Author Topic: SpaceX Falcon Heavy Discussion (Thread 3)  (Read 332211 times)

Offline hkultala

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #380 on: 04/11/2015 09:40 pm »
This might not be quite as big of an issue as is normally argued if they can launch from VAFB.  It might be possible to transport a wider diameter stage from Hawthorne to VAFB by boat/barge.  Though, they might lose the ability to test it in TX first.

VAFB only works for polar trajectories. No GTO launches from VAFB, and considerable payload hit for VAFB launches to earth escape trajectories.

Offline Jimmy Murdok

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #381 on: 04/11/2015 09:43 pm »
In a practical way you don't obtain substantial improvement with methane over querosene, the slight improvement on ISP (3,8%) is more than lost in the higher volume (22%). Falcon 9 is designed for road transport, if you switch to methane you have to increase the size of the tanks and you lose this capability, so it doesn't make sense.

This might not be quite as big of an issue as is normally argued if they can launch from VAFB.  It might be possible to transport a wider diameter stage from Hawthorne to VAFB by boat/barge.  Though, they might lose the ability to test it in TX first.

What is the advantage? Kerosene is already great, very dense and easy to storage. If you don't need to collect from Mars is better than methane.

Falcon 9 is the workhorse of SpaceX and will be for the next years, it's great advantage is it's practicality in all the ways.
 
The improvement would be a closed cycle Merline engine (Keroesene mini Raptor). This would improve the performance and keep it's practicalities. But this new Merlin should be cheap to produce and easy to maintain between launches to improve the current rocket.

I don't see any practical advantage on switchin F9/FH to methane.

FMPOV a good strategy would be to develop raptor with multiple combustion chambers like RD-170 family. Start with 2 chambers 500mlb symilar to RD-180 and later you can go to 1 chamber and have something better in (250mlb vs 200mlb) thrust and ISP than with Merlin. This smaller raptor I would adapt it for Kerosene and if it is cheap enough then use it for Falcon family in the same 9 + 1 configuration. Then you get a F9 with 16T to LEO and FH with 60T to LEO.

Offline Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #382 on: 04/11/2015 10:02 pm »
SpaceX isn't going to make a methane Merlin, end of story.
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Offline Ronsmytheiii

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #383 on: 04/11/2015 10:13 pm »
What is the advantage? Kerosene is already great, very dense and easy to storage. If you don't need to collect from Mars is better than methane.


Methane would significantly improve performance for the upper-stage, while not really helping at all for the booster stage. If SpaceX switched to a methane upper-stage, performance to GTO would improve significantly (which is a big money maker). They could lift large GTO payloads on a single core Falcon 9, or two large payloads on a Heavy.

It is too bad SpaceX isn't going to use their Raptor work for a Methane based upper-stage engine, would help them to pay for further development.

Offline dror

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #384 on: 04/11/2015 10:16 pm »
Does anyone think they will make a metholox Merlin engine?  If so, what kind of capacity would the Falcon heavy have converting all to metholox?

My bold

What I would like to know is the expected isp of a gas generator methalox engine compared to a kerolox gg engine, and that would be a good beginning to answer your question.

If the difference is not substantial , I would stick to the speculation (adopted from the mini BFR thread)  that with\without crossfeed, the next step is a reusable single raptor upper stage for FH, followed by replacing both F9R and FH cores with a 9 raptor reusable booster.

In a practical way you don't obtain substantial improvement with methane over querosene, the slight improvement on ISP (3,8%) is more than lost in the higher volume (22%). Falcon 9 is designed for road transport, if you switch to methane you have to increase the size of the tanks and you lose this capability, so it doesn't make sense.

Methane improves the reutilization of the engines through a cleaner combustion with les maintenance. The second good point of methane over querosene is the capacity of ISRU production in Mars.

What it would work would be a querosene closed cycle Merlin Engine to improve the ISP, with methane you would end up with a too long stick.

Methane has never been used for rockets because querosene and hydrogen work better. This might change with reutilization once you don't care about road transportation (BFR).

Well, the question was about a methalox Merlin (gas generator) , not about a kerolox mini Raptor (staged combustion) .
I reckon that was assuming the first option is easier to develop.

Thanks for your answer -
"the slight improvement on ISP (3,8%) is more than lost in the higher volume (22%)."

As I get it, since the rocket equation is exponential for isp, the 3,6% isp increase can't compare with the 22% volume reduction. Some math has to be made in order to know if the payload increases or decreases with these changes and the same total volume of the F9.
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Offline Jimmy Murdok

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #385 on: 04/11/2015 10:38 pm »
Well, the question was about a methalox Merlin (gas generator) , not about a kerolox mini Raptor (staged combustion) .
I reckon that was assuming the first option is easier to develop.

