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New Rocket Engine Successfully Tested
inetsee writes "XCOR Aerospace announced that their new methane-oxygen rocket engine has been tested successfully. This is reported to be the first successful test of an engine using the combination of methane and oxygen as fuel. The fuel has higher specific impulse than kerosene and oxygen, but until now has been thought to have too much 'technology risk'."
Do I have to be the first to point out that methane doesn't have a smell. This is the natural gas that gets piped into peoples homes - the smell is added so you can detect leaks.
Methane gas is utterly renewable. You can make it from shit, literally, and without any special equipment. The only special thing you need is a way to compress it to store it... say 200 psi tops? The only thing I can't find is a small compressor suitable for this purpose on a household scale. You can actually just run your waste into the bottom of a pond along with a steady flow of water, tent it, and capture methane - you bubble it through water to purify it. The compressing is the only issue left...
Side note: While searching for goodies I found this url which attempted to root my computer. No idea how successful it was, I'm off to go run defender and spybot.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
'risk' isn't quite what people are making it out to be. Risk is the fact that a methane engine hasn't been built and operated before. By building and operating a methane engine, and improving its design (making it regeneratively cooled, using cryogenic methane as a fuel, passing x-thousand lights without incident, etc) reduces its relative risk.
NASA uses a scale called Technology Readiness Levels (TRL) which you can read about if you like. Operating this device and documenting it can help raise the TRL of methane engines.
Additionally, it is a 'risk reduction' effort because it could be a replacement for the engine of the CEV which right now is (I think) kerosene+LOX. If that falls through for some reason (what, I don't know...) there is a second option on the table. Again, reducing risk.
And yes, according to Zubrin, we can manufacture methane on Mars where the CEV will be headed in 15-20 years, so an adaptation of this might be a retrofit to the CEV someday. (but please, be critical thinkers when you read Zubrin...)
That is all.
NASA only has so much money to spread around to different projects -- and much of where it goes is mandated by congress. Consequently, there's only so much engine research that they can finance.
Methane engines are interesting, but they're no panacea. Methane lines on the spectrum between kerosene (dense, comparatively high temperature, moderate ISP) and hydrogen (sparse, extremely low temperature, high ISP). Specifically:
Hydrogen@20K: 70kg/m^3 (fuel**), 358kg/m^3 (bulk**), 455.9 (ISP sec@100:1/20MPa)
Methane@112K: 423kg/m^3 (fuel), 801kg/m^3 (bulk), 368.3 (ISP sec@100:1/20MPa)
Kerosene-based (RP-1)@298K: 820kg/m^3 (fuel), 1026kg/m^3(bulk), 354.6 (ISP sec@100:1/20MPa)
Note that it's a rather small ISP gain over kerosene -- not close to the performance of hydrogen -- yet its density is halfway between kerosene and hydrogen. While a small gain in ISP can be a big boost in performance, that's a pretty big density hit.
A fuel that I find interesting is propane. While at its boiling point, it's not that interesting:
Propane@231K: 582kg/m^3 (fuel), 905kg/m^3 (bulk), 361.9 (ISP sec@100:1/20MPa)
But cool it to 100K, and you get:
Propane@100K: 782kg/m^3 (fuel), 1014kg/m^3 (bulk), 361.9 (ISP sec@100:1/20MPa)
Not only are these attractive numbers, but since the propane is similar in temperature to the LOX, they can share a common bulkhead. Of course, it can't go too much below that, or its viscosity will rise too much (at 100K, it's similar to kerosene).
To make methane significantly more dense, you have to go pretty darn cold (well below your LOX temps), and it's probably not worth hydrogen complexity for a fuel with an ISP like methane.
** - Fuel density is the density of the fuel alone. Bulk density is the density of the fuel plus stochiametric amounts of liquid O2.
Yes, I've read a poem. Try not to faint.
NASA is paying for the research through a contract with ATK. XCOR is a subcontractor.
See, XCOR can't make money flying their rocket-planes around so they have to have government contracts to foot the bills. It was like this before the X-prize and will remain to be.
Now the X-prize itself and the X-cup? Yes, cool. But credit where credit is due. This is NASA research, not X-Prize stuff.
Oh, forgot to mention: this assumes that the tanks aren't pressurized beyond the vapor pressure from the fuel (i.e., we're dealing with turbopump-driven rockets). Increasing pressure means a simpler turbopump (or even no turbopump) and denser fuel, but it gives you heavier tanks. Now, the pressure can help support the weight of the rocket better, but you only need so much structural support. In fact, I like SpaceX's notion for rocket design: when unpressurized, the rocket has just enough strength to be transported and brought into launch configuration, but not to withstand the forces of launch. Pressurization gives it the strength to launch.
Speaking of pumps -- what do others think of the flometrics design? I have to say, I like it.
Yes, I've read a poem. Try not to faint.
Bison are starting to replace cows as a reliable meat source
.019% of the global market. I wouldn't worry about methane production.: for every bison being raised for meat, there are 5,200 cattle.
I'm sure they are, for small-scale organic ranchers catering to prestige restaurants. For the other 99.98% of the market, cattle are still king. Compare the numbers: roughly 1.3 billion head of cattle worldwide (100m in the US), compared to only 350,000 bison remaining in the world, with 250,00 being raised for meat.
That means that bison have about
You catch enchiladas by picking them up behind the head and holding them underwater until they don't kick anymore -VeGas
One of the nice things about methane (like LOX, and unlike kerosene or for practical purposes hydrogen) is that it's potentially self-pressurizing; keep the tank at the right temperature, and you can maybe dispense with the pumps entirely. Depending on your cost-sensitivity and the performance you're trying to hit, this might or might not be a big win...
