Here on the earth we must pay a stiff price in energy to launch materials into space. That energy shows in the high speed which a rocket must achieve before it can escape from the gravity of the earth. Further, our atmosphere makes it impractical here to provide that high speed by ground-based machinery. In contrast, because of the low gravity of the moon and its vacuum environment, direct launch of lunar materials into space would be practical: per pound, the necessary cost in energy would be only 1/20 as great as from the earth, and on the moon ground-machinery, much more efficient than rockets, could provide the necessary launch speed. From the Apollo project we know that the unselected soils of the moon are typically 40% oxygen, 20% silicon, and 20-30% metals by weight. The metals, mainly aluminum, iron, titanium and magnesium, would be usable as construction materials. 2) The "bootstrap process". In the orbital-manufacturing approach, it would only be necessary to put into high orbit a relatively small quantity of equipment, corresponding in mass 1 2 approximately to one satellite power-plant. That equipment, ' in the form of a highly productive, human-operated manufacturing facility (SMF, space manufacturing facility), would process lunar surface materials to build others of its kind, as well as power satellites. In that way the growth in time of the number of power satellites would be geometric, like the series 1, 2, 4, 8, 16, 32 instead of linear, 1, 2, 3, 4, 5, 6, as would be the case for ground-launched satellites. 3) Dependence only on the vehicle system we are
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