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Notes on Nanofactories

 

This month's science essay is prompted by several questions about
nanofactories that I've received over the past few months. I'll discuss
the way in which nanofactories combine nanoscale components into large
integrated products; the reason why a nanofactory will probably take
about an hour to make its weight in product; and how to cool a
nanofactory effectively at such high production rates.

In current nanofactory designs, sub-micron components are made at
individual workstations and then combined into a product. This requires
some engineering above and beyond what would be needed to build a single
workstation. Tom Craver, on our [blog], suggested that there might be a
transitional step, in which workstations are arranged in a
two-dimensional sheet and make a thin sheet of product. The sheet of
manufacturing systems would not have to be flat; it could be V-folded,
and perhaps a solid product could be pushed out of a V-folded
arrangement of sheets. With a narrow folding angle, the product might be
extruded at several times the mechanosynthetic deposition rate.

http://crnano.typepad.com/crnblog/2005/11/what_does_extre.html#comment-11311211

Although the V-fold idea is clever, I think it's not necessary. Once you
can build mechanosynthetic systems that can build sheets of product,
you're most of the way to a 3D nanofactory. For a simple design, each
workstation produces a sub-micron “nanoblock” of product (each dimension
being the thickness of the product sheet) rather than a connected sheet
of product. Then you have the workstations pass the blocks "hand over
hand" to the edge of the workstation sheet. In a primitive nanofactory
design, much of the operational complexity would be included in the
incoming control information rather than the nanofactory's hardware.
This implies that each workstation would have a general-purpose robot
arm or other manipulator capable of passing blocks to the next workstation.

After the blocks get to the edge of the sheet, they are added to the
product. Instead of the product being built incrementally at the surface
of V-folded sheets, the sheets are stacked fully parallel, just like a
ream of paper, and the product is built at the edge of the ream.

Three things will limit the product ‘extrusion’ speed:

1) The block delivery speed. This would be about 1 meter per second, a
typical speed for mechanisms at all scales. This is not a significant
limitation.
2) The speed of fastening a block in place. Even a 100-nanometer block
has plenty of room for nanoscale mechanical fasteners that can basically
just snap together as fast as the blocks can be placed. Fasteners that
work by molecular reactions could also be fast.
3) The width (or depth, depending on your point of view) of the sheet:
how many workstations are supplying blocks to each workstation-width
edge-of-sheet. The width of the sheet stack is limited by the ability to
circulate cooling fluid, but it turns out that even micron-wide channels
can circulate fluid for several centimeters at moderate pressure. So you
can stack the sheets quite close together, making a centimeter-thick
slab. With 100-nanometer workstations, that will have several thousand
workstations supplying each 100-nanometer-square edge-of-stack area. If
a workstation takes an hour to make a 100-nanometer block, then you're
depositing several millimeters per hour. That's if you build the product
solid; if you provide a way to shuffle blocks around at the
product-deposition face, you can include voids in the product, and
'extrude' much faster; perhaps a mm per second.

Tom pointed out that a nanofactory that built products by block
deposition would require extra engineering in several areas, such as
block handling mechanisms, block fasteners, and software to control it
all. All this is true, but it is the type of problem we have already
learned to solve. In some ways, working with nanoblocks will be easier
than working with today's industrial robots; surface forces will be very
convenient, and gravity will be too weak to cause problems.

On the same blog post, Jamais Cascio [asked] why I keep saying that a
nanofactory will take about an hour to make its weight of product. The
answer is simple: If the underlying technology is much slower than that,
it won't be able to build a kilogram-scale nanofactory in any reasonable
time. And although advanced nanofactories might be somewhat faster, a
one-hour nanofactory would be revolutionary enough.

http://crnano.typepad.com/crnblog/2005/11/what_does_extre.html#comment-11299571

A one-kilogram one-hour nanofactory could, if supplied with enough
feedstock and energy, make thousands of tons of nanofactories or
products in a single day. It doesn't much matter if nanofactories are
faster than one hour (3600 seconds). Numbers a lot faster than that
start to sound implausible. Some bacteria can reproduce in 15 minutes
(900 seconds). Scaling laws suggest that a 100-nm scanning probe
microscope can build its mass in 100 seconds. (The non-manufacturing
overhead of a nanofactory--walls, computers, and so on--would probably
weigh less than the manufacturing systems, imposing a significant but
not extreme delay on duplicating the whole factory.) More advanced
molecule-processing systems could, in theory, process their mass even
more quickly, but with reduced flexibility.

