A Proposed Lunar Factory
We envision a single-step, single- pot, steady-state electrolysis process using common lunar soil as feedstock with little or no preprocessing. As the soil is fed into the cell, it is melted by "excess" electrical heat released into the melt owing to resistance. The total electrode surface area would be about 30 square meters each (because each electrode is divided into fins, as in a car battery), and the total cell volume about 1 cubic meter. The operating temperature would be between 1300°C and 1600°C depending on the type of container and electrode materials that are ultimately developed. The cell would produce 1.4 tonnes iron-silicon metal, 1 tonne oxygen, and about 3.5 tonnes slag in 24 hours, with an energy requirement of about 13 MWhr (or 47 GJ). The process would satisfy many of the criteria set forth above for early lunar technologies, including use of common and easily mined lunar soil as feedstock, absence of a need to supply reagents from Earth, and simplicity of the process combined with multiple products. Mass, size, and power requirements of the process are also competitive with alternative processes -(table 9). The low energy and mass requirements of the process are particularly important because the major expense in establishing a lunar oxygen factory is the cost of transporting the plant materials (including the required power plant) to the Moon (see Simon's discussion in volume 2).
All the processes that have been suggested for extracting oxygen from lunar materials and probably many that haven't yet been suggested deserve our careful consideration in determining which is the "best" process to be implemented on the Moon. However, all the processes require substantial additional study before we are able to judge their relative worth for extracting lunar oxygen; and, before an operational plant can be built, even more study will be required.
We note that there is not much time (we hope) before the chosen process will be needed on the Moon. If we are to ensure that an oxygen production plant is included in the early planning and development of a lunar base, we need to progress quickly in assessing the various proposed processes so that the concept of a lunar oxygen plant can become a part of everyone's idea of what a lunar base should be.
Although it is certainly too early to decide which oxygen extraction process is the best one, our preliminary work with magma electrolysis has increased our confidence in its promise. We feel that its theoretical advantages listed above, including relatively low energy requirements, low mass, simplicity, and versatility with respect to feedstock, are sufficient to warrant its consideration as one of the processes most likely to be used in the early mining of oxygen from the Moon.
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