hydroelectric and geothermal power among fringe sources (1 to 5 per cent) of energy. It has been very difficult to obtain widespread support for research on satellite power; the reason may be in part that no one with the resources to support such research on a large scale has been convinced that the necessary large improvement factors in powerplant cost and mass, and above all in lift costs, can be achieved on a reasonably short time scale with a high enough degree of certainty to justify investment. I think that with the addition of the orbital manufacturing concept, satellite power can become economically viable; that is the topic of the next section. Orbital Manufacturing: The use of lunar materials, and the "bootstrap process", are key elements in reducing the costs of satellite power. The use of lunar materials would circumvent the problem of lift cost ($/kgsy) and therefore of power plant mass (kg/kw). The bootstrap process would replace linear growth in the number of SSPS units by exponential growth. The establishment of the first SMF would require the transport of 3,000 to 10,000 tons to the lunar survace, and 10,000 to 40,000 tons to a high orbit, for example to one of the 2 Lagrange points L4 or L5. This is about the same total lift requirement as one single power satellite. The SMF would constitute a ''beachhead in space”, and once it is established its workforce
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