Author Topic: SpaceX Falcon Heavy Discussion (Thread 4)  (Read 713165 times)

Offline oldAtlas_Eguy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #340 on: 02/05/2016 05:48 pm »
Yes, you must actually calculate performance to a reference orbit of your choosing. That's better than Wikipedia (obviously), SpaceX (doesn't provide full orbit parameters and reserves some undefined amount of performance for reuse, according to Shotwell), and spaceflight101 (which isn't a primary source).

And because it gives you performance numbers to many different orbits, you can use it to calibrate your model much better than just giving a couple reference orbits (especially when it's "GTO" without specifying 1500 or 1800m/s-to-go)

But it does not give me the information I need to calculate anything. How can I use the calculation on this page to check my model of calculations if I don't know the masses they are assuming? Is the reference model in their calculations one with legs?

Back when the first TMI numbers went up on the SpaceX website I could use that with the data on SII engine performance and SII masses (wikipedia, spaceflight 101 and also the SpaceX website) to backwards calculate the speed the FH lofted the 2nd stage to in fully expendable mode. That gave me one point of sanity check for my model of FH operation.  This doesn't really give me any without knowing the numbers they used.
The values given by the orbit query is based on no margins (including no legs). No margins means no engine out either. The 1350 LEO and GTO values for v1.1 given by SpaceX included engine out margins + maybe a little more as well as attached legs and other recovery hardware margins. The two values gives the percentages or delta V/energy values for the stage deltas for no margins vs ASDS recovery for the v1.1. Now for FT we do not have any values.

Plus I do not think the numbers in the NASA query model will give you any answers since they are most likely a polynomial algorithm that given certain inputs returns an output. They may have no relationship to masses of stages or engine thrusts ISPs or anything else just a complex curve equation.
Or sure, but you can use it to back out realistic values for all those things and to test your model. If you know lift-off mass, Isp, thrust, and payload to multiple orbits, you could actually back out dry masses, especially for a simple vehicle.
Algebra gives us that given two solutions with two equations you can solve for 1 unknown. With three solutions you can solve for 2 unknowns ... Pick orbits that give you solvable for unknowns equations and you can back out all the data to the same level of accuracy that the solutions are given (looks to be 3 significant digits, maybe 4). You can do the back out analysis with a simple Basic program that iterates the unknown values until it matches up with the given solutions.

Offline fthomassy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #341 on: 02/05/2016 06:18 pm »
Algebra gives us that given two solutions with two equations you can solve for 1 unknown. With three solutions you can solve for 2 unknowns ... Pick orbits that give you solvable for unknowns equations and you can back out all the data to the same level of accuracy that the solutions are given (looks to be 3 significant digits, maybe 4). You can do the back out analysis with a simple Basic program that iterates the unknown values until it matches up with the given solutions.
One unknown can be solved per simultaneous equation.
gyatm . . . Fern

Offline oldAtlas_Eguy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #342 on: 02/05/2016 06:34 pm »
Algebra gives us that given two solutions with two equations you can solve for 1 unknown. With three solutions you can solve for 2 unknowns ... Pick orbits that give you solvable for unknowns equations and you can back out all the data to the same level of accuracy that the solutions are given (looks to be 3 significant digits, maybe 4). You can do the back out analysis with a simple Basic program that iterates the unknown values until it matches up with the given solutions.
One unknown can be solved per simultaneous equation.
Thank you, I got carried away with the plethora of unknowns.

Having the extra equation/answer helps in unknown value solution validation. I do the hunt for unknowns a lot of times by the iterative process by hand using a spreadsheet. Mainly where looking for payload sizes in a two part (destinations with different payloads same vehicle) problems such as landing on the Moon and then returning.

Offline fthomassy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #343 on: 02/05/2016 06:41 pm »
One unknown can be solved per simultaneous equation.
Thank you, I got carried away with the plethora of unknowns.

Having the extra equation/answer helps in unknown value solution validation. [snip]
Agreed, more data is more better :)
gyatm . . . Fern

Offline TomTX

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #344 on: 02/07/2016 08:44 pm »
One thing to keep in mind with all this discussion of larger payload fairings is road transport.  I doubt anything over the current size is going to be able to fit on the road in halves.  Will quarter slices get you back to small enough?  That adds more complexity.  Of course, there has been no mention of any actual payloads out there requiring larger than what is available now so much of this discussion is just burning pixels for fun.

5.2 meter diameter is road transportable within Texas. All you have to do is use the automated routing software on the State website and pay the appropriate oversize/overweight fee, use required pilot cars and such. You don't even need a human review/signoff of your routing.

It's not trivial, but big stuff for oil refineries, wind towers, et cetera gets moved on the road with some frequency.

Offline Geron

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #345 on: 02/09/2016 07:11 am »
Does anyone know the name of the music that plays at the end of the commercial space dev conference?

Offline spacenut

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #346 on: 02/10/2016 01:44 am »
Someone on another thread calculated to get a high ISP on a Raptor upper stage engine the diameter of the nozzle would be 4.8m.  Therefore it makes sense to have a 5.2m or slightly larger upper stage so the upper stage engine can be protected during launch by the interstage collar as well as a nice transition to the fairing. 

Offline Donosauro

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #347 on: 02/10/2016 03:12 pm »
Also, where the heck would you TEST such a huge fairing? As it is, 5m fairings barely fit at Plum Brook, which has the largest vacuum chamber in the world.

