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There are two distinct classes of fabrication production machines in any general-product self-replicating system parts or "bulk" fabrication and electronics or microcircuit fabrication. Appendix 5F is concerned exclusively with LMF subsystems required for bulk manufacturing. Microelectronics production in space manufacturing facilities is considered in section 4.4.3 and is the subject of Zachary (1981); estimated mass of this component of the original LMF seed is 7000 kg, with a power draw of perhaps 20 kW to operate the necessary machinery (Meylink, personal communication, 1980).

5F.1 Overall Design Philosophy

The plausibility of both qualitative and quantitative materials closure has already been argued in appendix 5E. A similar line of reasoning is presented here in favor of a very simple parts fabrication system, to be automated and deployed in a self-replicating lunar manufacturing facility. To rigorously demonstrate parts closure it would be necessary to compile a comprehensive listing of every type and size of part, and the number required of each, comprising the LMF seed. This list would be a total inventory of every distinct part which would result if factory machines were all torn down to their most basic components - screws, nuts, washers, rods, springs, etc. To show 100% closure, it would then be necessary to demonstrate the ability of the proposed automated parts fabrication sector to produce every part listed, and in the quantities specified, within a replication time of T = 1 year, starting from raw elemental or alloy feedstocks provided from the chemical processing sectors.

Unfortunately, such a detailed breakdown and analysis probably would require tens of thousands of man-hours even for the simplest of systems. Not only is the seed not a simple system, but the present baseline design is not conveniently amenable to this sort of detailed analysis. Thus, a completely rigorous demonstration of parts closure is beyond the scope of the present study.

However, it is possible to advance a plausibility argument based upon a generalized parts list common to many complicated machines now in use in various terrestrial applications (Spotts, 1968; von Tiesenhausen, unpublished Summer Study document, 1980). Although machines designed for construction and use in space may employ radically different components than their terrestrial counterparts, to a first approximation it may be assumed that they will be comprised generally of the same kinds of parts found in commonplace machines on Earth such as bolt, nut, screw, rivet, pulley, wheel, clutch, shaft, crank, rod, beam, wire, plate, disk, bushing, cable, wedge, key, spring, gasket, seal, pipe, tube, and hose. If this is valid, then a showing that all parts classes in the general parts list can be manufactured by the proposed automated fabrication system may serve as a valuable plausibility argument in favor of parts closure for that system.

The achievement of a sound design which incorporates the advantages of maximum economy in manufacture and functional requirements of a part is dependent upon the designer's ability to apply certain basic rules (Yankee, 1979). There are four recognized rules, equally applicable to terrestrial factories and lunar replicating machine systems, as follows:


 * 1) Design all functional and physical characteristics for greatest simplicity. As a general principle, service life of a part is greatly increased when design of that part is both simple and sturdy ("robust"). Performance is more predictable and costs (money, build time, repair time) are lower for simpler parts.
 * 2) Design for the most economical production method. The particular production design selected should, if possible, be optimized for the part or set of parts the system must produce. The production of scrap (input/output ratio) is one valuable index by which optimality may be compared. This factor is relatively simple to evaluate where only one part is manufactured. In multipart production lines the problem is far more complicated, since each of the many parts may be expected to have dissimilar optima. Consequently, only the production of the entire system can be truly optimum.
 * 3) Design for a minimum number of machining operations. All types of costs are lower when fewer operations are required to produce a part according to specifications. The greatest savings result when the number of separate processing operations necessary to complete a part is reduced. Multiple operations which can be combined into fewer operations, or functionally similar parts requiring fewer production steps, should be changed in a design. "Needless fancy or nonfunctional configurations requiring extra operations and material" should be omitted from the design (Yankee, 1979).