Thanks for your answer -
"the slight improvement on ISP (3,8%) is more than lost in the higher volume (22%)."

As I get it, since the rocket equation is exponential for isp, the 3,6% isp increase can't compare with the 22% volume reduction. Some math has to be made in order to know if the payload increases or decreases with these changes and the same total volume of the F9.

If you keep the same tanks you have 22% less fuel, no way it compensates throught ISP. Otherwise Musk would have gone for methane from the beginning.

In case you make bigger tanks (22%) then you increase the tank weight in small percentage and is here where you loose the small advantage in ISP.

Same engine for Kerosene, Methane, Hydrogen give ISP of: 355,368,456s. For Hydrogen you always need bigger tanks with isolation, so for same weight of fuel you have much more weight, but the ISP (+24%) here is making big big difference. In kerosene VS methane the difference is really small and you probably end up in something symilar. But in the particular case of Falcon rockets there is no discussion as the tank size is the big constraint that can not grow. But even if it could grow I don't see any advantage.

Offline dglow

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #386 on: 04/11/2015 11:39 pm »
Falcon 9 is designed for road transport, if you switch to methane you have to increase the size of the tanks and you lose this capability, so it doesn't make sense.

But in the particular case of Falcon rockets there is no discussion as the tank size is the big constraint that can not grow.

The F9 second stage could grow in length and remain road-transportable. The diameter is the constraint.

Your argument that the corresponding increase in dry mass might outweigh the benefits of switching to methalox stands. But don't argue that stage size/transport would prohibit such a move.

Offline groundbound

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #387 on: 04/11/2015 11:41 pm »
But in the particular case of Falcon rockets there is no discussion as the tank size is the big constraint that can not grow. But even if it could grow I don't see any advantage.

Tank diameter is not an absolute constraint. It is a constraint that SpaceX has placed upon itself to reduce costs, if it ever truly gets in the way of an important goal it will be discarded. A true need to get FH a much higher energy upper stage might be enough reason if that market opportunity ever materializes.

But that would be years down the road, and SpaceX will likely never encounter the business need.


Offline baldusi

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #388 on: 04/12/2015 12:36 am »
Well, the question was about a methalox Merlin (gas generator) , not about a kerolox mini Raptor (staged combustion) .
I reckon that was assuming the first option is easier to develop.

Thanks for your answer -
"the slight improvement on ISP (3,8%) is more than lost in the higher volume (22%)."

As I get it, since the rocket equation is exponential for isp, the 3,6% isp increase can't compare with the 22% volume reduction. Some math has to be made in order to know if the payload increases or decreases with these changes and the same total volume of the F9.

If you keep the same tanks you have 22% less fuel, no way it compensates throught ISP. Otherwise Musk would have gone for methane from the beginning.

In case you make bigger tanks (22%) then you increase the tank weight in small percentage and is here where you loose the small advantage in ISP.

Same engine for Kerosene, Methane, Hydrogen give ISP of: 355,368,456s. For Hydrogen you always need bigger tanks with isolation, so for same weight of fuel you have much more weight, but the ISP (+24%) here is making big big difference. In kerosene VS methane the difference is really small and you probably end up in something symilar. But in the particular case of Falcon rockets there is no discussion as the tank size is the big constraint that can not grow. But even if it could grow I don't see any advantage.
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.

Offline HIP2BSQRE

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #389 on: 04/12/2015 12:48 am »
Well, the question was about a methalox Merlin (gas generator) , not about a kerolox mini Raptor (staged combustion) .
I reckon that was assuming the first option is easier to develop.

Thanks for your answer -
"the slight improvement on ISP (3,8%) is more than lost in the higher volume (22%)."

As I get it, since the rocket equation is exponential for isp, the 3,6% isp increase can't compare with the 22% volume reduction. Some math has to be made in order to know if the payload increases or decreases with these changes and the same total volume of the F9.


If you keep the same tanks you have 22% less fuel, no way it compensates throught ISP. Otherwise Musk would have gone for methane from the beginning.

In case you make bigger tanks (22%) then you increase the tank weight in small percentage and is here where you loose the small advantage in ISP.

