Published in The Journal of the British Interplanetary Society, volume 51, pp. 145-152, 1998.
This document describes potential aerospace applications of molecular nanotechnology, defined as the thorough three-dimensional structural control of materials, processes and devices at the atomic scale. The inspiration for molecular nanotechnology comes from Richard P. Feynman's 1959 visionary talk at Caltech in which he said, "The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed---a development which I think cannot be avoided." Indeed, scanning probe microscopes (SPMs) have already given us this ability in limited domains. See the IBM Almaden STM Gallery for some beautiful examples. Synthetic chemistry, biotechnology, "laser tweezers" and other developments are also bringing atomic precision to our endeavors.
[Drexler 92a], an expanded version of Drexler's MIT Ph.D. thesis, examines one vision of molecular nanotechnology in considerable technical detail. [Drexler 92a] proposes the development of programmable molecular assembler/replicators. These are atomically precise machines that can make and break chemical bonds using mechanosynthesis to produce a wide variety of products under software control, including copies of themselves. Interestingly, living cells exhibit many properties of assembler/replicators. Cells make a wide variety of products, including copies of themselves, and can be programmed with DNA. Replication is one approach to building large systems, such as human rated launch vehicles, from molecular machines manipulating matter one or a few atoms at a time. Note that biological replication is responsible for systems as large as redwood trees and whales.
Another approach to nanotechnology is supramolecular self-assembly, where molecular systems are designed to attract each other in a particular orientation to form larger systems. Hollow spheres large enough to be visible in a standard light microscope have been created this way using self-assembling lipids. There are many other examples and this field is rapidly advancing. Biological systems can do most of what molecular nanotechnology strives to accomplish -- atomically precise products, active materials, reproduction, etc. However, biological systems are extremely complex and molecular nanotechnology seeks simpler systems to understand, control and manufacture. Also, biological systems usually work at fairly mild temperature and pressure conditions in solution -- conditions that are not found in most aerospace environments.
Today, extremely precise atomic and molecular manipulation is common in many laboratories around the world and our abilities are rapidly approaching Feynman's dream. The implications for aerospace development are profound and ubiquitous. A number of applications are mentioned here and a few are described in some detail with references. From this sample of applications it should be clear that although molecular nanotechnology is a long term, high risk project, the payoff is potentially enormous -- vastly superior computers, aerospace transportation, sensors and other technologies; technologies that may enable large scale space exploration and colonization.
This document is organized into two sections. In the first, we examine three technologies -- computers, aerospace transportation, and active materials -- useful to nearly all NASA missions. In the second, we investigate some potential molecular nanotechnology payoffs for each area identified in NASA's strategic plan. Some of these applications are under investigation by nanotechnology researchers at NASA Ames. Some of the applications described below have relatively near-term potential and working prototypes may be realized within three to five years. This is certainly not true in other cases. Indeed, many of the possible applications of nanotechnology that we describe here are, at the present time, rather speculative and futuristic. However, each of these ideas have been examined at least cursorily by competent scientists, and as far as we know all of them are within the bounds of known physical laws. We are not suggesting that their achievement will be easy, cheap or near-term. Some may take decades to realize; some other ideas may be scrapped in the coming years as insuperable barriers are identified. But we feel that they are worth mentioning here as illustrations of the potential future impact of nanotechnology.
One particularly intriguing possibility along this line is to utilize a carbon nanotube SPM tip to engrave patterns on a silicon surface. It should be possible to create features a few nanometers across. These would be perhaps 100 times finer than the current state of the art in commercial semiconductor photolithography. Further, in contrast to approaches such as electron microscope lithography for which the speed of operation now appears to be an insuperable obstacle for industrial production, nanotube SPM-based lithography can be accelerated by utilizing an array with thousands of SPM tips simultaneously engraving different parts of a silicon surface. Also, nanotube SPM lithography could provide a practical means to explore various futuristic electronic device technology ideas, such as quantum cellular automata, which require exceedingly small feature sizes. Needless to say, if these ideas pan out, they could literally revolutionize computer device technology, paving the way for systems that are many times more powerful and more compact than any available today.
For the near term, it should be noted that the semiconductor industry is a major market for SPM products. These are used to examine production equipment. High performance carbon nanotube tips should be of substantial value. NASA Ames is collaborating with Dr. Dai, now at Stanford, to develop these tips.
