What can we do with the water on the Moon? We ask Planetary physicist Philip Metzger
Following a long drip feed of ambiguities and highly suggestive hints, scientists have confirmed once and for all that the evidence for water on the Moon is rock solid. So now that we know the stuff of life awaits future explorers at the lunar poles, how easily will they be able to collect it? And what can they use it for when they do?
For decades scientists have sought to confirm the existence of water on the Moon. It has profound implications for our hopes of establishing a lunar outpost, which could serve as a base to propel crewed missions into deep space, and open up new possibilities for a prolonged presence on the Moon and its exploration.
In a paper published in Proceedings of the National Academy of Sciences this week, an international research team describe definitive evidence of exposed frozen water deposits at the poles. Resting in dark craters perpetually hidden from the Sun, the water is never subjected to temperatures above -250⁰ F (-157⁰ C), with spectroscopic evidence determining it to be in ice form, rather than vapor or liquid.
Talks of a lunar base have picked up again recently, with NASA directed to focus its attention on returning man to the Moon, the European Space Agency putting forward concepts of a so-called Moon Village and a slew of private companies vying to place landers and rovers on the surface as a starting point for lunar exploration.
This week's confirmation will only embolden these parties, because ice on the Moon might translate into all kinds of useful things. It could be distilled into potable water to drink, it could be converted into oxygen to breathe, it could be used to raise crops for sustenance and it could be turned into rocket fuel to send spacecraft on deep space missions. But how ready are we to exploit it?
Philip Metzger is a planetary physicist who worked on the roadmap for planetary surface technologies at NASA's Kennedy Space Center and co-founded KSC Swamp Works, a NASA innovation lab focused on developing technologies needed for living and working on the surface of the Moon and other bodies in the Solar System. Now at the University of Central Florida, Metzger continues his mission to help move civilization beyond its single-planet existence. He regards this week's discovery as a "truly remarkable piece of scientific work" with "important consequences." We asked him what it all means and what might come next.
Do we have a way of estimating how much water is present in these deposits?
The new measurements indicate concentration of the ice (how much is mixed in the dirt) at the surface. From physics-based models of how the ice got there, we can infer it may go down to be a few meters of depth. Very crude estimates are possible by putting these together.
How feasible is it for us to try and exploit it?
We are already developing concepts to extract the ice and performing economic analyses based on the types of hardware we will need. The United Launch Alliance funded myself and Julie Brisset at the University of Central Florida to perform computer modeling on extracting the ice through thermal methods, soaking heat into the ground so the ice changes into vapor and diffuses out of the soil.
They also funded George Sowers, Chris Dreyer, and their team at the Colorado School of Mines to develop estimates of the hardware needed to perform this extraction, and to estimate total costs of the operation. The results show that it can be extracted with a reasonable business case. The business looks much better if NASA becomes the key partner, and it will actually make NASA's lunar surface operations more affordable.
Other methods to extract the ice could be simply by scooping it up with a robot like RASSOR, developed by the Kennedy Space Center's Swamp Works specifically for this purpose. RASSOR would dump the icy soil into a processing unit that will heat it, vaporize the ice, and collect the vapors.
How can we distil it into potable water?
The ice is known to contain not just water but also hydrogen sulfide, methane, carbon monoxide, and a whole host of other volatile substances. We know this from the LCROSS spacecraft that crashed into the Moon and blew out a large volume of this ice to where we could see it. One way to help purify the ice is to vaporize it and then capture only the substances that will freeze above a certain temperature, allowing the other substances to escape into space. Other methods involve using membranes to allow only certain liquids to pass through. Some work has been done by NASA developing these methods already.
How might it be used to grow food on the Moon?
The lunar ice can also be used for agriculture, which will require lots of water. Once you have a closed-loop life support system set up, all the water passing through the plants and the humans who eat the plants will be recycled, so it will not be necessary to keep adding lots of water to the system. The large amounts are needed only for the initial setup, or for scaling up the number of humans on the Moon when more agriculture is needed. A bigger problem with lunar agriculture, though, is the long lunar nights. Plants are not adapted to that, so it will be necessary to have artificial lighting, which will require very large power systems.
Why and how might we convert it into breathable oxygen?
To make oxygen you simply electrolyze the water, running an electrical current through to separate the molecules into hydrogen and oxygen. Then you can use the hydrogen and oxygen as rocket fuel. To burn that hydrogen in a rocket, you will need every bit of the oxygen that you got when you made the hydrogen. Therefore, you do not want to use the oxygen for breathing, because if you do then you will have hydrogen left over that you cannot use for rocket fuel, and hydrogen on the Moon is too precious to waste.
You can easily get oxygen from ordinary lunar soil and rocks. The entire Moon is 42 percent oxygen by weight, but it contains almost no hydrogen. You do not need ice to get oxygen. You need it to get hydrogen, with the right amount of oxygen to burn that hydrogen. The byproduct of making oxygen from soil is metal, which is also useful at a lunar outpost. So I think the ice is mostly for making rocket fuel, while the soil is for making the breathing oxygen and metal.
What technological advances would be required to turn it into rocket fuel?
It will not take significant technological advances – no basic research. We already know how to build this kind of equipment. We only have to build it and test it. But the most important problem is that we do not know enough about the type of ice on the Moon yet, so we have not decided which set of extraction hardware we will want to build. We need to know if the ice is like a snow cone mixed with dirt, or is it a solid block of material, or is it dry soil mixed with golf-ball chunks of pure ice, or something else? We need to have robots on the lunar surface driving around measuring the physical state of the ice before we can decide.