A lunar base could be built from waterless concrete composed entirely of moon dust, according to US researchers.
NASA's Lunar Reconnaissance Orbiter will next year scout out a good landing site ahead of the 2020 mission that will put US astronauts back on the moon.
A four-strong team will spend seven days on the lunar surface, but NASA hopes to eventually have long-term moon bases.
However, building permanent structures on the moon would be astronomically expensive, says Houssam Toutanji, a civil engineer at the University of Alabama in Huntsville, US.
"It costs a tremendous amount of money to take even 1 kilogram of material to the moon," he says. "Depending on who you talk to, the cost could be $50,000 to $100,000."
Toutanji thinks those costs could be sidestepped by making concrete from moon dust, and moon dust alone.
Here on Earth, concrete is made from a pebbly aggregate bound together by water and cement. Lunar concrete could be made using plentiful moon dust as the aggregate, and binding it together using sulphur purified from lunar soil.
"You want the sulphur to be in a liquid or semi-liquid form to work as a binding agent," says Toutanji, which requires heating it to between 130 and 140 °C.
Once cooled, concrete made in that way quickly hardens like a rock. "Within an hour you get an ultimate-strength concrete," Toutanji says. "With normal concrete you have to wait seven days, in extreme cases even 28 days to get maximum strength."
To test the properties of lunar concrete, Toutanji and Richard Grugel, a geological engineer at NASA's Marshall Space Flight Center, also in Huntsville, used a simulated lunar soil.
They added 35 grams of purified sulphur to every 100 grams of dust and cast the mix into a number of small cubes about 5cm on a side. Those were exposed to 50 cycles of severe temperature changes, each time frozen down to -27 °C and then warmed back to room temperature.
Even after that treatment the concrete could withstand compressive pressures of 17 megapascals (roughly 170 times atmospheric pressure). If the material is reinforced with silica, which can also be derived from moon dust, this can be raised to around 20 megapascals.
Peter Chen of NASA's Goddard Space Flight Center in Greenbelt, Maryland, devised his own form of waterless concrete earlier this year, using epoxy as the binder.
"Toutanji and Grugel are of course correct in stating that, due to the high cost of going to the Moon, the amount of material to be transported must be kept to a minimum," he says.
Chen's concrete would require a supply of epoxy to be shipped to the moon, he concedes, but says once that is done it is simpler to make.
As well as a device to scoop up the soil, and a mixer to combine the soil and the epoxy, Toutanji and Grugel's concrete would also require a power source to bake sulphur out of lunar soil, and melt the concrete mixture, Chen points out.
But Toutanji thinks that those energy costs would still be lower than the costs of transporting raw material to the moon, although he has not worked out the logistics of powering the sulphur extraction and melting.
In the past researchers have claimed that temperatures of more than 1000 °C could be reached using solar furnaces that concentrate sunlight.