Isn't the vacuum chamber 100' in diameter and taller than that? The acoustic facility is smaller...

Yep, 100 feet in diameter, 122 feet high. But the loading doors are only 15.2 m (50 ft) square.

http://www.grc.nasa.gov/WWW/Facilities/ext/spf/index.html

Offline Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #348 on: 02/10/2016 05:09 pm »
Also, you have to actually test separation dynamics, and then you have to carefully slow down the fairing so it doesn't bang into your expensive thermal vacuum chamber.

Look at the tests they do with 5m fairings. There's not exactly a ton of extra room.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline sewebster

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #349 on: 02/10/2016 06:28 pm »
Also, you have to actually test separation dynamics, and then you have to carefully slow down the fairing so it doesn't bang into your expensive thermal vacuum chamber.

Look at the tests they do with 5m fairings. There's not exactly a ton of extra room.

Cool, thanks for the clarification. Here is a video link for those who hadn't seen it (like me):

Offline Ronsmytheiii

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #350 on: 02/11/2016 12:15 am »
Also, you have to actually test separation dynamics, and then you have to carefully slow down the fairing so it doesn't bang into your expensive thermal vacuum chamber.

Look at the tests they do with 5m fairings. There's not exactly a ton of extra room.

They have done bigger shrouds in the past (Skylab shroud seen in Plum Brook below)

http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-001462.html

Offline Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #351 on: 02/11/2016 12:25 am »
Also, you have to actually test separation dynamics, and then you have to carefully slow down the fairing so it doesn't bang into your expensive thermal vacuum chamber.

Look at the tests they do with 5m fairings. There's not exactly a ton of extra room.

They have done bigger shrouds in the past (Skylab shroud seen in Plum Brook below)

http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-001462.html
Indeed.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720022228.pdf
But notice that didn't cover the whole of Skylab, only a portion of it (the top part). Also, they had to assemble the fairing you see in that picture in two chunks, a top and a bottom. That'd be impractical for the huge composite fairings you see in SLS diagrams.

...additionally, that was significantly narrower at 6.6m in diameter vs the 8+m you see quoted for the SLS fairing (let alone the 10 and 12m fairings, the last one being almost twice as wide!), as well as shorter than the typical notional fairings (even though it still needed to be assembled out of two pieces!).


...it is possible to shoehorn it in there, but it is by no means terribly practical and would likely add weight to the fairing due to the need to assemble it inside the chamber.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline vapour_nudge

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #352 on: 02/11/2016 01:46 pm »
Looks like they've lost the Viasat-2 launch due to the FH delays  It has been redirected to Arianespace

Offline The Amazing Catstronaut

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #353 on: 02/11/2016 01:51 pm »
Looks like they've lost the Viasat-2 launch due to the FH delays  It has been redirected to Arianespace

Was to be expected - it's probably not going to be the last FH payload they lose.

Whilst I appreciate payload providers supporting rockets that have not yet launched and putting their money where their mouth is whilst doing so, It's not as sane a choice as putting your super-expensive future-insurance of a satellite on a rocket that has a concrete launch history.
Resident feline spaceflight expert. Knows nothing of value about human spaceflight.

Offline Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #354 on: 02/11/2016 02:03 pm »
Yeah it is, otherwise they'd be stuck with high prices forever. Without a rational willingness to try new rockets on the part of the customers, the price will never come down. It's perfectly sane to book early on a new rocket an then change if the rocket is delayed more than you are willing to tolerate. Both actions are perfectly sane and rational.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Nilof

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #355 on: 02/11/2016 05:12 pm »
What about building a fairing test rig on a reused first stage, and trying out the new fairing on a suborbital flight?
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #356 on: 02/11/2016 05:30 pm »
What about building a fairing test rig on a reused first stage, and trying out the new fairing on a suborbital flight?

Only if the test can replicate the same conditions as the regular flight

Online abaddon

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #357 on: 02/11/2016 05:34 pm »
What about building a fairing test rig on a reused first stage, and trying out the new fairing on a suborbital flight?

Only if the test can replicate the same conditions as the regular flight
In addition, you would also need to expend a brand-new second stage.  We're starting to talk about a very expensive test by this point.

Offline Nilof

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #358 on: 02/11/2016 06:34 pm »
In addition, you would also need to expend a brand-new second stage.  We're starting to talk about a very expensive test by this point.

I was thinking of suborbital flight with just the first stage and a structural prototype on top. No second stage, everything fully reusable.

What about building a fairing test rig on a reused first stage, and trying out the new fairing on a suborbital flight?

Only if the test can replicate the same conditions as the regular flight

That is likely the main issue. To be comparable to a thermovac chamber, the stage would have to provide a similar altitude profile to the actual launch. I don't know exactly how much delta-v would be necessary for that and if it's feasible for a reusable stage. Acceleration doesn't necessarily need to be simulated too closely though, since vacuum chambers don't simulate that at all.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #359 on: 02/11/2016 06:48 pm »

That is likely the main issue. To be comparable to a thermovac chamber, the stage would have to provide a similar altitude profile to the actual launch. I don't know exactly how much delta-v would be necessary for that and if it's feasible for a reusable stage. Acceleration doesn't necessarily need to be simulated too closely though, since vacuum chambers don't simulate that at all.

Yes, vacuum chambers do sim gravity.  They will put springs on the fairing.

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