Mark Whittington has an idea to solve the methane problem (no, not that methane problem--that one we'll solve by burning down the rain forests):

If NASA feels that building a methane/LOX engine is too risky for the ESAS, there is a solution. Make such an engine one of the Centennial Challenges. Critics of the Vision for Space Exploration will be less unhappy because that would be another piece of technology developed by non traditional means. NASA will benefit because it gets the engine for the CEV and Mars Lander relatively cheaply.

Well, maybe. The problem is, I guess I don't see LOX/methane engines as particularly risky, at least no more so than any other generic propulsion development. It's not a technology risk (in the sense that there may be some unknowns out there that prevent it from being possible) so much as a programmatic risk, in terms of schedule delays or cost overruns. NASA has a lot of experience with these in propulsion programs, so they're wary of new engine developments (though I suspect that XCOR has broken a lot of the conventional industry cost/schedule estimating models for propulsion system development). Our lack of methane propulsion isn't because it's a Hard Problem, but because no one has had sufficient requirement to date to fund it.

If we have unlimited money for prizes, I guess that a prize would be a good way to fund this, but prizes are better employed in those cases for which innovation is required to solve a really difficult problem that many have attempted and no one yet solved, not for a straightforward development program. Rather than offer a prize, I'll bet that someone like XCOR (or the other companies working on the problem) would be happy to take a fixed-price contract to develop engines to NASA's specs (they could use the technology contract they have from Marshall to develop a reusable cryo tank as a model), and it would be a lot cheaper than funding a cost-plus contract to Aerojet or Pratt. There are lots of other ways to do innovative procurement than offering prizes.

Interestingly, there's been one 'man-rated' methane rocket engine already...over 35 years ago:

http://en.wikipedia.org/wiki/Blue_Flame

...and for no more a prize than the prestige and bragging rights (and some good press for the sponsor) of breaking the land speed record.

I've always wondered, why methane? Why not kerosene, if you're going to go hydrocarbon / LOX?

why methane?

It's easier to make than kerosene, particularly if you want fine control over the composition, which is a consideration if you're making the fuel from space resources. It also delivers slightly higher Isp than kerosene, and its lower density is not as much of a problem in space where the tank (and rocket chamber) pressure can be lower than for engines operating at sea level.

Methane can be made by making syngas (CO + H2), adjusting the CO/H2 ratio, then passing the mixture over a methanation catalyst (nickel, I believe). Liquid hydrocarbons would require the use of a Fischer-Tropsch catalyst or something similar, and would produce a more complicated and difficult to control mixture of products.

> If we have unlimited money for prizes, I guess that a prize would be a good
> way to fund this, but prizes are better employed in those cases for
> which innovation is required to solve a really difficult problem that many
> have attempted and no one yet solved, not for a straightforward development program.

I think that's arguable. Critics of the X Prize will say it was not aimed at any unsolved problem (which is true unless you consider low cost to be part of the problem definition). The X Prize succeeded because the goal could be accomplished within the current state of the art. By contrast, the space elevator prizes require technology that is beyond the state of the art and are much less likely to be successful.

A more significant obstacle to Mark's proposal is his "lions for space exploration" who zeroed funding for Centennial Challenges in the NASA FY2006 appropriations bill (mainly due to NASA's repeated failure to answer Senate questions about what specific prizes NASA planned to offer).

This thread asserts Pratt & Whitney have already run their RL-10s on methane, at least in the lab. See post #3 or #4

Follow the link and take it for what its worth.

Isn't T-Space looking at pressure fed Methane or Propane engines?

I always thought the problem with liquid methane was the narrow range at which it is liquid under normal conditions. At standard pressure, methane liquifies at -161.5 C and freezes at -182.5 C. I think that adds to the engineering problem. I don't know how it handled under much higher pressures, but I wouldn't be surprised if the temperature range at which methane were liquid grew somewhat at high pressures.

