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APPENDIX D Energy and Power Materials A NOTE ON POWER SOURCES There is a continuing need for materials that can store large amounts of energy in small packages and use the energy efficiently. In materials terms, advanced energy storage requires materials that have high volumetric and gravimetric energy densities. While many of the approaches discussed in this report can affect several types of power sources, it is important to realize that no single power source is appropriate for all applications (see Figure D-1). A range of energy storage and conversion technologies will have central roles in engineered energy storage and delivery systems for powering DoD needs. High-energy needs are likely to be met with a liquid fuel because the energy density of liquid fuels, in reaction with air in an internal combustion device or fuel cell, is unsurpassed. High-power applications, on the other hand, are likely to require batteries, or more likely, hybrid power devices that combine a high-energy system (e.g., a fuel cell) with a high-power system (e.g., a powerful battery or electrochemical capacitor). Properly designed, a system can enjoy the benefits of both the high energy content of a liquid fuel and the high power of a battery. In the main body of this report, the committee attempts to show that some material improvements can affect several technologies. Batteries and fuel cells will both benefit from improved electrolytes and better methods to tailor electrochemical interfaces. Other improvements will affect one technology more than another or may even be specific to a single technology.
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FIGURE D-1 Military systems power requirements often follow a “step function,” so different power sources are needed for different applications. SOURCE: Carlin, Richard, ONR, Electric Power Sources for the Navy and Marine Corps, Presented at the Navy Grand Challenges Workshop, November 16-18, 1999. COMMERCIAL VERSUS MILITARY BATTERY REQUIREMENTS Many specific military requirements limit the use of commercial off-the-shelf (COTS) power sources. These include differences in required power and energy levels, in temperature operating range, in the need for shock resistance, in longevity requirements, and in reliability levels. Except in hybrid electric vehicles (HEVs), high-power batteries are generally not needed in the commercial marketplace, and even HEVs are not subject to the same performance demands that future defense applications will encounter. Materials for military use must also operate in a broader temperature range and under more rigorous environmental extremes than materials for commercial use. Military batteries must have a longer shelf life and lower self-discharge rates than typical commercial batteries.
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Furthermore, commercial devices are not held to the same reliability standards as military devices. The reliability driver for commercial power sources is to minimize warranty expenses; the reliability driver for future defense systems is mission success and soldiers’ lives. These differences, which are present in all the Services, are typified in the requirements for Navy batteries shown in Figure D-2. DIELECTRIC ENERGY STORAGE Capacitor dielectrics will continue to have an important role for DoD, particularly for energy storage, power conditioning, high-rate switching, and pulsed power for a range of future DoD systems. Compared to other forms of electrical energy storage, capacitors are lower in energy density FIGURE D-2 Military versus commercial requirements for batteries. SOURCE: Suddeth, David, Naval Surface Warfare Center, Managing Power Source Strategies for Navy Applications, Presented at Navy Conference in Crystal City, VA, December 11-13, 2001.
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but higher in power density (see Figure D-3), and they are more readily cycled at high frequencies. EXPLOSIVES AND PROPELLANTS Explosives Many of the key chemical explosives of military interest today were first synthesized in the late 1800s and, as with structural materials, moving from laboratory curiosity to general application of energetic materials has often taken 20 to 30 years, as shown in Table D-1 (Federoff, 1960). Important technological parameters for high explosives are energy release/ reaction propagation rate; energy density; and resistance to accidental explosion (insensitivity). Increased insensitivity to accidental detonation FIGURE D-3 Power versus energy density for selected mechanisms for electrical energy storage. SOURCE: Clelland, I., R. Price, and J. Sarjeant. 2000. Advances in Capacitor Technology for Modern Power Electronics. Pp. 145-148 in Proceedings of the 24th International Power Modulator Symposium, Norfolk, VA, IEEE, Piscataway, NJ.
