TALK about water, water everywhere, but not a drop to drink. Newly confirmed water on the moon could one day help sustain lunar astronauts but, problematically, it seems to be locked up as small concentrations of ice in the lunar soil. Nevertheless, a microwave device being developed by NASA could one day allow crews to harvest the water.
Last week, lunar scientists made a splash when they announced that three spacecraft 鈥� India鈥檚 Chandrayaan-1 craft and NASA鈥檚 Cassini and Deep Impact probes 鈥� have detected water鈥檚 spectral signature over much of the moon鈥檚 surface. Some of the water may have come from comet impacts, and some may be continuously created as protons 鈥� hydrogen ions 鈥� in the solar wind bind to oxygen atoms in the lunar soil. Such water should move around the moon as it repeatedly vaporises and is pulled back to the surface by gravity, before finally settling in shadowed craters at the poles.
So far, the water seems thin on the ground. A baseball-field-sized swathe of lunar soil might yield only 鈥渁 nice glass of water鈥�, says Chandrayaan-1 team member Carle Pieters of Brown University in Providence, Rhode Island.
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But if it could be harvested, lunar astronauts could drink it or split it into oxygen and hydrogen to make rocket fuel for return journeys. Though baking and processing dry lunar soil could release oxygen and hydrogen for fuel and other uses, that would take about 100 times as much energy as using lunar water.
Rocket fuel made on the moon might even help mount a human mission to Mars: the moon鈥檚 weaker gravity means it would take less energy to loft fuel into space for a Mars mission than it would from the Earth鈥檚 surface.
鈥淚t completely changes the space-flight paradigm,鈥� says Paul Spudis of the Lunar and Planetary Institute in Houston, Texas. 鈥淚t鈥檚 like building a transcontinental railroad to space.鈥�
So how could useful amounts of water be wrung from the small ice deposits? Microwaves could be the key, according to work by Edwin Ethridge of NASA鈥檚 Marshall Space Flight Center and William Kaukler of the University of Alabama, both in Huntsville.
The pair first demonstrated the method in 2006, using simulated lunar soil that had been cooled to moon-like temperatures of -150 掳C. Keeping the soil in a vacuum to simulate lunar conditions, they found that heating it with microwaves to just -50 掳C made the water ice vaporise. The vapour then diffused from pores in the soil into the vacuum above.
On the moon, the technique would be most efficient where water is most abundant 鈥� in purported ice-rich craters at the poles (blue in composite image, left, from Chandrayaan-1). A nuclear reactor inside a dark crater, or solar panels on its sunlit rim, could power a microwave source inside the crater. The vapour created could be collected with a cold metal plate held above patches of soil. The rising water vapour would condense as frost on the plate and 鈥測ou could scrape it off鈥�, Kaukler says.