DOW-UAP-D118, AAWSAP DIRD, Aerospace Applications of Programmable Matter, December 2009

This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD describes “programmable matter” as smart materials whose properties can be changed on command, potentially allowing spacecraft components to change function through software updates rather than physical repair or replacement. The report suggests that such materials could someday enable adjustable sensors, smart windows, heat control, energy collection, active camouflage, and systems that switch between different functions, making spacecraft more flexible and adaptable. At the same time, it presents the idea as highly speculative and emphasizes major technical obstacles, including manufacturing at extremely small scales, shielding against radiation and electromagnetic interference, managing temperature effects, reducing component failures, and preventing hacking or malicious control. Overall, the document presents programmable matter as a promising long-term concept over the next 50 years, while judging that simpler near-term uses such as smart windows and energy-saving surface materials are far more realistic than the more ambitious aerospace applications.

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14 December 2009
ICOD: 1 December 2009
DIA-08-0911-016
Aerospace Applications of
Programmable Matter
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Aerospace Applications of Programmable Matter
Prepared by:
Acquisition Support Division (DW0-3)
Defense Warning Office
Directorate for Analysis
Defense I ntelligence Agency
Author:
AAP Person 90
Administrative Note
COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized.
This product is one in a series of advanced technology reports produced in FY 2009
under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace
Weapon System Applications (AAWSA}.,..,i..i.~u.u.u.....:...w.i..u.u~i..i,....w.i....cUestions pertaining to
this document should be addressed to AAP Person 1 AAWSA Program
Manager, Defense Intelligence Agency, ATTN: CLAR DWO-3, Bldg 6000, Washington,
DC 20340-5100.
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Contents
Introduction...........................................................................................................iv
Four Kinds of Atoms .................................................................,...........,................... 1
Natural Atoms .................................................................................................... 1
Quantum Dots ............................................................, ........................................... 1
Photonics and Metamaterials ............................................................................. 3
Liquid Cry-stals ............................................................................................................. 4
"Impossible" Materials........................................................................................... 5
Advantages of Dynamic Materials ................................................................................... 5
Early Commercialization of Smart Materials ........................................................... 8
Thermal Management of Spacecraft ... .,. ........................................................................... 9
Energy-Scavenging Spacecraft Skins .................................. , ...................................... 11
Advanced Concepts in Programmable Materials ................................................... 12
Scenario for Possible Applications ................................................................................. 13
Directions for Future Research •• ■■ Ill■
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Conclusions .......................................................................................................... 16
Figures
1. Energy Levels of a Metal and a Semiconductor................................................,,, 2
2. Quantum Dot......................................................................... , ............................................. 3
3. Programmable Materials .................................................................................... 3
4. Wellstone Fiber.................................................................................................. 6
5. Assorted views of RavenWindow and RavenLight Filters in the Cold
(Transparent) and Hot (Reflective} State........................................................... 8
6. RavenWindow Smart Window Film Performance vs. Leading Incumbent Window
Filters...................................................................................................................... 9
7. Peltier Junction Heat Pump ..................................................................................... 10
Tables
1. Daily Household Energy Consumption (USA, 1993-1997)................................. 11
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Aerospace Applications of Programmable Matter
Introduction
For the owners of a $100 million satellite-a TV broadcast satellite, for
example-avoiding bankruptcy often depends on the spacecraft's continued
good health until its scheduled replacement is in orbit. Unfortunately,
numerous failure modes are possible, including blown fuses, failed sensors,
and browned-out solar arrays. The common trait of most such failures is that
they cannot be repaired from the ground. In addition, it is not typically
possible to repurpose a spacecraft or its components for new services that no
one foresaw at the time of manufacture. Either way, a new satellite is required.
However, when sensors, filters, emitters, and photovoltaic solar panels are
made of Programmable Matter smart materials, the solution to a component
failure or new mission requirement might be as simple as a software update.
Other advantages of dynamic materials include advanced energy management
and energy scavenging from a variety of sources. Smart materials can even
create new defensive capabilities, such as chameleon-style camouflage,
deflection of laser beams, and even outright invisibility.
If it becomes possible to change the properties of certain materials on demand,
based on remotely triggered instructions, the benefits for spacecraft-both
crewed and autonomous-will be considerable. This white paper-by no means
an exhaustive reference-is intended to serve as a primer on the principles
behind smart materials and their possible aerospace applications over the next
50 years.
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Four Kinds of Atoms
All matter is made of atoms and derives its properties, in part, from the fact that atoms
are discrete objects yet are so small and so close together that light waves cannot "see"
them individually. By extension, neither can electric and magnetic fields. To a photon,
or to a large electrical current, matter appears to be made up of continuous substances
rather than discrete building blocks. This fact is critically important in understanding the
optical, electrical, and even thermal properties of materials. Equally important are the
discoveries of recent decades, showing at least four different kinds of "atoms" that
meet this same general description.
NATURAL ATOMS
Natural atoms are the 92 elements of the periodic table. Actually there are more, but
the rest have unstable nuclei that will eventually fly apart Into smaller atoms and loose
subatomic particles that can damage the materials around them. For engineering
purposes, this makes them unreliable building blocks.
However, 92 building blocks allow for a staggering number of combinations, and all the
materials with which we are familiar-natural ones like coal and diamonds, ancient ones
like bronze and glass, and modern ones like silicon carbide and gallium arsenide-are
merely "Tinkertoy" sculptures of these natural atoms.
QUANTUM DOTS
A quantum dot is a very small grouping of tightly confined electrons whose collective
behavior resembles that of a natural atom. For this reason, quantum dots are
sometimes known as "artificial atoms."
