Metholox?

[Pipcard]

SpaceX intends to build a methane/liquid oxygen (Lox) engine, said founder Elon Musk, in a shift away from the highly refined kerosene rocket propellant (RP-1) that has powered the company’s previous engines.

Speaking at the Royal Aeronautical Society in London, SpaceX chief executive and lead rocket engineer Musk said Lox and methane would be SpaceX’s propellants of choice on a mission to Mars, which has long been his stated goal.

SpaceX’s initial work will be to build a Lox/methane rocket for a future upper stage, codenamed Raptor. The design of this engine would be a departure from the “open cycle” gas generator system that the current Merlin 1 engine series uses. Instead, the new rocket engine would use a much more efficient “staged combustion” cycle that many Russian rocket engines use.

Musk says that methane fuel has performance, cost and storage advantages over alternatives and could even be extracted from the Martian atmosphere for use in landing and ascent stages.

Although methane is known to be a better fuel for reusable engine operations in not having significant coking (carbon deposit) problems that kerosene has, Musk noted that this was not a main driver for the choice.

“The energy cost of methane is the lowest and it has a slight Isp (specific impulse) advantage over kerosene,” said Musk, adding that “it does not have the pain-in-the-ass factor that hydrogen has”. Hydrogen, another commonly used fuel, has storage and handling difficulties and the problem of hydrogen embrittlement.

Musk confirmed that he would not be seeking collaboration with the Russians, despite their lead in this technology, before adding however that “we might hire a few”. Musk also ruled out working with China, noting that they did not seem to want collaboration anyway.

How come no one seems to have used a combo of methane and liquid oxygen for a launch vehicle before? Most liquid propellants I have been seeing are the aforementioned LOX/Kerosene and LOX/LH2, as well as the toxic N2O4/UDMH.

I also came across this thread, which says using LOX/Methane gives us about 380 s of Isp in vacuum.

 

[MaverickSawyer]

Mainly because there's been little interest in doing so. If you needed thrust, you went with kerolox. If you wanted reliablility, you went storable hypergolics. If you wanted performance, you went LOX/LH2. The benefits of designing a whole new line of engines didn't seem worth it at the time.
Nowadays, LOX/CH4 can be considered semi-storable (relative to LOX/LH2, perhaps), and has almost as good of performance. It's lighter than Kerosene, but denser than hydrogen, so it fills a nice niche role there. With the rising interest in going to Mars, and using In Situ Propellant Production, LOX/CH4 research is rising rapidly. I'm not suprised that SpaceX is looking into this; I'm suprised it took them so long! :lol:

 

[Urwumpe]

You have to take what is there. On Mars is no refinery yet, but lots of Methane sources. Turning Methane into rocket fuel is easier then, than trying to build even a small refinery on Mars for getting rocket-grade kerosene fuel (which is a pretty oxymoron... kerosene is only better refinery junk, only slightly better than the stuff they drive ships with - RP-1 is just a stricter defined version of junk...)

 

[MikeB]

Would methane be liquified and/or compressed? Wouldn't that require a pretty strong (and weighty) tank? Would there be boil-off (if liquid) or pressure-relief? What sort of losses would occur over a several-month trip to Mars?

So many questions for the engineers among us . . .

 

[Urwumpe]

Methane is less annoying in terms of liquifying it than oxygen.

 

[MaverickSawyer]

Agreed. Methane is considered "Soft" cryogenic, like LOX. This is in comparison to hydrogen and helium, which are "Hard" cryo fluids. The methane would not have as bad of a boiloff issue as hydrogen, because it's relatively warm in comparison to LH2. Therefore, it's highly likely that you could liquify it. There's actually a plan in Mars Direct's plans that, IIRC, you compress the methane at outside temperatures on Mars, and it liquifies on the spot. Might be confusing it with the CO2 capture plan for the ISPP. Can't recall, and my copy of "The Case for Mars" is at home right now. :lol:

 

[Thunder Chicken]

XCOR has been playing with methane/oxygen engines:

 

[BruceJohnJennerLawso]

Agreed. Methane is considered "Soft" cryogenic, like LOX. This is in comparison to hydrogen and helium, which are "Hard" cryo fluids. The methane would not have as bad of a boiloff issue as hydrogen, because it's relatively warm in comparison to LH2. Therefore, it's highly likely that you could liquify it. There's actually a plan in Mars Direct's plans that, IIRC, you compress the methane at outside temperatures on Mars, and it liquifies on the spot. Might be confusing it with the CO2 capture plan for the ISPP. Can't recall, and my copy of "The Case for Mars" is at home right now. :lol:

Does Helium suffer from the same storability issues as hydrogen? (boiloff through the storage container its in)

 

[Urwumpe]

no. it is never stored in liquid form. except for space telescopes. otherwise you still have minimal leaking of helium. But not like hydrogen, which can slowly travel through metal because of chemical reactions

 

[MaverickSawyer]

[SARCASM]Gotta love hydrogen embrittlement, too... :dry: [/SARCASM]