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Comment by mholt | Hacker News Reader

> Harvesting the vast amounts of water on the Moon – the equivalent of the Great Salt Lake in Utah – could make the project commercially viable.

I didn't know this. But anyway, I live by the Great Salt Lake, and it's more like the Great Salt Puddle. Would that amount of water really sustain a colony? I suppose the base would have the most efficient water facilities ever invented, but still, it wouldn't last for long unless the water was recycled forever.

(I see, later, they refer to finding such ice as 'prospecting for gold' - I'm optimistic about our future in space, but this water situation is tricky. Ship it up there, maybe?)

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Shipping water to space or the Moon goes against the very core of this idea. There is water on the Moon, check out the Lunar Prospector mission for more information. That water is extremely useful, even for an entirely robotic solution because it is rocket fuel. The low gravity makes it an incredible asset. If we can get to it, the cheapest access to water and fuel in low earth orbit will come from the Moon.

Sending water & fuel to the ISS from the Moon is cheaper than sending it from Earth if you take a long enough view.

I'd also like to point out that nuclear propulsion (Nuclear Thermal Rockets, proven tech) is a viable option for Moon and Space craft. The Moon's surface is already being blasted with solar radiation from solar wind and flares.

Just imagine how useful some Moon uranium would be!

Water is useful as fuel (LOX and liquid hydrogen or methane), as reaction mass, and as radiation shielding when you're flying around.

Colonies will recycle their water. The ISS already partly recycles its water.

Water is heavy. A SpaceX Falcon-heavy has a maximum capacity of 21,200kg to transfer orbit - that's not going to go very far in a colony even if it's all water. Shipping it up there is really not an option.

Unless you have a space elevator...

Would it make sense to harvest asteroids for water and bring it to the moon?

I am thinking about just one spaceship which could go back and forth between some asteroid and a moon orbit. It shoots the water down to the moon, so that it does not even have to touch-down and take-off again. How much energy would be needed for such a mission? Probably it would be a very complex mission to get right, but once it is established you might have water for free on the moon.

I think the watery icy asteroids are a long way away. They also have a huge amount of kinetic energy, so they are hard to catch and move.

No!

Colonizing the Moon only makes sense if the water is there. If we're going to harvest water from asteroids, we should colonize them instead.

Besides what tdy721 and monk_e_boy said, water would be tricky to be had in our near-space neighborhood for two reasons. First, Earth, being a real planet, cleaned its surroundings of most of free-roaming objects. Besides the (domesticated) moon, there aren't that many wild objects around to look for. Second, water has a relatively low boiling point and on the Earth's distance from the Sun there is a lot of solar energy to melt the asteroid ice and boil away (like what we see happening on comets) before we can extract it, and then having difficulties with its handling after we have it due to very same reason.

>A SpaceX Falcon-heavy has a maximum capacity of 21,200kg to transfer orbit - that's not going to go very far in a colony even if it's all water

Well, can't you recycle ~100% of it? So you really only need to ship the maximum amount of water that will be in use at any one point.

Think of the food production alone - assuming a colony of a few thousand people, that would mean you'd need to be growing hundreds of tonnes of food at any given moment - most of which would consist of water you've brought with you (for example, a cabbage is 93% water). Of course that could largely be recycled, but even if you can get to 99% recycling you'll still need a rocketload of water very regularly to replace the water you lose or that's polluted beyond recycling.

It really doesn't make sense to take water with you. Just colonise somewhere that already has it.

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