Water, water, anywhere?

February 27, 2008 6:25 AM

We're making another effort to find water on the moon.Beginning in 1964 with the Ranger spacecraft, we've been lobbing things at poor old Luna. Lately we've been trying to find water there so that future explorers don't have to haul the stuff up the gravity well from Earth.

Water just is not compressible, you see, and we haven’t figured out how to dehydrate it, so we have to bring it with us where we go, reclycling endlessly, or rely on local supplies. The Clementine mission in 1996 gave us reason to think that substantial amounts of H2O exists locked up in ice at the bottom of craters at the lunar South Pole, where the sun doesn't reach. We tried to find it with the 1998 Lunar Prospector, with inconclusive results. We're gonna do our best to find out this summer with another lunar smackdown. If water-ice is there a new era of lunar exploration will commence. Maybe then Google can find that damn monolith.

posted by Guy_Inamonkeysuit (25 comments total)

Say what? Whitey on the moon?
posted by flapjax at midnite at 6:31 AM on February 27, 2008

The people of Piedmont are going to be pissed when they find this out.
posted by cashman at 6:50 AM on February 27, 2008

Of course, even if water were compressible it would still weigh the same amount. Smaller container, though.

Maybe they should just take a big drink before they go. Better yet, we should send up robots to manufacture water that would be waiting there for us when we get there. Capture ambient hydrogen from space plus some oxygen either from compounds on the moon (must be there, if the current formation hypothesis is right, right?) or from the "air" that does exist at that height, though barely.

(That last bit is facetious, though I think I must be mathematically correct, if not entirely practical.)
posted by DU at 7:09 AM on February 27, 2008

Scientists are priming two spacecraft to slam into the moon's South Pole to see if the lunar double whammy reveals hidden water ice.

I can see it working, slamming two aircraft into something led to the discovery of untold resources for this administration.
posted by Uther Bentrazor at 7:17 AM on February 27, 2008 [1 favorite has favorites]

DU, there're interesting hydrogen isotopes there already, like H3, that have applicability for things like fusion research. In fact, that's a big reason to go back -- to harvest that stuff from the lunar regolith. But it's spread pretty thinly and would take a fairly large industrial operation to scrape the stuff up. Same problem with space-borne hydrogen... scooping the stuff up takes energy and time -- and big scoops. Not practical for interplanetary travel, much less the local earth-moon route. Here's Wikipedia on the Bussard ramjet for interstellar travel for fans of Larry Niven's Known Space series.

Oxygen. Yep, it's there, lots of it -- the Artemis Project has been looking at harvesting lunar oxygen for quite a while now.

But it makes more sense to use local water, if any, than to manufacture it despite the abundant solar energy available... Just melting the buried ice would be lots easier, even though it's probably all mixed up with soil -- picture a really dirty snowball as opposed to chunks of berg ice.
posted by Guy_Inamonkeysuit at 7:33 AM on February 27, 2008

Oxygen is on the moon making up nearly half the contents of the soil, DU, and getting most of it free from the soil just takes a lot of heat, which is conveniently free two weeks each month if you've got large enough mirrors. It also stores nicely if you control the temperature, so you can accumulate it gradually for when you need it.

Hydrogen is the tricky part. It is in space as you suggest, in the solar wind). But it's in such thin quantities that it's not worth collecting from there. It's very lightweight for what it's worth, but even if you store it cryogenically it's not very dense so it needs big heavy tanks, and it can slowly leak right through tank walls. "Bring the hydrogen and combine it with on site materials" is probably still a useful strategy, but it could be much more convenient if there was a supply there waiting for us.
posted by roystgnr at 7:34 AM on February 27, 2008

Oxygen is on the moon making up nearly half the contents of the soil

Holy crap!

...but even if you store it cryogenically it's not very dense so it needs big heavy tanks, and it can slowly leak right through tank walls.