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TABLE D-1 First Synthesis of Chemical Explosives of Military Interest Material Year First Reported or Synthesized Year First Used in Large-Scale Service Nitroguanidine 1877 Tetryl 1879 1906 TNT 1880 1900 TATB 1888 PETN 1894 1930 RDX 1899 1935 Picric acid 1900 1910 HMX 1930 1970 NOTE: HMX was used as early as the 1950s in explosive compositions but only reached widespread use in about 1970. has been a major focus of modern explosives research over the past 40 years, and efforts continue to reduce sensitivity while increasing explosive energy. Over the last 50 years, the average power of military high explosives has increased by approximately 40 percent. All indications are that tomorrow’s weapon systems will be smaller than today’s. Unless they are to carry a disproportionate share of mass in weapons and explosive power, achieving the same energy on target will require higher energy density materials (HEDM). Is there room for additional improvement? Figure D-4 depicts the mass-based energy density spectrum (cal/gm) and the relative position of conventional high-energy chemistry within it. Conventional hydrocarbons based on oxygen and nitrogen (CHNO) explosive materials are at the low end, on the order of 103 cal/gm. New CHNO-based molecules combined with advanced approaches for achieving high surface areas and mixing components may be able to increase this figure several-fold—the equivalent of several centuries of progress. The figure indicates that there may be even much greater potential for HEDM based on alternative approaches. Some of the latter are currently only at the conceptual stage; others are just entering the basic research stage.
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FIGURED-4 Is there room for improvement for energetic materials? Energy density per unit mass. SOURCE: Ullrich, G.W., director, Weapons Systems, Office of the Secretary of Defense, Advanced Energetic Materials: Introduction and Overview, presented to the Committee on Advanced Energetic Materials and Manufacturing Technologies, National Research Council, Washington, DC, July 31, 2001. Propellants Propellants burn without exploding and contain all the oxygen they need for combustion (Alchavan, 1998). Ideal propellants are dense; occupy little space before burning; produce only low-molecular-weight gases and heat; show repeatable performance; yield acceptably low gas temperature and products to reduce gun damage; provide maximum gas output within the pressure limits of the gun; resist shock, impact, and heat; are safe to store and handle; and are low-cost and environmentally acceptable. Specific impulse (Isp) is one of the performance measures most often used for propellants. An additional measure of efficacy is the amount of oxygen needed to convert all oxygen to carbon dioxide and all hydrogen to water (Cooper and Kurowski, 1996). Propellants emit gas and heat but, in contrast to explosives, do not react faster than the bulk sound speed in the material. Traditional propellants (single-, double-, or triple-base materials) are composed of CHNO molecules that self-oxidize; they have historically been used in guns or small military rocket motors. In a separate class of materials is the composite propellant, which contains fuel and oxidizer as
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separate components, and which is used extensively in rockets and for gas generators other than in guns. The fuel often acts as a binder for the components. Although both liquids and solids have been employed as rocket/missile propellants,1 all major gun propellants today are solid.2 This report concentrates on opportunities in solid propellants because of their widespread use across DoD and their similarities to explosives. Key Issues for Energetic Materials Much effort over the past few decades has been directed to safety and process improvements in explosives and propellants. In particular, creating munitions insensitive to accidental detonation has been a major goal. Traditional approaches to development of insensitive materials for explosives and propellants have relied quite heavily on intuition. This process is time-consuming, with no guarantee of success. To date, there has been relatively little application of atomistic modeling to energetic materials formulation. The problem has been recognized by issuance of a Defense Strategic Research Objective (SRO) on Insensitive High-Energy Materials.3 A new paradigm is slowly evolving in which science-based models are supplementing, and in some cases replacing, intuitive approaches to munitions design. One estimate is that development time for propellants using current ingredients requires 10-15 years, whereas development of new materials and the associated formulations can require 25-40 years,4 in part because empirical testing requires use of multiple iterations at multiple scales. An important goal is to reduce this development time. 1 Hunley, J.D. “AIAA Invited Paper—The History of Solid-Propellant Rocketry: What We Do and Do Not Know,” paper presented at the 35th AIAA, ASME, SAE, ASEE Joint Propulsion Conference and Exhibit, Los Angeles, CA, June 20-23, 1999. 2 Forch, B.E., “Energetic Materials for the Objective Force,” paper presented by B.E. Forch, Army Research Laboratory, at the National Defense University, Ft. Leslie J. McNair, Washington, DC, July 9, 2002. 3 Forch, Brad E., and Betsy M. Rice, “Strategic Research Objective: Insensitive High-Energy Materials,” briefing presented to the Panel on Energy and Power Materials of the Committee on Materials Research for Defense After Next, National Research Council, Washington, DC, March 29, 2001. 4 Goldwasser, J., “Navy Energetic Materials Science and Technology Programs,” briefing presented to the Committee on Advanced Energetic Materials and Manufacturing Technologies, National Research Council, Washington, DC, July 31, 2001.
