Kinematic Self-Replicating Machines
© 2004 Robert A. Freitas Jr. and Ralph C. Merkle. All Rights Reserved.
Robert A. Freitas Jr., Ralph C. Merkle, Kinematic Self-Replicating Machines, Landes Bioscience, Georgetown, TX, 2004.
6.4.1 Show Feasibility of Molecular Assembler or Nanofactory
The hallmarks of the molecular assembler are molecularly precise positional assembly coupled with a capacity for massively parallel or replicative manufacturing.
(1) Exemplify Programmable Molecular Positional Assembly. The first objective requires the designer to embody and illustrate the principles of programmable molecularly precise positional assembly in a specific physical design for a molecular assembler. Manufacturing involves assembling parts, and parts can either be self-assembled, positionally assembled, or assembled by some combination of these two basic approaches. That is, parts are assembled either by (1) allowing the parts to move at random until they “settle in” to the right position (self-assembly), or by (2) actively positioning the parts in the desired location and orientation (positional assembly). Combinations of these two approaches may also used, such as jiggling a pin until it slides into a hole.
Self-assembly (e.g., Sections 4.1, 4.3, 4.4) is a well-known and extensively studied method of assembling molecular parts [1436-1440]. Positional assembly of molecular parts (e.g., Sections 4.2, 4.5-4.7, 4.9-4.17) is still a relatively new concept . While it has been experimentally demonstrated [3084-3088] that molecules and molecular parts can be positioned and assembled using positional devices such as the SPM (Scanning Probe Microscope), our ability to positionally assemble molecular parts is still in its infancy. Hence the first purpose of a new design would be to show the great potential of programmable positional assembly of molecular components. For example, our design (Section 4.11.3) employs two 7-degree-of-freedom positional devices (Stewart platforms [208, 215]) which, under appropriate programmatic control, could be used to fabricate the entire system.
One consequence of this design objective is that close attention must be paid to the stiffness of the positional device and of other system components in the mechanical loop from the tool tip to the workpiece. At the molecular scale, positional uncertainty caused by thermal noise is a significant design constraint [208, 2324, 2325]. It is difficult to accurately assemble molecular parts if positional uncertainty is too large, just as it is hard for someone with Parkinson’s disease to repair a wristwatch. If positional accuracy is to be maintained, key system structures must be adequately stiff.
(2) Exemplify Self-Replication in a Molecular Manufacturing System. An equally important objective is to embody and illustrate the principle of self-replication in a specific physical design for a molecular assembler. More broadly, the design objective is to demonstrate the feasibility of a self-replicating manufacturing system. While the theoretical literature on self-replicating systems clearly reveals a wide range of non-biological designs, there is still a general perception that “replicating systems” means “living systems.” This perception is grossly in error and lies at the root of much current confusion and misunderstanding about the long-term issues involved in the development and deployment of molecular assemblers.
Last updated on 1 August 2005