water would consist of 11% hydrogen from the earth, and 89% oxygen from the processing of lunar soils. If closed-cycle ecology turns out to be impossible, or takes a very long time to perfect, the fallback position would be to bring dehydrated food from the earth, and add water at the orbital facility. A full diet with plenty of energy for construction work would require about one pound per day, dehydrated, so the budget would be less than a quarterton per year per person. On the basis of experience in the 13 heavy construction industry on earth, the productivity should be frpm 10 to 30 tons/person-year, so even at the fallback position the economic benefit of having a man or woman working in high orbit would be 50 to 150 times larger than if the same person were to be working on earth. Transport of Lunar Materials: There is one necessary element in an orbital-manufacturing program that is qualitatively different from anything so far con- 2 strutted for use in space: that is the mass-driver the launchingmachine which would accelerate blocks of lunar material to escape velocity, provide them with precise guidance, and then release them to travel out from the moon to a collection point. On the basis of the design work which has been done so far, the mass-driver may be an aluminum track some 14 km in length, on which would move small vehicles passively guided by the effect known as dynamic magnetic levitation, already studied for urban transportation systems. Each vehicle, some 5 kg in mass and 50 cm in length,
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