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The development of novel energetic materials over time has relied on the intuition, ingenuity, and knowledge of experienced individuals and on extrapolation of the properties and structures of existing energetic materials to those of new materials. These complex materials will continue to be a fundamental contributor to U.S. national defense in the future. To streamline the R&D process in this area, effort should be directed at assembling and integrating the entire arsenal of materials development capabilities. These include use of (1) computation materials science in materials design to help identify promising new molecules and formulations; (2) new material synthesis approaches; (3) improved processing methods; (4) new characterization techniques; and (5) advanced modeling to reduce the expensive and time-intensive testing necessary to verify performance. Finding advanced approaches to computation materials science, combining first principles and known design rules with the results of well-designed experiments, has the potential for reducing the amount of time required to identify, develop, and verify the performance of new energetic materials. Already, molecular modeling techniques applied to the development of new energetic materials are showing promise of materials that provide enhanced energy density and insensitivity. It is important to understand the fundamental processes for initiation of energetic materials and, in the case of propellants, the associated fundamental combustion mechanisms. Having a comprehensive model of reaction processes in heterogeneous nanoscale energetic materials, taking into account details of initiation and propagation of reaction fronts, would help us understand these complex processes and would form a basis for design and development of novel energetic materials.5 Many of the materials that have already been identified as promising have no known synthesis routes. Others can be prepared, but only in gram quantities by costly means requiring either multistep synthetic approaches, expensive reagents, difficult-to-maintain experimental conditions, or combinations thereof. Making novel energetic materials available in large quantities for military use will require improved means for synthesis and 5 Wilson, W.H., munitions directorate, Air Force Research Laboratory, Eglin Air Force Base, “Advanced Energetic Materials Research,” paper presented to the Committee on Advanced Energetic Materials and Manufacturing Technologies, National Research Council, Washington, DC, July 31, 2001.
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new processes for combining these materials with others in complex formulations. As is discussed below, one promising avenue to new energetic explosives and propellants is to use nanomaterials technology and nanocomposite materials. In parallel with developments in the rest of this emerging field, this will require new techniques for characterizing these materials at different size scales, particularly the nanoscale. Of particular interest in these nanocomposite energetic materials are such factors as nanoparticle size, size distribution, morphology, surface chemistry, and composition. These variables have all been shown to be important in determining mechanical, barrier, and other properties of nanocomposites (Kornmann et al., 1998; Messersmith and Giannelis, 1995), and they will likely control the contributions of nanoscale components in energetic materials as well. Finally, the time required to field new energetic materials is long, due in no small part to the rigorous testing required to assure their performance, reliability, and safety. Again, use of new computational approaches may help compress this time schedule. LOGISTIC FUELS An overriding military concern in fuels technology is logistics. Fewer fuels mean a simplified logistics burden and the ability to provide energy, rapidly and flexibly, to the system that most requires it. From this perspective, all military systems would ideally run on a single fuel. Many current military propulsion systems have been designed to use a variety of petroleum-based fossil fuels, such as jet fuel (e.g., JP-5, JP-8) and diesel. These fuel families are exceedingly well-established in military applications and are supported by a strong logistics infrastructure. The panel recognizes that new electrochemical propulsion and power systems employing fuel cells are in various stages of design and development and it believes that their development as outlined in Chapter 4 is essential for the DoD applications of 2020. However, it also appears that current hydrocarbon military fuel families (jet fuel and diesel fuel) will continue to power most military platforms in 2020 due to their established position as workhorse fuels, combined with the cost and time required for propulsion system redesign to produce other fuels. Convergence to use of a single petroleum-based
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logistic fuel is also unlikely because diesel fuel, now used in a variety of trucks and military ground vehicles, will not flow readily in a jet engine, while gasoline is too volatile. Therefore, while there is a strong push toward novel fuels for fuel cell applications, in 2020 fuels for turbine and internal combustion engines used to transport men and materiel are expected to remain primarily hydrocarbon-based.6 Reformed diesel and jet fuels are also likely to retain a prominent role even when fuel-cell-based systems arrive in large numbers, due to the strong established base for these fuels. These conclusions are supported by examination of fuel-related developments in the commercial sector, which shows a continued push to improve petroleum-based fuels and power sources. In 2020, oil and natural gas are expected to remain the dominant energy supply for the United States, with civilian transportation fuels obtained primarily from hydrocarbons. Production of petroleum-based fuels is expected to peak between 2020 and 2040. Throughout the transportation sector a global shift to cleaner fuels is expected by 2020, raising energy efficiency and reducing greenhouse gas emissions. Concurrent efforts will be made to improve civilian transport efficiency by way of leaner burning internal combustion systems, hybrid electric vehicles, fuel cells, greater use of mass transportation, and telecommuting. The environment will drive changes in petroleum-based fuel formulation to reduce volatile organic compounds, NOx, particulates, and greenhouse gas emissions. Most industrialized nations will continue to seek reductions in SOx emissions in jet fuels while retaining fuel lubricity and performance. In the civilian sector, hybrid internal combustion/electric drives and other novel drive systems will evolve for automotive engines. Power sources in civilian automotive applications will include both petroleum fuels for Carnot cycle engines and hybrid gas-electric systems, with portions of the market being filled by approaches such as all-electric power, compressed or liquefied natural gas, or hydrogen. Because these latter approaches will need considerable new infrastructure to be effective, their widespread adoption is likely to be delayed. Improvements to today’s logistic fuel technology are expected to be largely evolutionary. While many of the problems are not materials-related 6 Gautam, R., “Fuels Processing,” briefing to the Panel on Energy and Power Materials of the Committee on Materials Research for Defense After Next, National Research Council, Irvine, CA, October 10, 2001.
