Author Topic: SpaceX Falcon Heavy Discussion (Thread 3)  (Read 332196 times)

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #200 on: 03/05/2015 10:27 am »
If you add the u/s stretch, presumably both of those numbers become obsolete. The FH one possibly before the first time it flies.

Is a second stage stretch confirmed?

Some have speculated that the added 10% volume can be done without a stretch.

For example:
http://forum.nasaspaceflight.com/index.php?topic=36815.msg1340204#msg1340204
« Last Edit: 03/05/2015 10:40 am by Dave G »

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #201 on: 03/05/2015 10:30 am »
It doesn't matter whether you can transport 220' towers *somewhere*.  The issues is the maximum load length possible on coast-to-coast routes between Hawthorne, McGregor, and the Cape.
and to the new Boca Chica launch site.

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #202 on: 03/05/2015 11:19 am »
I'm not buying it.  Look up Tonopah, NV,and U.S. 95.  Small town, mountainous terrain.  That's where I've seen those 212' long towers being pulled... 

From the link you provided earlier:
https://www.wind-watch.org/faq-size.php

Quote
How are the wind turbine components transported?

Transport of such large items and the cranes needed to assemble them often presents problems in the remote areas where they are typically built. Roads must be widened, curves straightened, and in wild areas new roads built altogether.

So it appears that, while there's no fixed limit, longer stages would tend to present more issues with road transport.

In any case, an informative discussion.
« Last Edit: 03/05/2015 11:27 am by Dave G »

Offline deruch

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #203 on: 03/05/2015 11:23 am »
I'm not buying it.  Look up Tonopah, NV,and U.S. 95.  Small town, mountainous terrain.  That's where I've seen those 212' long towers being pulled.  Unless there are major obstacles right outside the front gates of either Hawthorne, McGregor (which is a pretty wide open space, so not likely there) or Cape Canaveral, I doubt there will be any on the interstate route in between.

And what is the diameter of the long towers?  Can they be transported off the ground enough that they aren't going to get high centered?  or pinch when spanning dips?  ISTM that it isn't just one dimension in isolation, it may be  the combination that causes the problems.
« Last Edit: 03/05/2015 11:24 am by deruch »
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Offline Herb Schaltegger

Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #204 on: 03/05/2015 11:56 am »
Wait, is it quite true, though, that 120' is such a hard (okay, "firm") limit? I got the idea that length has a much less firm limit than height, which obviously over any distance greater than a few miles has serious issues due to bridges. I mean, once you're on the Interstate, it's not like there are that many sharp turns.

On-ramps and off-ramps, however, present all manner of pain-in-the-ass problems for transporting long objects.
How often would that be necessary?

Anyway, this is all a good argument for Return to Launch Site.

Beats the bejesus out of me. I'm just pointing out that very few interchanges on the U.S. interstate highway system exist where the transitions from surface streets to the highway consist of long, flowing curves and straight stretches. The vast majority have inconvenient right-angle interchanges with stop lights and such at the top/bottom of the ramps. Pull up your favorite mapping website or good old fashioned Rand-McNally and check the routes yourself.

Furthermore, once you're on those surface streets between the nearest interstate and the launch processing site, you still have the same intersection problem. There's a reason why the interstate trucking industry has a pretty much standardizws set of trailer lengths.
« Last Edit: 03/05/2015 11:57 am by Herb Schaltegger »
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Offline cambrianera

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #205 on: 03/05/2015 12:45 pm »
If you add the u/s stretch, presumably both of those numbers become obsolete. The FH one possibly before the first time it flies.

Is a second stage stretch confirmed?

Some have speculated that the added 10% volume can be done without a stretch.

For example:
http://forum.nasaspaceflight.com/index.php?topic=36815.msg1340204#msg1340204
All I see in that post is a clear indication of a stage becoming longer with time.
+10% vol means stretched, period.
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Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #206 on: 03/05/2015 01:06 pm »
If you add the u/s stretch, presumably both of those numbers become obsolete. The FH one possibly before the first time it flies.

Is a second stage stretch confirmed?

Some have speculated that the added 10% volume can be done without a stretch.

