the points which O'Neill (3) made with respect to SPS construction using NTM's was that the system must grow at a reasonably rapid rate using internal resources. This point still seems generally valid and should be subjected to much more analysis. At least one generalized model of growth via NTM's has been developed (6). One aspect of growth via NTM's is mass multiplication (7). This means that the total of all mass brought from Earth (reagents, equipment, support facilities, transportation fluids, etc.) should be significantly less than the total mass of NTM's processed by the system over its life. Ideally one would like an infinite ratio. That is, produce all goods from space resources and bring nothing from Earth. However, this is very likely not necessary for commerce in cis-lunar space and in fact the use of lunar resources may sharply decrease the cost of Earth to space transportation and allow a much greater materials commerce between cis-lunar space and the Earth than is generally anticipated. Woodcock notes that the use of lunar materials or nonterrestrial materials in general is not in the “main stream” of space industrialization research and planning. We vigorously disagree and assure the reader we are not overcome with dejection in the face of such rejection. Rather, we expect a flow of progress in NTM's interest which will shift the river banks of the main stream. We feel even Mr. Woodcock is getting into the swim (or drink) with us and welcome others to join. Naturally the water will have to be made in part from lunar and other NTM's. David R. Criswell Visiting Research Physicist California Space Institute (UC-San Diego) Edward H. Bock General Dynamics Corp. Convair Division, San Diego, CA REFERENCES 1. G.R. Woodcock, Space Settlements and Extraterrestrial Resources—What Benefits to SPS Construction, Space Solar Power Review (to be published). 2. U.S. National Aeronautics and Space Administration, Space Resources and Space Settlements, John Billingham er al., eds., NASA Special Publication 428, Technical Information Branch, Washington, DC, 1979. 3. American Institute of Aeronautics and Astronautics, Space-Based Manufacturing from Nonterrestrial Materials, Gerard K. O'Neill, ed., Progr. Astronaut. Aeronaut. 57, 1977. 4. General Dynamics Corporation, Convair Division, Lunar Resources Utilization for Space Construction: Final Report, Edward H. Bock, Study Manager, Contract No. NAS9-15560, 1979. 5. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, Extraterrestrial Processing and Manufacturing of Large Space Systems, NASA Contractor Report 161293, NASA, Washington, DC, 1979. 6. A.H. Goldberg and D.R. Criswell, The Economics of Bootstrapping Space Industries — Development of an Analytic Computer Model, Space Solar Power Review 3, 73-94, 1982. 7. R.D. Waldron et al.. Role of Chemical Engineering in Space Manufacturing, Chem. Eng. 86, 80-94, 1979. 8. American Astronautical Society, The Future United States Space Program, Proceedings of the 25th AAS Anniversary Conference, Adv. Astronaut. Sci. 38, 1979. 9. U.S. Department of Energy and U.S. National Aeronautics and Space Administration, Final Proceedings of the Solar Power Satellite Program Review, DOE/NASA, Washington, DC, 1980. 10. U.S. National Aeronautics and Space Administration, Radiation Energy Conversion in Space, Kenneth W. Billman, ed., Prog. Astronaut. Aeronaut. 61, 1978. 11. American Institute of Aeronautics and Astronautics, Proceedings of the Fourth Princeton/AIAA Conference on Space Manufacturing, J. Grey and C. Krop, eds., AIAA, New York, 1979.
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