Lunar Aluminum Applications
David L. Burkhead
Aluminum is an abundant material on the moon, and can be used in a
variety of applications. Rocket propellant and export to LEO may be two
Hydrogen/Oxygen engines are very efficient. However, if you're on the
moon, you may very well not want hydrogen
at all, not until you have an extraterrestrial source. The penalty in
lifting that hydrogen from Earth's surface (including lifting very large
tanks) may be higher than the penalty of using a lower Isp rocket that uses
indigenous fuels. Aluminum/oxygen is one possibility. The figures usually
published give it an Isp of about 270. That's on the low side, but it's a
dense fuel, so you can get pretty high mass ratios. Also the delta-v
requirements of most missions are much lower than that of launch from
Earth's surface to orbit.
On the production side of the equation, thanks to the US Bureau of Mines
we already have techniques to extract aluminum from feldspars (which are
plentiful on the moon). Perhaps the most adaptable to lunar
conditions is the melt-quench-crush-leach
process. Melt the rock (big
solar furnace, only runs during the lunar day), and quench it to glass,
then crush it. This breaks up the crystalline structure so that acids can
leach out the aluminum oxide. Precipitate the aluminum oxide and the rest
is identical to Earth-based processes.
In terms of exports, I did some economic type numbers on
just that kind of operation for my article "The Economics of Lunar Mining"
which appeared in the August/September 1993 issue of High Technology
Careers. The upshot is that lunar aluminum, delivered to Earth orbit, and
using current launch prices, will cost about $52,000 a ton. Compare that
with terrestrial materials also delivered to Earth orbit at more than $4
million a ton. I didn't include the use of lunar aluminum as a propellant
in the figures, or low thrust/high efficiency engines such as ion drives,
but it's pretty clear that either would drive down the cost of the lunar
aluminum, as would closing the life support system (I assumed a completely
open cycle life support system, with everything but oxygen lifted from
Earth). Likewise, lower launch costs would drive down the cost of both
lunar and terrestrial aluminum.
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