One way to minimize rocket transport from Earth is to take advantage of the resources already in space (5). Like terrestrial inputs, these materials would have to be delivered to some appropriate orbit. However, it has been estimated (6,7) that launching matter from the Moon using currently known techniques will require only 1/20 to perhaps as little as 1/200 the energy needed for even advanced Earth-launch systems. The primary reasons for this difference are that lunar transport does not have to contend with the Earth's gravity or atmospheric drag. In addition, lunar cargos do not necessarily have to be inside a complex and heavy cargo vessel to protect them from the atmospheric heat and pressure, as in terrestrial launches (7). Of course, facilities for operating with lunar soil do not currently exist. They would have to be provided from Earth. Nevertheless, since most machines are capable of processing many times their own mass each year (8), the total Earth- launched mass would still be only a fraction of that required in the terrestrial case. The extensive data base generated by ten years of lunar sample research and availability of lunar samples make it possible to design adequate production machines to convert lunar soils into a wide range of industrial feedstocks prior to return to the Moon (9, 10, 11, 12). Earth transport requirements could be reduced even further by using lunar soil to manufacture not only the final output, but also the “production” capital (5, 13, 14). This way, only a small seed facility would be required from Earth to initiate production. Despite growing interest in this final “bootstrapping” approach no parameterized economic model has yet been developed to analyze the potential benefits in detail. This study begins with the derivation of some basic equations which must apply to all models of space industry, regardless of whether they involve bootstrapping or even utilization of extraterrestrial materials. The difficulties in formulating a general bootstrapping mode are then discussed. Finally, attention is focused on a simplified model and the conclusions which can be derived from it. We hope this work will promote further analyses. GENERAL FRAMEWORK Two types of inputs that are required for any productive enterprise — expendables and capital. Expendables are materials and services which contribute to productivity only during the period in which they are made or purchased. Included in this group are chemical fuels, food, and reagents lost in process cycles. These items must be supplied regularly for production to occur. According to this usage, even personnel is considered an expendable, because crews must be periodically paid and rotated back to Earth. These inputs correspond roughly to recurring and nonrecurring costs (see Ref. 11). In contrast, capital goods do not have to be continuously supplied. Indeed, it will be assumed that, once operating, capital remains productive throughout the life of the project, so that the capital stock never decreases. Even with this assumption, the natural wearout of equipment can be accounted for in two ways. First, replacements for worn parts can be treated as an additional type of expendable. Alternatively, if the wearout rate exceeds the repair rate, resulting in disuse of some equipment, the operating capital stock can be considered constant, but with decreasing productivity. Other factors, such as expendable requirements, would also have to be adjusted accordingly.
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