applicable. More recently, the development of self-reproducing manufacturing facilities or plans using them has been undertaken at several locations in the United States. In 1978 and 1979, the Space Studies Institute (SSI) at Princeton University conducted a series of workshops on the subject, which led to the publication in 1980 of a plan for the use of partially self-reproducing manufacturing facilities on the moon and in space to construct solar power satellites. Masses and rates of self-reproduction of the manufacturing facilities were estimated, and a schedule partially worked out for this plan. NASA has conducted little relevant research, the exception being two general papers on self-reproducing manufacturing facilities by Von Tiesenhausen, at Marshall Space Flight Center. Also, X.R.I. of Santa Clara, California, has performed research on self-reproducing manufacturing facilities. One purpose of the study summarized here is to check the scheduling and cost estimates of the plan of the SSI. Thus one of the plans which is hypothesized and analyzed is based closely on the SSI plan, with some modifications made which would cause costs to be reduced. The SSI plan assumed that 10% of the mass of a copy of a manufacturing facility is equipment which is constructed on earth. More advanced self-reproducing manufacturing capabilities may be possible, once technology is sufficiently advanced, with the ability to reproduce a copy solely from materials in the environment; this will be referred to as pure self-reproduction. With such a capability, the amount of equipment imported from earth is further reduced, with a corresponding reduction in cost. Two plans which use pure self-reproducing manufacturing facilities on the moon and in space for the production of solar power satellites are analyzed. Except for the fact that pure self-reproduction is used, again the plans closely follow the SSI plan. In these two plans, and all others mentioned later which use pure self-reproduction, it is assumed that no humans are required in space to assist with operation of the facilities. In the extension of the SSI plan which uses partial self-reproduction, four weeks are spent in space by four humans, during the initial set up. In the NASA study of 1977 on Space Resources and Space Settlements, 3000 humans are eventually required in space. Since the moon contains insufficient quantities of some elements required for the construction of life-supporting facilities such as space habitats, the construction of habitats was not considered in the above plans. However, the carbonaceous chondritic asteroids may contain these elements, which include hydrogen, carbon, and phosphorous, so plans are worked out, using pure self-reproducing manufacturing facilities, to produce either or both solar power satellites and habitats. Plans using partial self-reproduction are not developed here since travel to asteroids to supply the additional equipment required for self-reproduction is more lengthy than to the moon; also the amount of self-reproduction required to create a manufacturing facility with sufficient capability to construct the habitats is so large that a great deal of equipment from earth would be required if only partial self-reproduction were possible. Finally, it may be necessary to use asteroids to have pure self-reproduction be possible at all, since some elements available on asteroids but not on the moon may be required in the facilities themselves.
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