Author Topic: SpaceX Falcon Heavy Discussion (Thread 3)  (Read 332268 times)

Offline groundbound

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #400 on: 04/12/2015 05:17 pm »
I think some of your figures might be a little off.  The estimate I've seen several times for the ISP of a vacuum Raptor is 380, and the best estimate I've seen for the ISP of the present upper stage Falcon is 345.  So this would be more like a 10% ISP improvement rather than 3.8%.  And with the exponential nature of the rocket equation, this is quite significant.

This ISP are between different fuels for same X engine. The big increase in ISP between merlin and raptor is mainly because of the full flow engine not because of the fuel. I think it would make a lot of sense to have a full flow engine for the upper stage and improve the ISP.
What I don't see is the switch to methane. A mini raptor methane upper stage would fit and maybe in 5 years we will see it in case they have a mini-raptor, but FMPOV a kerosene mini raptor would fit better. The switch between kerosene and methane "is not a big deal", so I don't see that crazy that once they have a mini raptor they adapt it to kerosene. But thats lot of speculation.
You're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.

Yup, my head hurts when even trying to think about full flow with gaseous kerosene.  ;D

Offline nadreck

Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #401 on: 04/12/2015 05:18 pm »
If there was to be a higher(er) energy FH upper stage with an in-house engine, I'd expect it to be something like this> 5.2m barrel size (the same diameter as the PLF) and the same length as the kerosene-fuelled U/S. Whilst a 'Merlin-M' has not evidently in development, I'd certainly consider having it in a 'paper only' development phase to minimise delays if extra beyond-LEO performance is needed and Raptor is further off than a Methane conversion of the Merlin-VAC.

There is a lot of 'ifs' in that and I doubt it would happen unless Musk were certain of a customer or two who needed the performance. That said, a 360-380s U/S would be an interesting addition to the vehicle.

The one thing I can see is that besides needing customers for the capabilities of such an upper stage (which I envisage at around the 200,000 to 225,000 kg of methalox propellant load), is that it really needs to be reusable to be worth the effort. My BOE treatment says you would get at most 8,000 - 10,000 kg for TPS/re-entry recovery stuff before the LEO capability dropped below 50,000kg. The other side of that coin is that the upper stage expendable capability tops out at 60,000 to LEO. Expendable new US makes no sense since it will cost more than twice the current US.
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 baldusi

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #402 on: 04/12/2015 06:21 pm »
But this is no case for SpaceX. They are going from RP-1 Gas Generator to Methane Full Flow. Big difference. And actual RSC Energyia engineer has calculated that a methane Falcon 9 with the same dimensions as v1.1, but engine performance as Raptor, would get 25tonnes to LEO and 8tonnes to GTO. That covers 100% of current market. And that's without the 10% tank lengething and propellant densification that SpaceX is implementing on the enhanced Falcon 9, nor 2050 aluminum tanks and other "cheap" enhancements. Probably could hit 30/10 with that.
If they do a mini Raptor upper stage, they'll probably move the cores later. They'll have the performance margin for upper stage reuse and validate everything for MCT for a lot less money than a whole new development.

Humm I cannot argue because I have no data but 25 tones losing 22% fuel mass is hard to believe. I would expect something similar to what you have now (13-14t to LEO). Zenit rocket with slightly less mass than F9 V1.1 and best full flow kerosene engine works 13500kg to LEO. Maybe could be slightly better, but 25 tones... anyway, time will tell.
For starters, F9 v1.1 actually does about 16.5/17tonnes to LEO. Second, the Zenit-2 has a smaller upper stage in relationship. And third, the F9 v1.1 is around 95% of pmf in both first and second, while the Zenit-2 is 92% and 90%, respectively. Zenit-2 was a compromise with the Energyia boosters and has too much T/W and is just too heavy.

Offline Jimmy Murdok

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #403 on: 04/12/2015 06:23 pm »
You're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.

