Page:Advanced Automation for Space Missions.djvu/289

 The list includes reagents necessary for the production of microelectronic circuitry (Oldham, 1977), even though "wet chemistry" may not be necessary for this application in space manufacturing (Zachary, 1981). The team is unaware of any significant omissions in table 5.11, which demonstrates essential qualitative closure.

5E.2 Derivation of Minimum Requirements: Qualitative Materials Closure

The lunar substrate from which the required substances are extracted or manufactured has a mean global mineral content as shown in table 5.12. Source minerals for boron do not appear in this list, nor do the sources for volatiles implanted by the solar wind. A summary of all elements found to date in the lunar regolith samples returned by Apollo and Luna missions may be found in table 4.1.

To plausibly demonstrate materials closure, it must be shown that every item on the requirements list can be derived from other items on the list and that all elements are derived from those found in the lunar regolith. To fully and rigorously demonstrate closure, a detailed element-by-element breakdown of the entire factory would be required, giving the mass of each element or process chemical required followed by a convincing demonstration that such quantities could indeed be produced using only the amounts of other substances known to be available and an input of lunar material. This latter set of conditions is called quantitative closure.

Preparation of process minerals. A comparison of the list of process chemicals in category VI in table 5.11 with the minerals found in lunar soil (table 5.12) suggests that it may be possible to use raw lunar soil as input to the materials processing extraction machines if these minerals require no beneficiation. In the event such beneficiation is needed to obtain the specific minerals in separated form, the electrophoretic separation technique described in section 4.2.2 may be used. This method involves placing finely divided powdered lunar dust in aqueous (or slag, or other solvent) suspension which has a solvent pH tuned to match the isoelectric potential of the desired mineral species. A cross voltage is applied and all minerals but the one desired migrate away, leaving behind a purified residue - in the present case, anorthite and the category VII (table 5.11) process minerals may be recovered. Preliminary testing of the electrophoretic separation concept with simulated lunar soil has been successful (Dunning and Snyder, 1981).

aThese minerals are known to exhibit complex substitutions, particularly of elements as Y, Nb, Hf, U, and the rare earth elements that are concentrated in these minerals.

In addition, the electrophoretic technique may prove invaluable in separating out "trace minerals" from lunar soil, in particular apatite and possible differentiated boron-containing minerals which may exist in the lunar regolith.

Separation of iron. The magnetic properties of lunar soil are due almost entirely to the presence of metallic iron, which occurs in lunar soil as a free element in the amount of 0.5% by weight, roughly 5% of the total iron content of the lunar regolith. Since it is magnetic, metallic iron may be