One billion tons of lunar ice would keep a city of a million alive for only about a century
Martin Elvis and Jonathan McDowell calculate in Frontiers in Space Technologies that the water in the Moon's permanently shadowed polar craters, generously taken as one billion tons, would support a city of one million for only about 100 years even at the 98 percent recycling achieved on the International Space Station. Power is no obstacle: kilometre-tall solar towers on sunlit crater rims could deliver three gigawatts. Without tenfold better recycling or a far larger water supply, the authors conclude, large-scale long-term settlement is ruled out.
Science··Midday
The water runs out in about a century
The calculation, published in Frontiers in Space Technologies, compares two scenarios, a city of 100,000 and a city of one million, by estimating roughly how much power and water such populations would use on the Moon. The water comes from ice in permanently shadowed regions near the poles, which orbiting spacecraft have mapped; the authors deliberately take the most generous figure, about one billion tons. Even so, with 98 percent of the water recycled, the level the International Space Station achieves, a city of one million uses the supply up in about 100 years. Elvis and Jonathan McDowell, both astronomers at the Smithsonian Astrophysical Observatory, present the figure as a first feasibility estimate rather than an observation.[1], [2]
Power is the easy part: three gigawatts from the crater rims
Power turns out not to be the limit. The rims of the permanently shadowed craters sit in almost continuous sunlight, and the authors calculate that kilometre-tall towers covered with photovoltaic arrays on those rims could generate three gigawatts of electricity, enough for a large city without nuclear reactors. Solar panels could even be manufactured on the Moon, given the amount of silicon in its surface.[1], [2]
Tenfold recycling or a much bigger reservoir
Recycling is what stretches the supply. With no recycling at all, a billion tons would last a city of one million only a few years, and a town of 100,000 about 20 years. Raising recovery from the space station's 98 percent to a level roughly ten times better, or finding a water reserve comparably larger than the one assumed, is what the authors say would be needed before large-scale, long-term habitation of the Moon becomes tenable; short of that, their result rules it out. The estimate rests on explicit assumptions about consumption, and the authors present it as a feasibility check rather than a measurement.[1], [2]