On the slower side, the first nanofactory can't very well take much
longer than an hour to make its mass, because if it did, it would be
obsoleted before it could be built. It goes like this: A nanofactory can
only be built by a smaller nanofactory. The smallest nanofactory will
have to be built by very difficult lab work. So you'll be starting from
maybe a 100-nm manufacturing system (10^-15 grams) and doubling sixty
times to build a 10^3 gram nanofactory. Each doubling takes twice the
make-your-own-mass time. So a one-hour nanofactory would take 120 hours,
or five days. A one-day nanofactory would take 120 days, or four months.
If you could double the speed of your 24-hour process in two months
(which gives you sixty day-long "compile times" to build increasingly
better hardware using the hardware you have), then the half-day
nanofactory would be ready before the one-day nanofactory would.

Tom Craver pointed out that if the smaller nanofactory can be
incorporated into the larger nanofactory that it's building, then
doubling the nanofactory mass would take only half as long. So, a
one-day nanofactory might take only two months, and a one-hour
nanofactory less than three days. Tom also pointed out that if a one-day
tiny-nanofactory is developed at some point, and its size is slowly
increased, then when the technology for a one-hour nanofactory is
developed, a medium-sized one-hour nanofactory could be built directly
by the largest existing one-day nanofactory, saving part of the growing
time.

In my "primitive nanofactory" paper, which used a somewhat inefficient
physical architecture in which the fabricators were a fraction of the
total mass, I computed that a nanofactory on that plan could build its
own mass in a few hours. This was using the Merkle pressure-controlled
fabricator, [see "Casing an Assembler"], with a single order of
magnitude speedup to go from pressure to direct drive.

http://www.foresight.org/Conferences/MNT6/Papers/Merkle/

In summary, the one-hour estimate for nanofactory productivity is
probably within an order of magnitude of being right.

The question about cooling a nanofactory was asked at a talk I gave a
few weeks ago, and I don't remember who asked it. To build a kilogram
per hour of diamond requires rearranging on the order of 10^26 covalent
bonds in an hour. The bond energy of carbon is approximately 350 kJ/mol,
or 60 MJ/kg. Spread over an hour, that much energy would release 16
kilowatts, about as much as a plug-in electric heater.

Of course, you don't want a nanofactory to glow red-hot. And the
built-in computers that control the nanofactory will also generate quite
a bit of heat--perhaps even more than the covalent reactions themselves.
So, fluid cooling looks like a good idea. It turns out that, although
the inner features of a nanofactory will be very small--on the order of
one micron--cooling fluid can be sent for several centimeters down a
one-micron channel with only a modest pressure drop. This means that the
physical architecture of the nanofactory will not need to be adjusted to
accommodate variable-sized tree-structured cooling pipes.

In the years I have spent thinking about nanofactory design, I have not
encountered any problem that could not be addressed with standard
engineering. Of course, engineering in a new domain will present
substantial challenges and require a lot of work. However, it is not
safe to assume that some unexpected problem will arise to delay
nanofactory design and development. As work on enabling technologies
progresses, it is becoming increasingly apparent that nanofactories can
be addressed as an integration problem rather than a fundamental
research problem. Although their capabilities seem futuristic, their
technology may be available before most people expect it.


Chris has studied nanotechnology and molecular manufacturing for more than a decade. After successful careers in software engineering and dyslexia correction, Chris co-founded the Center for Responsible Nanotechnology in 2002, where he is Director of Research. Chris holds an MS in Computer Science from Stanford University.

Copyright © 2004-2005 Chris Phoenix

 


The Center for Responsible Nanotechnology(TM) (CRN) is an affiliate of World Care(R), an international, non-profit, 501(c)3 organization. All donations to CRN are handled through World Care. The opinions expressed by CRN do not necessarily reflect those of World Care

 

 

The contents of this page, including the views expressed above, are the responsibility of the author. They do not represent the views or policies of Nano Tsunami Dot Com, except where explicitly stated.

 

 

Chris Phoenix

CRN Director of Research

 

 
 


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