interest for lunar mineral operations as it has a high abrasion resistance and hence is useful for pumping of granular materials or slurries. Many of the applications of cast basalt could also be filled by the use of metals, which have the added advantage of flexibility under the expected severe thermal stress, but metals would require more extensive lunar processing and hence may not constitute a valid option, particularly in the early stages. Foamed Silicate Melts For many construction applications, both on the Moon and in space, considerable advantage would accrue from causing the fused silicate melt to foam before solidifying. This provides much more volume of product per unit of material processed (and per unit of energy expended), and it also provides a lower density product. Fused silicate melt to be used in an SPS would probably be foamed in space and not on the Moon. Various possible foaming agents have been considered, including sodium sulfate plus carbon and even oxygen (evolved on electrolysis of the melt during reduction of iron). Possibly only carbon need be used; it would form CO bubbles. If
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