Thursday, 24 September 2009

Water on the Moon

'Moondrops'In today's Times, there's a front page story saying the the Indian Chandrayaan-1 probe, carrying NASA's Moon Mineralogy Mapper has now found signs of what might be significant amounts of (presumably frozen) water on our Moon.

For anyone who wants bullet points to explain why this is potentially a game-changer, here they are:

  • Water + electricity = life support
    Humans need water and air to survive (along with temperature control). With enough solar cells, the Moon's not short of electrical power – no pesky atmosphere to get in the way – but water and air are biggies. If the water's already there, we can tick one box, and using electricity to electrolyse water gives us hydrogen and oxygen. Oxygen lets us tick the second box. Normally we breath atmospheric-pressure air, with 20% oxygen and nearly 80% nitrogen, but we can use pure oxygen at a lower pressure, if we can deal with the additional fire risk associated with pure O2. It'd be nice to have a decent local supply of nitrogen, too, but not strictly necessary.

  • Water + heat + rock = building materials?
    Use solar furnaces to roast moondust, or break moonrock into pulverised dust and drive off the more volatile elements, then add water ... and we might just have ourselves a form of locally-sourced readymix concrete.

    You know how in films where moonbases are often all shiny white metal? To start with, they'd probably look more like adobe mud huts, or holes in the ground, with all the shiny stuff on the inside (apart from the solar panels). What you'd ideally want is big thick walls at least ten or so feet thick, on all sides, to buffer the temperature changes and block some of the radiation when the sun does annoying things with solar flares. Perhaps you'd want to maximise your protection from flare radiation without tunnelling, by by building in the bottom of a deep crater, near one of the poles ... which is also where we're hoping that some of surviving "accessible" ice might be found.

    Our building materials don't have to be incredibly strong, or even airtight, we could build a crude hollow blocky mesa as our surface structure and inflate a pressurised mylar balloon inside or below for living quarters. But it'd be nice to be able to pour a bit of concrete around the balloon to minimise accidents, and it'd be handy to turn moondust into something more manageable. Other than that, we're stuck trying to stack up rocks and fill sandbags with dust. In a vacuum. Not good. Quite how you're supposed to work with concrete in a vacuum without the water immediately boiling off, I don't know, but I'm sure that some clever concrete technologists are working on it. Supercooling, perhaps?

    One problem with building at the bottom of a polar crater is that having a few kilometres of rock in a straight line between you and the Sun isn't so good for solar power. So you'd probably want an array of thin foil mirrors around set up around part of the crater rim, redirecting and focusing concentrated sunlight down onto your generators. Luckily, your mirrors can be ultra-lightweight, there's no weather to damage them, and no intervening air to soak up the transmitted energy. Using reflectors minimises the amount of heavy power cabling, and also the number of solar generators, and depending on the shape of the ice formation that you're trying to exploit, an aimable solar furnace might also be handy for mining.

  • Hydrogen + Oxygen = rocket fuel
    Hydrogen and oxygen burn rather well together to turn back into water, giving a nice roaring flame. That's the reaction that drives the shuttle's main engines. Given a solar farm and enough time, it'd be nice to have a local fuel production plant on the Moon, making rocket fuel simply from local materials. We'd probably need a robotic refueller to pick up H2 + O2 from the plant, fly back to Earth orbit, find the satellite and fill up its tanks (or swap a standardised empty satellite launch tank with a nice pre-refilled one).

  • H2 + O2 + fuel cell = mobile power
    Fuel cells have a capacity that's only limited by the amount of hydrogen and oxygen you have to feed them. If you're building a water-splitting plant anyway, you might want to send along a spare set of empty fuel cells.

  • Water+ electricity + rock + atmosphere = food
    Sure, we can set up a hydroponics lab to grow our own veggies in space, recycle biomass, and use the plants help remove CO2 and other nasties from the air ... and in theory we can get pretty damned close to a sealed self-perpetuating system. But in practice, you need topups, and safety margins, and an awful lot of water to get the thing started (as the name "hydroponics" kinda suggests). If you're going to be growing algae or fungus or plants to eat, there's a lot of water locked up in the system while they're going through their cycle. Industrial biological reactors usually need whole tanks of the stuff, and water's actually pretty heavy. If water's costing you thousands of dollars per kilo to ship from Earth, it's not cheap stuff. It's probably not quite as expensive as gold, but with current shuttle per-kilo launch costs, it's in the ball-park.

With water, the moon becomes a solar-powered robotically-constructed and remotely-operated gas station and hydroponics plant, remote-controllable from the Earth, with a mild gravity penalty. It can have its own fleet of little refuelling craft, powered by locally-produced lunar rocket fuel.

Without water, its just a big chunk of rock with some handy boulders to hide behind when there's a bad solar storm.

Anyone whose job involves thinking a decade or two ahead about future lunar, manned or deep space payload missions will be watching this story very carefully.

see also: Ice Splat on Mars

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