[Bauschlicher 97a] computationally studied storing data in a pattern of fluorine and hydrogen atoms on the (111) diamond surface (see figure). If write-once data could be stored this way, 1015 bytes/cm2 is theoretically possible. By comparison, the new DVD write-once disks now coming on the market hold about 108 bytes/cm2. [Bauschlicher 97a] compared the interaction of different probe molecules with a one dimensional model of the diamond surface. This study found some molecules whose interaction energies with H and F are sufficiently different that the force differential should be detectable by an SPM. These studies were extended to include a two dimensional model of the diamond surface and two other systems besides F/H [Bauschlicher 97b]. Other surfaces, such as Si, and other probes, such as those including transition metal atoms, have also been investigated [Bauschlicher 97c].
Among the better probes was C5H5N (pyridine). Quantum calculations suggest that pyridine is stable when attached to C60 in the orientation necessary for sensing the difference between hydrogen and fluorine. Half of C60 can form the end cap of a (9,0) or (5,5) carbon nanotube, and carbon nanotubes have been attached to an SPM tip [Dai 96]. Thus, it might be possible using today's technology to build a system to read the diamond memory surface.
[Avouris 96] has shown that individual hydrogen atoms can be removed from a silicon surface. If this could be accomplished in a gas that donates fluorine to vacancies on a diamond surface, the data storage system could be built. [Thummel 97] computationally investigated methods for adding a fluorine at the radical sites where a hydrogen atom had been removed from a diamond surface.
Helical logic is a theoretical proposal for a future computing technology using the presence or absence of individual electrons (or holes) to encode 1s and 0s. The electrons are constrained to move along helical paths, driven by a rotating electric field in which the entire circuit is immersed. The electric field remains roughly orthogonal to the major axis of the helix and confines each charge carrier to a fraction of a turn of a single helical loop, moving it like water in an Archimedean screw. Each loop could in principle hold an independent carrier, permitting high information density. One computationally universal logic operation involves two helices, one of which splits into two "descendant" helices. At the point of divergence, differences in the electrostatic potential resulting from the presence or absence of a carrier in the adjacent helix controls the direction taken by a carrier in the splitting helix. The reverse of this sequence can be used to merge two initially distinct helical paths into a single outgoing helical path without forcing a dissipative transition. Because these operations are both logically and thermodynamically reversible, energy dissipation can be reduced to extremely low levels. ... It is important to note that this proposal permits a single electron to switch another single electron, and does not require that many electrons be used to switch one electron. The energy dissipated per logic operation can likely be reduced to less than 10-27 joules at a temperature of 1 Kelvin and a speed of 10 gigahertz, though further analysis is required to confirm this. Irreversible operations, when required, can be easily implemented and should have a dissipation approaching the fundamental limit of ln 2 x kT.
Note that with very fast computation energy use and heat dissipation
become a severe problem. One approach to addressing this issue is reversible
[Drexler 92b] used a more speculative methodology to estimate that a
four passenger SSTO weighing three tons including fuel could be built
using a mature nanotechnology. Using McKendree's cost model, such a
vehicle would cost about $60,000 to purchase -- the cost of today's
high-end luxury automobiles.
These studies assumed a fairly advanced nanotechnology capable of
building diamondoid materials. In the nearer term, it may be possible
to develop excellent structural materials using carbon nanotubes.
Carbon nanotubes have a Young's modulus of approximately
one terapascal -- comparable to diamond.
Studies of carbon nanotube strength include
[Treacy 96], [Yacobson 96], and [Srivastava 97a].
[Drexler 92a] proposed a nanotechnology based on diamond and
investigated its potential properties. In particular, he examined
applications for materials with a strength similar to that of diamond
(69 times strength/mass of titanium). This would require a very mature
nanotechnology constructing systems by placing atoms on diamond
surfaces one or a few at a time in parallel. Assuming diamondoid
materials, [McKendree 95] predicted the performance of several existing
single-stage-to-orbit (SSTO) vehicle designs. The predicted payload to
dry mass ratio for these vehicles using titanium as a structural
material varied from < 0 (the vehicle won't work) to 36%, i.e., the
vehicle weighs substantially more than the payload. With hypothetical
diamondoid materials the ratios varied from 243% to 653%, i.e., the
payload weighs far more than the vehicle. Using a very simple cost
model ($1000 per vehicle kilogram) sometimes used in the aerospace
industry, he estimated the cost per kilogram launched to
low-Earth-orbit for diamondoid structured vehicles should be $153-412.
This would meet NASA's 2020 launch to orbit cost goals. Estimated
costs for titanium structured vehicles varied from $16,000-59,000/kg.
Although this cost model is probably adequate for comparison, the
absolute costs are suspect.