Same engine for Kerosene, Methane, Hydrogen give ISP of: 355,368,456s. For Hydrogen you always need bigger tanks with isolation, so for same weight of fuel you have much more weight, but the ISP (+24%) here is making big big difference. In kerosene VS methane the difference is really small and you probably end up in something symilar. But in the particular case of Falcon rockets there is no discussion as the tank size is the big constraint that can not grow. But even if it could grow I don't see any advantage.
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.

baldusi,

Is that what you think Spacex will do?  How long do you think that this development would take?  Do you think Spacex will do a min-raptor upper stage or just use the BO engine to replace the current upper stage?  How much would estimate this would cost?  How would this affect Spacex prices?

Offline Jimmy Murdok

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #390 on: 04/12/2015 02:28 am »
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.

Offline MP99

Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #391 on: 04/12/2015 08:02 am »
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

Offline GORDAP

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #392 on: 04/12/2015 11:50 am »
Well, the question was about a methalox Merlin (gas generator) , not about a kerolox mini Raptor (staged combustion) .
I reckon that was assuming the first option is easier to develop.

Thanks for your answer -
"the slight improvement on ISP (3,8%) is more than lost in the higher volume (22%)."

As I get it, since the rocket equation is exponential for isp, the 3,6% isp increase can't compare with the 22% volume reduction. Some math has to be made in order to know if the payload increases or decreases with these changes and the same total volume of the F9.

If you keep the same tanks you have 22% less fuel, no way it compensates throught ISP. Otherwise Musk would have gone for methane from the beginning.

In case you make bigger tanks (22%) then you increase the tank weight in small percentage and is here where you loose the small advantage in ISP.

Same engine for Kerosene, Methane, Hydrogen give ISP of: 355,368,456s. For Hydrogen you always need bigger tanks with isolation, so for same weight of fuel you have much more weight, but the ISP (+24%) here is making big big difference. In kerosene VS methane the difference is really small and you probably end up in something symilar. But in the particular case of Falcon rockets there is no discussion as the tank size is the big constraint that can not grow. But even if it could grow I don't see any advantage.

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.

If SpaceX goes this route, I don't think they'd stick to the present volume and diameter for the 2nd stage.  They'd probably go with a larger diameter (hmm, maybe about the diameter of the hammerhead shroud?) and probably a little heavier overall.  Yes, they'd lose road transport, but I think that's much less important if the stage becomes reusable, which would be the whole point of this exercise.  In the Reddit AMA Musk said they couldn't (or wouldn't) pursue reusability for the second stage due to the difficulty of doing it with a relatively low ISP stage.  I've got to think that admission sticks in his craw just a little bit, given how he's repeatedly stressed 'rapid and essentially complete reusability' for a good while now.

With a heavier US and payload they'd have to stiffen the center core a little more, but they're already doing this, so it would just be a bit more of the same.  Also, staging would occur earlier in the flight, but this helps the cause of reusability, since it may be the difference between RTLS for the center core versus barge landing for many flights.

I think a beefier, more energetic upper stage really makes sense for the Falcon Heavy, but probably not for the Falcon 9.  If they go down this route, I'd think it signals that they view the FH as their workhorse for the next 5-8 years (versus the F9), which may make sense given their plans for a constellation, and maybe some other big ventures we're not aware of yet.  And if they do the new Raptor based US, I'd bet the next evolutionary step would be to replace the 3 stick heavy with a single stick Raptor based 1st stage.
« Last Edit: 04/12/2015 11:51 am by GORDAP »

Offline clongton

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #393 on: 04/12/2015 12:23 pm »
Do you think Spacex will do a min-raptor upper stage or just use the BO engine to replace the current upper stage?

SpaceX is not going to use a non-SpaceX engine in any of its launch vehicles - period. Whatever they use will be built in-house.
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Offline Kabloona

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #394 on: 04/12/2015 02:07 pm »
Do you think Spacex will do a min-raptor upper stage or just use the BO engine to replace the current upper stage?

SpaceX is not going to use a non-SpaceX engine in any of its launch vehicles - period. Whatever they use will be built in-house.

Unicorns would have to dance in flame ducts before Musk would use an engine from Jeff Bezos.  ;)

http://spacenews.com/37389musk-calls-out-blue-origin-ula-for-phony-blocking-tactic-on-shuttle-pad/
« Last Edit: 04/12/2015 02:18 pm by Kabloona »

Offline Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #395 on: 04/12/2015 02:14 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
Should be able to throttle lower than that.
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Offline GORDAP

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #396 on: 04/12/2015 03:41 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.

Offline Ben the Space Brit

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #397 on: 04/12/2015 04:41 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.
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Offline Jimmy Murdok

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #398 on: 04/12/2015 04:48 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.

Offline Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #399 on: 04/12/2015 04:59 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.
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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

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