Falcon 9 Kerosene to Falcon 3 Methane

[Aussie_Space_Nut]

Given that the Raptor engine is 3 times more powerful than Merlin.

Given the Helium woes of Falcon 9.

Given that ITS will use boiled off Oxygen to pressurize the oxygen tank and boiled off methane to pressurize the methane tank.

Given that both the Raptor and Merlin are approximatly the same physical size.

Given the conservative initial merlin performance and the way that performance grew over time, hopefully we see the same with Raptor.

Obviously you can't just swap out the F9's Merlin's for Raptors.

But would the re-design required to go from a F9 Kerosene to a F3 Methane be outrageously difficult or not?

Would the basic F9 structure design, whats above the Octoweb, be ok to re-use?

(Have I got all my "givens" right?)

[Arcas]

As far as I know, none of the Falcon 9 failures were due to kerosene, or the Merlin engines. I don't see any reason to completely scrap the Falcon 9 for zero benefit.

[Patchouli]

It would pretty much be a new rocket.
Might as well detune the Raptors and make the first stage larger and run five of them to keep similar engine out capability and powered landings.

[TrevorMonty]

Cheaper to fix their He issues, most of their competitors use He without a problem.

[Hobbes-22]

They might not be able to throttle down a Raptor enough to get a reasonable deceleration for landing.

[Radical_Ignorant]

Possible in far, far away future. Many things make sense, too many to address most of them with limited resources. Once ITS is done maybe they will replace F9s with something like X7 or whatever, but for now he stated clearly that one more iteration of F9 and team working on it is switching to ITS, Dragon2 is finished and team working on it is switching to ITS, FH is done and team working on it is switching to ITS. Goal is clear and making additional goals will only slow down advancement on their stated main goal.

[darkenfast]

I personally think that it makes more sense for SpaceX to concentrate on fixing Falcon 9 and turning it and FH into a RELIABLE revenue-generating workhorse for the next fifteen years.  They need the money and they need the track record if they are to succeed in their long-term goals.

[A_M_Swallow]

As I have said elsewhere, as part of the ITS development project SpaceX may want a flying test bed for the raptor engine. 42 may be the answer to everything but 42 engines makes a very complex initial design. A single engine or what ever will fit into the Falcon 9's airframe may make a better test bed. Stretching the tanks and adding a faring can come next.

[Nilof]

That first stage has been really reliable so far. I think a bigger Raptor upper stage makes sense and would allow first stage RTLS for more missions, but for now I don't see any reason to change the first stage.

[Hobbes-22]

As I have said elsewhere, as part of the ITS development project SpaceX may want a flying test bed for the raptor engine. 42 may be the answer to everything but 42 engines makes a very complex initial design. A single engine or what ever will fit into the Falcon 9's airframe may make a better test bed. Stretching the tanks and adding a faring can come next.

Flying test beds haven't been used in rocket development for a long time. I.e. nobody thinks it's worth the effort.

[A_M_Swallow]

As I have said elsewhere, as part of the ITS development project SpaceX may want a flying test bed for the raptor engine. 42 may be the answer to everything but 42 engines makes a very complex initial design. A single engine or what ever will fit into the Falcon 9's airframe may make a better test bed. Stretching the tanks and adding a faring can come next.

Flying test beds haven't been used in rocket development for a long time. I.e. nobody thinks it's worth the effort.

Other than the Falcon 1.

[envy887]

As I have said elsewhere, as part of the ITS development project SpaceX may want a flying test bed for the raptor engine. 42 may be the answer to everything but 42 engines makes a very complex initial design. A single engine or what ever will fit into the Falcon 9's airframe may make a better test bed. Stretching the tanks and adding a faring can come next.

9-Raptor ITS tanker

[First Mate Rummey]

I think it could make sense:
- much higher ISP: + 50+ seconds at both sea level and higher altitudes
- having a single big engine product line - raptor - enabling scale economy
- dismiss all RP-1 management, just specialise on methane
- opportunity to test and optimise raptor in an improving way, like was done with Merlin, while getting money from launching payloads
- possibly would use 4-5 raptors, they still probably can be accommodated on current FS, higher thrust will reduce gravitational losses, while possibly still have some engine out capability (in case of an engine failure the payload would be saved while losing the FS - no landing)
- possibly coupled with increased composite use - higher costs can be compensated by increased recover possibility
- raptor can throttle down to 20%, Merlin only to 39% - so to still be able to recover FS
- cheaper propellant
- methane can give increased reusability
- overall more competitive against Blue Origin's New Glenn

That being said it may still not be doable or worth the effort to redesign this way the FS, which is still a good performer. Will see.

[spacenut]

Kerosene is a more dense fuel.  Methane will take a more volume for the same amount of thrust.  That is why kerosene has mostly been used for first stages.  The F9 and FH were designed to be road transportable.  Also, the Raptor engine will be larger than the Merlin.  I don't know by how much, but you won't get 9 under the F9, you would only get maybe 3 at the most due to nozzle size.  Then you may not have enough volume for the three for the rocket. 

