Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: ratacat on 18/01/2013 08:10:37
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Is it possible? I just starting wondering about this subject, and my knowledge of all related things is pretty minimal, so I thought I would ask you guys!
From what I've gathered online tonight...
1. Generally things don't transfer much heat in space due to the distinct lack of particles.
2. Maybe one could cool down liquid/gaseous methane in space with infrared light?
3. Don't go to yahoo answers with your space questions.
Thanks for your time,
Ratacat
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Keep in mind, that with low pressures, liquids can tend to evaporate, and solids will tend to sublime. So, even if one froze methane, one might wish to keep it enclosed and pressurized to prevent sublimation. Some outer moons likely have enough atmospheric pressure to prevent sublimation. Although, if one could apply a liquid or gas water spray to it (at a very cold temperature), it might insulate it quite effectively.
A good target temperature would be below the triple point of methane, (90.7K) below which liquid does not exist, although one might be able to choose a higher temperature/pressure combination.
Fortunately, the "background" temperature in space is about 2.7K. However, anything exposed to the sun is much hotter. The sun, of course, is cooler the further one travels from the sun, so it gets rather chilly beyond Pluto.
Some of the polar moon craters, in year-around 100% shade are about 30K, at least for a thin surface layer. These would be adequate to freeze Methane, provided there was adequate pressure to keep it from subliming.
One option for open space (not on the moon), would be to create a device somewhat like the James Webb Space Telescope Sun Shield (http://www.jwst.nasa.gov/sunshield.html) According to the design specs, it is supposed to keep the telescope at -233 °C, or about 40K which should be sufficient to freeze methane, provided adequate pressure. It is, however, also designed to be located in the partial shade of the L2 Lagrange point. (http://en.wikipedia.org/wiki/Lagrangian_point), so temperatures at the same distance from the sun, not shaded by the Earth would be somewhat higher.
One could, of course, also build a helium or neon refrigerator. Compressing, and rarefying the gas. It should be effective, even with hot-side coil temperatures somewhat higher than the freezing point of the methane. Shade, of course, is always helpful in space. Heat sinks can still radiate heat, even without an atmosphere and fan.
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There is a slight problem: Since space is a (pretty good) vacuum, where do you get your methane from?
You could go to Titan, one of the moons of Saturn, which has methane in the atmosphere, and is thought to sometimes experience methane rain. Or you could go further out to the Kuiper belt, where objects are expected to contain solid methane for the mining.
You could also carry liquid methane from Earth in tanks - and if you really needed solid methane, you could bring that in well-insulated containers, too.
But for most purposes, liquid methane is more convenient, since it can be piped around instead of being shovelled around; liquid methane is more chemically reactive than the solid, requires less insulation, and doesn't take up much more space.
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Now, that is an idea.
Build a cryogenic solid rocket.
The freezing point of oxygen is about 54K.
The freezing point of methane is about 90K.
One could potentially build a solid rocket at 54K with stoichiometric oxygen/methane mix. It would burn fast, but with some luck, it might not detonate.
If one chose methane as a fuel. It could likely be mined from the outer planets & moons. But, of course, one would also need oxygen or some other oxidizer which would need to be produced from an energy intensive reduction of oxidized compounds found on the planets.
Solid methane might be easier to transport than liquid methane, except for the sublimation problem mentioned earlier.
Containers would also have to deal with expansion upon melting.