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The concept of the soldier as a system led to a prototype of the first Land Warrior (LW) system, which combined electronics, weapons, and power sources in a single ensemble.
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The 100-W regime included niche applications such as high-demand laser target designators and future microclimate cooling capabilities. Finally, the 1- to 5-kW regime was assumed to include the most power-intensive capabilities, such as portable power generators, rechargers for rechargeable batteries, and future exoskeleton devices.
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. 100 W average power Develop smart hybrid systems with small engines and fuel cells.
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Like metal/air batteries, fuel cells are air-breathing devices that cannot operate when submerged in water. Future acceptance of fuel cells on the battlefield will be determined to a great degree by logistics, because current prototypes are fueled by the nonstandard logistics fuels (methanol and hydrogen)
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Recommendation 8b: For the 1- to 5-kW regime, the Army should develop the ability to process standard logistics fuels as needed for emerging high-specific-power PEM and solid oxide fuel cells. LAND WARRIOR SYSTEM Correctly matching power source technologies (sources)
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Since 1997, the energy efficiency of circuits has improved by at least a factor of five. By one measure, this improvement in reducing power demand is greater than the improvement in rechargeable batteries, since time between recharges has increased only 20 percent.
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Concepts for powering the reduced needs of future soldiers should take advantage of likely reductions in the scale and distribution of power demand and consider options such as energy-harvesting to provide reliable power sources at such low power levels. Recommendation 11: The Army should aim for a future soldier system capable of no more than 2-W average power, 5-W peak power.
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Ideally, the military should develop and acquire new equipment only on the basis of such models, so that the lifetime of the equipment can be maximized. Recommendation 12: The Army should develop a modeling capability for soldier equipment that includes power sources and also enables detailed simulation, verification, and analysis of power requirements for given operational parameters.
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, which will be referred to throughout this report as Energy-Efficient Technologies. Dismounted soldiers act as both sensors and shooters, and the Land Warrior suite of electronics is intended to improve combat effectiveness by giving them increased situational awareness.
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Power for wireless transmissions will dominate energy demand. Research should be conducted in multiple areas: including advanced fuel cells, microturbines, and thermophotovoltaic converters, for the far future.
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It described many of the relevant applications of soldier electronics and categorized energy demand in distinct regimes. As a result of the workshop, the Army TABLE 1-1 Consideration of Relevant Technologies by Previous Studies, the Workshop, and the Present Study Technology NRC 1997 Study ASB Study JASONs Study ARL/CECOM Workshop Present Study Primary battery C C C C C Rechargeable battery C C C C C Fuel cells (hydrogen)
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STUDY APPROACH The statement of task contained multiple tasks requiring specific areas of expertise to ensure their accomplishment. As a result, committee members were selected who had expertise in the relevant technologies, including primary and rechargeable batteries, fuel cells, electrochemical devices and systems, small engines, hybrid systems, and low-power electronics and design, as well as in military logistics and operations.
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Chapter 6 (Future Warrior Design Concepts) discusses promising approaches to design and integration of future soldier systems, barriers to implementation of energy solutions for soldier systems, and the impact of user interaction on power demand.
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These assumptions enable power source options from the ARL/CECOM workshop to be compared with options and conclusions from the present study. The statement of task specifies average power requirements and periodic peak power requirements but not duty cycles.
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Meeting the Energy Needs of Future Warriors TABLE 2-1 Overview of All Power Source Alternatives Power System State of the Art, 1997a State of the Art, 2003 Item Considered Scaling Laws Impact on Soldier Power Primary battery (includes metal/air) Mature.
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POWER SOURCE SOLUTIONS Batteries represent the ideal solution for soldier power and energy applications. Only when every effort has been made to conserve and manage energy and it is found that batteries cannot meet requirements should air-breathing systems, such as fuel cells or small engines, be considered.
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There are three important issues that need to be addressed when making comparisons between figures of merit for the various power sources. The first is encountered when energy storage and energy conversion devices, e.g., batteries and fuel cells, are to be compared.
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The y intercept in the figure is the dry mass of the energy converter and the slope is the product of the energy content of the fuel and the system energy conversion efficiency. These issues are explained in detail in the earlier report (NRC, 1997)
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72 9.94 20 1,440 145 9 NOTES: Table is sorted by system mass. TRL, technology readiness level; JP-8, jet propellant 8; PEM, proton exchange membrane; SOA, state of the art; IC, internal combustion; DMFC, direct methanol fuel cell; LW, Land Warrior; SOFC, solid oxide fuel cell.
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Meeting the Energy Needs of Future Warriors FIGURE 2-2 24-hr mission at 20-W average power. FIGURE 2-3 72-hr mission at 20-W average power.
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Meeting the Energy Needs of Future Warriors FIGURE 2-4 24-hr mission at 100-W average power. FIGURE 2-5 72-hr mission at 100-W average power.
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. The solid oxide fuel cell (SOFC)
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Such prepackaged fuels will enhance the attractiveness of fueled energy conversion alternatives. Some energy conversion technologies in the 20-W power range may be capable of operating on bulk logistics fuels.
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. Develop smart hybrid systems with batteries and energy conversion power sources.
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The three near-term objectives are these: Develop smart hybrid systems with fuel cells and high-power batteries or electrochemical capacitors. Develop small fuel processors for logistics fuels, methanol, ammonia, and other viable fuels.
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Findings for the 1- to 5-kW Average Power Regime Fuel cells offer lower signatures than IC engines. Stirling engines offer potentially low thermal and acoustic signatures.
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The various sources of power have different characteristics, as depicted for fuel cells and batteries in Figure 3-2. This figure shows the variation in efficiency with power output for a typical rechargeable battery and a direct methanol fuel cell.
