intelligence is available without cost, other than that included in the $3xl09 cost of computers used in design and control, as in the extended S.S.I. plans. 6. The rotation of the asteroids is not modified at first, while the space manufacturing facilities self-reproduce. Only when the space manufacturing facilities reach a great enough throughput to construct the large mass driver reaction engines that will be used to transport the asteroids to earth orbit is equipment to de-spin the asteroids constructed, and this construction and de-spinning take place immediately before the large mass driver reaction engines are constructed. It will be assumed that the despinning, including construction of equipment for de-spinning, takes one month. Since the space manufacturing facilities operate while the asteroids rotate at first, a stalk carrying the solar cells used to power the space manufacturing facilities protrudes from the pole of the asteroid to prevent shadowing, or other provision is made so that the space manufacturing facility can operate at its usual rate of construction. 7. During return of the first asteroid, 104 space manufacturing facilities and mass driver reaction engines are constructed for travel to 104 other asteroids, for use in additional habitat construction. Each of the new asteroids in turn sends out 104 additional space manufacturing facilities and mass driver reaction engines to other asteroids, until the resources of the solar system are exhausted. If only habitats are constructed, the 104 space manufacturing facilities are also sent out in this way, but from the 10^ t asteroid instead of the 10° t asteroid. The scheduling in this case will be presented also. Transportation 1. The retrieval of asteroid 1977HB, discussed in SP-428, will be used as an example. However, another asteroid would probably be used, since this asteroid may not have the assumed mass used in the following calculations, or contain the required elements. 2. For 1977HB, the AV required from low earth orbit to rendezvous with the asteroid is 9.4 km/s. 6.4 km/s is required for earth escape, and 3.0 km/s more to reach the asteroid [49], The return to earth orbit requires AV 3.0 km/s. Gravity assisted trajectories using the earth, moon, and Venus are used. 3. The maximum acceleration in the return is determined by the requirement that a AV of 2.04 km/s be supplied in 653 days = 21.5 mo. The total length of the return is determined by the fact that it begins July 1, 1985, and ends September 23, 1989, and is therefore about 1523 days or 51 months [50]. 4. The time between departure from low earth orbit and arrival at the asteroid is 214 days = 8 months [51], 5. The time for travel between the first and second asteroid is assumed the same as between low earth orbit and the first asteroid, 8 months. The AV between the first and
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