October 4, 2009
Space Exploration Sets Sail on Lunar Water
A cislunar transport system will revolutionize space travel (NASA artwork by Pat Rawlings)
Water is an extremely useful substance in space. The recent finding of water on the Moon has generated considerable comment in the space community; a quick search on Google using the phrase “lunar water” returns over 7.66 million hits. Lunar water’s significance lies not in its role as a medium for the presence of extraterrestrial life but rather in its potential to support terrestrial life—ours—as humanity moves beyond Earth. The Moon is the port from where we will navigate—the safe harbor where we will learn how to live and work productively in space and from where we will set sail into our Solar System, thereby ensuring the survival of our species.
The three principal uses for this water are life support, energy storage, and rocket propellant.
We can easily imagine drinking water. We need about 2 liters of water per day under ordinary circumstances. Water is also a constituent of food, both unprepared and preserved, adding at least another liter to that total. In addition to consumed water, we can also use water to make oxygen, replenishing the air we bring with us to create a breathable atmosphere. Water is over 85% oxygen by weight and the liquid is easily broken into its constituent gases by passing an electrical current through it.
Another way that water supports life is by offering shielding and protection against solar and galactic cosmic radiation. Water harvested from the Moon can fill the outer jackets of surface habitats, protecting not only human life and technology within it, but also the plants that we will want to grow there, both for food supply and carbon dioxide scrubbing of the habitat air. Thus, water supports life on the Moon as both a consumable and as a building material.
A second main use of water is less often considered. We can break down water into its component gases using electricity, but the process can also be reversed – hydrogen and oxygen gas can be combined to generate electricity in a device called a fuel cell. When these gases combine, they generate electrical energy and make water as a by-product. This technique was used in the Apollo spacecraft for power and water production. When combined with another technique to generate electrical power (e.g., arrays of solar cells or a nuclear reactor), we make a completely reversible, self-sustaining power and water system. Thus, the water becomes a medium of energy storage – during lunar night, we combine hydrogen and oxygen to make water and electrical power while during the daytime, we reverse the process by using electrical power generated by sunlight to disassociate the water back into its constituent gases. Such a rechargeable fuel cell system enables permanent, sustainable human presence on the Moon.
The third important use for lunar water is for the production of rocket fuel. Liquid hydrogen and oxygen are the most powerful chemical rocket propellants known. By manufacturing rocket propellant from lunar water, we make the Moon a refueling station and logistics depot in space. The critical value of this ability is that such rocket fuel not only permits our routine access to and from the Moon, but also enables access to any other point in cislunar space (the volume of space between Earth and Moon.)
All satellites reside in cislunar space. Numerous remote-sensing satellites are found in low Earth orbit. GPS elements reside in moderately high (few hundred kilometer) orbits. Communication satellites are found at geosynchronous orbit, 35,000 km above the Earth. Other specialized satellites occur at different altitudes. At present, we cannot access these satellites with either human or robotic spacecraft. So we design, build and fly these space assets, use them for a time then abandon them, replacing them as needed with new satellites—at great cost. The ability to reach valuable space assets routinely with people and machines allows us to change the way we conduct business in space. Instead of the current “fly and throw away” template, we can build extensible, maintainable and upgradeable systems.
Very large, distributed space systems will enable new capabilities, such as global communications using hand held cell phone-sized equipment, anywhere in the world at any time. New remote-sensing platforms can be built to look at any corner of the globe at any wavelength in unprecedented detail. Telescopes built on the Moon’s far side, where they will be shielded from Earth’s radio noise, can scan the universe in new areas of the spectrum. These and many more capabilities are enabled by a cislunar transportation system and will vastly improve life on Earth.
By understanding and using the resources of our Moon, we can push out to the stars. An abundance of water on the Moon fundamentally allows us to change the rules of exploration and spaceflight to our advantage. We stand at the threshold of a new understanding of how the Moon evolved and works—and works to humanity’s advantage.