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per se, their solutions could lead to improvements in military fuels. Modifying refinery yield to improve fuel quality (e.g., by reducing sulfur) or to optimize yield of one particular fuel fraction is one such evolutionary approach. Another is fuel interconversion using ring-opening reactions. These can convert cycloaliphatics or aromatic compounds to branched aliphatics. This would facilitate conversion of various components of diesel fuel to jet fuels of different types. Accomplishing this would require improved catalysts. The technology appears to be feasible, but there is no real economic incentive to accomplish it in the civilian market. Changing the scale of a process to provide higher heat and mass transfer or to optimize yield is a developmental approach that appears to be predominantly a chemical engineering challenge. However, at the lower end of the size scale, it devolves into solving materials-related engineering problems because the size of components must become quite small. Here, large numbers of MEMS or mesoscale processors are used in parallel to improve yield, reduce emissions, provide more rapid heat and mass transport, enhance reaction rate, and improve safety. This microscale process intensification approach could result in revolutionary rather than evolutionary processing capabilities if the design and manufacturing difficulties associated with combining large numbers of very small processors and components into a single practical system can be overcome. In summary, for logistic fuels most changes through 2020 will remain evolutionary. Potentially revolutionary advances in fuels will come from using micro/MEMS-based chemical approaches to processing logistic fuels. Other advances that relate to methods for on-board reforming of logistic fuels and for storing fuels like hydrogen are discussed in the section on fuel cells in Chapter 4. FUEL CELLS Description Fuel cells are devices that directly convert chemical energy into electrical energy and, because they do not involve combustion, are not Carnot-limited. The principle of operation of a fuel cell is illustrated in the text of the Energy and Power Materials Panel report (Chapter 4). Much as in a battery, the components in a fuel cell that make direct electrochemical conversion possible are an ion-conducting electrolyte, a cathode, and an
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and (4) briefly points out materials issues. The goal of this appendix is not to identify all likely materials, because the panel did not have the resources to do so. Rather, it was to give the interested reader a brief view of the potential effects of changes in electric propulsion on ship design. Increased DoD Needs for Electrical Power Generation Some key reasons that use of electric power is likely to increase in DoD systems are the following: The force as a whole will have fewer uniformed personnel. Eliminating sailor positions will decrease the direct and indirect personnel costs of defending America. However, the tasks to which those people were assigned may not be eliminated, so more automation, robotics, and power must replace them. Components of the DoD will be greener. While a major tenet of green philosophy is conservation, removing pollution from the environ-ment is not without an energy cost. Preprocessing of fuels and post-processing of exhaust will push demand. Reducing a ship’s waste stream or increasing shipboard air quality, for example, will require more electrical power. Information technology (IT) will consume an increasingly large amount of power. For example, aboard-ship IT consists of not only the ship’s computer network, but also the transmitters and receivers to move information on and off the vessel. As signals become more complex, the power needed to generate and process signals must increase. DoD is moving in the direction of more-electric systems, including electric propulsion. In January 2000 the Secretary of the Navy announced that the next generation of warships would be propelled by an electric drive system. Advantages of Electric Propulsion in Ship Design Compared to the standard mechanical drive system that uses reduction gears, there are many advantages to an integrated electric propulsion system:
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Increased power flexibility allows significant amounts of power to be directed either to the ship’s service power system, to the ship’s propulsion system, or to weaponry, depending on the situation. Increased design flexibility eliminates the reduction gear and the drive train, opening a completely new design space for future ships and allowing large, heavy power-generating equipment to be located anywhere in the ship. Reduced total ownership cost means that power generators can operate at a more efficient speed almost continuously, thus significantly increasing efficiency while reducing fuel cost and engine room staffing. Leveraged commercial electronic and electromagnetic technology replaces reliance on a mechanical drive manufacturing base that no longer produces commercial vessels, with reliance on equipment (e.g., insulated gate bipolar transistors) already available from the commercial power