Why not store it connected to some oxygen atoms? I think Earth engineers have some experience constructing leak-proof containers for hydrogen-oxygen compounds.
posted by DU at 8:04 AM on February 27, 2008

Water can be compressed... I used to know an engineer who worked with one of those cutting tools that shoots a beam of water that can poke through steel. He mentioned at the time that the water was compressed by almost 1/3 to get the results they needed. Not that that takes away from the weight or anything.
posted by grimcity at 8:29 AM on February 27, 2008

"Why not store it connected to some oxygen atoms?"

That works for long-term storage (assuming you've also got enough energy to quickly crack the hydrogen apart when you need it separate for something like rocket fuel), but it's not great for transport. Two hydrogen atoms have two protons, one oxygen atom has sixteen protons and neutrons, so H2O weighs nine times as much as the hydrogen it contains. At that cost, unless you need to transport the oxygen too it's cheaper to just take hydrogen and accept that your tanks will arrive a little heavier and a little less full than you'd like.
posted by roystgnr at 8:41 AM on February 27, 2008

People need what, 2 liters of water per day? A liter of water weighs 1 kg. It costs about $25,000 to put 1kg into low-earth orbit.

So rather than doing all this, why not just put 1000kg of water into LEO for the use of any manned lunar mission to rendez vous with and fill up their tanks. How expensive could it be to put this much in a stationary lunar orbit? It has to be cheaper than extracting it using the still theoretical methods described. Of course, doing it the simple way doesn't provide for lifelong careers at Nasa.
posted by Pastabagel at 8:43 AM on February 27, 2008

..it's not great for transport.

I think we are talking past each other. I'm envisioning this as being water for human consumption in a lunar base.
posted by DU at 8:47 AM on February 27, 2008

Because water is so common, we think of it as a "normal" liquid, but it is most unusual. If it were not for these anomalies, little--if any--life on earth would exist.
posted by weapons-grade pandemonium at 8:48 AM on February 27, 2008

If you can do it all onsite, it makes more sense and requires far fewer earth-based resources than launching water into LEO. Let's assume that there is water at the lunar pole. So you extract it there... but your base is probably going to be elsewhere rather than down South where the sun (your energy source) can only be accessed from collectors atop high mountain peaks. How to get the water to your base? Forget pipes. And not from orbit... shifting a mass of water around up there is going to be expensive. Solution? Mass drivers. Shoot the stuff in frozen form inside containers made from metal extracted from the regolith... drop it where you like. But I dunno, I am not a rocket scientist -- maybe someone can educate me on this.

Jeez, I feel like Robert Heinlein. Where's Mike?
posted by Guy_Inamonkeysuit at 8:56 AM on February 27, 2008

Forget pipes. And not from orbit... shifting a mass of water around up there is going to be expensive.

How about this: You mine the oxygen. You get the hydrogen and the momentum from the solar wind. You use a magnetic field (I assume these are H ions, but the principle would remain) to guide the H+ into a pile of O. Using a bunch of math and stuff, you've got this all aimed right towards a collector on your moonbase, where you effectively have a continuous rainstorm.

(Even aside from the "math and stuff" this seems pretty impractical. The mass of H, even 2 * H is well below that of O, but then again the original velocity was pretty high.)
posted by DU at 9:04 AM on February 27, 2008

If you can do it all onsite, it makes more sense and requires far fewer earth-based resources than launching water into LEO.

Who cares? Earth based resources are cheap. The fact is that even if you extract water from the moon, you still have to send parts, materials, and food from earth (or soil or fertilizers, etc) on a regular and ongoing basis. So you already have to build infrastructure to move stuff from here to there regularly. The idea of an autonomous moon base that supports humans is fantastical and nonsensical.

Adding water as just one more thing to move is simply an incremental additional cost. But extracting water from the moon involves enormous fixed cost and plant that is only used for one thing. You have to ship all the equipment for the extraction operations which is certainly going to weigh more than 1000kg.

