Rocket fuel from dirt... Let's cook!
October 2, 2013 11:03 AM   Subscribe

For a book I am ghostwriting, I'm researching how a Mars colony might support itself. Perchlorates in the martian soil can be refined out to produce solid rocket fuel. My question is -- how would the stuff be manufactured?

A useful by-product is oxygen, which would certainly be useful for the colony. Say a colony has 200 people. How big an installation would be needed to provide oxygen for them by reducing the perchlorates? And what might that installation look like in terms of hardware?
posted by Guy_Inamonkeysuit to Science & Nature (9 answers total) 3 users marked this as a favorite
I can't see perchlorate mining making any sense. The percentage is too low, unless you've found an ore body.
posted by Chocolate Pickle at 11:32 AM on October 2, 2013

I think perchlorate would be a problematic source of breathable oxygen anyway, because if you're releasing oxygen from it, you're probably also releasing chlorine, which is poisonous.

I'd think that iron oxide or carbon dioxide would be better sources. Or water, if you've found a bunch of ice.
posted by Chocolate Pickle at 12:01 PM on October 2, 2013

Wikipedia says -- Lithium perchlorate, which decomposes exothermically to produce oxygen, is used in oxygen "candles" on spacecraft, submarines, and in other situations where a reliable backup oxygen supply is needed.
posted by Guy_Inamonkeysuit at 12:19 PM on October 2, 2013

It's typically (metal)Cl04 -> (metal)Cl + 2O2. The chlorine goes from +7 to -1, no Cl2 at 0 is evolved.

Something has to oxidize to drive the reaction. Iron shavings are a common source. So the folks on Mars are going to need to produce that too. Not impossible, but needs more infrastructure and power.

The real problem with perchlorates is that they're very unstable, evidenced by their use as an oxidizer for explosives. This is a big risk with oxygen candles. If they get dirty, they turn into bombs. The submarine HMS Tireless had one blow up, killing two sailors in 2007. Apparently this was caused by some oil getting into the candle, which caused it to explode.
posted by bonehead at 1:39 PM on October 2, 2013

Maybe use oxygen instead of perchlorate. A relatively rich source of water was found on Mars very recently (this week I think). One could do electrolysis on the water (using solar or nuclear power) to obtain hydrogen and oxygen, which could be combined as rocket fuel, albeit with some disadvantages.
posted by exogenous at 1:43 PM on October 2, 2013

I was at a conference this weekend that touched on this very subject.

You're asking about ISRU - In Situ Resource Utilization.

For Mars missions, two commonly proposed ISRU propellant solutions are:

Methane (CH4) + Oxygen (O) -- you get the carbon (C) from the carbon dioxide (CO2) in the atmosphere, the hydrogen (H) from the water (H2O) that has now been shown to be bound up in the soil everywhere, and the oxygen (O) from both of the above places.

Hydrogen (H) and Oxygen (O) -- mined as above. This solution requires cryo cooling of liquid H2 which is already hard to do on Earth. But the exhaust is non-polluting ...

Both of these solutions assume limitless energy, which frankly is an easy assumption because solar power is getting to that point. We're even starting to use solar for missions to Jupiter (where the sun is far weaker) instead of nuclear.

Gotta love the periodic table!
posted by intermod at 1:43 PM on October 2, 2013

They come usually packed in a metal can or barrel. Here's a typical mine refuge system, with generation and consumption figures. Here's one being used on the ISS. NASA calls them Solid Fuel Oxygen Generators (SFOGs).
posted by bonehead at 1:44 PM on October 2, 2013

I like the idea of mining hydrogen. It's a great low-density fuel, which means it would be more efficient given Mars's thin atmosphere and low gravity. And despite its own explosive potential, it seems safer to deal with than the perchlorates in the soil.
posted by Guy_Inamonkeysuit at 6:22 AM on October 3, 2013

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