industry. Commonality allows major pieces of electric propulsion equipment to be used in virtually every warship in the U.S. Navy, facilitating modular spare parts usable across platforms. Reduced environmental emissions result from integrating the ship’s service and propulsion power systems. Remaining prime movers can operate at high efficiency, reducing exhaust emissions. Enhanced modularity provides parallel design processes and facilitates modernization and repair on vessels while significantly reducing manufacturing cost. Reduced overall maintenance requirements allow prime movers to operate at their peak performance range at relatively constant power levels for long periods. Increased payload capacity reduces fuel load out, allowing the platform more weapons or ones with greater range, or keeping them longer on station time. Increased automation means that automatic or autonomic systems carry the burden of operating the system, reducing the number of people in the loop. Flexibility/upgradability allows DoD to replace existing combat systems with new ones that use significantly more power without signifi-cantly affecting maximum vessel speed.
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DoD-Specific Technology Needs An array of issues must be addressed before electric propulsion systems become a reality. Many are unique to DoD and will require new approaches to system design and architecture, advanced modeling of electromagnetic characteristics, and, equally important, advances in new materials and processes for making them. Some of the major considerations from the DoD perspective include: Power density. The real estate aboard a military vessel is in high demand, yet DoD is challenged to insert more payload into smaller and cheaper vessels. Because space requirements in today’s commercial market are not as restricted the military cannot leverage on industry. High power levels. One way the marine industry is attempting to mitigate the power density problem is by raising the power levels associated with the propulsion system, but this raises a myriad of issues not previously experienced by marine propulsion engineers. The potential power required of DoD weapon systems only exacerbates the problem. Thermal management becomes an even more critical design criterion and safety of operators and maintenance workers demands more attention. Electromagnetic interference. As automation pervades every area of combat, electromagnetic interference soon becomes critical. Power conditioning equipment is susceptible to the electrical noise generated by the high current and high voltage loads and sources that surround it. Electromagnetic characteristics can also contribute to the ship signature. The commercial industry does not support research in this area, but it is critical to DoD. Shock and impact. This area receives no attention from industry, but it clearly must be addressed for DoD. Related Materials Issues A key near-term concern is high-frequency switching and the associated thermal management problems in a power-dense environment. While silicon carbide switching technology is now under development, by 2020 it may be necessary to have available additional options for high-tempera-ture and efficient power-switching and conditioning components. Power electronics were discussed in Chapter 5. Many of the materials technologies already described may help solve these large-scale power problems. For example, increased use of DC power components could eliminate the
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need for power conditioning and simplify its distribution. DC promotes the use of components whose raw electrical output is DC, such as fuel cells, and DC has attendant benefits in terms of signature reduction, survivability, and damage control. The need to carry large amounts of power at low loss while minimizing the volume of power carriers argues for advanced high-temperature superconductors with high critical currents. Similarly, the need for minimizing volume aboard military platforms argues for high-temperature superconducting (HTS) motors, which will have a profound impact on ship architecture, performance, and staffing requirements. These motors should have major advantages over conventional induction motors: It is projected that they will be only 20 percent of the size and 33 percent of the weight of conventional motors. If built in the nearer term, such motors would likely use HTS ceramic superconductors in a metal matrix operating at 77 K (liquid nitrogen). New MgB2 superconductors show considerable promise but at present have a Tc of only 39 K, and would probably run in liquid hydrogen coolant gas. While liquid hydrogen might be acceptable in a civilian application, there are serious concerns about producing and storing significant amounts of it on a warship, where hydrogen’s high explosivity would be a real issue in combat. Nevertheless, as MgB2 and other alloys appear, the Tc may increase to the point where inert liquid gases could provide cooling. Other materials developments useful for all-electric platforms are advanced dielectric materials for capacitors and high-strength composites for flywheels and compulsators; specific materials developments identified for these components