[Issacs 66] and [Pearson 75] proposed a space elevator -- a cable
extending from the Earth's surface into space with a center of mass at
geosynchronous altitude. If such a system could be built, it should be
mechanically stable and vehicles could ascend and descend along the
cable at almost any reasonable speed using electric power (actually
generating power on the way down). The first incredibly difficult
problem with building a space elevator is strength of materials.
Maximum stress is at geosynchronous altitude so the cable must be
thickest there and taper exponentially as it approaches Earth. Any
potential material may be characterized by the taper factor -- the
ratio between the cable's radius at geosynchronous altitude and at the
Earth's surface. For steel the taper factor is tens of thousands --
clearly impossible. For diamond, the taper factor is 21.9 [McKendree
95] including a safety factor. Diamond is, however, brittle. Carbon
nanotubes have a strength in tension similar to diamond, but bundles of
these nanometer-scale radius tubes shouldn't propagate cracks nearly as
well as the diamond tetrahedral lattice. Thus, if the considerable
problems of developing a molecular nanotechnology capable of making
nearly perfect carbon nanotube systems approximately 70,000 kilometers
long can be overcome, the first serious problem of a transportation
system capable of truly large scale transfers of mass to orbit can be
solved. The next immense problem with space elevators is safety -- how
to avoid dropping thousands of kilometers of cable on Earth if the
cable breaks. Active materials may help by
monitoring and repairing small flaws in the cable and/or detecting a
major failure and disassembling the cable into small elements.
[Drexler 92b] used a more speculative methodology to estimate that a four passenger SSTO weighing three tons including fuel could be built using a mature nanotechnology. Using McKendree's cost model, such a vehicle would cost about $60,000 to purchase -- the cost of today's high-end luxury automobiles.
These studies assumed a fairly advanced nanotechnology capable of building diamondoid materials. In the nearer term, it may be possible to develop excellent structural materials using carbon nanotubes. Carbon nanotubes have a Young's modulus of approximately one terapascal -- comparable to diamond. Studies of carbon nanotube strength include [Treacy 96], [Yacobson 96], and [Srivastava 97a].
To make active materials, a material might be filled with nano-scale
sensors, computers, and actuators so the material can probe its
environment, compute a response, and act. Although this document is
concerned with relatively simple artificial systems, living tissue may
be thought of as an active material. Living tissue is filled with
protein machines which gives living tissue properties (adaptability,
growth, self-repair, etc.) unimaginable in conventional materials.
Active materials can theoretically be made entirely of machines.
These are sometimes called swarms since they consist of large numbers
of identical simple machines that grasp and release each other and
exchange power and information to achieve complex goals. Swarms change
shape and exert force on their environment under software control.
Although some physical prototypes have been built, at least one patent
issued, and many simulations run, swarm potential capabilities are not
well analyzed or understood. We briefly discuss some concepts here.
For a summary of swarm concepts see [Toth-Fejel 96].
[Michael 94] proposes brick-shaped machines of various sizes
that slide past each other to assume a variety of shapes.
He has generated a large number of videos showing computer
simulations of simple motions. Although his web site
contains rather extravagant claims, this work has received a
U. K. patent.
[Yim 95] built a small swarm with macroscopic (size in inches)
called polypod, built a simulator of polypod, and
programmed it to move in various ways to study locomotion.
There are two brick shaped components in polypod,
one of which has two prismatic joints
linked by a revolute joint.
The second component is a cubic
connector with no mechanical motion.
Polypod is programmed by
tables for each member of the swarm. Each member is
programmed to move at various speeds in each
degree of freedom for certain amounts of time. The
swarm components are implicitly synchronized so there is
no clock signal.
[Hall 96] proposes a swarm with 10 micron dodecahedral components each
with 12 arms that can move in and out, rotate a little, and grab
and release each other. This concept is called the
"utility fog." [Hall 96] estimates that the utility fog
would have a density of 0.2, tensile
strength of 1000 psi in action and 100,000 psi in a passive mode, and
have a maximum shear rate of 100 km/second/meter.
[Bishop 95] proposes a swarm consisting of
100 nanometer brick-shaped components that slide past each
other to change shape.
[Globus 97] proposes a swarm with two kinds of components -- edges and
nodes. The terms "node" and "edge" are chosen to correspond to
those in graph theory.
The roughly spherical nodes are capable of attaching to five
edges (for a tetrahedral geometry with one free edge per node) and
rotating each edge in pitch and yaw. The rod-like edges are capable of
changing length, rotating around their long axis, and
attaching/detaching to/from nodes.
Component design, power distribution and control software are
significant challenges for swarm development. Consider that with 10
micron components a cubic meter of swarm would contain about
1015 devices, each with an internal computer communicating
with its neighbors to accomplish a global task.