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The amount of water discovered recently is tiny. You write enthusiasticly in your book about using implanted solar wind hydrogen but over the whole Moon this is equivalent to the water in a single small lake. The recently discovered water is probably not much more abundant, especially if it sublimates away during the daytime and is replaced on the same timescale. This is not enough water to establish a self sustaining community on the Moon, much less to use as radiation shielding instead of the much more abundant regolith. As for using it as rocket fuel, this is really useful only if you can establish a self sustaining community to build, maintain and operate the spacecraft. In any case the amount of equipment you would need to transport to the Moon to establish that community would be well beyond the capability of a transportation system based on chemical rockets. If you use nuclear rockets the propellent can be whichever fluid is most convenient, which for the Moon would be liquid oxygen since you could exract oceans of the stuff from the lunar rocks.
Comment by Eric Paul Brunner — October 5, 2009 @ 7:05 pm
Hi Eric,
Wrong, on just about every one of your points. First, even before this new discovery, we estimated about 10 billion metric tonnes of water in the lunar polar areas on the basis of Lunar Prospector neutron and Clementine radar data. That’s an amount of water roughly equivalent to the Great Salt Lake, hardly a minor amount. If converted to hydrogen and oxygen, it could launch from the Moon a rocket the mass equivalent of a Space Shuttle every day for over 2000 years. Second, you don’t need a “community” and industrial plant to make propellant. Much of the preliminary work can be done with robots teleoperated from the Earth. Resource extraction can be demo’ed by small machines about the size of an office desk. The size of a water extraction machine that could make several tonnes of water per month is not much bigger than the payload of a single lander.
So, you’re wrong about the quantity, wrong about the resource processing, and wrong on the difficulty of establishing a new capability.
Comment by Paul D. Spudis — October 6, 2009 @ 5:04 am
[...] Paul Spudis looks at the role that H2O plays in the space economy in Space Exploration Sets Sail on Lunar Water [...]
Pingback by Carnivals of Space a Go Go - Out of the Cradle — October 7, 2009 @ 12:29 am
Whilst waiting for the LCROSS Post Impact Presser, I take time off (with metaphorical fingers crossed) to respectfully disagree with your third utilisation of any watery bonanza. Any ‘low hanging’ polar hydrogen will be too precious a commodity to throw away as rocket fuel. Indeed any particularly scenic “Ice Caves of Shackleton” should be protected as a (tourist) resource for future generations! (Or, shh, perhaps even constructed!) And as Dennis Wingo has pointed out; lunar food production is just as important. With the bonus that the hydrogen and nitrogen stays in the life support loop… in one form or another! Last, but not least, we will need DEEP swimming pools for the lunar high diving competitions! And which would you rather have; a personal zero gee swimming pool (and handy radiation shelter) or a single shuttle launch?
Whilst conceding that a renewable hydrogen supply by the ‘daily’ harvesting of solar protons could be a game changer. Although certainly a logistical nightmare. And, come to think of it, an ethical one too. Will future generations thank us if we disfigure Luna with strip mines? Even if they are on Farside. However there are alternatives: Al/LUNOX will get you off the Lunar surface and for heavy lift there is always the (original) nuclear option: the original Orion! Cargo can use the “Big Rock” throwing Lunar Authority catapult.
Once in space, most of our mutually agreed cis-lunar spacefaring architecture can take the form of tele-operated robotic vehicles, that use SEP and a gentler pace of living. Water and eventually rock shielded habitats in LLO, GSO and Lagrangian points will morph into proper O’Neillian settlements where humans can perform the tele-tasks that require zero time delay and repair the repair sats. Again water will be too precious…
In the short term hydrogen WILL be used as fuel, as quicker transits WILL be required. Leveraged by LUNOX as oxidiser. But surely the hydrogen (and nitrogen) will be initially sourced terrestrially via the new generation space companies and space gas stations. In the medium term, utilising the PROFAC concept, we can totally outsource these gases from out of the Well. In the long term we must get over the nuclear hangup and a develop a serious ceramic that will allow us to use LUNOX as the working fluid in a Nuclear Thermal Rocket.
By this time we should have a “Flexible Path” to CHON rich NEOs and have discovered that Phobos/Deimos is loaded with the stuff. But again, even with these sources, the water (hydrogen) will be too useful as water to a growing offworld population. Indeed I suspect that it won’t be until we reach the Main Belt that water as fuel will no longer be an issue. Super heated steam powered rockets anyone!
