Author Topic: SpaceX Falcon Heavy Discussion (Thread 3)  (Read 223656 times)

Online Lars-J

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #40 on: 02/17/2015 04:27 PM »
I read somewhere that the 4 strap ons burn with the core and transfer fuel to the core at the same time.  Then they drop off and the core continues.  Maybe they don't since they are smaller.  However I read that years ago.

That is incorrect. There is no propellant transfer. The boosters just jettison when they are empty, and the core (called stage 2) just burns longer because it has larger tanks.

Offline TrueBlueWitt

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #41 on: 02/17/2015 04:29 PM »
Purely FWIW, I think that RL-10C's thrust is too low for use on Falcon Heavy, even if you use cross-feed on the core and boosters. Staging is just too low and slow (because of RTLS performance limitations). Given that limitation and given that I think that Messrs Musk and Bezos would prefer to gouge out their own eyes than work together, the only hydrolox engine likely to be used on Falcon Heavy, IMHO at least (for a certain percentage of 'likely' anyway) is MB-60.

They have a long fairing.. Would s  Centaur fit in the fairing with s high C3 Sat? RL-10 powered S3 would have plenty of thrust. S2 did the heavy lifting in earth's gravity.

Online Nate_Trost

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #42 on: 02/17/2015 04:29 PM »
There is a simple question and simple answer in regards to Falcon Heavy cross-feed development.

Q: Why would SpaceX develop cross-feed for Falcon Heavy?
A: Because it is necessary to meet sufficient demand for customer payload requirements.

It isn't going to happen just because. It would happen because it was necessary for enough paying customers that would justify the development cost, or a customer needed it badly enough to pay for it. And it isn't really clear that that is something that is going to happen in the next 15 years. SpaceX themselves won't need it: their long-term Mars plans revolve around BFR. Any reusable SpaceX BFR in 10-15 years would make a cross-feed FH obsolete.

So who is the customer? And don't say Bigelow. At this point, it seems a rather long shot that he ever pulls together several hundred million dollars to develop, build and fly even one of the smaller modules, much less a larger one. And, again, if you're the *only* customer for a cross-feed Falcon Heavy, guess who gets to foot the tab for development?

Offline Lobo

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #43 on: 02/17/2015 05:09 PM »
Hopefully this is the right thread for this question.

Has SpaceX said anything for sure about if they plan to upgrade LC-40 to handle FH?

I'd assume they would, perhaps after 39A is up and fully functional becuase an upgrade to LC-40 like that will mean it'll be out of commission for awhile, and their manifest is packed right now.

But I don't recall anything for sure about it, other than an old comment by Elon saying they might build a FH HIB at a 90 degree angle to the F9 HIB.  I think that was before 39A was in the mix, so they could keep flying F9 while upgrading to FH.  With 39A operational, I think they can just fly from there and tear down the F9 HIB and build the FH HIB there

Or will they just leave LC-40 launching F9 only?

They have mentioned doing it, but plans change, and most of those comments were pre-39A acquisition. Now that they have 39A I don't see them being in a hurry do it. Perhaps never. But it also depends on two additional factors:
 - What will be the ratio of F9 to FH launches going forward?
 - How quickly will the Texas launch pad come online (presumably built to support FH from the beginning)

Agreed, I was just wondering if there was any more recent information out there about their plans.

Myself, I'd think they will upgrade it, for the added flexibility of having the ability to launch FH from there.  But it'd probably wait until after a Boca Chica pad were operational and they had the launch capacity to take LC-40 off line for awhile. 

One question, -could- they rebuild the existing HIB to accomodate FH?  Given the location of the flame duct?  It's located to the side of the pad, rather than in "front" like SLC-4E, LC-39A, and Boca Chica's concept art.  That means the far side booster's exhaust would have to cut accross the central and duct-side booster.  Would that be an issue?  Looks like Titan was arranged at 90 degrees to how FH would be, with each booster discharging directly out the "front" so there's no crossing of exhaust.  Looks like LC-41 with Titan was like that too in the pic below, as well as SLC-4E.  The Titan MSS's on all of those retracted to the side.  SpaceX used the  Titan MSS rails to transport F9 on LC-40 so it came from the side, rather than from the "back" like SLC-4E.  Ok for a single core LV, but for a tri-core?   I figured it would be so there'd be shorter inturruption to pad operations, but that might be the way FH would have to sit on the pad.  It'll probably mean the existing HIB is torn down as I don't know if they can make a pad accessable from two directions.