This scenario requires a very advanced swarm that can operate
in an atmosphere and on orbit in a vacuum. Besides the many and
obvious difficulties of developing a swarm for a single environment,
this provides additional challenges. Note that a simpler swarm might
be used for aircraft payload handling.
NASA's mission is divided into five enterprises:
Mission to Planet Earth, Aeronautics,
Human Exploration and Development of Space,
Space Science, and Space Technology. We will
examine some potential nanotechnology applications in each area.
Mission to Planet Earth
EOS Data System
The Earth Observing System (EOS) will use satellites and other
systems to gather data on the Earth's environment.
The EOS data system will need to process and archive >terabyte
per day for the indefinite future. Simply storing this quantity of data
is a significant challenge -- each day's data would fill
about 1,000 DVD disks. With projected write-once nanomemory densities
of 1015 bytes/cm2
[Bauschlicher 97a] a year's worth of EOS data can be stored on a small
piece of diamond. With projected nanocomputer processing speeds of
1018 MIPS [Drexler 92a], a million
calculations on each byte of one day's data would take one second on
Given a mature nanotechnology, it should be possible to build sensors
in balloon-borne systems approximately the size of bacteria. With
replication based manufacturing, these should be quite inexpensive. If
the serious communication and control problems can be solved, one can
imagine spreading billions of tiny lighter-than-air
vehicles into the atmosphere to measure wind currents and atmospheric
composition. A similar approach might be taken in the oceans -- note
that the oceans are full of floating microscopic living organisms that
can sense and react to their environment. Smart dust might sense the
environment, note the location via a GPS-like system, and store that
information until close enough to a data-collection point to transfer
the data to the outside world.
Aeronautics and Space Transportation Technology
The strength of materials and computational capabilities previously
discussed for space transportation
should also allow much more advanced aircraft. Stronger,
lighter materials can obviously make aircraft with greater
lift and range. More powerful computers are invaluable in
the design stage and of great utility in advanced avionics.
Active surfaces for aeronautic control
MEMS technology has been used to replace traditional large control
structures on aircraft with large numbers of small MEMS controlled
control system was used to operate a model airplane in a windtunnel.
Nanotechnology should allow even finer control -- finer control than
exhibited by birds, some of which can hover in a light breeze with very
little wing motion. Nanotechnology should also enable extremely small
A reasonably advanced nanotechnology should be able to make
simple atomically precise materials under software control.
If the control is at the atomic level, then the full range
of shapes possible with a given material should be achievable.
Aircraft construction requires complex shapes to accommodate
aerodynamic requirements. With molecular nanotechnology, strong
complex-shaped components might be manufactured by general
purpose machines under software control.
The aeronautics mission is responsible for launch vehicle development.
Payload handling is an important function. Very efficient payload
handling might be accomplished by a very advanced
swarm. The sequence begins by placing each
payload on a single large swarm located next to the shuttle orbiter. The
swarm forms itself around the payloads and then moves them
into the payload bay, arranging the payloads to optimize the
center of gravity and other considerations. The swarm holds
the payload in place during launch and may even damp out some
launch vibrations. On orbit, satellites can be launched
from the payload bay by having the swarm give them a gentle push.
The swarm can then be left in orbit, perhaps at a space
station, and used for orbital operations.
Aerospace vehicles often require complex checkout procedures to
insure safety and reliability. This is particularly true of
reusable launch vehicles. A very advanced swarm with some
special purpose appendages might be placed on a vehicle.
It might then spread out over the vehicle and into all
crevices to examine the state of the vehicle in great detail.
Human Exploration and Development of Space
has the greatest potential to revolutionize human access
to space by dropping the current $10,000 per pound cost
of launch, but this was discussed above. Other less dramatic
Active materials can theoretically be made entirely of machines. These are sometimes called swarms since they consist of large numbers of identical simple machines that grasp and release each other and exchange power and information to achieve complex goals. Swarms change shape and exert force on their environment under software control. Although some physical prototypes have been built, at least one patent issued, and many simulations run, swarm potential capabilities are not well analyzed or understood. We briefly discuss some concepts here. For a summary of swarm concepts see [Toth-Fejel 96].
[Michael 94] proposes brick-shaped machines of various sizes that slide past each other to assume a variety of shapes. He has generated a large number of videos showing computer simulations of simple motions. Although his web site contains rather extravagant claims, this work has received a U. K. patent.
