In situ propellant production

[bobcvn65]

Can anyone help with information on a system I remember hearing about a while ago? I think it was called "ACER", but I'm unsure. It takes in oxygen while in flight and somehow converts it to liquid, stores it, then uses it for fuel.

Any information would be greatly appreciated. Thanks in advance.

 

[GregLocock]

wrong acronym. See

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

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[bobcvn65]

Thanks for the reply. Do you think that this system could somehow be more efficient in a low temperature,low pressure, carbon-dioxide atmosphere such as Mars. Would it be possible to have a Mars aeroplane that could produce fuel, store it, then drop it on the surface of Mars for future return missions? ISPP(In-situ propellant production) is a great idea for a Mars mission, but it has a higher risk of contamination by dust from the surface. If this ISPP was somehow at a higher altitude...

 

[GregLocock]

I haven't the faintest idea. I don't see how CO2 is going to work as a fuel for that matter. Filters are not an unusal technology, flying at several miles just to avoid using filters seems a trifle perverse.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[btrueblood]

I've seen data that showed dust in Mars atmosphere persists to very high altitudes (partially due to the "fluffy-ness" of its atm., i.e. the density gradient is shallow relative to Earth's); the dust has had eons to acheive very fine particle sizes, and there is little to no water to help agglomerate and precipitate it out.

 

[bobcvn65]

Well I know that 3M makes a filter called "Filtrete" that is composed of permanently charged fibers that capture particles that are smaller than the openings between the fibers, but the problem is that this filter must be large enough to minimize pressure drop.

I only bring this up because ISPP research seems to have reached a brick wall in terms of its requirement that the sorbent bed, sorbent cooler, pump, storage of CO2 is so dependent on nighttime and daytime and thermal controls and the Martian atmosphere and blah blah blah blah blah, that wouldn't it be worth visiting the issue of a more mobile system?

 

[btrueblood]

IIRC, the idea is to react CO2 and water, cracking tehm to create methane and oxygen, with perhaps some carbon monoxide left over, or mixed with the methane. The main issues were to have a ready source of water, the most likely being near the polar caps. (Flying around means you are getting your water source from where, exactly?) Location near the poles gives trouble because the mean insolation is going to be reduced, and solar panels are already marginal as a power source at Mars' distance from the sun. The obvious alternative is to fly a nuclear reactor as the propellant plant's power source, but that is fraught with political difficulties these days. To my mind, dealing with dust is a minor problem, you will be getting a lot of dust and dirt mixed with your incoming water (look at the banded ice formations that the MGS photos show), and will have to have a settling pond and/or filters for that, so "washing" the incoming CO2 stream to remove the dust is not unfeasible.

All of this is mostly moot; without a few spare trillions of dollars, nobody is seriously considering the development of these systems, and that is what is "stalling" research.

 

[monkeydog]

This smells like a school project.

 

[bobcvn65]

Actually, I was just doing some research into Zubrin's "Mars Direct" approach. I'm reading a book called "The Case for Mars" and have become quite interested in some of his ideas. The polar caps on Mars are CO2. The reaction is actually called the "Sabatier" reaction:
CO2+4H2->CH4+2H2O
The methane is stored after the reaction and the water goes through electrolysis after which O2 is stored and H2 is sent back to react with the CO2.
The entire process is heavily dependent on a "sorbent bed", which contains zeolite that adsorbs CO2 at night and is heated during the day to pressurize the system.
Their problem is that in order to "recharge" the zeolite, it must be cooled down further than Mar's ambient, and the other gases that were adsorbed in the bed must be driven off by use of a fan.

Brtrueblood and "monkeydog" - All of this requires more energy obviously, so I thought that maybe someone could give a little feedback on the idea of having the entire plant airborne, which would decrease the need for a fan to drive off the undesirable gases in the sorbent bed, and increase the cooling requirements needed for it; instead I get false information on the actual process of the reaction that produces the propellant, someone actually suggesting a polar lander (which would actually have to drill through several feet of dry ice before hitting water ice), someone who honestly thinks that "solar panels are already marginal as a power source at Mars' distance from the sun" and another who, while not offering any useful reply at all, thinks that my interest lies in a school project.

THANKS

 

[monkeydog]

bobcvn65,

No need to take offense to comments.

One of my senior projects in school was to design a turbofan engine for an unpiloted aircraft on Mars (circa 1971). Your questions were going right down the same path I went many moons ago. As you know eng-tips has a policy on students trying to get others to do their homework.

I was just pointing out how your questions seemed.

No apologies,
Monkedog

 

[btrueblood]

Gee, sorry to try and help. But your concept of an airborne fuel production plant is about as whacked as I've ever heard. How are you going to supply motive power for your airplane, and provide enough residual power to supply your fuel production plant as well? That was Greg's point, and you haven't answered it. I pointed out that the dust persists to high altitude in Martian atmosphere, and negates the ONLY justification you have for your aircraft, you don't answer that point. Your idea that flying around is somehow going to reduce the need for cooling fans for the absorber bed are nuts, all that means is you need to add more engine power to overcome the added drag of the flow diverted thru the absorber bed, in addition the the lift and drag performance already required of your aircraft. You claim that my reaction is false information, and yet the H2 that you show reacting with the CO2 comes from where exactly -- that's right, water; and the reaction you would use more economically is the water-gas reaction if you could find some carbon deposits, but let's not discuss that, since you won't be landing, instead you're planning, what, to carry around a blimp full of H2 that you brought with you or something? You claim a polar lander is a dumb idea, know any other place on Mars that has confirmed water ice deposits? Yes, there is some CO2 in solid form there too, hey - why do you need an absorber if you can just shovel in raw dry ice, and let it evaporate to pressurize your system, leaving dust contaminants behind? Do you really propose to power your idea with solar cells, and have you any idea what their potential lifespan is for Martian environment?

I read Zubrin's Case for Mars papers 20+ years ago as a grad student, researching methods to reject waste heat on Mars for fixed nuclear power plants. They are good studies, but were old when I read them. There's better data out there today.

But all you can do is whine that we're not helping you realize your dream of soaring above Mt. Olympus. Go away, kid, ya bother me.

 

[monkeydog]

bobcvn65,
You should have just been honest and up-front here.
thread31-123561
How's the project coming?

 

[bobcvn65]

Never went to ERAU, but still living on your tax dollars as a disabled vet.

 

[monkeydog]

Off topic,
But thank you for your service and sacrifice.

 

[ASEI]

Hmm. I've read about this before. Manufacturing propellant on the surface allows you to get away with much less propellant for the round-trip.

However, it means depending on remote equipment to operate correctly to fuel the return flight. I wouldn't launch the manned mission until a supply of fuel has already been generated on the surface plant. Backup fueling schemes might also be required - who knows what a month of dust storms would do to the connectors? Or a tank leak might do in the eight month trip out to Mars?

If your propellant plant was airborne, the only thing it could pick up would be the CO2. I suppose you could have an essentially coal powered rocket, but off the top of my head, I don't think that it would give you decent Isp. And coal's a solid. Even if it would work in a solid-rocket stup, solid propellants are tough to transfer to an existing engine - you basically have to form them into solid rockets somehow.