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.