A lot of us around here would like to see a Mini-BFR rocket with about a 7m diameter and 9 Raptors with a one or two raptor upper stage the same diameter.  Fully reusable and could match or exceed FH in capability with only one rocket. 

[Jim]

I think it could make sense:

It make no sense

It could not use existing facilities.  It require redesign of both vehicle and facilities.

And it can't be for landing, too high of thrust.

[DJPledger]

Fully dev. and mass produce the 1MN dev. version of Raptor to produce a Falcon 9 Methane. Use center engine to land it like the current F9.

[Kansan52]

IMHO, the Achilles heel of this proposal is that the two S2 loses were causes by He system failures. The original failure was a strut holding part of the system, not the HE system itself.

Dumping the F9 for an F3m seems over the top and not required and wouldn't be a Falcon anymore.

[Toast]

I personally think that it makes more sense for SpaceX to concentrate on fixing Falcon 9 and turning it and FH into a RELIABLE revenue-generating workhorse for the next fifteen years.  They need the money and they need the track record if they are to succeed in their long-term goals.

I agree, and I think that's why they're looking at freezing the Falcon 9 design after this next upgrade. It'll help them increase flight rate, and focus on quality as well. Then their engineering efforts can move to ITS, leaving Falcon 9 as a mature platform. Later, if the Falcon 9 becomes less competitive, they can reallocate resources to develop a new rocket altogether with lessons learned from the Falcon 9 and possibly the ITS. That's essentially what replacing Merlins with Raptors would entail, anyways, so no point encumbering themselves by starting from their existing rocket. Starting from scratch could let them use more composite structures, reassess the rocket's proportions and thrust-to-weight ratio, improve reusability and reduce refurbishment requirements, etc. If their landing success rate is good enough, they may even decide that keeping the cores road-transportable is less important, too, since they'll only need to be shipped once.

[DOCinCT]

I personally think that it makes more sense for SpaceX to concentrate on fixing Falcon 9 and turning it and FH into a RELIABLE revenue-generating workhorse for the next fifteen years.  They need the money and they need the track record if they are to succeed in their long-term goals.

I agree, and I think that's why they're looking at freezing the Falcon 9 design after this next upgrade. It'll help them increase flight rate, and focus on quality as well. Then their engineering efforts can move to ITS, leaving Falcon 9 as a mature platform.

Musk already stated that once the Falcon design/engineering is done next year they will turn their focus to the Mars adventure.  Without real competition, other than maybe the Chinese (ULA is not even close with Vulcan), SpaceX will have another 6+ years or so to maximize income from F9 and FH, especially as reuse drives down the cost per flight.
A methane powered Falcon would be a redesign a wider diameter would be needed to accommodate any added fuel volume.  The current 3.7m design is about at the end of it's structural limit for it's length.
Delta V is 5m and Vulcan projected as 5.4m with B-4 engines; makes it easier to dear with overly wide payloads.  If FM followed a similar path a new manufacturing line would be needed.  Musk already highlighted the economies of having an engine the same size as a Merlin.  So why spend money for a product without a customer?

[dror]

Musk already stated that once the Falcon design/engineering is done next year they will turn their focus to the Mars adventure.  Without real competition, other than maybe the Chinese (ULA is not even close with Vulcan), SpaceX will have another 6+ years or so to maximize income from F9 and FH, especially as reuse drives down the cost per flight.
A methane powered Falcon would be a redesign a wider diameter would be needed to accommodate any added fuel volume.  The current 3.7m design is about at the end of it's structural limit for it's length.
Delta V is 5m and Vulcan projected as 5.4m with B-4 engines; makes it easier to dear with overly wide payloads.  If FM followed a similar path a new manufacturing line would be needed.  Musk already highlighted the economies of having an engine the same size as a Merlin.  So why spend money for a product without a customer?

The part in Bold was shown to be false in prior threads.
Any booster with dV greater than 1500 will have more performance per volume as methalox then as kerolox. More so with subcooled methalox.

...
...
So in summary, a methalox Falcon 9 family built with small Raptor-like cousins can be the same size as the existing Falcon 9 family.  It will however be even more reusable, carry more to orbit, mass less, damage the pad with less thrust, and be burning an even cleaner propellant mix.  To me, this seems like it would be a worthy long-term upgrade to the Falcon 9 family.  To others I’m sure it is not, so please sound off below about the math posted above, what you think of a methalox Falcon 9, and whether you think it would be worth the change.

[envy887]

Raptor will probably first fly on Grasshopper/DC-X style tests of the ITS upper stage. There's no real reason to fly it before that.

Falcon 9 needs to stop changing and just fly as often as possible.