Of couse all this is moot if Robots are to be our only explorers. But look how popular the LCROSS “moonbombing” mission was: trending #1 on twitter no less.
One post presser comment (paraphrased from Marvin the Martian): “Where was the kaboom? There was supposed to be an moon-shattering kaboom!”
The December conference will be a long time to wait but papers (and careers) come first; hopefully with some good news. But from an initial impression this Space Cadet still thinks we need ‘Bots – lots of ‘Bots – followed by humans for a real ground truth.
PS by my calculation 18,920,000 m^3 and that doesn’t support any human life at all!
Dave
Comment by brobof — October 9, 2009 @ 11:19 am
Dave,
Our estimate is that about 10 billion metric tonnes (that 10^9 tonnes, about 3 orders of magnitude greater than your estimate) occur within the upper few meters of each pole; this estimate is based on botht he extent of shadow area, the strength of the enhanced Clementine radar signal, and the corroboration of excess hydrogen from the Lunar Prospector neutron data. That’s only within the shadowed areas; more probably exists outside this zone, which is what the M3 instrument was seeing.
I’m not worried about using lunar water; there’s plenty for everybody. Special areas of great beauty on the Moon can be set aside as a preserve or national monument, but I am not willing to declare a priori vast tracts of lunar land off limits to mining and resource harvesting, especially as we don’t know yet exactly where and in what condition are most of the resources.
But, to each his own.
Comment by Paul D. Spudis — October 9, 2009 @ 2:07 pm
Paul,
Awsome post as always! Keep them coming please! The sooner the better
WRT using LUNH2 as rocket fuel, I see both sides of the story. On the one hand, maybe we should just let the market decide on the best allocation of resources. But on the other, there is the recognition that markets may not always make the best decisions overall. E.g., economically, WRT to whale hunting, arguably it is more economical to hunt a whale species to extinction, literally, and then investing the profits in other ventures. But that’s not right–we wouldn’t want to go there.
No matter how you slice it, the Moon is Dune.
The Great Salt Lake seems like a bunch of water, but it’s one of those places that are a mile wide and an inch deep. Volume-wise, the Great Salt Lake is roughly on the same order as Lake Mead, the USA’s largest manmade reservoir.
Water to the Moon is like rice is to Japan. Economically, it would make more sense to farm out Japanese rice production to other places where land and labor are far cheaper. But I don’t blame them for protecting their rice farmers from the effects of foreign competition.
It would be one thing if true market forces could work their majic. But the Moon will be a “comnand and control” economy during its initial stages. So the decision will come down to trade studies. I’m just guessing, but I would think that sacrificing food production capacity for rocket fuel in order to import food from Earth will not make sense economically.
Then again, there is the QWERTY phenomenon. The QWERTY keyboard layout was designed in order to slow down typing speeds, because the old typewriters would get jammed if you typed too fast. Now we are stuck with what was once a good market decision.
What we don’t want to do is to get locked into a decision just because of legacy rocket hardware issues. That is, we shouldn’t be burning up lunar hydrogen just because that’s what our rocket engines are designed to use. There are practicable alternatives. A 450+ Isp isn’t necessary to lift stuff off the Moon’s surface. The old hypergolic propellent used on the LEM had an Isp of ~ 300s. Aluminum/LO2 should have an Isp of ~ 280 s. The low Isp does not render the concept impractical for lunar gravities–though if used on Earth, it rapidly leads to absurd mass fractions.
I think we can all agree that a few million USD for John Wickman to develop his Al rocket designs a little more would be money well spent.
Comment by Warren Platts — October 10, 2009 @ 1:53 pm
Hi Warren,
Two points in response to your post.
First, I agree that other propellant possibilities should be examined and experimented with. In fact, I look upon all of lunar ISRU (at the moment) as an experiment — is it possible? If so, how difficult is it? And finally, is it worth doing? Once we have some real data from the surface of the lunar poles, we’ll be able to answer such questions intelligently. I note in passing that lunar water is only a convenient form of hydrogen, not the only form of it on the Moon. Hydrogen is present as implanted solar wind and thus, trillions of tonnes are present on the Moon. A principal rule of mining is to get the easy stuff first, then move on to the harder (i.e., lower grade) ores.
