Author Topic: SpaceX Falcon Heavy Discussion (Thread 4)  (Read 512683 times)

Offline Meltro

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1000 on: 05/04/2016 08:47 PM »
Yes but with a T:W of 1.6 FH isn't exactly clawing its way off the pad. Isn't Antares at something like 1.1?
I was hoping that somebody with a bit more knowledge and time than me had run the numbers on it as it is obviusly a tradeoff.

Off the top of my head, would need individual weight of the Merlin engines, empty core weight, weight of fuel, an isp profile for the engines, drag coefficients for the individual boosters as well as the core and payload, structural integrity limits...I'd love an excuse to dust off my dynamics texts but I think we're too soft on a lot of these numbers to build a real meaningful answer. That isn't to say I couldn't plug in numbers, but small deviations in the above could generate radically different answers on whether or not an idea is feasible. You'd get an answer, but it would probably be meaningless.
Right you are, Ken

Offline nadreck

Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1001 on: 05/04/2016 09:02 PM »


Off the top of my head, would need individual weight of the Merlin engines, empty core weight, weight of fuel, an isp profile for the engines, drag coefficients for the individual boosters as well as the core and payload, structural integrity limits...I'd love an excuse to dust off my dynamics texts but I think we're too soft on a lot of these numbers to build a real meaningful answer. That isn't to say I couldn't plug in numbers, but small deviations in the above could generate radically different answers on whether or not an idea is feasible. You'd get an answer, but it would probably be meaningless.

The numbers I use are

Merlin engines around 450kg
Empty core weight 25.6t with legs, 23.1t without
ISPSL 282
ISPVac 311

I ignore drag and structural limits, and in this problem solving instance I think it is irrelevant because you are reducing thrust and speed through the air
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Meltro

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1002 on: 05/04/2016 09:10 PM »
Having 2500 less kg on the central core is not going to give you more than a 30m/s advantage on the central core in expendable mode, with the lightest payload and it drops a bit from there.

Is there a central thread somewhere for known figures on vehicle masses? I seem to have self nerd-sniped.

edit: thank you, now just need S2 weight. Might be crawling through wikipedia for a bit.
« Last Edit: 05/04/2016 09:11 PM by Meltro »
Right you are, Ken

Offline Meltro

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1003 on: 05/04/2016 09:17 PM »
I ignore drag and structural limits, and in this problem solving instance I think it is irrelevant because you are reducing thrust and speed through the air

True enough, was thinking more along the lines of a complete simulation. My only caveat would be the possibility of the falcon throttling down around max-q due to structural limits, which would favor the reduced-engine profile slightly. If it never throttles down, I would agree with you 100%.
Right you are, Ken

Offline nadreck

Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1004 on: 05/04/2016 09:25 PM »
I ignore drag and structural limits, and in this problem solving instance I think it is irrelevant because you are reducing thrust and speed through the air

True enough, was thinking more along the lines of a complete simulation. My only caveat would be the possibility of the falcon throttling down around max-q due to structural limits, which would favor the reduced-engine profile slightly. If it never throttles down, I would agree with you 100%.

Actually on my FH spreadsheet (see the other posts that one links to)  I presume it throttles down 24 seconds in (actually not throttling down, but shutting down 2 of the 9 centre core engines to start fuel conservation, it is well below maxQ speeds at that point. Oh and for the record I don't presume the gravity turn starts until 26 seconds in.

Honestly I need to play with the assumptions for the initial boost phase given the latest thrust numbers, but I haven't yet.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline nadreck

Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1005 on: 05/04/2016 09:37 PM »
Having 2500 less kg on the central core is not going to give you more than a 30m/s advantage on the central core in expendable mode, with the lightest payload and it drops a bit from there.

Is there a central thread somewhere for known figures on vehicle masses? I seem to have self nerd-sniped.

edit: thank you, now just need S2 weight. Might be crawling through wikipedia for a bit.

Hmm it is often a matter of discussion, you can check out the previous Falcon Heavy thread http://forum.nasaspaceflight.com/index.php?topic=36806.msg1332177#msg1332177
and around when I put together the FH spreadsheet (then later updated it for Full Thrust) we certainly had some discussions around the numbers we should use. But no I don't know of anywhere authoritative and I just try my best with the numbers I can find out. I also have tried back engineering numbers, for example if you are confident in the estimates for the 2nd stage parameters, you can figure out the speed at which the stage had to have separated at to check the modelling of the booster core.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Meltro

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1006 on: 05/04/2016 09:44 PM »

Actually on my FH spreadsheet (see the other posts that one links to)  I presume it throttles down 24 seconds in (actually not throttling down, but shutting down 2 of the 9 centre core engines to start fuel conservation, it is well below maxQ speeds at that point. Oh and for the record I don't presume the gravity turn starts until 26 seconds in.

Honestly I need to play with the assumptions for the initial boost phase given the latest thrust numbers, but I haven't yet.

Yay, numbers! Thank you. I noticed you used the SL Isp down the line, is there any good way to refine that? I'm thinking linearization against atmospheric density but I don't know the specifics on how atmosphere/pressure/(velocity?) affect Isp.
Right you are, Ken

Offline CraigLieb

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1007 on: 05/04/2016 09:49 PM »
We were told that the partially built test stand had been abandoned, for now.

Also, that the reason to not test a triple core at McGregor is that it would have to be disassembled for transportation then reassembled and retested at the launch site.

Another consideration why they might be taking this approach
Waiting to gather all the stages at McGregor adds delays which could be leveraged testing the individual stages as they are made/delivered. If you test them together, and if there is an issue with one engine, you may have to test fire all three again adding extra firings to the other stages that have no problems.