For example:
http://forum.nasaspaceflight.com/index.php?topic=36815.msg1340204#msg1340204
All I see in that post is a clear indication of a stage becoming longer with time.
+10% vol means stretched, period.

Did you read the post?  I'll quote it here:

Quote
Actually, upper stage tank volume +10% does not necessarily mean the outer structure needs to be stretched. A good example is the good old Ariane 4 - its LH2 third stage was modified twice in history (first flight 1988, first modification in 1992 and the second in 1994) to allow for slight increases in the fuel capacity with just internal tank stretches of inches. Each stretch brought about 100-150 kg increase in GTO payload capacity.

(bold mine)
« Last Edit: 03/05/2015 01:08 pm by Dave G »

Offline Kabloona

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #207 on: 03/05/2015 01:13 pm »
Yes, but the graphic shows that the first two stretches did, in fact, grow the overall length of the stage.

Only the final stretch maintained the same stage length, by tweaking the tanks and skirt lengths by a few centimeters.

The scale of the tank growth anticipated on F9 is more consistent with the first two stretches shown in the diagram, both of which increased stage length.
« Last Edit: 03/05/2015 01:17 pm by Kabloona »

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #208 on: 03/05/2015 01:26 pm »
Yes, but the graphic shows that the first two stretches did, in fact, grow the overall length of the stage.

Only the final stretch maintained the same stage length, by tweaking the tanks and skirt lengths by a few centimeters.

The scale of the tank growth anticipated on F9 is more consistent with the first two stretches shown in the diagram, both of which increased stage length.

To be clear, I'm not trying to argue that the second stage won't be stretched, I'm just trying to figure out if we've confirmed this definitively, or if this is speculation based on certain assumptions.

Who knows what tricks SpaceX has up their sleeve?

Offline Kabloona

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #209 on: 03/05/2015 01:46 pm »
No confirmation that I've seen.

Offline guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #210 on: 03/05/2015 01:49 pm »
No confirmation that I've seen.

You mean confirmation besides Elon Musk saying it in a Twitter?

Offline Kabloona

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #211 on: 03/05/2015 01:58 pm »
No confirmation that I've seen.

You mean confirmation besides Elon Musk saying it in a Twitter?

Sigh. Yes, we know Elon has tweeted that tank volume  will increase by 10%. That's why we're having this discussion.

The question is whether that will result in a length increase in the overall stage. I believe it will. Others believe it might not. But no one from SpaceX has confirmed what the actual effect on overall stage length, if any, will be.
« Last Edit: 03/05/2015 02:06 pm by Kabloona »

Offline cambrianera

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #212 on: 03/05/2015 02:04 pm »
Everything can be imagined or speculated: bulges, external auxiliary tanks, modified pressurization with removal of He COPV tanks etc...
But a one meter stretch of the stage is so simple that "+10% vol" can't mean anything different.

@Dave G
yes I read the post and I saw the figure, showing (as Kabloona said) an ever increasing stage.
Moreover for Falcon 9 there are no "internal tank stretches", the tank is the external structure, therefore tank stretch -> stage stretch.
« Last Edit: 03/05/2015 02:13 pm by cambrianera »
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Offline llanitedave

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #213 on: 03/05/2015 02:10 pm »
I'm not buying it.  Look up Tonopah, NV,and U.S. 95.  Small town, mountainous terrain.  That's where I've seen those 212' long towers being pulled... 

From the link you provided earlier:
https://www.wind-watch.org/faq-size.php

Quote
How are the wind turbine components transported?

Transport of such large items and the cranes needed to assemble them often presents problems in the remote areas where they are typically built. Roads must be widened, curves straightened, and in wild areas new roads built altogether.

So it appears that, while there's no fixed limit, longer stages would tend to present more issues with road transport.

In any case, an informative discussion.


I believe they're talking more about locations such as this:


http://homework.uoregon.edu/pub/class/es202/wind7.jpg


But yeah, there's no doubt that longer stages complicates transport to a certain extent.  However, we're just talking about a fairly minimal stretch for the first stage boosters that's still much less than the maximum that can travel on at least a fair number of public highways.  I think it's less of a problem than some people here are making it out to be.
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Offline guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #214 on: 03/05/2015 02:11 pm »
Sigh. Yes, we know Elon has tweeted that tank volume  will increase by 10%. That's why we're having this discussion.

