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In the Case for Mars a system is described where methane is created from hydrogen imported from Earth. The URL below describes a system where the methane is turned into aromatic hydrocarbons. This reduces the amount of hydrogen which needs to be imported to Mars by a factor of 4 over the methane fuel created by the Sabatier reaction.
(Note: aromatic hydrocarbons are ones that contain benzene rings. They have a distinctive smell which results in their class name.)
// Go to the link below and then look for the article called "
Mars Aromatic Hydrocarbon and Olefin Synthesis System"
http://www.pioneerastro.com/projects.html
Benzene (C6H6) is created with the reactor described in the article. Note that the chemical has 1 hydrogen for every carbon atom. Thus the fuel needs less hydrogen per carbon to be burnt by the oxidizer.
There has been significant advances in the field of using catalysts to turn methane into aromatic fuels as this would allow methane (natural gas) to be economically moved from natural gas fields which are too remote for a gas pipeline. One problem is coking (carbon build up) on the catalysts. This article describes techniques which lower the speed of the reaction but greatly extends the life of the catalysts making it suitable for working on Mars.
The group also created better catalyst for this reaction (Mo-Zr/HZSM-5 zeolite catalyst).
the key formula is:
6 CH4 --> C6H6 + 9 H2 + heat
Benzene and liquid oxygen have a Isp close to LOX/Kerosene. Small amounts of toluene (C7H8) and naphthalene (C10H8) impurities does not affect performance. (In fact if burnt in a slightly oxygen rich environment the naphthalene actually gives a slight boost in Isp.)
This great boost in efficiency means that the hydrogen can now be shipped to Mars as either water or methane which are much more reliably stored in vacuum environments. This is important as it allows this process to be used by small probes where hydrogen boil off would be a real problem.
Another advantage of this system is it takes less power than the Sabatier system. Additionally it requires less O2 oxident and this further reduces power requirements.
SUMMARY:
This system makes sample return missions and human missions to Mars cheaper and more reliable.
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This is from the Pioneer Astononautics website:
"Although all the compounds listed in Table 1 are usable as high quality fuels, their potential as feedstock to plastic production processes should be briefly mentioned.
Ethylene has been called the key to the plastics industry. In terrestrial applications, it is the precursor for many different varieties and grades of polyethylene, which is the most widely utilized plastic in the world.
Propylene is the precursor for polypropylene, which is the second largest volume commodity terrestrial plastic at this time and is widely used for textiles.
Toluene is not directly used as a plastic monomer, but is usually converted to benzene and/or directly combined with ethylene or propylene. With various further processing steps, these chemicals end up in products as diverse as polystyrene, styrene-butadiene rubber, Nylon, polyurethane, epoxies, aspirin, and explosives.
While these applications will be irrelevant to robotic and early human missions, they are potentially very valuable when it is time to build a permanent outpost on Mars."
see:
Use of Aromatic Hydrocarbons.
Nice to see Dr. Robert Zubrin's company is still working towards the Mars colony.
Warm regards, Rick.
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RickSmith,
Really interesting and i think a must for a real mars mission is to fuel at Mars.
I wonder why a condenser isn't thought about much in the fuel schemes.
Mars has water vapor in the atmosphere so a condenser should work to make a water frost.
Then broken down to liquid 02 and hydrogen is simple chemistry.
With a condenser we also get necessities for the people on mars, water and oxygen.
Science facts are only as good as knowledge.
Knowledge is only as good as the facts.
New knowledge is only as good as the ones that don't respect the first two.
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I wonder why a condenser isn't thought about much in the fuel schemes.
Hi nickname, everyone.
The reason is simply the extremely low vapor pressure of H2O in
the Martian atmosphere. In order to get that water you have to
cycle a huge amount of air. This requires big air intakes, fans
etc. Remember any moving parts are a weak point because of
the ultra fine dust.
In the reactors Dr. Zubrin is planning, a small hole is opened
and CO2 enters the reaction chamber after going thru a dust filter.
It is sealed off and the gas is processed. Repeat as needed. No
blowers, compressors, etc. are needed.
Let me work out the math. The percentage of water in the atm
ranges from about zero up to 0.03%. Let us say that you want
6 tonnes of Hydrogen (enough to power the Mars Direct rocket).
Now water is 2/18ths hydrogen by mass. So you would want
6 tonnes / (2/18) = 54 tonnes of water.
So if you take a cubic liter of Martian air. I don't know what this
would mass but I can approximate this from the Ideal Gas Law.
(Basically take CO2 at standard temperature and pressure and
lower the temperature and pressure. (Any one know the exact
mass of a liter of Martian air?)
Anyway, using the ideal gas law my approximation for the
Martian air is 0.0045 grams / liter (of this near vacuum at 6mBar).
Since only 0.03% (at best) of this is H2O we need
0.0003 * 0.0045 g / liter or about 0.00,000,14 g / liter of water
in the Martian air. Since we need 54 tonnes of water this is:
0.00,000,14 g / liter / 1,000,000 g / tonne = 1.4E-11 tonnes per liter.
So we need:
54 tonnes / 1.4E-11 tonnes / liter = 3.9E12 liters of air.
Since 1,000 liters are in a cubic meter we will need to blow
3,900,000,000 cubic meters of air thru the condenser (assuming
the condenser is 100% efficient). Call it 4 billion cubic meters.