are described elsewhere in the report. The panel did not have the resources to address in depth all the materials issues in this area, but recommends that this be done once a preliminary design for an all-electric platform is completed and device operating parameters are identified. This may result in identifying new materials needs in such categories as high-temperature (1000°F) low-loss electrical insulation; high-performance heat sinks; or EMI shielding materials. Integrated platform electrical power and propulsion systems will also require improved modeling and analytic tools and advanced algorithms to model effects and interactions among systems and material characteristics in this highly complex environment. Detailed system modeling tools must reflect integrated power-system control and transient response as well as modeling local components. It is vital to understand how electromagnetic parameters scale differently from either hydrodynamic characteristics or
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thermal parameters; scaling the electric propulsion system is a challenging task, but there is a shortage of empirical data to support this type of modeling, and the database must be more robust if development costs for full-scale electric propulsion systems are to be contained. PROJECTED LIGHTWEIGHT ARMOR AREAL DENSITY GOALS Table D-3 presents projected areal density (AD) goals for lightweight body armor and transparent armor in the period 2000-2030. The main body of this report contains additional information. DOD RELIANCE ON ENERGY SOURCES National energy dependence, particularly reliance on energy imports, has been the subject of considerable policy discussion for many years and national energy source and consumption trends continue to be discussed, debated, and addressed at the highest levels in this country because of their implications for national security. While this is not strictly a materials issue, the committee agreed that a brief discussion of total DoD energy usage, dependence on various sources, and energy dependence through 2020 was desirable. This section examines the major energy sources: fossil fuels and nuclear energy. TABLE D-3 Goals for Future Armor Areal Density Areal Density (lb/ft2) Armor Type Threat Present Projected, 2010–2015 Projected, 2020–2030 Fabric torso protection Fragments 1.38 1 0.75 Rigid fabric helmet Fragment 2.12 1.7 1.5 Rigid fabric/composite torso 0.30-caliber ball 6.1 3.5-4.5 <3.5 Torso 0.30 AP 6.5-7.5 <5 <3.5 Transparent 0.30 AP 23-33 <10.5 <8 (glass/polymer) (ceramic/polymer) (ceramic/polymer) SOURCE: S. Wax, DARPA, personal communication; J. Ward and P. Cunniff, Soldier Systems Center, Natick, personal communication; Cunniff (1999a,b); and DARPA (1998).
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Dependence on Fossil Fuel In FY97 total U.S. energy consumption from all sources was 94.21 quads (1 quad = 1 × 1015 British thermal units [BTUs]). For that year, total federal government usage of energy was 1.53 quads. DoD used 1.13 quads in fossil fuel energy, approximately 1.2 percent of the U.S. total (DOE, 1999)—down from 1995, when DoD energy usage was 1.4 percent (1.19 quads) of the U.S. total of 87.3 quads (DOE, 1997). Of the DoD total for FY97, 58 percent (approx. 0.65 quads) was used for actual support of military operations and training, with the remainder used for buildings and nontactical vehicles. Major energy sources were traditional fuels for military platforms (e.g., jet fuel, diesel) and natural gas and electric power supplied by a variety of land-based systems for fixed installations. No matter how it is calculated, it is clear that DoD energy usage to support the warfighter and military platforms is a very small percentage of total U.S. energy consumption. In addition, during a major crisis national security needs will be given priority, and DoD should have access to whatever energy is needed to assure continuity of its operations. While it is therefore likely that sufficient energy will be available to the DoD in future crises, a question remains about the form in which that energy would be supplied. In particular, will DoD energy consumption patterns change between now and 2020 and, if so, how? First, 42 percent of DoD’s energy consumption today is supplied to buildings, other fixed assets, and nontactical vehicles. Most of these installations are located within this country, and the energy sources supplying their needs are likely to be those supplying energy to other U.S. infrastructure. The current strong push within the government to reduce energy consumption per square foot by using high-efficiency energy systems and smart technology is expected to continue. At the same time, there is a push to reduce the number of installations by consolidation; this should reduce energy consumption for DoD-owned real property and buildings. Increased efficiency in use, transmission, storage, and production, combined with reduced demand and more efficient systems, offer considerable potential for reduction in this DoD sector. The other 58 percent of DoD energy consumption is used to power military platforms for operations and for training (the latter being a major contributor to energy consumption, as it is present during peacetime as well as war). There is a continuing push here, too, for enhanced fuel efficiency for many reasons. A recent report of the Defense Science Board
