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By W. E. Bradley, June 1980

At a recent meeting a member of the NASA Advisory Council expressed excitement at the positive conclusions reached by the June 1979 Woods Hole Symposium concerning self-replicating mechanical systems. He said that he could not understand why a subject of such interest and importance to the exploration and utilization of space should be approached so timidly. Earnestly, he added: "After all, a lathe can produce a lathe, properly operated; nowadays numerically controlled lathes are available; so why not program one to reproduce itself?"

My reaction was the following:


 * A lathe cannot produce another lathe without many added subsystems (e.g., driving motor, tool grinder, tool bit production, etc.).
 * Some contemplation of the self-replicating system problems at the practical engineering level has been undertaken by a few individuals in the past few months. This work is incomplete as yet, but is aimed at practical, demonstrable systems with only a few critical parts supplied from outside the- system, including energy and raw materials for device fabrication. Energy and raw materials appear here in the role of "nutrient," the supply necessarily increasing as the system grows.
 * The self-replicating system is indeed of great interest on fundamental grounds.
 * The subject is appropriate to and important to NASA.

The work of the past few months (prior to the present study) relevant to self-replicating systems (SRS) is incomplete but has brought to light some principles and ideas of interest.

5A.1 Preliminary Investigation of the Self-Replicating Machine Shop

The town of Muncy is located in a somewhat remote part of central Pennsylvania. It is remarkable because of a nearly self-sufficient machine manufacturing capability in the Sprout-Waldron Company (now a division of another corporation, and therefore subject to change without notice). This company has manufactured agricultural and food-processing equipment as well as heavy machinery for the paper industry, especially pulp grinders. I became acquainted with them while searching for machines able to produce dense pellets for use as solid fuel from agricultural cellulosic wastes.

In the course of my visit, I was shown an excellent machine shop, a foundry, a woodworking shop, and a factory assembly space in which their machines were put together, painted and tested. They also had complete drafting and design engineering facilities. Of special interest was their toolmaking and repair shop, with which all of the milling machines, lathes, jig borers, punch presses, and so forth were kept in fine working order.

This complex, with the possible exception of the foundry, seemed to be a system which, with human assistance, could duplicate itself. In retrospect, it seems worthwhile to explore the possibility that the human operators might be replaced by general purpose automata, manufactured almost completely by the complex itself. The result would then be a major component of a self-replicating system. To complete the system would require manufacture of a prime power source which could be expanded as the complex grows, manufacture of a shelter system (sheds with roofs, walls, windows, and doors) similarly expandable, and possibly a casting and/or forging subsystem, and electronic and computer components of the automata. The foundry with its requirement for refractory furnace linings and high temperatures is a special problem and in some versions of the system may be bypassed.

Present machine shops. Each machine in a machine shop has a functional domain or "scope," assuming unlimited operator attention and guidance. Thus, a lathe (with no attachments) is able to produce objects with cylindrical symmetry having axial length and maximum diameter determined by the "bed length" and the "swing" of the machine. It can also make threads (helical structures), and, to a limited extent, can also make straight-line cuts or grooves which are more properly the work of a milling machine. Lathes can drill holes most readily on the axis of a workpiece of cylindrical symmetry and can achieve a high degree of accuracy of concentricity for this one type of drilling. Most drilling, however, is best accomplished on a jig borer.

The second major machine type in a shop is some form of drill press, or, better, a jig borer. The workpiece is held