[Yim 95] built a small swarm with macroscopic (size in inches) components called polypod, built a simulator of polypod, and programmed it to move in various ways to study locomotion. There are two brick shaped components in polypod, one of which has two prismatic joints linked by a revolute joint. The second component is a cubic connector with no mechanical motion. Polypod is programmed by tables for each member of the swarm. Each member is programmed to move at various speeds in each degree of freedom for certain amounts of time. The swarm components are implicitly synchronized so there is no clock signal.
[Hall 96] proposes a swarm with 10 micron dodecahedral components each with 12 arms that can move in and out, rotate a little, and grab and release each other. This concept is called the "utility fog." [Hall 96] estimates that the utility fog would have a density of 0.2, tensile strength of 1000 psi in action and 100,000 psi in a passive mode, and have a maximum shear rate of 100 km/second/meter.
[Bishop 95] proposes a swarm consisting of 100 nanometer brick-shaped components that slide past each other to change shape.
[Globus 97] proposes a swarm with two kinds of components -- edges and nodes. The terms "node" and "edge" are chosen to correspond to those in graph theory. The roughly spherical nodes are capable of attaching to five edges (for a tetrahedral geometry with one free edge per node) and rotating each edge in pitch and yaw. The rod-like edges are capable of changing length, rotating around their long axis, and attaching/detaching to/from nodes. See figure.
Component design, power distribution and control software are
significant challenges for swarm development. Consider that with 10
micron components a cubic meter of swarm would contain about
1015 devices, each with an internal computer communicating
with its neighbors to accomplish a global task.
This scenario requires a very advanced swarm that can operate in an atmosphere and on orbit in a vacuum. Besides the many and obvious difficulties of developing a swarm for a single environment, this provides additional challenges. Note that a simpler swarm might be used for aircraft payload handling.
With a sufficiently advanced nanotechnology it might even be possible to directly generate food by non-biological means. Then agriculture waste in a self-sufficient space colony could be converted directly to useful nutrition. Making this food attractive will be a major challenge.
For colonization applications one would ideally provide the same radiation protection available on Earth. Each square meter on Earth is protected by about 10 tons of atmosphere. Therefore, structures orbiting below the van Allen belts would like 10 tons/meter2 surface area shielding mass. This would dominate the mass requirements of any system and require one small asteroid for each 11 meter2 of colony exterior surface area. A 10,000 person cylindrical space colony such as Lewis One [Globus 91] with a diameter of almost 500 meters and a length of nearly 2000 meters would require a minimum of about 90,000 retrieval missions to provide the shielding mass. The large number of missions required suggests that a fully automated, replicating nanotechnology may be essential to build large low Earth orbit colonies from small asteroids.
A nanotechnology swarm along with an atomically precise lightsail is a promising small asteroid retrieval system. Lightsail propulsion insures that no mass will be lost as reaction mass. The swarm can control the lightsail by shifting mass. When a target asteroid is found, the swarm spreads out over the surface to form a bag. The interface to the sail must be active to account for the rotation of the asteroid -- which is unlikely to have an axis-of-rotation in the proper direction to apply thrust for the return to Earth orbit. The active interface is simply swarm elements that transfer between each other to allow the sail to stay in the proper orientation. Of course, there are many other possibilities for nanotechnology based retrieval vehicles.
For energy collection, molecular manufacturing can be used to make solar photovoltaic cells at least as efficient as those made in the laboratory today. Efficiencies can therefore be > 30%. In space applications, a reflective optical concentrator need consist of little more than a curved aluminum shell < 100 nanometers thick (photovoltaic cells operate with higher efficiency at high optical power densities). A metal fin with a thickness of 100 nanometers and a conduction path length of 100 microns can radiate thermal energy at a power density as high as 1000 W/m2 with a temperature differential from base to tip of < 1 K.By comparison, the U.S. built Photovoltaic Panel Module solar cells currently used on the Mir Space Station and planned for use on the International Space Station generate about 118 W/kg.
Accordingly, solar collectors can consist of arrays of photovoltaic cells several microns in thickness and diameter, each at the focus of a mirror of ~100 micron diameter, the back surface of which serves as a ~100 micron diameter radiator. If the mean thickness of this system is ~1 micron, the mass is ~10-3 kg/m2 and the power per unit mass, at Earth's distance from the Sun, where the solar constant is ~1.4 kW/m2, is > 105 W/kg."
Calculations with oxygen [Merkle 94] suggest that a diamondoid sphere ~0.1 microns in diameter should easily hold oxygen at ~1,000 atmospheres. While higher pressures are feasible, they offer declining returns. At higher pressures, the pressure-volume relationship becomes severely non-linear and the density approaches a limiting value. Other gases might also be stored if diamondoid spheres can be built, but the analysis has not been done.
