The goal of molecular manufacturing (MM) is to build complex products with almost every atom in its proper place. This requires creating large molecular shapes and then assembling them into products. The molecules must be built by some form of chemistry. Many MM proposals assume that building shapes of the required variety and complexity will require robotic placement (covalent bonding) of small chemical pieces. Once the molecular shapes are made, they must be combined to form structures and machines. Again, this is probably done most easily by robotic assembly. Theoretical studies have shown that it should be possible to build diamond lattice by mechanically guided chemistry, or mechanochemistry. By building the lattice in various directions, a wide variety of parts can be made—parts that would be familiar to a mechanical engineer, such as levers and housings. A robotic system used to build the molecular parts could also be used to assemble the parts into a machine. In fact, there is no reason why a robotic system can't build a copy of itself. In sharp contrast to conventional manufacturing, only a few (chemical) processes are needed to make any required shape. And with each atom in the right place, each manufactured part will be precisely the right size—so robotic assembly plans will be easy to program. A small nano-robotic device that can use supplied chemicals to manufacture nanoscale products under external control is called a fabricator.

More than forty years ago, Richard Feynman said, "The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom."  Molecular nanotechnology includes only one additional, and relatively easy, step: combining the small shapes and machines produced by individual chemical workstations into large products. The easiest way to do this is to combine small pieces into larger pieces, and then join those to make still larger ones. This process is called convergent assembly, and it can be used to make products large enough to be used directly by people. CRN has published a peer-reviewed paper, titled "Design of a Primitive Nanofactory", showing how large numbers of fabricators can be combined to create a personal nanofactory (PN) capable of making human-scale products. It appears that this might be accomplished in as little as a few months after the first fabricator is built. The resulting PN would be easy to program to make a wide variety of products, including duplicate PNs.

Although there are several possible ways to develop an MM capability, the best way appears to be the creation of fabricators and then nanofactories that can make diamond lattice (as explained above). Diamond is very strong, and can be used to build a wide variety of useful gadgets including motors and computers. This implies that the products of a nanofactory will also be strong, and that active functionality can be extremely compact. For example, an engine powerful enough to drive a car would fill less than a cubic centimeter, and a modern supercomputer would require less than a cubic millimeter. Diamond structure would be at least ten times as strong as steel for the same weight—probably closer to 100 times as strong. Because of the simple, and massively parallel, manufacturing used by a nanofactory, the complexity of a product would not affect either the manufacturing cost or the time to build it. A new design—any new design—could be built in just a few hours. A nanofactory, like an fabricator, will be able to duplicate itself. Nanofactories will be as cheap as any other product, so any desired number of nanofactories can be built. Since nanofactories can be used for final manufacturing as well as rapid prototyping, product design will not have to concern itself with "manufacturability."  As soon as a prototype is designed, it can be built. As soon as the prototype is approved, mass production can be started—and finished a few hours later.

The design of an MM version of a product will actually be easier than today's process. Instead of designing a shape and then worrying about how to whittle down a block of material or carve out a mold, the designer simply specifies the shape—and the nanofactory will create diamond structure to fill the specified volume. Instead of worrying about fastening parts together, the designer can simply tell the CAD software that they should be attached. The surfaces to be joined will be covered by the CAD software with a simple mechanical interlocking mechanism (described in CRN's Nanofactory paper), and the convergent assembly process only needs to press them together. Because power and computer functionality will be much smaller than today's devices, the designer will have much less difficulty in making the functional parts of the design fit into the space required. And because a vast range of products can be specified by a single CAD system and manufactured by a single nanofactory design, a well-trained MNT designer will be able to design a large number of products, just as a well-trained software engineer can write a wide variety of programs.

The strength and power of products, the compactness of their functional components, and the ease and speed of design and production, combine to make MM a very useful technology. Vast amounts of money can be saved in the product design process, in manufacturing, in distribution and warehousing. New product lines can be designed, manufactured, and marketed in a few weeks. The same efficiencies apply to military hardware as well. Each new weapons system could be developed and deployed much more quickly and cheaply. Prototypes and tests would be generated much faster and cost far less. Since a prototype design could be immediately manufactured in any desired quantity, deployment would also be much faster. New kinds of weapon systems could be contemplated. Both commercial and military/governmental organizations will have a strong incentive to fund the rapid development of MM, even at a cost of billions of dollars.

As described above, a fabricator is a small machine that can create precise shapes out of molecules, assemble those shapes into machines, and ultimately duplicate itself when supplied with the necessary broadcast instruction stream. The duplication is necessary because a single fabricator could not build more than a small number of tiny products. A fabricator is a worthwhile goal, because although it can't make large products, many fabricators can be combined to form a nanofactory. CRN has published a technical paper describing the process and techniques required to bootstrap from a sub-micron fabricator to a personal nanofactory; it appears that this can be done in a few months if suitable design and analysis is done beforehand. So we can assume that a fabricator project will include a nanofactory project, and that a useful nanofactory will appear within months of the first fabricator.