[garidan]

Not worth opening a new thread I chose this one.
Now that we are near the demo flight of Falcon Heavy and the last block 5 evolution of Falcon, do we have to wait for ITS to see fly some new hardware (Dragon 2 apart)?
Only Space X knows how much time it will take, but ITS is so big it requires a completely new infrastructure it will take years to build and get the permissions let alone fly something.
And being big, costly and reusable, it will build 2 ITS at most in the first years, to learn and improve it.
So, if Raptor is 1-2 years away from being ready to fly, why not prepare the transition to raptor and methane while building all the infrastructure?
And when finally ITS will be flying, will every payload be carried by it ? Will SpaceX still manufacture and "recondition" both Merlins and Raptors ?
I think there are time and human resources now to fill that gap and develop Raptor and knowledge on methane as rocket fuel.
Keep the Falcon dimensions so to use the same tools and processes, keep as much as possible the same height so to reuse pad infrastructure, even if with methane lines added, target only the heavy version, where the reduction of engines Raptor can bring is worth the effort and fuel volume is more fitted to methane being less dense.
With all the said constraints, you can fit 2 Raptors for each core, 6 Raptors total which are roughly 22 Merlins.
Using crossfeed you can have the central core still full of fuel when the side boosters separate to fly back (at a much lower velocity).
Probably you need less fuel (more volume than RP1 but only 6 raptors), so the central core can be lower and fit a larger second stage with raptor (it was said to require 5m diameter) and fitted for large payloads and fairings. The heavy configuration could help sustain that larger second stage using side boosters as a more robust whole frame.
Anyway initially the upper stage can be the same as Falcon, Merlin RP1, just to test while flying reliably the S2 and delivering true payloads.
Crossfeed here would be very useful to maximaze volume utilization by methane: side booster are actually an extension of the volume of the central core and preserve totally the fuel in it, which is at any effect a second stage while S2 becomes the third stage.
Crossfeed here would be easier to do, just one connection for methane line from each side booster to its own raptor in the central core. LOX for the central core engine instead would be taken from the start from the central core.
So just one pipe, one valve for each booster (just to simplify the concept).

What is difficult from the very idea of this? Reusability, because 2 engines bring to an asymmetrical one engine reentry burn. Only SpaceX can simulate this, but using 3 legs instead of four to displace the weight toward the "return engine" CG can be brought back toward the center.
If this is not enough, "baloons" inside the opposite wall in the core filled at the right moment with methane gas could displace the fuel toward the same engine, bringing some tons of fuel weight on its side and "centering" the CG on the burning engine.

This xxx heavy rocket could be lighter than Falcon heavy, having 9 instead of 12 legs, not having COPVs, having a simpler engine mount (2x3 instead of 9x3).
Performance could be good.

[macpacheco]

F9 / FH design was grounded by the requirements of expendable missions + road transportability (optimize for construction cost and ease of ground transportation).
SpaceX now has a way to fully reuse boosters and upper stage reuse is mostly a matter of having lots of spare performance (for deorbit+landing burns plus a lot of TPS for re-entry).
When we add to this the fact that despite of its higher ISP and higher T:W, raptor rockets need to be thicker so road transport need to be given up.
Even with deep cryo methane, a given volume of methane contains less impulse than the same volume of RP1. RP1 is heavier for sure, but FH/F9 design is limited by stage thickness and stretching stages further is a bad idea.
This suggests any partial usage of Raptor on F9/FH is a kludge that produce limited benefits.
The more I think about this, the more I think the best way is go Raptor all the way, to a mini ITS (meaning a big upper stage with lots of engines) or a Raptor Falcon 9 on steroids (single engine upper stage + 7-9 raptors on the booster). Either way we should end up with a boosters that might be reusable 100x without refurb and upper stages that could be reflown dozens of times without refurb too.
A new rocket that's unconstrained by road transport can achieve FH expendable performance with full reuse. In fact it should be designed without any contingency for any expendable usage. Its reuse all the way. It doesn't matter if it costs ~5x as much as a FH.
Trying to squeeze limited raptor usage in between probably doesn't save enough expended upper stages for the redesign cost. Better aim for a rocket that could be a workhorse for several decades instead.
Remember that it costed SpaceX one billion (so far) to figure out reuse. F9 Block I design costed US$ 400 million. Above that, it ties down lots of engineers that could be better used for more permanent ideas. Better to "waste" a few hundred million in 50 or even 100 more 2nd stages being wasted than divert engineers from getting a mini ITS flying sooner.
From a 1/3 thrust Raptor to 75+% thrust its probably a matter of 6-12 months more in testing/development. Better go all the way.
Besides the new workhorse rocket doesn't need to wait until Raptor testing is complete to be designed. ITS design apparently will go into high gear soon.

Remember, FH sounded easy, but it reality it was crazy hard to design. What seems simple for you or me might turn out to be very hard do actually get done.