Offline MTURN91750

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #44 on: 02/17/2015 06:02 PM »
There is a simple question and simple answer in regards to Falcon Heavy cross-feed development.

Q: Why would SpaceX develop cross-feed for Falcon Heavy?
A: Because it is necessary to meet sufficient demand for customer payload requirements.

It isn't going to happen just because. It would happen because it was necessary for enough paying customers that would justify the development cost, or a customer needed it badly enough to pay for it. And it isn't really clear that that is something that is going to happen in the next 15 years. SpaceX themselves won't need it: their long-term Mars plans revolve around BFR. Any reusable SpaceX BFR in 10-15 years would make a cross-feed FH obsolete.

So who is the customer? And don't say Bigelow. At this point, it seems a rather long shot that he ever pulls together several hundred million dollars to develop, build and fly even one of the smaller modules, much less a larger one. And, again, if you're the *only* customer for a cross-feed Falcon Heavy, guess who gets to foot the tab for development?

I think with any other launch vehicle company you're right, but SpaceX's goals are different. Even on SpaceX's website they mention using the Falcon Heavy to take crews to Mars so getting as much performance out of FH seems logical. Bigelow might be a good way to pay for some the development. That extra performance also might help in development with the MCT. I always thought that the MCT and BFR were going to be developed in parallel so I could see how a better performing Falcon Heavy might be useful to test MCT technology before the BFR is ready. Just saying it won't be developed because today's customers don't have a need for it seems like a very simplistic view of SpaceX's goals and business model.
« Last Edit: 02/17/2015 07:45 PM by MTURN91750 »

Offline Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #45 on: 02/17/2015 06:06 PM »
The multi-core BFR posts are out of date. Musk has made fairly clear recently (in the MIT talk, I believe?) that the BFR will be single-core (though they were looking at multi-core before), I think due to operational reasons.
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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #46 on: 02/17/2015 06:53 PM »
1 - Could the M1D thrust upgrade and prop densification fully compensate no cross feed ?
2 - Just because SpaceX mentioned a few times flying people to Mars on Falcon Heavy doesn't mean it's still in the cards. SpaceX has shown multiple times the ability to evolve its plans. Don't get hung up on words from many years ago if they don't get reinforced (with more words or actions).
Looking for companies doing great things for much more than money

Offline punder

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #47 on: 02/17/2015 07:00 PM »
Purely FWIW, I think that RL-10C's thrust is too low for use on Falcon Heavy, even if you use cross-feed on the core and boosters. Staging is just too low and slow (because of RTLS performance limitations). Given that limitation and given that I think that Messrs Musk and Bezos would prefer to gouge out their own eyes than work together, the only hydrolox engine likely to be used on Falcon Heavy, IMHO at least (for a certain percentage of 'likely' anyway) is MB-60.

Are there any known plans to install (or use existing) LH2 infrastructure at SLC-4E or 39A?  I just don't see SpaceX dealing with LH2 at all.  LH2 is extremely high cost, high maintenance technology that limits materials, design and processes not just on the rocket but on the pad.

Online spacenut

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #48 on: 02/17/2015 07:01 PM »
Seems like throttling down the core while throttling up the boosters works ok. 

However, they could have cross feed with the kerosene only, by having the core built with a small kerosene tank and larger oxygen tank while the boosters could have smaller oxygen tanks and larger kerosene tanks.  That way only the kerosene is cross fed using easier more traditional equipment to disconnect. 

They could also stretch the core while shortening the boosters so they drop off earlier.  Seems like no matter what they do, the most cost effective will be there option.

Offline MTURN91750

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #49 on: 02/17/2015 07:26 PM »
1 - Could the M1D thrust upgrade and prop densification fully compensate no cross feed ?
2 - Just because SpaceX mentioned a few times flying people to Mars on Falcon Heavy doesn't mean it's still in the cards. SpaceX has shown multiple times the ability to evolve its plans. Don't get hung up on words from many years ago if they don't get reinforced (with more words or actions).

