"The principles of physics, as far as I can see, do not speak against the possibility
of maneuvering things atom by atom. It is not an attempt to violate any laws; it is
something in principle, that can be done; but in practice, it has not been done because we
are too big."
Richard Feynman, 1959.
NASA applications of molecular nanotechnology
Al Globus, David Bailey, Jie Han, Richard Jaffe, Creon Levit, Ralph
Merkle, and Deepak Srivastava
Published in The Journal of the British Interplanetary Society, volume 51, pp. 145-152,
Laboratories throughout the world are rapidly gaining atomically precise control over
matter. As this control extends to an ever wider variety of materials, processes and
devices, opportunities for applications relevant to NASA's missions will be created. This
document surveys a number of future molecular nanotechnology capabilities of aerospace
interest. Computer applications, launch vehicle improvements, and active materials appear
to be of particular interest. We also list a number of applications for each of NASA's
enterprises. If advanced molecular nanotechnology can be developed, almost all of NASA's
endeavors will be radically improved. In particular, a sufficiently advanced molecular
nanotechnology can arguably bring large scale space colonization within our grasp.
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.
The applicability of manufacturing at an ever smaller scale is nowhere more self-evident
than in computer technology. Indeed, Moore's law [Moore 75] (an observation not a physical
law) says that computer chip feature size decreases exponentially with time, a trend that
predicts atomically precise computers by about 2010-2015. This capability is being
many directions. Here we will concentrate on those under development by NASA Ames and her
partners. For a review of many other approaches see
Carbon Nanotube SPM Tips
Carbon nanotubes [Iijima 91] can be viewed as rolled up sheets of graphite from 0.7 to
many nanometers in diameter. The smaller tubes are single molecules. [Dai 96] placed
carbon nanotubes on an SPM tip thus extending our ability to manipulate a single molecule
with sub-angstrom accuracy. Not only are the tips atomically precise, but they should have
approximately the same chemistry as C60, and thus be functionalizable with a wide variety
of molecular fragments [Taylor 93]. Functionalizing carbon nanotube tips will allow
mechanical manipulation of many molecular systems on various surfaces with sub-angstrom
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
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.
Data Storage on Molecular Tape
It is possible to store data on long chain molecules (for example, DNA) and it may be
possible to read these data with carbon nanotube tipped SPMs. Existing DNA synthesis
techniques can be used to write data. If the different DNA base pairs can be distinguished
with a carbon nanotube tipped SPM, then the data can be read non-destructively (current
techniques allow a destructive read). However, the difference between base pairs is not
great. If the base pairs cannot be distinguished, techniques for attaching modified
enzymes to specific base pair sequences [Smith 97] could be used. Certain enzymes (DNA
(cytosine-5) methyltransferases) attach themselves onto a specific sequence of base pairs
with a covalent bond. The enzyme then performs its operation and breaks the bond. [Smith
97] modified the enzyme such that the initial covalent bond was formed but the subsequent
operation was disrupted. The result is that DNA synthesized with the target base pair
sequences at the desired location can force precise placement of the enzymes. The presence
of an enzyme could represent 1 and its absence 0. Enzymes are sufficiently large that
distinguishing their presence should be straightforward. If the DNA/enzyme approach proves
impossible, a wide variety of other polymer systems could be examined.
Data Storage on Diamond
[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
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.
Carbon Nanotube Electronic Components
As mentioned before, carbon nanotubes can be described as rolled up sheets of graphite.
Different tubes can have different helical windings depending on how the graphite sheet is
connected to itself. Theory [Dresselhaus 95, pp. 802-814] suggests that single-walled
carbon nanotubes can have metallic or semiconductor properties depending on the helical
winding of the tube. [Chico 96], [Han 97b], [Menon 97a], [Menon 97b], and others have
computationally examined the properties of some of hypothetical devices that might be made
by connecting tubes with different electrical properties. Such devices are only few
nanometers across -- 100 times smaller than current computer chip features. For a number
of references in fullerene nanotechnology see [Globus 97].
