:xenia_blahaj: 
SciFi though:
I wonder how realistic it would be for a space based culture, mostly STL, to peg their commodity currency to a liter of water. With the value mostly depending on the cost of extraction and purification.
Since water is so useful in space.
The big problem is that water is very heavy for its cost (it's cheap to extract and purify), so shipping costs will dominate. For a commodity currency, you want something that is high value for little mass. That way, the commodity's value is relatively flat across locations.
If there is no such thing, then you probably don't want to use a commodity currency at all.
Solar grade silicon might be a good candidate.
I mean, here on Earth silicon dioxide is super super common. It's sand. Look at all the deserts. Earth is a silicon planet.
But electronics grade silicon is expensive. It's valuable. And that's here on Earth, the silicon planet!
Therefore, I can imagine solar panel grade silicon being valuable in space also. Although there are alternative solar panel technologies...
But in any case, I think you wouldn't want a commodity currency at all. Fiat currencies have too many advantages over a commodity currency.
It's just that when the local governments are too weak to back up strong fiat currencies (often due to dominance of foreign markets), people have to make do.
@isaackuo @nyrath
Which is the idea in my setting...
Extra-cis-lunar settlements have to make due, after Earth gets knocked out of commission for a time thanks to an artificial local killer (250ktonne lighter meant to transport material to an orbital factory) being deliberately made to hit Beijing. This leading to a three way civil war in China, the other space nations locking up cis-lunar space tighter the a rats ass, a limited Kessler cascade destroying one of the Orbital elevators, and on top of that one hell of an economic crisis that lasts for decades.
So a commodity currency is a quick and easy method to get the space borne economy going again after the period of immediate survival.
Though that doesn't mean that they won't switch their currency to a fiat one after a time.
@MeiLin @isaackuo @nyrath Yes, but water is ubiquitous in space (out beyond the triple point zone Earth orbits in—it's scarce on Venus, although it's present at Mercuriy's poles). There's a lot of it in the Martian regolith, it condenses in cold traps on Ceres, the ring systems of the gas giants are most probably dirty water ice, and so on. You might have to wait a few years for your solar-electric water harvesting barge (that uses water as reaction mass!) to return, but it's not rare.
@cstross @MeiLin @isaackuo @nyrath that occasional water barge would generate huge boom/bust cycles on your water based economy. Also be a big fat target for water currency hoarders.
I suspect hoarding life support resources would be very frowned upon in space.
I wonder if guillotines work on Mars.
SpaceMarie Antoinette: "Ha, ha, ha! Let them drink wine!"
@SkipHuffman @cstross @MeiLin @isaackuo
I'm sure guillotines would work fine on Mars if the blade was spring loaded or rocket propelled or something.
Sounds like extra engineering time, but the airlock would be just as effective.
@cerebrate @SkipHuffman @swope @nyrath @cstross @MeiLin
In my country, people are pretty open about ... well ...
On one side, they openly want to get rid of all the "bad" Jews.
On the opposite side, they openly want to get rid of all the Zionists.
If I say, "Maybe we get rid of no Jewish people?" well that's when people figure out I'm a weirdo and they're like, "What's wrong with you?"
@cerebrate @swope @nyrath @SkipHuffman @cstross @MeiLin
I live in the USA. That's well over half of the population around here. Well over half of us support the police having de facto immunity to murder non-white people all they want, and a good fraction of those of us who oppose that nevertheless support murdering some other folks to utopia.
OTOH, if you wish to bar USAians from entry to your Mars colony ... okay, give that a go?
@cerebrate @swope @nyrath @cstross @MeiLin @isaackuo I'm pretty sure we are /mostly/ kidding