To describe how this trick is accomplished, it is first necessary to talk about electrons
and how they behave. Most materials are either conductors, which permit the free flow
of electrons, or insulators, which resist it. Semiconductors are insulators that are
capable of conducting electrons above a certain threshold energy-a useful trick that
makes integrated circuits and other electronics possible. The most familiar
semiconductor is silicon, which is used to make the vast majority of microchips found in
tod;;iy's consumer ;;ind industri;;il electronics. Aecl;'l~1se silicon's n;;itive Q){ide, SiO?, is the
main component of sand and rocks, it is readily available and relatively inexpensive. In
addition, when melted, purified, and hardened into sheets, silicon dioxide serves as one
of our familiar insulators and building materials: glass. Unlike most other
semiconductors, silicon is also nontoxic.
The electrical properties of a semiconductor like silicon are of course fixed by the laws
of physics. Atoms hold electrons in shells that increase in size, capacity, and potential
energy the farther they are from the nucleus. "Valence" electrons are found in full (or
nearly full) shells, where there are few empty spaces through which electrons can
move. These electrons tend to stay at home, so their levels exhibit a large electrical
resistance and do not permit electricity to flow. "Conduction" electrons are found in
shells that are more than half-empty and have lots of open space, enabling electrons to
travel freely through them and move easily from one atom to another. Between these
layers is a "band gap" of forbidden energies. Here, there exist no electrons at all-ever.
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Conduction Band
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Figure 1. Energy Levels of a Metal and a Semiconductor. In a metal, many electrons reside in the conduction
band and can be pushed to neighboring atoms with only a tiny addition of thermal or electrical energy. In a
semiconductor, enough energy must first be added to excite the electron out of the valence band, across the band
gap, and into the conduction band. Thus, to conduct electricity, semiconductors require much higher voltages and
temperatures than do metals.
Electrons below the band gap of a semiconductor behave as though they were in an
insulator, while electrons above the band gap behave as though they were in a
conductor. They flow easily and can be used to store or transport energy and
information.
The difference between a metal and an insulator is that the outermost electron shell of
a metal atom is more than half-empty. It has lots of conduction electrons and lots of
room for them to move around. An insulating material, such as sulfur, has an outer
shell that is almost completely filled. All its electrons are valence electrons­
homebodies that do not like to travel. Semiconductors have outer shells that are
approximately half-filled. With the input of energy, their electrons can jump to a higher
level where they find open space to travel through. Conduction electrons can also be
"donated" by neighboring atoms.
A "quantum dot" is simply a very small structure-usually on the order of 5-20
nanometers-that contains a modest number of conduction electrons, which it confines
in all three dimensions and prevents from leaving the structure. In addition, because
the Heisenberg uncertainty principle requires position uncertainty to increase when
particle momentum is restricted, the trapped electrons are unable to hold a well-defined
position and instead behave as standing waves that resemble the orbitals of, and
exhibit many of the same properties as, a natural atom.
However, there are two major differences between a quantum dot and a natural atom.
First, there are far more than 92 possible configurations-an infinite number, in fact­
for the confined electrons. Thus, with quantum dots it is possible to create designer
atoms with properties that simply do not occur on the periodic table. If we want to, we
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can exert precise control over their optical, electrical, thermal, and magnetic properties
rather than simply selecting these properties from the limited catalog nature has
provided.
Barrier
Figure 2. Quantum Dot. A quantum dot confines electrons in a very small volume of space, forcing them to
behave as standing waves. Their structure thus resembles the electron clouds or "orbitals" of an atom.
Second, it is possible to pump electrons in and out of a quantum dot using electric
fields. Thus, instead of a single designer material, it is possible to create a
programmable material whose "atoms" can be changed on demand, allowing a bounded
but infinite variety of material properties that can be summoned or dismissed at will.
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Figure 3. Programmable Materials. Various structures use electric fields to vary the confinement properties of
quantum dots and can be assembled into bulk materials.
PHOTONICS AND METAMATERIALS
"Sub-wavelength" features are objects implanted on or embedded in a transparent
material that are larger than atoms or molecules but smaller than a wavelength of light.
They can have significant effects on the optical properties of the material, since they
change the way it responds to electric and magnetic fields. However, because they are
too small to be "seen" by the photons interacting with them, they do not directly block
the passage of light. The result is a transparent material whose optical properties
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(permittivity, permeability, index of refraction, and coefficients of reflection,
transmission, and absorption) do not necessarily match those of any natural material.
Photonic crystals exploit this principle by varying the density or refractive index of a
material in a regular, periodic way. Just as light is affected by the spacing of atoms in a
natural crystal, it can be affected by the (much larger) spacing of sub-wavelength
features in a photonic crystal. Thus, photonic crystals can efficiently reflect some
wavelengths of light while absorbing, transmitting, bending, or scattering others. This
can be useful, for example, in telecommunications, where a single optical fiber may
carry thousands of different signals. Because similar effects occur naturally in many
gemstones (opal, for example), photonic crystals can also serve as artificial gems.
Whereas photonic crystals are generally insulators, another class of materials-called
superlattices-is made from semiconductors, metals, and other substances stacked in
very thin layers. Such materials "look" like crystals to the electrons and photons moving
through them but can have properties that do not occur-or occur only weakly-in
nature. Two examples are "magnetoresistive" materials made from alternating layers of
iron and a nonmagnetic material such as chromium, Even in very tiny quantities, such
materials can be used to sense magnetic fields with much greater sensitivity than can
any natural material and are widely used in hard disk drives and digital compasses.
In a "metamaterial," the sub-wavelength features are conductive metals surrounded by
a transparent dielectric material such as glass, air, or empty space. In much the same
way a metal rod interacts with radio waves and can thus serve as an antenna, the
"atoms" of a meta material create strong resonances at particular wavelengths that can
have more profound effec