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(2001) examined DoD fuel reliance and found that greater fuel efficiency could lead to many benefits, among them enhanced platform stealth, reduced logistics tail, reduced vulnerability of supply lines, and an ability to build up forces faster. As an example, one goal of the Army transformation is to field a future combat system that is lighter weight, more mobile, and more fuel-efficient, because fuel today accounts for 70 percent of the Army tonnage that must be shipped. There are several ways to reduce DoD fossil energy dependence. More use of alternative energy sources is one. Nuclear and solar power both have potential for certain DoD applications, and geothermal may have some naval applications. Wind and hydropower are unlikely to provide primary power for major platforms. Novel materials can affect many of these modes and may reduce DoD energy consumption through more efficient propulsion technologies; lightweight, high-specific-stiffness and strength structures; vehicle armor approaches that do not rely solely on areal density for protection but use lighter materials and novel protection schemes to reduce weight; higher-energy-density batteries, and fuel cells capable of direct electrochemical conversion; improved fuels; and smart electronics that use energy more effectively. Higher efficiency energy-harvesting materials and devices (e.g., PV conversion) might also augment available energy in specific circumstances. The full panel report (Chapter 4) discussed the reliance on logistic fuels. It was concluded that both jet fuel and diesel would still be required by 2020, augmented perhaps by methanol, hydrogen (reformed from logistic fuels or otherwise manufactured), and possibly other hydrocarbons. That conclusion is discussed in the fuel cell section of the chapter. In summary, DoD fossil fuel energy consumption currently represents only a small fraction of total U.S. energy consumption. Because of the systems and infrastructure already in place, it is likely that major energy sources currently used will still be of primary importance in 2020. In particular, fossil fuels will remain crucial to the majority of land and aerospace propulsion applications. While DoD energy sources are likely to reflect those used by society at large, the gradual introduction of new materials, systems, and capabilities and more efficient technology will improve energy usage. In the case of fuel cells, there is likely to be a gradual shift toward alternative fuels by 2020. On the whole, however, it is likely that current fuels (JP-8, diesel, and nuclear) will still make up the bulk of energy sources used by DoD systems in 2020.
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Dependence on Nuclear Energy Within the DoD, the Navy has been the primary user of nuclear power. The decades of nuclear power effectiveness that emerged from the early days of Adm. Rickover’s Nautilus program have been impressive. In 1986 the U.S. Navy was operating or building 6 aircraft carriers, 9 cruisers, 39 ballistic missile submarines, and 97 attack submarines, all with nuclear propulsion plants, without any major incidences or measurable release of contamination. Removing warship reliance on fossil fuel provides a significant military advantage. America’s military commitments will continue to be worldwide. The ability of our nation’s foremost projectors of power, the nuclear aircraft carriers, to transit to any location in the world at sustained flank speed is currently hindered only by the fact that the support ships that must accompany them are conventionally powered. America’s nuclear-powered vessels are able to remain on station indefinitely, while the fossil-fueled vessels require significant infrastructure for fuel support. Over the past 30 years, much of the controversy over nuclear power has been focused on civilian nuclear facilities. High-visibility accidents that released radioactivity at Three Mile Island, Chernobyl, and recently in Japan have heightened public concern about the safety, environmental impact, and total cost associated with harnessing nuclear energy. This directly affects DoD strategy for further acquisition of nuclear-powered assets. Indeed, only the unique requirements of aircraft carriers and submarines justify the cost of incorporating nuclear propulsion plants today. However, the current revolution in warship propulsion system design combined with the evolving all-electric warship offer an opportunity for DoD to reevaluate its use of nuclear power as an energy source. Consider the following: Today the world’s energy comes from petroleum (~40 percent), coal (~25 percent), natural gas (~25 percent), hydroelectric (~5 percent), and nuclear (~5 percent). Well over 95 percent of the mobile power generated by DoD platforms (tanks, boats, ships, trucks/autos, aircraft) use petroleum. DoD mobile platforms rely predominantly on fuel oil from sources that the United States does not control. Because even the most efficient fossil fuel engines consume their own weight in fuel within half a day, fuel storage determines overall