As Paul mentions, methane is a lot easier to make on Mars (and anywhere else you have water and carbon) than most fuels, and handles relatively well.

A fixed price contract with performance clauses is a prize. It is a sole-source prize to one participant. If the contract is competed on a cash basis, it is a sole-source prize that goes to the company willing to compete for the lowest prize. NASA needs to trade that off against increasing the likelihood that the selected company will "win". That is where NASA might select a company with better history or credentials rather than the low bid.

A sole-source or limited competition prize gets the participant(s) to commit to devoting resources because of the higher chance of winning. Such a prize also reduces the resources devoted to racing (not rocket racing leagues--but patent-style races). If there are many players seeking to win a prize, resources are devoted to being first that are wasted if the project can be completed more inexpensively at a slower pace and the savings justifies the increased technology risk in the interim. Resources devoted by teams that do not know they are not competitive are also wasted.

A radical way to offer a development contract would provide the maximum amount of cash for successful development that NASA is willing to pay, but the potential participants bid cash for the opportunity. If all companies have equal access to capital, that would provide additional incentive for development by the best firm while keeping costs in check. As it is, XCOR is a startup that does not have the same access to capital as Aerojet or Pratt. This would tilt any competition based on performance bonding or auctioning the right to get a fixed price contract at a pre-set fee.

Prizes are easier to not pay than fixed-price contracts with performance targets. Prizes are therefore also easier to go unwon than fixed-price development contracts.

I always thought the problem with liquid methane was the narrow range at which it is liquid under normal conditions.

If that's a problem, the catalysts could be tweaked to also make some C2 and C3 hydrocarbons, although this would give up some of the simplicity of an all-methane system. The extra components will depress the melting point. A eutectic mixture of methane and ethane (70%/30%) melts around 72 K. Ternary mixtures, and mixtures with alkenes, can have even lower melting points.

Paul,
How difficult is it to make, say propane instead of methane? Propane seems like a much better choice propellant-wise (almost as good of Isp as methane, but much denser, particularly if subcooled), and I heard mention from Henry Spencer that there were methods of catalytically converting CH4 into propane (C3H8?). The fact that subcooled propane is denser than room temperature kerosene, but gives 10-20s better Isp, doesn't coke, and has much better coolant properties tends to get me interested.
~Jon

How difficult is it to make, say propane instead of methane?

You can make propane with a Fischer Tropsch catalyst (Fe, Co, or Ru, instead of Ni). The problem is you have less control over the result than if you're just going for methane.

Basically, FT has two 'knobs' you can control: the probability of adding a carbon to a growing chain (which is attached to the catalyst), and the probability of having the chain come off the catalyst (terminating the chain growth). So, you can get propane, but you'll also get ethane, butane, and various other hydrocarbons.

Commercially, the FT conditions are optimized to produce longer chains (since the goal is to produce liquid transportation fuels), and there's then a post-processing step where the noncondensible gases are recycled back to the gasifier and the too-long chains (waxes) are reacted under pressure with hydrogen to break them down into shorter chains.

I think it wouldn't be terribly hard to make methane with a smaller fraction of ethane and propane, and small amounts of C4+ hydrocarbons.

Thinking differently, I imagine it might be possible, if you have methane, to make higher hydrocarbons by radiolysis. This could be a good approach if you have a space nuclear reactor; just exploit the neutrons and gammas from the reactor, possibly mixing some 3He with the methane to make the neutrons couple more efficiently. You'd need to ensure you don't make too much unstable stuff like acetylene, though.

cuddihy asked: "...why Methane?"

As Thoreau said, "In the long run men hit only what they aim at."

Not only is methane simpler to come by on Mars than other propellants -- it is also found in abundance at Jupiter and the rest of the outer Solar System.

Back when methane from fermenting manure was hip fuel for residential schoolbusses, it came to my attention that it is the equivalent of 120 octane. Very attractive to a hotrodder, but from what I understand about the problems liquifying it I don't see using it as a lift fuel.