It makes more sense to test them as they are built, work out any issues with stages individually (in the already tried and true process) then (as stated so aptly above).
Colonize Mars!

Offline nadreck

Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1008 on: 05/04/2016 11:34 PM »

Yay, numbers! Thank you. I noticed you used the SL Isp down the line, is there any good way to refine that? I'm thinking linearization against atmospheric density but I don't know the specifics on how atmosphere/pressure/(velocity?) affect Isp.

You are welcome.

Yes I use sea level ISP and the reason I do is I trade being conservative there off against losses to air resistance and gravity losses on the centre core and 2nd stage (which are minor, but exist). I do account for gravity loss on the side cores though.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline cscott

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1009 on: 05/05/2016 02:02 AM »
People were discussing this. The current guess is: they will test single sticks one after another in McGregor but the final integration and static fire of FH will happen in Florida. One of the reasons: no sign of triple core hold-down hardware at McGregor.

Spacex Kremlinology question: does this imply anything long term about how FH fits (or doesn't) into the current ecosystem of Hawthorne-build, Mcgregor-test, FL/Vandy-launch?
Well, note that they're already doing all the inspection/test/validation/refurb work for the recovered cores at the Cape.  So they must have already built up their test stand/equipment/engineer infrastructure at the Cape.  Testing/validating FH would presumably build on those resources.

There is speculation that MCT might be built/tested/flown all at the Cape.  If so, this might be a baby step in that direction.  But you don't need MCT to justify it---they clearly intend to recover and refly more and more cores, and they don't want to have to ship cores back and forth to McGregor.  So there will certainly be increased capabilities at the Cape over time.  Assuming a large proportion of recovered/reflown stages in some years time, I wouldn't be surprised to see McGregor transition more to Raptor/MCT R & D, with new-stage validation work less frequently required.

They'll probably need to eventually do refurb/validation work at Vandenberg, too.
« Last Edit: 05/05/2016 02:05 AM by cscott »

Offline Arcas

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1010 on: 05/05/2016 02:10 AM »
I can't wait for rocket boneyards like we have with aircraft.
The risk I took was calculated, but boy am I bad at math.

Offline guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1011 on: 05/05/2016 04:59 AM »
There is speculation that MCT might be built/tested/flown all at the Cape.

There is no way SpaceX would do that unless the range is ready to support daily flights.

Offline cscott

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1012 on: 05/05/2016 12:59 PM »
There is speculation that MCT might be built/tested/flown all at the Cape.

There is no way SpaceX would do that unless the range is ready to support daily flights.
I'm not endorsing that theory, just reporting it.  As the rest of my post argues, you don't need to believe in MCT at the Cape in order to expect continuing migration of test/validation/refurb work from McGregor to the Cape.
« Last Edit: 05/05/2016 01:01 PM by cscott »

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1013 on: 05/05/2016 01:09 PM »

Well, note that they're already doing all the inspection/test/validation/refurb work for the recovered cores at the Cape.  So they must have already built up their test stand/equipment/engineer infrastructure at the Cape.


There was nothing to build up.  There is no difference in the GSE needed to prepare a new vehicle for launch or a previously flown vehicle.

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1014 on: 05/05/2016 01:11 PM »
People were discussing this. The current guess is: they will test single sticks one after another in McGregor but the final integration and static fire of FH will happen in Florida. One of the reasons: no sign of triple core hold-down hardware at McGregor.

They may only static fire one or two FH at the Cape.  Static fire at the Cape for F9 is going to go away

Offline Mike_1179

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1015 on: 05/05/2016 01:19 PM »
People were discussing this. The current guess is: they will test single sticks one after another in McGregor but the final integration and static fire of FH will happen in Florida. One of the reasons: no sign of triple core hold-down hardware at McGregor.

They may only static fire one or two FH at the Cape.  Static fire at the Cape for F9 is going to go away

For how long did other expendable launch vehicles do static fires before they moved to the wet dress rehearsal that ULA does now? Is the fact that SpaceX has continued to do firings instead WDR this long out of the ordinary?

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1016 on: 05/05/2016 02:33 PM »

For how long did other expendable launch vehicles do static fires before they moved to the wet dress rehearsal that ULA does now? Is the fact that SpaceX has continued to do firings instead WDR this long out of the ordinary?

Only Delta IV did one static fire.  You would have to go back to the 50's for other vehicles static fires.  And it wasn't static fires or WDRs, they did both.  They continued with WDR's.  Shuttle did one static fire for new orbiters and then didn't do WDR's. Atlas doesn't do anything now. Any problem that WDR would uncover would be found during the launch countdown.  They see it as only a schedule risk. 

Online abaddon

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1017 on: 05/05/2016 02:46 PM »
They may only static fire one or two FH at the Cape.  Static fire at the Cape for F9 is going to go away
Even with a reused core?

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1018 on: 05/05/2016 02:48 PM »
They may only static fire one or two FH at the Cape.  Static fire at the Cape for F9 is going to go away
Even with a reused core?

don't know about that.

Online wannamoonbase

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1019 on: 05/05/2016 02:48 PM »
I've always seen Static Fires as a SpaceX practice to establish confidence in hardware (both ground and flight), people and vet procedures. 

Even now they don't have that many reps on launching and they are continuously changing things.  Jim's right, they will go away once the confidence level is high enough and the launch team and hardware mature enough. 

Finally if they want to launch every 2 weeks the static fire has to go away.
SpaceX, just a few things planned for 2018: FH, Starlink Prototypes, Block 5, Dragon 2, Increased launch rate.

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