ium, silicon, glasses and ceramics. Native asteroidal steel (nickel-iron) is present in lunar fines at roughly 1% concentration; it can be separated from the fines by a magnet. In so far as known, it is very depleted in hydrogen, carbon, and nitrogen. These elements are of course necessary for a biological ecology. With what we know now, a fully self-sufficient economy is not likely on the Moon because of scarcity of volatile materials. Recycling might reduce consumption so that an import-export balance could be struck if an export economy can be created on the Moon. Richer ores may be found; analysts speculate on the possibility that water ice may be found in perpetually dark crater bottoms at the lunar poles. The Moon is actually not at all well known; we have a few surface samples from a few sites. Mars is less well known than the Moon, but we do know that Mars has water, CO2 and nitrogen. A fully self-sufficient biological ecology should be possible on Mars in so far as raw materials availability is concerned. The moons of Mars are thought to be like carbonaceous chondrites which would mean that they possess these substances also. Asteroids are believed to include types rich in metals as well as organics. Moons of the outer planets apparently contain large quantities of water ice, ammonia and methane. Thus usable quantities of all economically useful elements are available off Earth. Extreme caution is appropriate, however, when thinking of trade and transport of bulk resources or commodities in space. The high energy cost of space transport, even with the most energy-efficient means imaginable, will in most cases incur costs far exceeding the value commonly accorded bulk resources. The energy cost of space transport, in fact, is the prime motivator for use of extraterrestrial resources as an alternative to shipping from Earth. If resources are needed, e.g. for a construction project in orbit, it probably makes sense to obtain them from the least energy cost location. This will usually not be Earth. But one should not imagine that food grown on Mars will be routinely traded for steel made on the Moon. Alternative Uses of Extraterrestrial Resources In this paper, I consider three ways of using extraterrestrial resources: (1) application where found, i.e. on a cosmic body, for missions conducted on that body—this includes refuelling of transportation systems at or on a cosmic body, as in a lunar logistics system; (2) export to use elsewhere in space, as in the use of lunar resources for a construction project in geosynchronous orbit or export of lunar oxygen to low Earth orbit; and (3) export to earth for use in terrestrial economies. The simplest way of using resources in situ is to use them unprocessed or slightly processed, e.g. beneficiated. Unprocessed resources are useful for radiation shielding, a common need for space missions. On the Moon, graded regolith can be used to fill shielding containers surrounding nuclear reactors. This simple use of lunar resources can greatly reduce the transport mass for lunar reactor powerplants. Martian soil is presumably also suitable for such use. Many concepts and analyses have been published, e.g. Mendell (1985) and Faughnan and Maryniak (1985), proposing use of lunar resources on the Moon at various levels of refinement, from ‘lunar-crete' to winning metals and making fibre- reinforced composites. Possible uses range from construction of pressurized shelters to diverse lunar manufacturing industries. Opportunities for refuelling also exist. Oxygen is plentiful on the Moon and could be advantageously used in hydrogen-oxygen propulsion systems. If water is found on the Moon, complete refuelling would be possible. Extraction of water from the moons
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