You mean that the production of a methane stage combustion engine is easier because methane produce less corrossion in plumbing and combustion chamber than the dirty kerosene?


Offline Owlon

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #404 on: 04/12/2015 06:36 pm »
You're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.

You mean that the production of a methane stage combustion engine is easier because methane produce less corrossion in plumbing and combustion chamber than the dirty kerosene?

More or less. The Raptor engine will be full flow staged combustion, so it will have both an oxygen-rich and methane-rich preburner. Kerosene-rich preburners just aren't done because they cause horrible coking problems in the turbine. There may be more to it to that, but that's my basic understanding of the issue.

Offline Jimmy Murdok

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #405 on: 04/12/2015 06:38 pm »
For starters, F9 v1.1 actually does about 16.5/17tonnes to LEO. Second, the Zenit-2 has a smaller upper stage in relationship. And third, the F9 v1.1 is around 95% of pmf in both first and second, while the Zenit-2 is 92% and 90%, respectively. Zenit-2 was a compromise with the Energyia boosters and has too much T/W and is just too heavy.
Yep, let me re-read the SpaceX methalox forum I forgot that the data from Dimitry gave that high numbers.

Offline Jimmy Murdok

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #406 on: 04/12/2015 06:43 pm »
More or less. The Raptor engine will be full flow staged combustion, so it will have both an oxygen-rich and methane-rich preburner. Kerosene-rich preburners just aren't done because they cause horrible coking problems in the turbine. There may be more to it to that, but that's my basic understanding of the issue.

That makes sense. So RD-engine family derivatives to methane are "easy", but Raptor to kerosene would be way too complicated. That's big advantage on methane. Thanks.

Offline tp1024

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #407 on: 04/12/2015 07:03 pm »
You're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.

You mean that the production of a methane stage combustion engine is easier because methane produce less corrossion in plumbing and combustion chamber than the dirty kerosene?

More or less. The Raptor engine will be full flow staged combustion, so it will have both an oxygen-rich and methane-rich preburner. Kerosene-rich preburners just aren't done because they cause horrible coking problems in the turbine. There may be more to it to that, but that's my basic understanding of the issue.

Well I can imagine that. But in this case I don't understand how the normal gas generator cycle can work.

The gas generator is also kerosene rich and the gas gets pushed through the turbine just fine, before being dumped as one big black sooty stream of evil. So maybe the coking problem is with the injectors into the burning chamber instead? Those are fairly small orifices and should be much more vulnerable to coking.

Offline MP99

Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #408 on: 04/12/2015 07:25 pm »
If Raptor is 500k lb thrust and Merlin vacuum is 200k lb thrust, that is a lot more thrust.  Would the upper be widened to hold more fuel, or stretched?  Unless the Raptor vacuum can be throttled down.

If you assume 550 klbf for the vac version (~250 tf), that would need a minimum ~20t payload for 6g burnout @ 50% throttle.

Fine for LEO with FHR, but not for GTO / escape unless they go with FHE (maybe recover the boosters?)

Good for a prop tanker for MCT, though.

Cheers, Martin

Wouldn't this be 6g only if the upper stage itself was massless?  I think the present one is about 4 mt empty.  Switching from Merlin to Raptor probably will add 1 mt.  If it's to be reusable, then you also would be looking at adding TPS, legs, grid fins + hydrolics, etc., not to mention the landing fuel.  I can easily see this approaching 10 mt total.  So at 50% throttle and a 20 mt payload, you'd only be looking at about 4 g at burnout.

 :-[

Urk, yes. You're right.

If the stage (+ etc) is 5T, then a payload would need to be 15t. Assuming min throttle of 50%, as disupted by robotbeat.

With the current 4t stage and 6T+ GTO payload in RTLS form, that would still need a doubling of the dry mass delivered to GTO (10t+ to ~20t), regardless of how much is stage, and how much payload.

cheers, Martin

Offline Space Ghost 1962

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #409 on: 04/12/2015 07:37 pm »
You're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.