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Typical efficiency for DMFC and battery. SOURCE: Adapted from data from Ball Aerospace 20-W fuel cell.
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In Figure 3-4, point B and point C are loads with the same average power, 75 W/kg, but the battery delivers a much higher capacity for point B than for point C The reason for this is that the load of point B is a constant 75 W/kg, but the load of point C is an intermittent discharge with a peak power of 300 W/kg and a 25 percent duty cycle.
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tent discharges, the capacity at a continuous discharge of the peak power is a better estimate than the capacity at a continuous discharge of the average power. The typical power demand of mobile systems usually includes several periods of peak demand interspersed with potentially long periods of very low demand.
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Thus, for a hybrid power source involving Zn/air as one of the components, the low-temperature effect might necessitate a bigger Zn/air cell to achieve the same performance as at room temperature. HYBRID ANALYSIS FOR THE SOLDIER SYSTEM The component electronics of the soldier system will operate on duty cycles that vary significantly in power needs, so there are varying needs for high specific power and high specific energy.
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In the latter category fall (1) the battery + battery hybrid (an extremely high specific energy and low specific power battery such as the lithium/(CF)
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Safe at low specific energy and low discharge rates. At high specific energy and high discharge rates, units may explode or rupture, dispersing toxic chemicals.
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Meeting the Energy Needs of Future Warriors FIGURE 3-6 Soldier power demand for 20-W average, 50-W peak 10 percent of the time. Performance comparison for batteries alone, fuel cell alone, and hybrid battery + fuel cell.
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; fuel cells (with low energy output but high energy density related to their use of high-energy fuels) ; and engine-driven generators (with high outputs and high energy densities but problematic noise and heat signatures)
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The information gathered will be used to validate the models and provide realistic boundary conditions for total energy, average power, peak power, and duty cycles for various missions. The validated models should lead to more effective planning and designs.
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Meeting the Energy Needs of Future Warriors 4 Soldier Energy Sinks This chapter describes power demand characteristics of the electronics needed for soldier applications—the soldier power sinks. It discusses both low-power and high-power electronics applications (the latter include laser designators, microclimate cooling, and exoskeletons)
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Clearly, reducing power demand should be a major consideration in designing laser designators. The committee expects that the energy efficiency of such devices can be improved, but it did not know enough about such devices to recommend specific improvement techniques.
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Meeting the Energy Needs of Future Warriors on developing load-carrying devices that will increase the speed, endurance, and load-carrying capacity of soldiers in combat environments. This program, like the microclimate cooling efforts, is in its early development phase, and the committee did not analyze the relative merits of solutions on the drawing boards.
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If one reviews the capabilities of electrohydraulic and electromechanical FIGURE 4-2 Generalized Ragone plot of different power sources. Only engines have both the high specific energy and high specific power needed for exoskeletal devices.
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It considers such things as the weight carried by dismounted soldiers engaging in multiple operational scenarios; how to transport the batteries, energy-producing fuels, or other consumables to the soldiers when needed; and the costs of acquiring and supporting the energy sources appropriate to different power demands. Standardization Enhanced electronics equipment and weaponry make the dismounted infantry soldier a formidable fighter, but the logisticians who support the soldier must now add electric power to the other essentials—ammunition, food, and water—that must be supplied to the battlefield.
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This makes open architectures and versatile power sources desirable. In general, the electronics equipment and the power sources for the dismounted soldier should be engineered together as a system capable of performing with high reliability and human-factored to minimize interference with all conceivable postures and positioning.
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For example, it is likely that radios developed for dismounted soldiers and SOF will continue to have quite different designs and require separate development and testing. Industrial Base Issues Maintaining suppliers, particularly suppliers of special-purpose power sources that have no commercial counterparts, will require effort.
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Proceeding with the direct methanol fuel cells used in this example is yet another undertaking that demonstrates the dynamic tension between new technologies with increased capabilities and the logistics systems that must support soldiers in their use of the new capabilities in combat. Technologists are dissuaded from pursuing a promising new opportunity when they have little confidence that it will be incorporated into operational use.
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On the other hand, the attractiveness of a one fuel cell/one battery solution cannot be denied. One way to reap the benefits of both untethered subsystems and a master central power source is to colocate the batteries with the components that require relatively large amounts of power and energy.
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It involves a high specific energy/low specific power system for steady loads and a high specific power/low specific energy system for peak demands. Comparison of OFW Concepts with Land Warrior Peak power demand anticipated for the LW ensemble will not change appreciably under the initial OFW-ATD concept.
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Meeting the Energy Needs of Future Warriors TABLE 5-1 Comparison of Estimated Power Requirements of Land Warrior System, by Function (All Peak Power) Function Land Warrior, 1997a (W)
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It also supports continued research into advanced energy sources and is particularly interested in direct methanol fuel cells. Committee Observations on Initial OFW-ATD Concepts The assumption that future soldiers will be resupplied every 24 hr does not necessarily modify the goal of 72-hr self-sufficiency.
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Due consideration must be given not only to the various power sources and sinks, but also to designs for electronics integration and power management. The OFW LTI will propose systems for integration, but neither the LTI nor the Army PEO have enough influence over concurrent acquisition efforts to effectively reduce power demand in the main electronics subsystems.
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Recognizing and broadcasting over congested areas more evenly distributes power demand among all the nodes. Radio network simulations have been developed that accurately model radio power demand and these could be used to evaluate the energy efficiency of various protocols.
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Active Skim View for:
Meeting the Energy Needs of Future Warriors (2004) Pages 1-50