Molecular Electronic Components
Several authors, including [Tour 96], have described methods to produce conjugated
macromolecules of precise length and composition. This technique was used to produce
molecular electronic devices in mole quantities [Wu 96]. The resultant single molecular
wires were tested experimentally and found to be conducting [Bumm 96]. The three and four
terminal devices have been examined computationally and look promising [Tour 97]. The
features of these components are approximately 3 angstroms wide, about 750 times smaller
silicon technology can produce.
From [Merkle 96]:
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
electro- static 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.
One study not conducted by Ames or partners is particularly worth mentioning since it
places a loose lower bound on the computational capabilities of molecular nanotechnology.
[Drexler 92a] designed a number of computer components using small diamondoid rods with
knobs that allow or prevent movement to accomplish computation. While this tiny mechanical
Babbage Machine is probably not an optimal computational engine, its calculated
performance for a desktop computer is 1018 MIPS -- about a million times more powerful
than the largest supercomputer that exists today (Fall 1997).
Note that with very fast computation energy use and heat dissipation become a severe
problem. One approach to addressing this issue is reversible logic.
[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.
[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].
[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] calculates that lightsails made of 20 nm aluminum in tension should achieve
an outward acceleration of ~14 km/s per day at Earth orbit with no payload and minimal
structural overhead. For comparison, the delta V from low Earth to geosynchronous orbit is
3.8 km/s. Lightsails generate thrust by reflecting sunlight. Tension is achieved by
rotating the sail. The direction of thrust is normal to the sail and away from the Sun. By
directing thrust along or against the velocity vector, orbits can be lowered or raised.
This form of transportation requires no reaction mass and generates thrust continuously,
although the instantaneous acceleration is small so sails cannot operate in an atmosphere
and must be large for even moderate payloads.
Today, the smallest feature size in production systems is about 250 nanometers -- the
smallest feature size in computer chips. Since atoms are an angstrom or so across and
carbon nanotubes have a diameter as small as 0.7 nanometers, atomically precise molecular
machines can be smaller than current MEMS devices by two to three orders of magnitude in
each dimension, or six to nine orders of magnitude smaller in volume (and mass). For
example, the size of the kinesin motor, which transports material in cells, is 12 nm. [Han
97a] computationally demonstrated that molecular gears fashioned from single-walled carbon
nanotubes with benzyne teeth should operate well at 50-100 gigahertz. These gears are
about two nanometers across. [Han 97c] computationally demonstrated cooling the gears with
an inert atmosphere. [Srivastava 97c] simulated powering the gears using alternating
electric fields generated by a single simulated laser. In this case, charges were added to
opposite sides of the tube to form a dipole. For an examination of the state-of-the-art in
small machines see the 1997 Conference on Biomolecular Motors and Nanomachines.
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) 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
[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.
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 the desktop.
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 surfaces. This 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 aircraft.
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.
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.
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
Human Exploration and Development of Space
Nanotechnology-enabled Earth-to-orbit transportation 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 technologies include:
High Strength and Reliability Materials
Space structures with a long design life (such as space station modules) need
high-reliability materials that do not degrade. Active materials might help. The machines
monitor structural integrity at the sub-micrometer scale. When a portion of the material
becomes defective, it could be disassembled and then correctly reassembled. It should be
noted that bone works somewhat along these lines. It is constantly being removed and added
by specialized cells.
On Demand Spares and Tools
To effect timely repairs, space stations require a large store of spare parts and tools
that are rarely used. A mature nanotechnology might create a "matter compiler,"
a machine that converts raw materials into a wide variety of products under software
control. Contemporary examples of very limited matter compilers are numerically controlled
machines and polypeptide sequencers. With a substantially more capable
nanotechnology-based matter compiler, a space station crew could simply make spare parts
and tools as needed. The programs could be stored on-board or on the ground. New tools
invented on Earth could be transferred as software to the station for manufacture. Once
used, unneeded tools and broken parts could be ionized in a solar furnace, transferred
using controlled magnetic fields, and the constituent atoms stored for later manufacture
into new products.