You can go to SpaceX's website right now and find this exact quote under Falcon Heavy:

Quote
http://www.spacex.com/falcon-heavy: Falcon Heavy was designed from the outset to carry humans into space and restores the possibility of flying missions with crew to the Moon or Mars.

I'm not getting hung up on anything. I'm just pointing out something that's on SpaceX's website TODAY mentions using the Falcon Heavy for Mars.
« Last Edit: 02/17/2015 08:39 PM by MTURN91750 »

Offline AncientU

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #50 on: 02/17/2015 07:32 PM »
There is a simple question and simple answer in regards to Falcon Heavy cross-feed development.

Q: Why would SpaceX develop cross-feed for Falcon Heavy?
A: Because it is necessary to meet sufficient demand for customer payload requirements.

It isn't going to happen just because. It would happen because it was necessary for enough paying customers that would justify the development cost, or a customer needed it badly enough to pay for it. And it isn't really clear that that is something that is going to happen in the next 15 years. SpaceX themselves won't need it: their long-term Mars plans revolve around BFR. Any reusable SpaceX BFR in 10-15 years would make a cross-feed FH obsolete.

So who is the customer? And don't say Bigelow. At this point, it seems a rather long shot that he ever pulls together several hundred million dollars to develop, build and fly even one of the smaller modules, much less a larger one. And, again, if you're the *only* customer for a cross-feed Falcon Heavy, guess who gets to foot the tab for development?
When will people stop thinking/stating with certainty that anything is CLEAR in the future, especially 10-15 years hence?  In the year 2000, would you or anyone have been certain that we'd be where we are in space launch business in 2015? 

Stop, please. (You don't have a clue. None of us has a clue.)
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Offline MTURN91750

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #51 on: 02/17/2015 07:43 PM »
The multi-core BFR posts are out of date. Musk has made fairly clear recently (in the MIT talk, I believe?) that the BFR will be single-core (though they were looking at multi-core before), I think due to operational reasons.

Point taken. I'll modify my post.
« Last Edit: 02/17/2015 08:01 PM by MTURN91750 »

Offline dror

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #52 on: 02/17/2015 08:14 PM »
The multi-core BFR posts are out of date. Musk has made fairly clear recently (in the MIT talk, I believe?) that the BFR will be single-core (though they were looking at multi-core before), I think due to operational reasons.


It was at the reddit AMA :

[]FoxhoundBat 12 points 20 minutes ago
In order to use the full MCT design (100 passengers), will BFR be one core or 3 cores?

[]ElonMuskOfficial 6 points a minute ago
At first, I was thinking we would just scale up Falcon Heavy, but it looks like it probably makes more sense just to have a single monster boost stage.

" but it looks like it probably makes more sense "
Hardly conclusive. I wouldnt dissmiss the tri core concept altogether based on a triple disclaimed sentence.
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Offline mfck

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #53 on: 02/17/2015 08:46 PM »
The multi-core BFR posts are out of date. Musk has made fairly clear recently (in the MIT talk, I believe?) that the BFR will be single-core (though they were looking at multi-core before), I think due to operational reasons.


It was at the reddit AMA :

[]FoxhoundBat 12 points 20 minutes ago
In order to use the full MCT design (100 passengers), will BFR be one core or 3 cores?

[]ElonMuskOfficial 6 points a minute ago
At first, I was thinking we would just scale up Falcon Heavy, but it looks like it probably makes more sense just to have a single monster boost stage.

" but it looks like it probably makes more sense "
Hardly conclusive. I wouldnt dissmiss the tri core concept altogether based on a triple disclaimed sentence.
Well, it's a 3-sigma statement...

Online spacenut

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #54 on: 02/17/2015 08:47 PM »
I could see some use in Falcon heavy for Mars, but as a ferry to an L1 or L2 assembly area using Dragon as a taxi to ferry astronauts or colonists.  Also to ferry some smaller items, supplies, or even some fuel, but a big rocket would still be needed for the larger items needed. 

Offline punder

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #55 on: 02/17/2015 10:46 PM »
When will people stop thinking/stating with certainty that anything is CLEAR in the future, especially 10-15 years hence?  In the year 2000, would you or anyone have been certain that we'd be where we are in space launch business in 2015? 

