Sience Topic 2

Simple Nanofactories vs. Floods of Products

Chris Phoenix, Director of Research, Center for Responsible Nanotechnology

In last month's essay, I explained why even the earliest meter-scale nanofactories will necessarily have a high throughput, manufacturing their own mass in just a few hours. I also explained how a nanofactory can fasten together tiny functional blocks--nanoblocks--to make a meter-scale product. The next question is what range of products an early nanofactory would be able to build.

For several reasons, it is important to know the range and functionality of the products that the nanofactory will produce, and how quickly new products can be developed. Knowing these factors will help to estimate the economic value of the nanofactory, as well as its impacts and implications. The larger the projected value, the more likely it is to be built sooner; the more powerful an early nanofactory is and the faster new products appear, the more disruptive it can be.

Because a large nanofactory can be built only by another nanofactory, even the earliest nanofactories will be able to build other nanofactories. This means that the working parts of the nanofactory will be available as components for other product designs. From this reasoning, we can begin to map the lower bound of nanofactory product capabilities.

This essay is a demonstration of how CRN's thinking and research continue to evolve. In 2003, I published a peer-reviewed paper called "Design of a Primitive Nanofactory" in which I described the simplest nanofactory I could think of. That nanofactory had to do several basic functions, such as transporting components of various sizes, that implied the need for motors and mechanical components also in a variety of sizes, as well as several other functions. However, not long after that paper was published, an even simpler approach was proposed by John Burch and Eric Drexler. Their approach can build large products without ever having to handle large components; small blocks are attached rapidly, directly to the product.

The planar assembly approach to building products is more flexible than the convergent assembly approach, and can use a much more compact nanofactory. Instead of having to transport and join blocks of various sizes within the nanofactory, it only needs to transport tiny blocks from their point of fabrication to the area of the product under construction. (The Burch/Drexler nanofactory does somewhat more than this, but their version could be simplified.) This means that the existence of a nanofactory does not, as I formerly thought, imply the existence of centimeter-scale machinery. A planar nanofactory can probably be scaled to many square centimeters without containing any moving parts larger than a micron.

Large moving parts need to slide and rotate, but small moving parts can be built to flex instead. It is theoretically possible that the simplest nanofactory may not need much in the way of bearings. Large bearings could be simulated by suspending the moving surface with numerous small load-bearing rollers or "walkers" that could provide both low-friction motion and power. This might actually be better than a full-contact surface in some ways; failure of one load-bearing element would not compromise the bearing's operation.

Another important question is what kind of computers the nanofactory will be able to build. Unlike my "primitive nanofactory," a simple planar-assembly nanofactory may not actually need embedded general-purpose computers (CPU's). It might have few enough different components that the instructions for building all the components could be fed in several times over during construction, so that information storage and processing within the nanofactory might be minimal. But even a planar-assembly nanofactory, as currently conceived, would probably have to incorporate large amounts of digital logic (computer-like circuitry) to process the blueprint file and direct the operations of the nanofactory fabricators. This implies that the nanofactory's products could contain large numbers of computers. However, the designs for the computers will not necessarily exist before they are needed for the products.

Any nanofactory will have to perform mechanical motions, and will need a power source for those motions. However, that power source may not be suitable for all products. For example, an early nanofactory might use chemicals for power. It seems more likely to me that it would use electricity, because electric motors are simpler than most chemical processing systems, since chemical systems need to deliver chemicals and remove waste products, while electrical systems only need wires. In that case, products could be electrically powered; it should not be difficult to gang together many nanoscale motors to produce power even for large products.

The ability to fasten nanoscale blocks to selected locations on a growing product implies the ability to build programmable structures at a variety of scales. At the current level of analysis, the existence of a large nanofactory implies the ability to build other large structures. Because the nanofactory would not have to be extremely strong, the products might also not be extremely strong. Further analysis must wait for more information about the design of the nanofactory.

Sensing is an important part of the functionality of many products. An early nanofactory might not need many different kinds of sensing, because its operations would all be planned and commands delivered from outside. One of the benefits of mechanosynthesis of highly cross-linked covalent solids is that any correctly built structure will have a very precise and predictable shape, as well as other properties. Sensing would be needed only for the detection of errors in error-prone operations. It might be as simple as contact switches that cause operations to be retried if something is not in the right place. Other types of sensors might have to be invented for the products they will be used in.

Nanofactories will not need any special appearance, but many products will need to have useful user interfaces or attractive appearances. This would require additional R&D beyond what is necessary for the nanofactory.

The planar assembly approach is a major simplification relative to all previous nanofactory approaches. It may even be possible to build wet-chemistry nanofactory-like systems, as described in my NIAC report that was completed in spring 2005, and bootstrap incrementally from them to high-performance nanofactories. Because of this, it seems less certain that the first large nanofactory will be followed