Similar results have been achieved experimentally with
C60 [Joachim 97]. The electrical properties of a
C60 molecule were changed by applying pressure to the
molecule with an SPM tip.
Smaller, lighter spacecraft are cheaper to launch (current costs
are about $10,000/lb) and generally cheaper to build. Diamondoid
structural materials can radically reduce structural mass,
miniaturized electronics can shrink the avionics and reduce
power consumption, and atomically precise materials and components
should shrink most other subsystems.
Thermal protection is crucial for atmospheric reentry and other tasks.
The carbon nanotubes under investigation at NASA Ames and elsewhere may
play a significant role. Most production processes for carbon
nanotubes create a tangled mat of
nanotubes that has a very low mass-to-volume ratio. Like graphite,
the tubes should withstand high temperatures but the tangled mat should
prevent them from ablating. This may lead to high temperature
How to gain such control is a major, unresolved issue. However, it is clear that computation will play a major role regardless of which approach -- positional control with replication, self-assembly, or some other means -- is ultimately successful. Computation has already played a major role in many advances in chemistry, SPM manipulation, and biochemistry. As we design and fabricate more complex atomically precise structures, modeling and computer aided design will inevitably play a critical role. Not only is computation critical to all paths to nanotechnology, but for the most part the same or similar computational chemistry software and expertise supports all roads to molecular nanotechnology. Thus, even if NASA's computational molecular nanotechnology efforts should pursue an unproductive path, the expertise and capabilities can be quickly refocused on more promising avenues as they become apparent.
As nanotechnology progresses we may expect applications to become feasible at a slowly increasing rate. However, if and when a general purpose programmable assembler/replicator can be built and operated, we may expect an explosion of applications. From this point, building new devices will become a matter of developing the software to instruct the assembler/replicators. Development of a practical swarm is another potential turning point. Once an operational swarm that can grow and divide has been built, a large number of applications become software projects. It is also important to note that the software for swarms and assembler/replicators can be developed using simulators -- even before operational devices are available.
Nanotechnology advocates and detractors are often preoccupied with the question "When?" There are three interrelated answers to this question (see also [Merkle 97] and [Drexler 91]):
[Avouris 96] Ph. Avouris, R. E. Walkup, A. R. Rossi, H. C. Akpati, P. Nordlander, P.-C. Shen, G. G. Ablen and J. W. Wyding, "Breaking Individual Chemical Bonds via STM-Induced Exitations," Surface Science, 1 August 1996, V363 N1-3:368-377.
[Babadzhanov 1993] Pulat B. Babadzhanov, "Density of meteoroids and their mass influx on the Earth,"Asteroids, Comets, Meteors 1993, Proceedings of the 160th symposium of the International Astronomical Union, Belgirate, Italy, 14-18 June 1993, A. Milani, M. Di Martino and A. Cellino, editors, pages 45-54.
[Bauschlicher 97a] Charles W.Bauschlicher Jr., Alessandra Ricca and Ralph Merkle, "Chemical storage of data," Nanotechnology, volume 8, number 1, March 1997 pages 1-5.
[Bauschlicher 97b] Charles. W. Bauschlicher and M. Rosi, "Differentiating between hydrogen and fluorine on a diamond surface", submitted to Theor. Chem. Acta.
[Bauschlicher 97c] Charles. W. Bauschlicher and M. Rosi, unpublished.
[Bishop 95] Forrest Bishop, "The Construction and Utilization of Space Filling Polyhedra for Active Mesostructures," WWW page.
[Bumm 96] L. A. Bumm, J. J. Arnold, M. T. Cygan, T. D. Dunbar, T. P. Burgin, L. Jones II, D. L. Allara, James M. Tour, P. S. Weiss, "Are Single Molecular Wires Conducting?" Science, volume 271, 22 March 1996, pages 1705-1707.
[Chico 96] L. Chico, Vincent H. Crespi, Lorin X. Benedict, Steven G. Louie and Marvin L. Cohen, "Pure Carbon Nanoscale Devices: Nanotube Heterojunctions," Physical Review Letters, volume 76, number 6, 5 February 1996, pp. 971-974.
[Chyba 93] Christopher F. Chyba, Paul J. Thomas, and Kevin J. Zahnle, "The 1908 Tunguka explosion: atmospheric disruption of a stony asteroid," Nature volume 361, 7 January 1993, pages 40-44.
[Dai 96] H. Dai, J. H. Hafner, A. G. Rinzler, D. T. Colbert and R. E. Smalley, "Nanotubes as Nanoprobes in Scanning Probe Microscopy," Nature 384, pages 147-151, (1996).