Here's a link to an old plan for Mars operations leveraging the ease of obtaining methane and oxygen on Mars.
I am the one true god. However, as an atheist, I don't believe in myself. I guess I have a self-esteem problem.
Actually, the gas that makes flatulence stink is hydrogen sulfide. There's not enough to hurt you in the average fart, but it's still pretty poisonous, and it can build up to dangerous levels in the manure pits from animal farms. Methane itself, CH4, is odorless.
At atmospheric pressure, methane freezes at a temperature about half a kelvin above that at which oxygen boils (about 90.7 kelvins and 90.2 kelvins, respectively, if I've looked things up correctly).
:) It's hard enough to design systems with two tanks. Designing a methane/LOX system with one? Perhaps it's counterintuitive to many, but at the *very* least, it would be *significantly* more difficult, but I suspect it would not even be possible.
Obviously, I know nothing about the operational pressure ranges, but one can easily infer that mixed-phase flows would likely result if you tried to use both from a single tank. I wouldn't want to see what that would do to a rocket engine turbopump. (Well, actually, since high-speed cameras are fairly cheap these days... um...)
Rocket science is already rocket science.
Ion engines are very efficient, problem is they don't generate much thrust and therefore don't really help with "getting there faster". Deep space one pioneered ion propulsion technology. Can't do nuclear propulsion like Project Orion due to international treaties and what not. Basically anything other than chemical propulsion is experimental and no one is willing to foot the bill to make the technology mature.
If you are about to mod me down, keep in mind that this post was most likely sarcastic.
That appeared to me to be a nice illustration of "shock diamonds".
:)
You can get some really interesting designs out of high-speed flows, especially when you throw in some bright combustion.
I am partial to US technology in most matters but South Korea successfully tested a 20,000lb thrust methane engine last year. I believe that Japanese have something similar.
an ill wind that blows no good
Great info! I just want to add, because people tend to forget, that Isp and Thrust are related but separate quantities. Heavy hydrocarbons and polymers are good first-stage propellants because they give high thrust (F=ma). They use the big thrust to get up off the pad, then drop those stages for the higher-Isp propellants.
>Does anybody have any idea what this guy's talking about?
:-)
It isn't rocket science
The most important concept being taken for granted here is "specific impulse" or I(subscript)sp. It's pounds (force) of thrust divided by fuel burn rate in pounds (weight) per second. If you have an Isp of 300, then (oversimplifying outrageously) you'd use 1/300th of your fuel to hover for a second.
Higher Isp is very good. It appears in an exponent in the "rocket equation" (see Wikipedia). Small improvements make big differences in what you can accomplish. To get a high Isp for a given energy content, you want the fuel to be really really light.
One tradeoff is that the lightest fuel we have is hydrogen, which takes up ridiculous amounts of room, which means the tanks are larger and heavier. Plus you have the fun of pumping and storing something only 20 degrees from absolute zero. Sometimes a denser fuel with lower Isp gives you a better system design.
The Saturn V first stage burned kerosene and oxygen. It didn't have to lift its own weight very far. The upper stages had to be light and were hydrogen/oxygen.
Here's why.
Isp relates pretty directly to exhaust velocity. The difference is a unit conversion and some small correction factors.
Speed and force are separate ideas. Thrust is proportional to Isp *times the mass flow rate*. Throwing something heavy out the exhaust gives you more kick, but lifting and carrying something heavy is inefficient.
Ion drives show the tradeoff really well. They have spectacular Isp but the mass flow rate is a trickle. They have tiny amounts of thrust, but great fuel efficiency.
Specific impulse is what you need for efficient deep space travel. Thrust is what you need in order to correct the mistake of being on a planetary surface.
The bottom line is that NASA has rocket engines that can do everything they want. The relevant point is, different rocket engines do some tasks better than others. Methane has its selling points, which the article notes, but it doesn't simply put all other fuels to shame or anything like that.
NASA has wanted to have a methane engine option for quite a while, but since they have other functional options, they haven't been willing to take money away from other projects to develop it. It's a risk in the sense that it's not a proven design (see my final two paragraphs). As such, they haven't made a commitment to it for any particular project. Now they've finally funded ATK (who sub-contracted X-Cor) to develop the engine, I believe with funding from the Constellation program.
The first studies that NASA did for the Orion CEV had it using a methane/oxygen engine for the extra performance. However, because of the timeline involved and the challenge in getting reliable performance from a non-hypergolic engine in deep space, they chose the safer and cheaper route from an engineering perspective of using a proven hydrazine fueled engine (from the Boeing Delta 2 upper stage) like the shuttle and apollo craft. It sounds like a methane engine may still be used for the new Lunar Surface Access Module (lander), which is on a slower development timeline than the Orion, and as an upgrade to the CEV.
I want to note that almost all flight-restartable rocket engines (off-hand, the only exception I know of is the old Saturn V J-2 second stage engine) use hypergolic fuels. Hypergolics are fuels which spontaneously ignite when combined. The shuttle uses methyl-hydrazine and nitrogen tetroxide, which has a performance not far below kerosene and oxygen, the major drawback being its instability and toxicity.
The reason for accepting the drawbacks of hypergolics is they ignite with incomparable reliability. Before NASA is willing to commit to having a manned mission 150,000 miles from earth depend entirely on a non-hypergolic engine, they have to be absolutely sure that when they pour frigid oxygen and methane together together in the cold of space and throw a spark that it will ignite reliably and controllably. You can't just send an astronaut back there with a Zippo and a can of carb cleaner and hope for the best.