Thursday, January 13, 2011

"Demandite" and Resources in Space

“Demandite” is the word used by mineral economists to describe the materials that must be provided-- usually by mining-- to meet the needs of civilization. In the usual terrestrial setting, air and water are assumed to be freely available, and fossil fuel (natural gas, crude oil, and coal) is considered a necessity. In space, where dependence on solar energy is the norm, and where air and water must be “mined”, the numbers are different. The proportions of mineral needs, however, are otherwise generally similar. You can then ask how much of each material (iron, carbon, nitrogen, aluminum, copper, oxygen, water, nitrogen, etc.) is needed to be in circulation to support one person, depending on “renewable” (inexhaustible) solar energy to drive industry, agriculture, and recycling. We can then compare those requirements to the natural resources available on bodies in nearby space, and calculate how many people could be supported at each of those locations.

The proportions of these necessary materials (the relative abundances of water and iron, for example) are very different on the Moon, Mars, and nearby asteroids. The Moon, for example, is severely deficient in all volatile elements, including carbon, nitrogen, hydrogen, and chlorine, Mars, with its tenuous atmosphere and widespread ice deposits, fares better. But best by far is the match between the composition of near-Earth asteroids (NEAs) and “space-based demandite”. The 1000 or so kilometer-sized near-Earth asteroids contain enough of every essential element to support a population of 10 billion people from now until the Sun dies of old age. The NEAs, however, are a renewable resource: in nature, the rate at which NEAs are lost by collision with planets and ejection from the Solar System is compensated by recruitment of fresh asteroids kicked into near-Earth space by Jupiter’s gravitational interactions.

But what about the main Asteroid Belt? The answer is startling: the Belt contains one million times as much mass as the entire NEA population. Again depending on the Sun for power, the Belt could support a population of 10 million billion people-- a million times the ultimate carrying capacity of Earth. With that many people, wouldn’t we be running out of solar power? Not really-- even under these extreme assumptions, we would require less than one millionth of the Sun’s output energy.

The non-renewable resources available to Earth-bound humanity are finite. The resources available to a space-faring humanity are effectively infinite.


L Gertsch said...

And space-sourced mineral resources can be sustainable, as well. With a large enough source volume to draw from, even mineral deposits that form excruciatingly slowly (in human terms) can be extracted at a lower rate than we use them.

Anonymous said...

Hello Dr. Lewis,

Your book "Mining the Sky" is one of my favorites. I noticed, though, that in the chapter on lunar development you did not consider "Lunatron" electromagnetic launchers, rotating tethers, or lunar space elevators (which studies have shown could terminate beyond the Earth-Moon L1 and L2 points and could even begin near the Moon's poles, even using Kevlar or Spectra fibers for the cable material) for getting to and from the lunar surface inexpensively. These non-rocket transportation systems could "close the (economic) case" for setting up shop on the Moon. With such inexpensive transportation options, a lunar industrial infrastructure could also aid asteroid resource extraction activities, as asteroidal ice could be "winched down" lunar space elevators and cached in the permanently-shadowed craters at the Moon's poles. Have you looked into these possibilities? It would be a shame if our large, nearby natural satellite couldn't have a useful role in space industrialization and colonization.

Sincerely Yours,

James *Jason* Wentworth