Energy-Efficient Technologies for the Dismounted Soldier (1997)

The Committee on Electric Power for the Dismounted Soldier, under the auspices of the Board on Army Science and Technology of the National Research Council, examined the power requirements of the dismounted soldier in both the near- to mid-term (to 2015) and the longer term (to 2025). In the process, the committee reviewed both energy supplying technologies such as batteries and fueled systems, and energy-consuming technologies such as communications, sensors, and computers. In each of these areas, the committee assessed the potential for commercial technology to meet the Army's needs and tried to determine what it would take for the Army to take full advantage of commercial technology.

The Army Land Warrior system, which includes a computer/radio subsystem, an integrated helmet assembly subsystem, and a weapons subsystem, is being developed to increase the effectiveness of the dismounted soldier on the battlefield. The system is integrated by a general-purpose computer similar to a laptop personal computer and consists of radios, display systems, sensors, and other electronics (shown in Figure ES-1). In the field, the Land Warrior system is expected to weigh approximately 40 pounds and draw more than 50 W of electricity with all subsystems operating. Land Warrior will be used by all members of an infantry squad, the basic Army combat unit.

The first Land Warrior units are scheduled to be fielded in 1999. The Army expects to have 34,000 in service by the year 2003. Because the complete ensemble will include all of the electronics that will require power for the dismounted soldier, the committee used the Land Warrior system as a baseline for analyzing near- and mid-term power requirements on the battlefield.

The Army Soldier System Command (SSCOM) is responsible for meeting requirements for the "soldier as a system." The SSCOM Project Manager-Soldier, at Fort Belvoir, Virginia, is responsible for coordinating the engineering and manufacturing development of the Land Warrior system with a program for the

insertion of new technology, under the direction of the Natick Research, Development and Engineering Center in Natick, Massachusetts. Advanced concept technology demonstrations and advanced warfighting experiments involving new power sources and electronics, many of them developed by the Army Communications-Electronics Command, are being conducted in tandem with the Land Warrior program to help finalize the system design.

Ongoing ''digitization" experiments to incorporate information technologies are helping to bring the power requirements for dismounted soldier systems into focus. Electronics being developed to enhance command and control, survivability, lethality, mobility, and sustainment will increase the demand for energy on the battlefield into the Army After Next time frame (to 2025). The dismounted soldier, in both the near- and far-term, will require a combination of energy sources and electronic systems that will extend the range and duration of operations, enable substantial reductions in weight and bulk, and minimize the soldier's vulnerability to detection by the enemy.

The committee was organized into panels representing the four general technology areas necessary for meeting the energy needs of the dismounted soldier: energy sources and systems; low power electronics and design; communications, computers, sensors, and displays; and networks, protocols, and operations. After assessing the technologies in each area, the committee found that efforts to improve the efficient use of energy are likely to be substantially more successful than efforts to increase the supply of energy.

Of the compact energy supply systems the committee considered, rechargeable batteries and fuel cells, the principle energy sources today, are likely to continue to be used for the foreseeable future. The initial Land Warrior systems will be powered by nonrechargeable, Army-standard batteries with specific energy of 150 Wh/kg. In the near future, lithium rechargeable batteries will approach 200 Wh/kg and will have longer lifetimes than today's rechargeable batteries. For missions beyond the capacity of batteries, small fuel cell systems that exploit the higher specific energies of liquid and gaseous fuels will be used as battery chargers. These systems weigh as little as 2.5 kg (including fuel and intermediate storage battery).

Other technologies with high potential for future soldier energy systems include thermophotovoltaic (TPV) systems, alkaline-metal thermal-to-electric converters (AMTEC), microturbines, and human-power systems. The Army's immediate goal should be to develop a hybrid system consisting of a fueled primary source and a rechargeable battery for intermediate storage.

The Semiconductor Industries Association National Technology Roadmap for Semiconductors, a guideline updated every three years, has charted dramatic increases in the number of transistors per chip by as much as 8 orders of magnitude (10⁸, or a factor of 100,000,000) compared with 1960. Since 1960, the semiconductor industry—with the help of federal funding for research and development—has cut the feature size of integrated circuits in half every six years and is expected to continue at that pace until at least 2005. The primary industry goal has been to enable vastly more complex "systems on a chip," and this has led the industry to search for ways to reduce energy dissipation by adopting lower voltage standards for operation and reducing or eliminating interconnections.

The resulting energy-efficient technologies have increased the capabilities and reduced the weight of electronics systems. New computer-aided design tools that minimize power complement the advances in low power electronics. For example, a basic application-specific integrated circuit design can be implemented in a high level design language, and the design can simply be recompiled periodically in the latest circuit technology. Also, low power software can be specifically coded to minimize energy consumption.

Commercial developers have learned that they can meet stringent military requirements, such as reduced bulk, weight, and cost, by actively pursuing more energy-efficient systems. Consumer products, such as cellular phones, pagers, and personal digital assistants, have a strong focus on energy efficiency and provide functional capabilities comparable, and in many cases superior to, those likely to be developed or adapted by the Army.