An advanced nanotechnology might be able to build filters that dynamically modify
themselves to attract the contaminant molecules detected by the air and water quality
sensors. Once attached to the filter, the filter could in principle move the offending
molecules to a molecular laboratory for modifications to useful or at least inert
products. A swarm might implement such an active filter if it was able to dynamically
manufacture proteins that could bind contaminant molecules. The protein and bound
contaminant might then be manipulated by the swarm for transportation.
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
Sleeping through RCS firings
Sleeping crew members in the shuttle experience considerable pain and sleep disruption
when the reaction control system fires and they collide with the cabin walls. If crew
members were connected to the walls by a swarm, the swarm could absorb most or all of the
force before the crew member struck the wall. The swarm could then gradually return the
crew member to center (without the oscillations associated with bungee cords) in
preparation for the next firing.
For resupply, spacecraft docking is a frequent necessity in space station operations. When
two spacecraft are within a few meters of each other, a swarm could extend from each, meet
in the middle, and form a stable connection before gradually drawing the spacecraft
Zero and Partial G Astronaut Training
A swarm could support space-suited astronauts in simulated partial-g environments by
holding them up appropriately. The swarm moves in response to the astronaut's motion
providing the appropriate simulation of partial or 0 gravities. Tools and other objects
are also manipulated by
the swarm to simulate non-standard gravity.
Smart Space Suits
Active nanotechnology materials (see active materials) might enable construction of a
skin-tight space suit covering the entire body except the head (which is in a more
conventional helmet). The material senses the astronaut's motions and changes shape to
accommodate it. This should eliminate or substantially reduce the limitations current
systems place on astronaut range of motion.
Small Asteroid Retrieval
In situ resource utilization is undoubtedly necessary for large scale colonization of the
solar system. Asteroids are particularly promising for orbital use since many are in near
Earth orbits. Moving asteroids into low Earth orbit for utilization poses a safety problem
should the asteroid
get out of control and enter the atmosphere. Very small asteroids can cause significant
destruction. The 1908 Tunguska explosion, which [Chyba 93) calculated to be a 60 meter
diameter stony asteroid, leveled 2,200 km2 of forest. [Hills 93] calculated that 4 meter
diameter iron asteroids are near the threshold for ground damage. Both these calculations
assumed high collision speeds. At a density of 7.7 g/cm3 [Babadzhanov 93], a 3 meter
diameter asteroid should have a mass of about 110 tons. [Rabinowitz 97] estimates that
there are about one billion ten meter diameter near Earth asteroids and there should be
far more smaller objects.
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.
Extraterrestrial Materials Utilization
Extraterrestrial materials brought into orbit could be fed into a high- temperature solar
furnace and partially ionized. Magnetic fields might then be used to separate the nuclei.
These are fed in appropriate quantities to a matter-compiler to build the products
Several authors, including [Freitas 98] have speculated that a sufficiently advanced
nanotechnology could examine and repair cells at the molecular level. Should this
capability become available -- presumably driven by terrestrial applications -- the small
size and advanced capabilities of such systems could be of great utility on long duration
space flights and on self-sufficient colonies.
Self-replicating systems permit efforts of great scope to be pursued economically.
Adjusting the environment on another planet to suit the tastes of humans is one such
undertaking. Heating and cooling can be achieved by (among many other methods) using
space-based mirrors. Chemical modifications of the planetary surface and atmosphere can be
achieved in relatively short periods by the use of self-replicating systems that absorb
sunlight and raw materials, and convert them into the desired products. Much as plants
changed the environment of the earth to what we see today, so self-replicating molecular
manufacturing systems might more rapidly convert the environments of other planets.
As interstellar trips might last many years, the ability to conserve supplies by
maintaining some crew members in a suspended state would be useful. An extremely advanced
nanotechnology might use molecular manipulations of each cell to provide (a) better
methods of slowing or suspending the metabolic activity of crew members and (b) better
methods of restoring metabolic activity to a normal state when the destination is reached.
