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

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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 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,

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Four Kinds of Atoms .................................................................,...........,................... 1 Photonics and Metamaterials ............................................................................. 3 "Impossible" Materials........................................................................................... 5 Advantages of Dynamic Materials ................................................................................... 5 Early Commercialization of Smart Materials ........................................................... 8 Advanced Concepts in Programmable Materials ................................................... 12 Scenario for Possible Applications ................................................................................. 13 1. Energy Levels of a Metal and a Semiconductor................................................,,, 2 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 1. Daily Household Energy Consumption (USA, 1993-1997)................................. 11

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Aerospace Applications of Programmable Matter 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

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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 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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UNCLASSIFIED// FOR OFFICIAL USE 01\Lf Conduction Band z Conduction Band w Band Gap a: Valence Band Metal Semiconductor 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