It seems like the the primary purpose of this moon base would be to extract water to support the people living at the base. This is precisely the kind of shuttle-space station wasted effort symbiosis that we shouldn't be trying to replicate.
posted by Pastabagel at 9:08 AM on February 27, 2008

But moon-based resources are even cheaper, and there's plenty of minerals and so forth there already -- no need to schlep more of that stuff up the gravity gradient. The soil needs processing, true, but it is far from fantastical or nonsensical. The primary purpose of a moon base would be to learn how to live on the fucking moon.

Listen, if it were me, we'd be on our way to Mars or Europa right now. But it isn't up to me, so I will take anything I can get that will lift us off this fucking rock. If that is a NASA-themed moonbase, count me in. If it's the Chinese up there instead of us, I'm good with that, too. In a couple of hundred years it won't matter.
posted by Guy_Inamonkeysuit at 9:29 AM on February 27, 2008

Whenever we send up a shuttle, or put someone on a station, the water on board in more or less a constant amount, right? I mean, they recycle everything over and over again, do they not?

And then they just bring it all back down with them when they land. So why not off-load all the water just as they are getting ready to come out of orbit? Eventually, we would have a fairly big stockpile of it sitting out there in orbit for use when we needed it.

Not that I think that any efforts to create or find water off of Earth are a bad idea or anything, I just think we might be missing a fairly easy way to get a usable supply into a location where it might help.
posted by quin at 9:59 AM on February 27, 2008

Water just is not compressible

Yes, it is.
posted by jeblis at 10:19 AM on February 27, 2008

We're whalers on the moon! We carry a harpoon! But there ain't no whales so we tell tall tales and we sing our whalin' tune!
posted by SmileyChewtrain at 10:23 AM on February 27, 2008 [2 favorites has favorites]

CHA
posted by rusty at 11:06 AM on February 27, 2008

We are talking past each other. People aren't excited by water on the moon because they need it to drink. Shipping a couple liters a day is no big deal for a base, and if you recycle it efficiently enough and only bring up enough from Earth to replace losses that's probably no big deal for even a large colony. Having locally produced water for crops/hydroponics might be very valuable in the long term, but that's not where the immediate interest is.

In the short term, water on the moon is exciting because water is rocket fuel.

Sure, you've got to put a lot of energy into it to crack it apart first, but energy can be conveniently carried around in nuclear fuels, or you can even just let it fall like manna out of the sky if you've got solar panels (or even just mirrors and heat engines) to collect it. Once you break apart the H2 and the O2, what you're left with is arguably the best chemical rocket fuel on Earth and is even better for lifting off from the Moon's lower gravity.

And that's important, because while you don't need a lot of drinking water every day on the Moon, you do need a lot of rocket fuel when it's time to come home. Half the weight of the ascent stage of the Apollo Lunar Module was fuel, tons of fuel just to get it up into orbit to where the astronauts could use the Service Module's tens of tons of fuel to get the rest of the way home. Those tens of tons of fuel, in turn, had to be lifted off Earth by thousands of tons of fuel, which is part of the reason why the Saturn V looked like a skyscraper and required a skyscraper's complement of people to keep it running. The laws of physics make the ratio of fuel to payload increase exponentially with increasing velocity requirements of your trip. The laws of economics make the easiest ways to handle that (e.g. building huge spaceships with thin engineering margins and throwing them away each trip) unpleasant. So, any chance to break up one trip into two trips with a refueling in between is worth a look.
posted by roystgnr at 12:08 PM on February 27, 2008 [1 favorite has favorites]

So, we're off to fuck up another celestial body. When does it end?
posted by Eekacat at 4:26 PM on February 27, 2008

It all sounded nicely clever and economical until they said 79 million dollars.
posted by DenOfSizer at 6:27 PM on February 27, 2008

why not take the trillion dollars we've spent in Iraq and put it into lunar exploration. maybe the moon is made of oil, not cheese.
posted by lemuel at 8:44 PM on February 27, 2008

Mr. Show predicted years ago that America will blow up the moon.
posted by dammitjim at 7:04 AM on February 28, 2008