You mean that the production of a methane stage combustion engine is easier because methane produce less corrossion in plumbing and combustion chamber than the dirty kerosene?

More or less. The Raptor engine will be full flow staged combustion, so it will have both an oxygen-rich and methane-rich preburner. Kerosene-rich preburners just aren't done because they cause horrible coking problems in the turbine. There may be more to it to that, but that's my basic understanding of the issue.

Well I can imagine that. But in this case I don't understand how the normal gas generator cycle can work.

The gas generator is also kerosene rich and the gas gets pushed through the turbine just fine, before being dumped as one big black sooty stream of evil. So maybe the coking problem is with the injectors into the burning chamber instead? Those are fairly small orifices and should be much more vulnerable to coking.

Stop going OT for this thread - take it to Q/A or Merlin or Raptor thread. Simple answer: GG combustion temps too low - "underburn", CC combustion temps "overburn" thus coking/etc, FFSC attempts ideal combustion of an almost ideal hydrocarbon. No Merlin/F9 methane. End of dumb OT.

Offline notsorandom

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #410 on: 04/13/2015 06:50 pm »
If there was to be a higher(er) energy FH upper stage with an in-house engine, I'd expect it to be something like this> 5.2m barrel size (the same diameter as the PLF) and the same length as the kerosene-fuelled U/S. Whilst a 'Merlin-M' has not evidently in development, I'd certainly consider having it in a 'paper only' development phase to minimise delays if extra beyond-LEO performance is needed and Raptor is further off than a Methane conversion of the Merlin-VAC.

There is a lot of 'ifs' in that and I doubt it would happen unless Musk were certain of a customer or two who needed the performance. That said, a 360-380s U/S would be an interesting addition to the vehicle.
A few days ago in another thread I worked out some very crude numbers for a Methane powered Falcon Heavy upper stage. Well not really, I used a fuel with methane's ISP and RP-1's density for a best case, unrealistic, yet super easy to calculate figure. Even if one could just up the ISP to 370s the payload goes up only by 3-4 mt. Falcon Heavy would not see even that much improvement to its LEO payload since the tanks would get bigger and heavier. One might be able to make the upper stage deliver a bigger portion of the total Delta V of the rocket by changing the stage sizes and do other tricks. However methane is not likely to to increase the payload to the point where replacing the upper stage and its engine is worth the headache.

Offline Ben the Space Brit

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #411 on: 04/13/2015 07:17 pm »
A cryogenic upper stage's purpose wouldn't be anything to do with LEO performance - that's already high enough with kerosene. It's point would be to increase BLEO performance. More of the 55-ish tonnes to LEO being sent through TOI.
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Offline Rebel44

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #412 on: 04/15/2015 09:40 pm »
SpaceX Sends Air Force an Outline for Falcon Heavy Certification - See more at: http://spacenews.com/spacex-sends-air-force-an-outline-for-falcon-heavy-certification/#sthash.0Wzwy5m7.dpuf

Quote
COLORADO SPRINGS, Colo. — SpaceX says it sent the U.S. Air Force an updated letter of intent April 14 outlining a certification process for its Falcon Heavy rocket to launch national security satellites.

SpaceX hopes to have its Falcon Heavy rocket certified by 2017, Gwynne Shotwell, the company’s president and chief operating officer, told SpaceNews in an April 14 interview.
- See more at: http://spacenews.com/spacex-sends-air-force-an-outline-for-falcon-heavy-certification/#sthash.0Wzwy5m7.dpuf

Offline rcoppola

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #413 on: 04/15/2015 10:56 pm »
SpaceX Sends Air Force an Outline for Falcon Heavy Certification - See more at: http://spacenews.com/spacex-sends-air-force-an-outline-for-falcon-heavy-certification/#sthash.0Wzwy5m7.dpuf

Quote
COLORADO SPRINGS, Colo. — SpaceX says it sent the U.S. Air Force an updated letter of intent April 14 outlining a certification process for its Falcon Heavy rocket to launch national security satellites.

