chinese.

[Antares]

What do you do when you look at Cape failures from the 50s?  Point and laugh.  Why would they put that out?  No one likes to see a starving engine.  Turbomachinery was not meant to be free.

Except that the range can't "blow up" a Falcon 1.  It has TTS not FTS.  Thrust termination.

[Patchouli]

The thought that SpaceX desires to be revolutionary in technology makes me squint.  That's not it at all.  Elon sought to minimize the cost function while providing sufficient performance to make money.  Main example: Why develop two turbopumped engines when you can develop one and then not have to deal with the hassle of purging for H2?  Well, maybe it's worth it because of the lost performance.  Scribble, scribble.  Nope, the lost performance is well worth the cost savings of another engine and H2.  BTW, in case any newbs are about to ask, you can't pump H2 with a pump designed for kerosene.

Also not having to handle thousands of gallons of lH2 at the launch site can save a lot of money as well.

Liquid hydrogen is insanely cold -423°F/-253°C and you have to add refrigeration systems very expensive ones at that to keep it liquid plus add a vent and flare valve to the launch complex to burn off gaseous hydrogen from the rocket.

Of course many people here know that already but to those who don't to put it in prespective it's so could nitrogen becomes an ice at those temps.

What the rocket must deal with so must the launch complex fuel handling hardware except it must store the fuel for long term vs just deal it with for a few hours.

wiki has a good page on it and lists drawbacks
http://en.wikipedia.org/wiki/Liquid_hydrogen

I wouldn't be surprised at all to learn that the hydrogen handling equipment at the cape costs more then the entire development budget for Falcon 1 and 9.

I have no idea what it costs but it's likely was very expensive because they reused the old Apollo equipment on the shuttle.

[dmc6960]

Let me know any comments or crits.

Three nits:
Flight 1 did not explode.  That is one of the dangers it demonstrated.  It fell more or less intact and fueled onto the reef.

Actually, Flight 1 DID explode on its way down, well above the reef.  I have that on eyewitness accounts, both live and on video.  However, no video or photos were ever released to reinforce the very impression you have cited.

So where did it explode?  The payload fairing?

The 2nd stage-mounted camera filmed its entire ascent and subsequent descent into the drink.  The rocket stays completely intact that whole ride down.  What happens after it hits the water I do not know.  SpaceX has had this entire video on their website since shortly after the flight.  It shows the rocket tipping over as the engine shuts down, and a long trail of flame is shooting out of the engine area as leaking fuel and shutdown residuals are still burning.  About halfway through the fall the camera's viewing window gets covered in a liquid (either kerosene or water, I'm guessing kerosene), and its visible that the flames from the engine later go out.  Although at this point its hard to see, there is a lighter stream still coming out of the engine area, this could be kerosene, lox, cold gaseous oxygen, cold helium, or everything.  Towards the end of the fall, the camera window clears up a little bit, to see the horizon with a decent perspective (rocket is falling stable on its side at this point) and right before it cuts out you can make out waves in the water.  Seems like it was intact all the way down to me.

HOWEVER......

Compare this to the movie that was posted here on NSF within minutes of the flight.  It DOES appear to have exploded in that movie, but yet still visibly makes it all the way down to the water.  Seems to me that if the rocket exploded, the camera would go dark at that time.  So the explosion as seen on the video here is not an explosion at all, it is an illusion created by recording a live internet video stream that has many missing frames and many garbled frames.

View them side by side if you like....

SpaceX official onboard video....
http://www.spacex.com/F1-001-Launch-RocketCam2.wmv

NSF recorded webcast....
http://www.nasaspaceflight.com/_docs/2242.wmv


I viewed the first two launch attempts live.  I cringed live when I saw the thermal blankets flapping around (which actually wasn't the problem but we [NSF members] thought it was at the time, and my video feed cut out before showing the rocket actually falling).  I also cringed live on the second launch when I saw the first stage hit the kestrel engine bell (I saw what happened, couldn't figure out why those SpaceX folks in the background were cheering) and I gringed even more when I saw the oscillations right before the feed was cut (again, my viedo feed cut out earlier than others, as I never saw the full rotation of the 2nd stage as some did).  However I no longer have internet at home (tight buget).  I'm hoping not to miss this launch live.  I'm a rootin' for them.  Go SpaceX!!!

[nobodyofconsequence]

Don't buy that explanation. Have seen enough crash videos that haven't gone dark. There's always been enough energy in the caps or inductors that you get a few hundred milliseconds more. What lets you believe that its a compression artifact?

So what for the past. Musk says to write it off. Fine. Lets see the current work. If it works, that's good enough. If not, he says he'll try again. I'll watch.

Don't need any theories. It exploded. Get over it.

[kevin-rf]

Seems to me that if the rocket exploded, the camera would go dark at that time.

Why? It would only go dark if the "exposion" destroyed a critical part of the camera/power/transmitter link. During one of the X-15 ground tests the engine exploded with Crossfield in the cockpit, he calmly walked away from it.

Depends how it explodes, for instance if you dump a large amount of fuel in the air and it ignites most people on the ground will think it exploded... Regardless of the plane crash you will always have a witness that claims it was on fire and another that thought it exploded.

Witnesses claimed the titanic went down intact while others swore it broke in half. (History has shown it broke)

[jimvela]

Depends how it explodes, for instance if you dump a large amount of fuel in the air and it ignites most people on the ground will think it exploded... Regardless of the plane crash you will always have a witness that claims it was on fire and another that thought it exploded.

Witnesses claimed the titanic went down intact while others swore it broke in half. (History has shown it broke)

Seeing something with one's own eyes does not equate to understanding what one saw... let alone correctly remembering it later.

[dmc6960]

Don't buy that explanation. Have seen enough crash videos that haven't gone dark. There's always been enough energy in the caps or inductors that you get a few hundred milliseconds more. What lets you believe that its a compression artifact?

So what for the past. Musk says to write it off. Fine. Lets see the current work. If it works, that's good enough. If not, he says he'll try again. I'll watch.

Don't need any theories. It exploded. Get over it.

Did you watch the movie from SpaceX's website or not?  It clearly shows the rocket going up, falling down, and having some pretty impressive flames shooting out of the engine area while doing it, but clearly not exploding while on the way down.  Could it have exploded upon impact?  Certainly!  I just think way too many people have gotten the wrong impression about what the rocket actually did based on the movie posted here at NSF.

Movie from SpaceX - No compression artifacts
Movie recorded from webcast posted here on NSF - Major compression artifacts