Second, we want propellant for more than just lifting payloads off the Moon. Propellant export creates a market for propellant in cislunar space. And that is the real reason to go to the Moon — to create a long-lasting, reusable, refuelable space transportation system. We need propellant not only for orbit change but attitude control and minor maneuvers. The goal is to make a system that can routinely access not only the lunar surface, but all other points in cislunar space as well, for a variety of reasons — maintenance, construction, tourism, etc. We might need LOX-LH2 systems for quite some time. My only point is that there is a lot of water on the Moon, certainly enough to keep us in business until we are able to access and mine the asteroids.
Comment by Paul D. Spudis — October 11, 2009 @ 5:58 am
[W]e want propellant for more than just lifting payloads off the Moon. Propellant export creates a market for propellant in cislunar space. And that is the real reason to go to the Moon — to create a long-lasting, reusable, refuelable space transportation system. We need propellant not only for orbit change but attitude control and minor maneuvers. The goal is to make a system that can routinely access not only the lunar surface, but all other points in cislunar space as well, for a variety of reasons — maintenance, construction, tourism, etc.
I think I see what you’re saying. I foresee a day when the only commodity that will be lifted from the gravity well of Earth will be humans. Why pay to launch a satellite from Earth when the same satellite can be manufactured on the Moon and be launched for much less?
In this regard, I’ve been dieing to ask you this question:
You used to work on the Clementine project. As you know, it was partially underwritten by the old SDIO. That is, Clementine was meant to be a test of “Brilliant Pebbles” technology. But the Brilliant Pebbles concept would have required a constellation of a thousand or more satellites. So the SDIO was very interested in researching cheaper ways to launch payloads into LEO, as evidenced by their support of the Delta Clipper SSTO project, among others.
So my question is why was SDIO and DARPA so interested in the MOon? The Brilliant Pebbles technology itself could have been just as easily tested within LEO or GEO: places where real satellites are in orbit. Instead they combined the mission with a survey of the Moon’s poles. But why?
I’m just guessing that they were thinking that the Moon might make a good place for a satellite factory that could cheaply place thousands of satellites into LEO. I cannot find any open source literature to support my contention, despite extensive searching. But it makes sense. They were researching cheap launch methods. They have a history of thinking outside the box. So they were curious about the amount of water on the Moon in case there was enough of it to make it economical to launch satellites from the Moon. Weren’t they?
I’m not asking you to violate any Secret clearances or anything, or to give up any classified information. But any light that you can legally shed on this question would be very much appreciated.
Comment by Warren Platts — October 12, 2009 @ 9:45 am
Hi Warren,
So my question is why was SDIO and DARPA so interested in the MOon?
First, Clementine was a project solely of SDIO (later BMDO) and DARPA had nothing to do with it. And actually, they weren’t particularly interested in the Moon. The Clementine mission came about largely at the instigation of my colleague, Stu Nozette, who came up with the idea of a lunar and asteroid flyby with a Brilliant Pebble (BP) spacecraft in 1989. If any single person deserves significant credit for getting Clementine as a lunar mission, it’s probably Stu. A key event was getting NASA to agree to co-sponsor the mission, providing a science team (paid for by NASA). Clementine was initiated in 1992 and launched in 1994.
The SDIO interest in Clementine was to test a variety of small spacecraft technologies and sensors that had been developed as part of the SDIO BP program over several years. The Moon was selected as a target because we knew a bit about its surface properties, so it would offer a good test of the BP sensor suite. It was only after we got into the lunar orbit that we found the poles to be interesting and the bistatic radar experiment was improvised after we were already at the Moon (if we had known about the large shadow beforehand, we might have included a neutron spectrometer as part of the payload.)
Nothing classified or more conspiratorial than that. Sorry.
Comment by Paul D. Spudis — October 12, 2009 @ 2:07 pm
Please, give veracity to the calculations, comments, given references, that is formal scientific literature ( and el al. documents)
Comment by Oscar M Brandt — November 15, 2009 @ 6:50 pm
Oscar,
Feel free to check the numbers yourself. I suggest that you start with the total water estimate we made in the Clementine bistatic radar paper:
Nozette S. et al. (1996) The Clementine Bistatic Experiment. Science v. 274, n. 5292, p. 1495-1498.
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