SpaceX hopes to have its Falcon Heavy rocket certified by 2017, Gwynne Shotwell, the company’s president and chief operating officer, told SpaceNews in an April 14 interview.
- See more at: http://spacenews.com/spacex-sends-air-force-an-outline-for-falcon-heavy-certification/#sthash.0Wzwy5m7.dpuf
Interesting. It is after all exactly what the last Assured Access Congressional Hearing was requesting. I believe it was something to the effect of, "Please have that FH ready as soon as possible." A 2017 certification, IMO, puts real pressure on ULA in that it makes needing to extend the RD-180 past 2019 a mute point. (Except for the VI issue) This is going to get very interesting. Not that it isn't already.
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Offline guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #414 on: 04/16/2015 06:28 am »
Interesting. It is after all exactly what the last Assured Access Congressional Hearing was requesting. I believe it was something to the effect of, "Please have that FH ready as soon as possible." A 2017 certification, IMO, puts real pressure on ULA in that it makes needing to extend the RD-180 past 2019 a mute point. (Except for the VI issue) This is going to get very interesting. Not that it isn't already.

Right, it is the signal to Congress and the Airforce. We will be ready by 2017, will you delay us? At the congressional hearing I recall Gwynne Shotwell talking about 2018 and when the Airforce General was asked if that is realistic he said something like "It is optimistic but I won't bet against SpaceX".

Vertical Integration is not an issue IMO. When the demand is there they will have it ready by end of 2016. They have the plans ready to execute at LC-39A and no doubt can do the same in Vandenberg.


Offline dglow

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #415 on: 04/16/2015 07:26 am »
Surprising...

Quote from: Gwynne Shotwell
Shotwell said she expects the Falcon Heavy rocket to fly once this year, three times in 2016 and three to five times in 2017.
“The market is huge,” she said. “The market is bigger in the commercial marketplace than it is for the single stick Falcon 9.”

Offline Ben the Space Brit

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #416 on: 04/16/2015 10:50 am »
Surprising...

Quote from: Gwynne Shotwell
Shotwell said she expects the Falcon Heavy rocket to fly once this year, three times in 2016 and three to five times in 2017.
“The market is huge,” she said. “The market is bigger in the commercial marketplace than it is for the single stick Falcon 9.”

Very. I'm not saying that she's misstating but I do wonder who the potential customers in the 50t IMLEO/17t GTO market might be.
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Offline spacenut

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #417 on: 04/16/2015 11:59 am »
I looked on the launchs coming up.  Can't find it now to link it.  However, one Falcon Heavy in 2016 0r 2017 was going to launch 17 satelites at one time. 

Offline e of pi

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #418 on: 04/16/2015 12:11 pm »
Surprising...Very. I'm not saying that she's misstating but I do wonder who the potential customers in the 50t IMLEO/17t GTO market might be.
I think the better way of thinking about it is the number of customers in the >6t to GTO market at a price of roughly $100m. That's about half Ariane, and competitive with Proton without the issues of working with Russians. Even without employing the ful capacity, Falcon Heavy can be the cheaper $/kg option. The customer doesn't have to be using the full capacity to choose FH, they just have to be looking for (1) more than F9R can lift and (2) not seeing a competing launcher in the class that can match that price.

Offline guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #419 on: 04/16/2015 12:18 pm »
competitive with Proton without the issues of working with Russians.

Working with the USA is a PITA as well. As it is ESA finds it easier to keep buying Soyus even at inflated prices and flying them from Kourou than sending satellites to the USA for launch.

But yes Falcon Heavy with reusable boosters and central core will be very competetive if cost will be as anticipated by SpaceX.

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