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systems weight, and fuel supply dominates logistics concerns. Over nearly 50 years, nuclear accidents have been few and the DoD track record on nuclear safety has been nearly flawless. Investment in nuclear power R&D is low compared with investment in oil, gas, wind, and photovoltaics, yet it has been estimated that, with sufficient investment, nuclear generation of electricity can be cheaper than generation by a combined-cycle gas plant. DoD’s strategic vision of an all-electric warship/combat vehicle highlights advantages of nuclear generation for (1) warfighting effectiveness, (2) reduced total ownership costs, and (3) increased survivability. Nuclear electric generators may significantly increase specific power output. A new generation of high-power-density nuclear power plants is possible but would require substantial R&D investment. Feasibility studies of thermonuclear-PV direct energy conversion being conducted at the Knoll’s Atomic Power Laboratory show the clear potential of this technology. As noted elsewhere in this report, fuel cells are considered a desirable energy source for future defense systems. The continuously renewable hydrogen used by fuel cells of the future could come from nuclear power plants (see the section above on fuel cells). Near-term refinement and deployment of fuel cell power plants, using the existing fossil-fuel delivery infrastructure would make possible long-term use of fuel cell power plants by all facets of DoD. Fusion reactors continue to show great promise. These reactors do not have the dangerous radioactive byproducts of the fission reactor, but they are technologically much more challenging. Dependence on liquid fossil fuels began in the last half of the 19th century and throughout the 20th mankind has relied on them heavily. However, their price stability and availability cannot be guaranteed in the 21st century. Diversification of DoD energy sources to use more nuclear power is strategically prudent as well as technically and economically justified. Advances in the materials used in electromagnetic machinery, such as high-field permanent magnets and high-temperature superconductors, present opportunities to increase electrical power density and efficiency. Some of the potential for materials developments in these areas is discussed elsewhere in this report. The Energy and Power Panel did not have the resources to fully investigate materials challenges in this area but believes that key DoD platforms are likely to require nuclear energy in 2020 and beyond, and the rationale for increased attention to nuclear power systems and associated materials for DoD platforms is sound.
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Technologies linked with advances in nuclear power that require further exploration include: Material technologies for motors and generators, such as superconducting magnets, cryogenic coolers, current collectors, high-field permanent magnets, liquid cooling, and active noise control; Materials with high thermal conductivities that are radioactively inert; Fusion reactor materials (likely to stretch beyond 2020); Materials and concepts for acceptable nuclear waste disposal and storage; Materials for very low harmonic motor controllers; Materials and designs for high-power-density and high-performance solid-state inverters and converters; and Electrical substitutes for systems and components that now rely on fluid transport for energy and actuation. REFERENCES Alchavan, J.A. 1998. The Chemistry of Explosives. Cambridge, UK: Royal Society of Chemistry Information Services. Clelland, I., R. Price, and J. Sarjeant. 2000. Advances in capacitor technology for modern power electronics . Pp. 145-148 in Proceeding of the 24th International Power Modulator Symposium, June, Norfolk, VA. Piscataway, NJ: IEEE. Cooper, P.W., and S.R. Kurowski. 1996. Introduction to the Technology of Explosives. New York: VCH Publishers. Cunniff, P.November, 1999a. Dimensionless parameters for optimization of textile-based body armor systems. Proceedings of the 18th International Symposium on Ballistics, San Antonio, TX. Lancaster, PA: Technomic. Cunniff P. November, 1999b, Assessment of small arms (ball round) body armor systems. Proceedings of the 18th International Symposium on Ballistics, San Antonio, TX. Lancaster, PA: Technomic. DARPA (Defense Advanced Research Projects Agency). 1998. DARPA/ARO/ARL Transparent Armor Materials Workshop Proceedings, November 16-17, 1998, Annapolis, MD. Defense Science Board, Task Force on Improving Fuel Efficiency of Weapons Platforms. January 2001. More capable warfighting through reduced fuel burden. Washington, DC: Office of the Under Secretary of Defense for Acquisition, Technology and Logistics. Available online at <www.acq.osd.mil/dsb/fuel.pdf>. Accessed April 21, 2002. DOE (Department of Energy). 1997. Annual Report to Congress on Federal Government Energy Management and Conservation Programs for Fiscal Year 1995, U.S. Department of Energy. DOE. 1999. Annual report to Congress on Federal Government Energy Management and Conservation Programs for Fiscal Year 1997, U.S. Department of Energy.
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