this paper are up to the delivery of only the first solar power satellite. Means to transport the solar power satellites from the factory to geosynchronous earth orbit are not considered in SP-428. but are considered in the other plans. Asteroid Resources Plans Since elements lacking in the moon but present in asteroids may be required if self-reproducing factories are to be developed by the time their use in these plans is desired, two plans which use self-reproducing manufacturing facilities on asteroids are presented here. These elements include C and H, which are present in carbonaceous chondritic asteroids. Asteroids of the necessary composition which are in an orbit from which they can be returned to high earth orbit by the plans considered here, and which are of the desired size and speed of rotation, are not now known, but are expected to be discovered [4], Only one manufacturing facility is required initially, instead of the two required in the extended S.S.I. plans, to begin use of extraterrestrial resources. When it attaches itself to an asteroid, it begins pure self-reproduction, and no further equipment is brought from earth. The plans described here yield space habitats in addition to solar power satellites, and mass estimates for the habitats are derived. After producing a copy of itself, the space manufacturing facility is brought to a second asteroid, and self-reproduction proceeds on both. Both asteroids are returned to earth, and solar power satellites are produced from the first, while habitats are produced from the second. During the return, more space manufacturing facilities are sent to other asteroids, for construction of additional habitats. Since the moon does not contain P, H, and C, all of which are required for space habitats, their construction was not considered in the plans which use lunar resources. N is also required in habitats, and it is not known to me whether there are any carbonaceous chondritic or other asteroids which contain enough of this element. Lunar Resource Use Followed by Asteroid Use If pure self-reproduction using asteroidal resources is not at first possible, the plans for lunar resource use may be followed first, and a self-reproducing factory sent to an asteroid later, when available. It may also be desirable to use lunar resources first even if pure self-reproduction is possible, since the time between beginning of operations and arrival of first solar power satellite at geosynchronous earth orbit is less in some cases. Because of the similarity of these plans to the others of this paper, they will not be analyzed. Detailed Description of Plans S.S.i. Summary In S.S.I., equipment with mass 371 is placed on the moon, and 70 t of equipment are placed in a high earth orbit [5]. Required use of the space shuttle is stated to cost
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