The question is whether that will result in a length increase in the overall stage. I believe it will. Others believe it will not. But no one from SpaceX has confirmed what the actual effect on overall stage length, if any, will be.

Sigh indeed. We have a few items we can assume fixed. They will not invent new tooling for the upper stage. They will not reinvent the Merlin vac engine by doing fancy things like a retractable nozzle vac extension.

What is left as a reasonable assumption is a small stretch. Everything else is just fancy imagining, which is nothing new on SpaceX threads. IMO of course.

How long are the second stage tanks, without engine, just the tanks? That gives how much in cm a 10% stretch is.

Offline cambrianera

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #215 on: 03/05/2015 02:20 pm »
How long are the second stage tanks, without engine, just the tanks? That gives how much in cm a 10% stretch is.
About 9 meters, consistently with 90 t propellant load.
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Offline deruch

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #216 on: 03/05/2015 02:55 pm »
Everything can be imagined or speculated: bulges, external auxiliary tanks, modified pressurization with removal of He COPV tanks etc...
But a one meter stretch of the stage is so simple that "+10% vol" can't mean anything different.
A different meaning that could, hypothetically, be possible:
Chilled LOX gets more "densification gains" than chilled RP-1 (~9% vs. ~5%, respectively), thereby altering the balance of prop:LOX to excess LOX when tanks are full.  Additionally, increased thrust M1d may also have optimum performance with an altered fuel mixture (slightly less LOX). -----> Between higher density and lower fuel mix, less LOX volume is needed.  Current tank sizes are no longer optimized and moving the bulkhead to increase RP-1 tank volume (at the expense of LOX tank volume) re-establishes optimum.  +10% vol (in RP-1 tank) without stage stretch. 

The problem is that Elon announced this all via twitter which really doesn't allow much flexibility for complex/nuanced explanations.  Personally, I think that there is a small stretch, but the above hypothesis could also fit with the currently available public information.
« Last Edit: 03/05/2015 03:04 pm by deruch »
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Offline guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #217 on: 03/05/2015 03:46 pm »
How long are the second stage tanks, without engine, just the tanks? That gives how much in cm a 10% stretch is.
About 9 meters, consistently with 90 t propellant load.

Thanks. That would translate into 90cm stretch max.  With LOX in the upper tank it would mean the inlet for tanking would need to move by few cm only. That can be done without any modification to the TEL.

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #218 on: 03/05/2015 04:12 pm »
A different meaning that could, hypothetically, be possible:
Chilled LOX gets more "densification gains" than chilled RP-1 (~9% vs. ~5%, respectively), thereby altering the balance of prop:LOX to excess LOX when tanks are full.  Additionally, increased thrust M1d may also have optimum performance with an altered fuel mixture (slightly less LOX). -----> Between higher density and lower fuel mix, less LOX volume is needed.  Current tank sizes are no longer optimized and moving the bulkhead to increase RP-1 tank volume (at the expense of LOX tank volume) re-establishes optimum.  +10% vol (in RP-1 tank) without stage stretch.

The scenario you outline above is quite interesting.  Could be more optimal than a stage stretch.  All things being equal, every pound of additional second stage mass is a pound less max payload.

Yes, a simple stage stretch may be the right answer, but it's interesting to consider other possibilities...



Offline edkyle99

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #219 on: 03/05/2015 04:17 pm »
Sigh. Yes, we know Elon has tweeted that tank volume  will increase by 10%. That's why we're having this discussion.

The question is whether that will result in a length increase in the overall stage. I believe it will. Others believe it might not. But no one from SpaceX has confirmed what the actual effect on overall stage length, if any, will be.
It has to increase the length.  The stage uses a common bulkhead and is cylindrical.  I doubt there is any room in the interstage for a 10% volume increase.  More thrust needs more propellant to achieve best results, so this stretch seems in line with the up-thrusted engines and with the needs of Falcon Heavy.

 - Ed Kyle 
« Last Edit: 03/05/2015 04:19 pm by edkyle99 »

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