With all subsystems operating simultaneously, the Land Warrior radios, computer, displays, and sensors are estimated to have a total power requirement of more than 50 W. The committee determined that a notional system of comparable functions based on available commercial technologies could be built before 2001 with a total system power requirement of less than 4 W. This order-of-magnitude difference would not involve breakthroughs in technology but would require the Army to focus on energy efficiency as a primary design goal.

The Land Warrior system architecture is handicapped by relying on a single general-purpose computer to perform computational, signal processing, and radio interface tasks. The soldier computer would be in continuous operation with estimated power requirements of 15 W. Following the commercial trend of using low power, dedicated, special-purpose processors in the radios, sensors, and other subsystems and using state of the art fabrication technology would cut the computer operating power requirement to 100 mW. Power requirements for computing are expected to decline rapidly in the coming decades, and the committee estimates that a computer with substantially greater functionality,

including a voice-recognition interface, would require only 1 mW by the year 2015.

Transmitters in the soldier and squad radios present the greatest challenge to energy saving because the energy needed to transmit a bit is set by physical limits. The power requirements increase rapidly with distance, yet future operations doctrine will increase the distances involved in squad operations and increase bandwidth and data rate requirements. Thus although the energy costs of computing, sensing, and displaying are likely to decline rapidly, the energy for wireless transmissions will increase and eventually dominate the energy demand of the dismounted soldier systems.

Systems considerations, including the design and operation of network architectures and data communication protocols, can substantially reduce the power requirements for battlefield communications. Savings can also be achieved by reducing the time that subsystems are in standby mode "listening" for relatively infrequent stimuli. Computers and radios could be placed in "sleep mode" with technology similar to that of cellular telephones and pagers.

Using a peer-to-peer architecture, the radio network could be optimized to distribute communications and computing tasks among network terminals. Energy use could be concentrated in a designated master terminal to minimize the power required by the network as a whole. The master terminal would synchronize all of the soldier terminals, so that each terminal would only have to wake up for 1 millisecond of every 20 to 100 milliseconds to check for traffic and could sleep in the intervals.

A "multihop" architecture (using intermediate signal repeaters to transmit information between widely separated terminals) would lower energy consumption by reducing transmission ranges. The algorithms are complex, but they are already being investigated under Defense Advanced Research Products Agency (DARPA) sponsorship. As the energy cost of computing declines, trade-offs between computing and communications capabilities could be made to improve the energy efficiency of dismounted soldier systems.

Terrestrial wireless communications could be supplemented by other means, such as emerging multisatellite systems, which would give soldiers access to a global network in addition to the high-bandwidth soldier network. Direct broadcast satellite technology might also be adapted.

The Land Warrior system will fall short of the vision of the digitized battlefield because of excessive power requirements for computation and radio transmission. The program is on a course to field subsystems that, by and large,

are heavier, bulkier, and less functional than comparable systems that could be built using commercial consumer technologies. Over time, as commercial products continue to improve and possess capabilities that the Army is unable to field for itself, a crisis of major proportions will emerge. Energy availability may actually increase, but the Army will be unable to use the available energy-efficiently to achieve either its current objectives or future objectives for dismounted soldier operations.

This crisis has two components. The first involves the realization of current goals, such as battlefield digitization, and the relationship of these goals to the electrical energy used by the dismounted soldier. Unless a dramatic shift is made in the design of the soldier system and in the associated doctrine, the amount of energy storage required will preclude soldier mobility, even with expected advances in energy source technologies.

Second, unless the Army is able to exploit and track commercial technology in Army-specific designs, potential adversaries will be able to acquire capabilities superior to those available to the Army from commercial sources. Even more troublesome is that the Army will have to do more than catch up with and match commercial technologies. The Army's equipment must have a competitive edge over the equipment of potential adversaries.

Advanced energy concepts can only be realized if the Army focuses on energy use, just as successful commercial developers have. The Army will have to make three essential paradigm shifts:

• Energy strategy. The Army must focus on energy-consuming systems as well as energy source systems.

• System design. The Army must use a design approach that optimizes for energy use at all levels of the system design.

• Use of commercial technology. The Army must capitalize on advances in energy-efficient consumer electronics by using open system designs to simplify the incorporation and use of commercial data-processing and communications technology.

Research objectives aimed at meeting Army power requirements are listed in Table ES-1. The committee determined that three of these are essential to the combat effectiveness of the future dismounted soldier and offer the highest potential to influence Army After Next capabilities:

• development of a wireless communications network architecture for the battlefield that directly exploits commercial technology

• development of modeling and simulation capabilities to gauge the energy use of dismounted soldier systems

• continuation of active research to develop advanced fueled systems

Conclusion 1. The power requirements of the Land Warrior system will limit the effectiveness of dismounted soldiers on the digitized battlefield.