Molecular manufacturing should enable the creation of very precise mirrors. Unlike
lightsail applications, telescope mirrors require a very precise and somewhat complicated
shape. A swarm with special purpose appendages capable of bonding to the mirror might be
able to achieve and maintain the desired shape.
Virtual Sample Return
A very advanced nanotechnology would be capable of imaging and then removing the surface
atoms of an extra-terrestrial sample. By removing successive surface layers the location
of each atom in the sample might be recorded, destroying the sample in the process. This
data could then be sent to Earth. Besides requiring a very advanced nanotechnology, there
is a more fundamental -- but not necessarily fatal -- problem: as the outside layer of
atoms is removed the next layer may rearrange itself so the sample is not necessarily
As described earlier in the EOS section, smart dust could be distributed into the
atmosphere of another planet to characterize it in great detail.
Low Earth orbit spacecraft generally depend on solar cells and batteries for power.
According to [Drexler 92b]:
"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 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.
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."
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
A critical component in hydrogen/oxygen fuel cells is the PEM (Proton Exchange Membrane).
This membrane must (a) permit the passage of protons while (b) blocking everything else.
Present membranes do a rather poor job. One group at Ames is designing and computationally
testing PEMs to study possible energy mechanisms in early life. While these studies are
not meant to design optimal membranes for fuel cell use, the basic knowledge and approach
may be of value. Another proposal is to design a diamond membrane a few nanometers thick
with "proton pores." The pores might be lined with fluorine, oxygen and nitrogen
to create a region with a high proton affinity. In addition, a positionally controlled
platinum might be held at the mouth of the pore to verify that H2 can be catalytically
split into H+ and e-, and that the barrier for migration of the H+ into the pore is modest
in size. Nanotechnology must provide precise control over the manufacturing process of the
diamondoid PEM since the pores must be made very precisely.
Studies of H2 absorption and packing in carbon nanotubes and nanoropes are in progress at
NASA Ames and elsewhere. Nanotubes provide large pore sizes and nanoropes have different
pore sizes depending on interstitial and other locations. [Dillon 97] estimated that the
single walled nanotubes in their sample contained 5 to 10% by weight of H2. The nanotubes
were about 0.1 to 0.2% by weight of the total sample. Computational studies at Ames
suggest that to store 7-10% H2 in single walled nanotubes at room temperature the H2s must
be stored inside the tubes, not merely adsorbed on the walls [Srivastava 97d]. This work
suggests that carbon nanotubes might be developed into an excellent H2 storage medium
within 3-5 years.
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.
High strength light-weight materials will allow greater efficiency of energy storage as
Nano Electromechanical Sensors
Many kinds of ultraminiature electromechanical devices have utility on a miniaturized
space craft. It has been shown that manipulating carbon nanotubes changes their electrical
properties [Srivastava 97b]. This might be exploited to build nanometer scale strain
devices. This may be achievable within 3-5 years, and simulations along these lines are in
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
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
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
Many of the applications discussed here are speculative to say the least. However, they do
not appear to violate the laws of physics. Something similar to these applications at
these performance levels should be feasible if we can gain complete control of the
three-dimensional structure of materials, processes and devices at the atomic scale.
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]):
1.Nobody knows. There are far too many variables and unknowns. Beware of those who have
excessive confidence in any date.
2.The time-to-nanotechnology will be measured in decades, not years. While a few
applications will become feasible in the next few years, programmable
assembler/replicators and swarms will be extremely difficult to develop.
3.The time-to-nanotechnology is very sensitive to the level of effort expended. Resources
allocated to developing nanotechnology are likely to be richly rewarded, particularly in
the long term.
We would like to thank Steve Zornetzer, NASA Ames Research Center, for asking us to look
into molecular nanotechnology applications to NASA missions. Special thanks to Glenn
Deardorff and Chris Henze for reviewing the manuscript.
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Surface micromachined gyroscope
Magnified view of the comb structures
This type of gyroscope is manufactured using thick polysilicon
technology employing high aspect ratio comb structures as an electrostatic drive