[Dillon 97] A. C. Dillon, K. M. Jones, T. A. Bekkedahl, C. H. Kiang, D. S. Bethune, M. J. Heben, "Storage of hydrogen in single-walled carbon nanotubes," Nature, 27 March 1997, volume 386, N6623:377-379.
[Dresselhaus 95] M. S. Dresselhaus, G. Dresselhaus and P. C. Eklund, Science of Fullerenes and Carbon Nanotubes, Academic Press (1995).
[Drexler 91] K. Eric Drexler, Chris Peterson, and Gayle Pergami, Unbounding the Future, William Morrow and Company, Inc., (1991).
[Drexler 92a] K. Eric Drexler, Nanosystems: Molecular Machinery, Manufacturing, and Computation, John Wiley & Sons, Inc. (1992).
[Drexler 92b] K. Eric Drexler, Journal of the British Interplanetary Society, volume 45, number 10, pages 401-405 (1992).
[Freitas 98] Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities , Landes Bioscience, Georgetown TX, 1998.
[Globus 91] Al Globus, "The Design and Visualization of a Space Biosphere," 10th Biennial Space Studies Institute/Princeton University Conference on Space Manufacturing, Princeton University, May 15-18, 1991.
[Globus 97], Al Globus, Charles Bauschlicher, Jie Han, Richard Jaffe, Creon Levit, Deepak Srivastava, "Machine Phase Fullerene Nanotechnology," Nanotechnology, 9, pp. 1-8 (1998).
[Goldhaber-Gordon 97] D. J. Goldhaber-Gordon, M. S. Montemerlo, J. C. Love, G. J. Opiteck, and J. C. Ellenbogen, Proceedings of the IEEE, April 1997, V85 N4:521-540.
[Hall 96] J. Storrs Hall, "Utility Fog: The Stuff that Dreams are Made Of," Nanotechnology: Molecular Speculations on Global Abundance, B. C. Crandall, editor, MIT Press, Cambridge, Massachusetts, 1996; also in "Utility Fog," Extropy, 3rd (Part 1) and 4th quarter (Part 2), 1994. See WWW page Utility Fog: The Stuff that Dreams are Made Of.
[Han 97a] Jie Han, Al Globus, Richard Jaffe and Glenn Deardorff, "Molecular Dynamics Simulation of Carbon Nanotube Based Gears," Nanotechnology, volume 8, number 3, 3 September 1997, pages 95-102.
[Han 97b] Jie Han, M. P. Anantram, and Richard Jaffe, "Design and Study of Carbon Nanotube Electronic Devices," The Fifth Foresight Conference on Molecular Nanotechnology, 5-8 November, 1997, Palo Alto, CA.
[Han 97c] Jie Han, Al Globus, and Richard Jaffe, "The Molecular Dynamics of Carbon Nanotube Gears in He and Ne Atomspheres," The Fifth Foresight Conference on Molecular Nanotechnology, 5-8 November, 1997; Palo Alto, CA.
[Hills 93] Jack G. Hills and M. Patrick Goda, "The fragmentation of small asteroids in the atmosphere," The Astronomical Journal, March 1993, volume 105, number 3, pages 1114-1144.
[Iijima 91] Sumio Iijima, "Helical microtubules of graphitic carbon," Nature, 7 November 1991, volume 354, N6348:56-58.
[Issacs 66] John D. Issacs, Allyn C. Vine, Hugh Bradner and George E. Bachus, "Satellite Elongation into a True 'Sky-Hook'," Science, volume 151, 11 February 1966, pages 682-683.
[Joachim 97] C. Joachim and J. Gimzewski, "An Electromechanical Amplifier Using a Single Molecule," Chemical Physics Letters, volume 265, pages 353-357, 1997.
[McKendree 95] Tom McKendree, "Implications of Molecular Nanotechnology: Technical Performance Parameters on Previously Defined Space System Architectures," The Fourth Foresight Conference on Molecular Nanotechnology, Palo Alto, CA. (November 1995).
[Menon 97a] M. Menon, D. Srivastava and S. Saini, "Carbon Nanotube Junctions as Building Blocks for Nanoscale Electronic Devices," Semiconductor Device Modeling Workshop at NASA Ames Research Center, August (1997).
[Menon 97b] M. Menon and D. Srivastava, "Carbon Nanotube T-junctions: Nanoscale Metal-Semiconductor-Metal Contact Devices," submitted to Phys. Rev. Lett., (1997).