Designing a fabricator will not be easy. Mechanochemistry, the formation or breaking of chemical bonds under direct mechanical control, has been demonstrated, but it will take a lot more work to develop the mechanochemical techniques to build diamond and other strong materials. These techniques will require some basic research; however, preliminary work (by Eric Drexler, Robert Freitas, Ralph Merkle, and John Michelsen, for example) shows that there are several different kinds of mechanochemical reactions that should be able to build diamond. Unless all this work is wrong and no other techniques can be discovered, building atomically precise diamondoid shapes will be possible. The small-scale robotic device to do the required mechanochemical operations has to be designed, including the control system. This is mostly a matter of simple mechanics. The integration of the mechanochemical device with other devices to support the parts and product, deliver "feedstock" chemicals from an uncontrolled exterior to a well-controlled interior, and so on should also be relatively straightforward—at least compared with designing a spacecraft.

A modern spacecraft contains millions of parts (estimates for the Space Shuttle range from 2.5 to six million). A large spacecraft design must account for fluid dynamics, aerodynamics, vibration and resonance on many time scales, avionics and other control, chemical engineering, mechanical engineering, electrical engineering, combustion dynamics, hydraulics, cryogenics, and biomedical issues. (Thanks to an anonymous poster on Slashdot for pointing this out.)  By contrast, a fabricator design must account for chemistry, mechanical engineering including stiffness, control structures, and a different set of forces than we're used to at the macro-scale (e.g. van der Waals force). Note that many problems can be treated as mechanical engineering issues without greatly increasing the size and complexity of the fabricator. One example is thermal noise: as analyzed in Nanosystems, if the parts are stiff enough, it's not a problem even at room temperature.

If a fabricator project is not feasible today, it will surely be feasible in a few years. Most of the enabling technologies mentioned here, and many others as well, are being actively developed for their present-day commercial potential. As the technologies develop, they will reach a point where they can easily be re-used in a fabricator project. The mechanics of the project will become far easier in just a few years. The chemistry will become easier as more powerful computers are developed for simulation, but already it is feasible to test individual reactions in simulation. The question is not whether a fabricator project is feasible, but when it will become economically viable or a military necessity.

A new, large spacecraft or weapon system costs tens of billions of US$ to develop, and molecular nanotechnology will be far more useful than any single aerospace or weapons system. In today's dollars, total development cost for the original Space Shuttle was probably around $10-15 billion. At that rate, each part would have cost an average of $2,000-$6,000 to design. How many parts will a fabricator require?  Estimates of the atom count, based in part on comparisons with bacteria, frequently come in around 1 billion atoms. Diamond has 176 carbon atoms per cubic nanometer, so if each part were only one cubic nanometer, a fabricator might have 6 million parts—comparable to the Shuttle. With parts 10 nanometers on a side, it would have only 6,000 parts. For comparison, a typical four-cylinder automobile engine has about 450 parts and a bacterium may have 3,600 different molecules. As opposed to a "wet" design like a bacterium or a cutting-edge aerospace design, most of a fabricator's parts would not interact with each other and could be designed separately. It appears, then, that design of a fabricator falls somewhere between a car engine and the Space Shuttle in complexity. Construction, if not feasible today, will be feasible soon.

The Space Shuttle took less than ten years to design and build, from 1972 to 1981. The atomic bomb took only three years, from 1942 to 1945. Both of these programs involved more new science research and more development of new technologies and techniques than an assembler program would likely require. As analyzed above, they probably cost more too. The main question in estimating a timeline for fabricator development, then, is when it will be technically and politically feasible. There are probably five or more nations, and perhaps several large companies, that could finance a molecular fabricator effort starting in this decade. The technical feasibility depends on the enabling technologies. Even a single present-day technology, dip-pen nanolithography, may be able to fabricate an entire proto-fabricator with sufficient effort. At this point, we have not seen anything to make us believe that a five-year $10 billion fabricator project, starting today, would be infeasible, though we don't yet know enough to estimate its chance of success. Five years from now, we expect that a five-year project will be obviously feasible, and its cost may be well under $5 billion.

The National Science Foundation, and others, have estimated that even non-MM nanotechnology will be worth a trillion dollars or more by 2015. By the time people realize that it's possible to build a nano-based manufacturing system, it will probably be obvious that such a project would be quite profitable (in addition to the military imperatives). This implies that companies and/or governments will start crash programs, comparable perhaps to the Manhattan project. Of course there are other development scenarios, but we feel this is one of the more likely ones. We also cannot rule out the possibility that a large, well-funded, secret development program for molecular manufacturing has been in operation somewhere for several years and may achieve success sooner than any public program.

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