I just thought, I was using the minimum air pressure. If we
assume that we do this when the Martian air pressure is at its
highest, then we would need about half the volume that I
calculated above. (But the dust would be worse then. You
will have to make sure you don't get dust in your condensers.)
I'm making some estimates here so I wouldn't be surprised if
I'm off by 10 or 20%. But the point is that you would need a
LOT of blowing and compressing to get any reasonable amount
of water out of the Martian atmosphere.
Warm regards, Rick.
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RickSmith,
Thanks for the rough math on the condenser.
4 bcm is a pretty high number but not that great if we have it sitting on Mars for 6 months or 1 year before the crew arrives.
I didn't give the dust much thought, and you are right it will cause all sorts of troubles in all machinery.
Fans would be #1 on the problem list.
Seems like the biggest problem for a condenser on Mars moving large quantities of atmosphere is the dust.
Why not use a condenser that doesn't require moving large volumes of air.?
We could use pressure differential between a few tanks to form frost and avoid the massive air fans, as the air chills and condenses it will move itself.
It would be a pretty energy sloppy device moving and pressurizing fluids from tank A to B to C etc, but it does avoid the dust problems.
With a long copper coil between each tank we should be able to form a decent frost on each pressure and de pressure cycle.
A little heat on the frosted coil and we have a few drops of water.
Science facts are only as good as knowledge.
Knowledge is only as good as the facts.
New knowledge is only as good as the ones that don't respect the first two.
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Interesting idea. I suppose the real test of this idea will be how the use of aromatic fuels effects the mass ratio of the mission. This calculation will need to take into account both the reduced hydrogen payload mass and also the reduced specific impulse of a more carbon-rich fuel.
Also, the methane synthesis reaction is robust because of its simplicity and the simplicity and robustness of the equipment required to achieve it. The manufcature of armomatics will require additional chemical stages that will inevitably complicate the equipment.
The question is: Does the reduced H2 payload as a percentage of total fuel mass, pay off against the reduced specific impulse of the fuel and the additional complexity of the fuel manufcaturing process? Someone needs to run the numbers.
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Hi Everyone,
nickname, if you think about it, it's pretty impractical. Let us say that you have a big 1 meter wide opening and a turbine so that it will suck a cubic meter of air thru that gap every second. This needs to be filtered, and then moved over the condensers slowly enough to let all the water condense out. That means that there will be a LOT of condensers or that the air will have to be compressed. (If it is compressed it will be warmed of course.) You could have one set of condensers cooling the air while the next set is getting a bunch of compressed air. Then have some sort of vent to switch over each half cycle.
This all sounds big, heavy and not particularly reliable. A space probe may will have to make due with a smaller turbines, etc. so you wouldn't be able to pass 1 cubic meter per second. Assuming you can get a cubic meter per second then 2 billion seconds is well over 6 years. That will take a lot of power. Will it keep working that long? In practice you won't get 3% H2O year round. Also, you won't get 100% of the wisps of water vapor. I would guess that you would be lucky if you could do it in 12 or 15 years. Far easier and more reliable to just ship 6 tonnes of Hydrogen to Mars.
A billion is a really big number.
Antius, they worked out the numbers and this system means that you can ship methane to Mars rather than pure hydrogen. Shipping pure hydrogen means that you have to worry about the reliability and mass of high pressure tanks and cryogenic cooling. Methane under modest pressure will easily liquefy using moderate cooling in space or on Mars. Also, no matter how cold you get hydrogen, 15 percent of it will boil off in space so you have to ship that much extra. The numbers say that slightly more mass will be taken by this system but it will be much more reliable. This is why NASA is planning to use it for their sample return mission.
Warm regards, Rick.
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RickSmith,
Thanks, the numbers sure look dismal for water condensing.
I agree a power hungry complex beast and small returns of water don't make a lot of sense, even in a deep canyon the water numbers maybe only double.
To bad though as a condenser would have been ideal for the people.
Maybe a lesson in that about where to place people and machines on Mars.
Near the poles and humans can go collect water as ice.
They have an assured way to get home with simple chemistry if something serious happens to a chemical factory.
If a Mars visit is a 1 year stay then ice as shelter radiation protection is excellent.
For any chemical reactions i think a deep canyon is best for a thicker atmosphere with quicker more reliable reaction times and a little more radiation protection as a bonus.
If we can down size the original plan weights because we simply land the machine in a canyon with twice the atmospheric pressure and twice the efficiency of chemical synthesis.
We might save quite a bit more cargo we have to launch to Mars. $$$
Aromatic Hydrocarbon and Olefin Synthesis should be much more efficient with the added bar pressure in a canyon?
Less power needed ,less weight, less time for the reactions etc etc.
Near the pole in a deep canyon would be ideal.
I think that is the most likely place life would have clung on the longest anyway, so a good place to explore.
Science facts are only as good as knowledge.
Knowledge is only as good as the facts.
New knowledge is only as good as the ones that don't respect the first two.
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That is right. Pretty much any place you land over 40 degrees you will find water somewhere near by. (Of course it is frozen rock hard.) But explorers shouldn't have too much trouble digging up a few blocks of ice / mud per day. That would be plenty of water and everything that can be made from it.
Warm regards, Rick.
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