[Merkle 94] Ralph C. Merkle, "Nanotechnology and Medicine," Advances in Anti-Aging Medicine, Vol. I, edited by Dr. Ronald M. Klatz, Liebert Press, 1996, pages 277-286.
[Merkle 96] Ralph C. Merkle and K. Eric Drexler, "Helical Logic," Nanotechnology (1996) volume 7 pages 325-339.
[Merkle 97] Ralph C. Merkle, "How long will it take to develop nanotechnology?" WWW page.
[Michael 94] Joseph Michael, UK Patent #94004227.2.
[Moore 75] Gordon Moore, "Progress in digital integrated circuits," 1975 International Electron Devices Meeting, page 11. See the figure: approximate component count for complex integrated circuits vs. year of introduction and the following figures from Miniaturization of electronics and its limits, by R. W. Keyes, IBM Journal of Research and Development, Volume 32, Number 1, January 1988.
[Pearson 75] Jerome Pearson, Acta Astronautica 2 pages 785-799 (1995).
[Rabinowitz 97] David L. Rabinowitz, "Are Main-Belt Asteroids a Sufficient Source for the Earth-Approaching Asteroids? Part II. Predicted vs. Observed Size Distributions," Icarus 1997 May, V127 N1:33-54.
[Smith 97] Steven. S. Smith, Luming M. Niu, David J. Baker, John A. Wendel, Susan E. Kane, and Darrin S. Joy, "Nucleoprotein-based nanoscale assembly," Proceedings of the National Academy of Sciences of the United States of America, March 18 1997, V94 N6:2162-2167.
[Srivastava 97a] Deepak Srivastava and Steve T. Barnard, "Molecular Dynamics Simulation of Large-Scale Carbon Nanotubes on a Shared Memory Architecture," SuperComputing 97 (1997).
[Srivastava 97b] Deepak Srivastava, Steve T. Barnard, S. Saini and M. Menon, "Carbon Nanotubes: Nanoscale Electromechanical Sensors", 2nd NASA Semiconductor Device Modeling Workshop at NASA Ames Research Center, August 1997.
[Srivastava 97c] Deepak Srivastava, "Molecular Dynamics Simulations of Laser Powered Carbon Nanotube Gears," submitted to Nanotechnology.
[Srivastava 97d] Deepak Srivastava, "H2 packing in Single Wall Carbon Nanotubes and Ropes by Molecular Dynamics Simulations," unpublished (1997).
[Taylor 93] R. Taylor and D. R. M. Walton, "The Chemistry of Fullerenes," Nature, volume 363, N6431, 24 June 1993, pages 685-693.
[Thummel 97] H. T. Thummel and C. W. Bauschlicher, "On the reaction of FNO2 with CH3, t-butyl, and C13H21," J. Phys. Chem., 101, 1188 (1997).
[Toth-Fejel 96] Tihamer Toth-Fejel, "LEGO(TM)s to the Stars: Active MesoStructures, Kinetic Cellular Automata, and Parallel Nanomachines for Space Applications," The Assembler, Volume 4, Number 3, Third Quarter, 1996
[Tour 96] James M. Tour, "Conjugated Macromolecules of Precise Length and Constitution. Organic Synthesis for the Construction of Nanoarchitectures," Chemical Review, January-February 1996, volume 96, pages 537-553.
[Tour 97] James M. Tour, Masatoshi Kozaki and Jorge M. Seminario, "Molecular Scale Electronics: Synthetic and Computational Approaches To Nanoscale Digital Computing," unpublished 1997.
[Treacy 96] M. M. J. Treacy, T. W. Ebbesen and J. M. Gibson, "Exceptionally High Young's Modulus Observed for Individual Carbon Nanotubes," Nature 381, 678 (1996).
[Wowk 96] Bryan Wowk, "Phased Array Optics," Nanotechnology: Molecular Speculations on Global Abundance, B. C. Crandall, editor, MIT Press, Cambridge, Massachusetts, 1996.
[Wu 96] Ruilan Wu, Jeffry S. Schumm, Darren L. Pearson, and James M. Tour, "Convergent Synthetic Routes to Orthogonally Fused Conjugated Oligomers Directed towards Molecular Scale Electronic Device Applications," Journal of Organic Chemistry, volume 61, number 20, pages 6906-6921.
[Yacobson 96] Boris I. Yacobson, C. J. Brabec and J. Bernholc, "Nanomechanics of Carbon Tubes - Instabilities Beyond Linear Response," Physical Review Letters, 1 April 1996, V76 N14:2511-2514.
[Yim 95] Mark Yim, "Locomotion With A Unit-Modular Reconfigurable Robot," Stanford University Technical Report STAN-CS-TR-95-1536.