Stop, please. (You don't have a clue. None of us has a clue.)

Interesting you should say that.  I'm re-reading "To Reach the High Frontier: A History of U.S. Launch Vehicles" edited by Roger Launius, published in 2002 but with material no later than 2001 at the latest.  There is no mention of SpaceX at all.  Atlas 5 and Delta 4 were still in the works.  A very different time.

Offline MTURN91750

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #56 on: 02/17/2015 11:00 PM »
Has anybody seen any recent information on whether or not SpaceX will develop a larger fairing for FH? This to me seems like another item that would only be paid for if a customer wants it, but it also seems like a much cheaper upgrade than cross-feeding.
« Last Edit: 02/17/2015 11:00 PM by MTURN91750 »

Offline AncientU

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #57 on: 02/18/2015 12:05 AM »
Has anybody seen any recent information on whether or not SpaceX will develop a larger fairing for FH? This to me seems like another item that would only be paid for if a customer wants it, but it also seems like a much cheaper upgrade than cross-feeding.
I requested just that information from SpaceX a while back... for a project I'm working.
No answer received.  Must be time to ask again.

There is certainly room to go longer, to 18m range mentioned up thread, and/or wider to around 6m.
At 45-50 mT to LEO/20ish to GTO, they will be severely volume limited with present fairing.
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Offline IainMcClatchie

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #58 on: 02/18/2015 12:08 AM »
If you go full throttle on the core and the two boosters you are hauling the mass of all three until you run out of propellant. If you throttle back on the core it still has propellant after you dump the mass of the boosters.

Thank you.  Dumping the boosters at lower speed would have a large effect.  That's what I was looking for.

I thought of perhaps another way to do full cross-feed without affecting the bottom of the rocket at all.  The boosters are taller than the core stage.  You could arrange for each booster to have two LOX tanks and two kerosene tanks, one set half the size of the other.  The smaller kerosene tank sits above the main kerosene tank, and significantly, the bottom of the smaller booster kerosene tank sits above the top of the core kerosene tank.  It drains into the core kerosene tank by gravity feed.  Similarly, the bottom of the smaller booster LOX tank sits above the top of the core LOX tank, and drains by gravity feed as well.  Note that gravity feed is fairly powerful, as the accelerations before booster burnout are over 3G.

This scheme is perfect cross-feed, but with the added weight of two more tank bulkheads and the cross piping and unions.  No special lines are needed to blow the cross piping clear of propellant before closing the valves and disconnecting.  The pressurization system of the booster propellant tank can positively drain all the fluid into the core tanks before separation.

Given that at separation you'd have nearly full core tanks, the propellant burn before separation is always the same and any throttling down just postpones the booster separation and increases gravity losses.  Once past max Q you'd ramp all the engines to 100% and leave them there through booster ECO at around 155 seconds.

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #59 on: 02/18/2015 12:27 AM »

I thought of perhaps another way to do full cross-feed without affecting the bottom of the rocket at all.  The boosters are taller than the core stage.  You could arrange for each booster to have two LOX tanks and two kerosene tanks, one set half the size of the other.  The smaller kerosene tank sits above the main kerosene tank, and significantly, the bottom of the smaller booster kerosene tank sits above the top of the core kerosene tank.  It drains into the core kerosene tank by gravity feed.  Similarly, the bottom of the smaller booster LOX tank sits above the top of the core LOX tank, and drains by gravity feed as well.  Note that gravity feed is fairly powerful, as the accelerations before booster burnout are over 3G.

This scheme is perfect cross-feed, but with the added weight of two more tank bulkheads and the cross piping and unions.  No special lines are needed to blow the cross piping clear of propellant before closing the valves and disconnecting.  The pressurization system of the booster propellant tank can positively drain all the fluid into the core tanks before separation.

Given that at separation you'd have nearly full core tanks, the propellant burn before separation is always the same and any throttling down just postpones the booster separation and increases gravity losses.  Once past max Q you'd ramp all the engines to 100% and leave them there through booster ECO at around 155 seconds.

that doesn't make any sense.  The few feet of head pressure is not going to matter and it is a waste to have separate tanks

also, there is no need to blow the lines clear before closing valves.

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