The preferred destination is the lunar libration point L2,t behind the Moon as seen from the Earth. Here the payloads are intercepted by a mass catcher and transferred to another vehicle for delivery to a space factory, typically at L5 (another lunar libration point). [3] At the space factory, these materials are processed to derive engineering materials (aluminum, glass, iron, titanium, silicon, and oxygen are likely products). The engineering materials are used to fabricate the space settlement pressure vessel, shielding and interior structures and equipment; later, after the settlement is established, solar power satellites are fabricated from the materials. [4] Completed SPSs are moved to their operational geosynchronous orbit and enter commercial service. (Many variants on this scenario have since been published.) O'Neill's seemingly circuitous scheme can be shown to result in less recurring transportation cost for SPS hardware. The primary leverage is that transportation energy from the lunar surface to geosynchronous orbit is only a fifteenth of that from Earth's surface to geosynchronous orbit. Further, the mass driver can be more efficient in imparting energy than can a conventional rocket system. Purpose of This Paper This paper is intended to challenge two views widely held by space resources advocates and to suggest an evolutionary rather than all-up or bootstrap approach to space resources utilization. The challenges are [1] potential cost savings accruable through use of large habitats that allow extended space crew tours of duty (years vs months) may be the economic lever that allows utilization of extraterrestrial resources. The conventional view, albeit unstated, seems to be that extraterrestrial resources will provide the economic lever that allows (or demands?) the large habitats. This is a mild challenge since it is only a difference in viewpoint. It is, however, related to the second challenge, the latter being a much stronger and more controversial one. [2] My second challenge asserts that the available estimates of labor required to manufacture SPSs from extraterrestrial materials (e.g., Ref. 6) are low by a wide margin, and that the economic advantages claimed for extraterrestrial resources for SPS manufacture may not exist. A major part of the paper thus deals with cost estimation techniques and their application to this question. I do not foresee an early resolution of the labor content issue, as the present knowledge base is simply inadequate. I conclude the paper with an evolutionary approach to extraterrestrial resources and with recommendations for further research in this field. The use of large “settlement” habitats and of extraterrestrial materials are seemingly inextricably linked in the usual scenario, as summarized above. However, the potential economic benefits of space settlements probably have little to do with utilization of extraterrestrial resources. The economics of space settlements are dominated by the costs of transportation of people from Earth, while economic use of extraterrestrial resources is mainly related to costs of transportation of cargo and cost of its subsequent use in manufacture of artifacts. These are separate and distinct questions that may be independently analyzed. They may then be considered jointly, tThese libration points are quasistable orbit locations in the Earth-Moon system. They were mathematically discovered by Lagrange in his analyses of the restricted three-body problem in celestial mechanics and are called Lagrangian points; they are numbered LI through L5.
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