This study has shown that the Land Warrior system is far less energy efficient than it could be. It will fall short of meeting the needs of the digitized battlefield principally because of excessive energy demands for computation and radio transmission. The Land Warrior program is on a course to field subsystems

that are heavier, bulkier, and less functional than they would be using state of the art consumer technology. This is because the Army has failed to address energy efficiency in system and subsystem designs. The Land Warrior program provides for the incorporation of advanced technology, but the scope of necessary enhancements will require special funding and command emphasis by the Army.

Commercial equipment is available with the energy efficiencies the dismounted soldier needs. The Army cannot continue to rely primarily on improvements in energy storage, which only mask equipment inefficiencies. A coherent approach to prevent the problem from growing to crisis proportions will require concerted efforts by both the Army Acquisition Executive and the Army Materiel Command.

Recommendation 1a. Army leadership must emphasize the importance of reducing energy demand to achieve energy sufficiency for future dismounted soldiers. Meeting near- and far-term needs will require major changes in Army thinking. Paradigm shifts in energy strategy, system design, and the use of commercial technology are absolutely essential to avert a crisis. The new paradigms must be translated into top-down initiatives.

Recommendation 1b. The Army should accelerate the development and insertion of enhancements to the Land Warrior system, focusing on improvements to the computer/radio subsystem because the estimated power requirements for communications and computing functions in Land Warrior are clearly excessive.

Recommendation 1c. The Army Acquisition Executive should make energy efficiency a priority consideration in evaluating contractor performance in future procurements of electronics for the dismounted soldier.

Conclusion 2. Advanced fueled systems and energy-efficient technologies are both necessary to achieve energy sufficiency for soldiers in the Army After Next time frame.

Dramatic improvements in the energy efficiency of systems for the dismounted soldier are already available as a result of advances in low power electronics and commercial consumer technologies. Reducing energy consumption will mean that available energy sources will be able to support longer missions using smaller and lighter energy sources and that new functions can be added to increase the soldier's capabilities. Paying attention to energy consumption through equipment design, as well as increased awareness and enforcement of power discipline, will also yield ancillary benefits, including lighter components, reduced susceptibility to detection, lower cooling requirements, and simplified logistical support. These dramatic improvements, combined with limited increases in the specific energy of sources and improved storage capabilities afforded by

advanced fueled sources, will make energy sufficiency possible for dismounted soldiers in the Army After Next even for the most problematic requirement, microclimate cooling.

Recommendation 2a. To achieve energy sufficiency, the Army should set research objectives that focus on energy-efficient technologies. Energy efficiency is the key to success for the Army After Next.

Recommendation 2b. The Army should support use of computer-aided design tools for systems and integrated circuits specifically optimized for low power performance. If the necessary design tools are not available commercially, the Army should support its own development programs, perhaps in conjunction with related DARPA efforts. Army contractors for electronic systems should be required to use energy-optimizing design tools.

Recommendation 2c. The Army should support the development of mission-specific software for dismounted soldier systems. General-purpose software is wasteful and not energy-efficient.

Recommendation 2d. The Army should support the development and use of low power software, in which each instruction is written or compiled to minimize power requirements. New tools may be required for specific military applications.

Recommendation 2e. The Army should use dedicated electronic circuits wherever possible to minimize power requirements. Application-specific integrated circuit (ASIC) technology can achieve the efficiencies of custom circuits and hardware and still be cost effective.

Recommendation 2f. The Army should establish and enforce standards of awareness and discipline for energy consumption in dismounted soldier operations.

Conclusion 3. Access to commercial technology must be improved.

The Army will not be able to meet the goal of digitizing the battlefield unless it improves its ability to adapt and benefit from commercial consumer technology. Subsystems in the Land Warrior system, for example, will be obsolete compared with commercially available consumer electronics before the system is fielded. Military radios that meet the strict definition of commercial off-the-shelf equipment in most cases are not built to the same energy efficiency standards as consumer electronics. The fact that Army developers or suppliers of military electronics also develop, produce, and market consumer electronics is no guarantee that advances in consumer electronics will be carried over into military systems. The committee found that the consumer and military business units of

large corporations are substantially and deliberately isolated from each other and that technology used in military systems sometimes lags substantially behind the technology in consumer systems produced by the same company.

The Army, through the science and technology insertion component of the Land Warrior program, recognizes the need to build flexibility into the process for acquiring advanced technology. Institutional provisions for experimentation, such as the Advanced Warfighting Experiment at Fort Hood, and spiral developments providing for continuous design feedback, can accelerate the incorporation of applicable technologies.

Recommendation 3a. Army procurement strategy should include provisions for keeping pace with advances in the semiconductor industry. Even if it is fielded in increments, state of the art technology should be fielded in small quantities so that systems can be upgraded frequently. In addition to requiring energy-efficient technologies, Army design and procurement contracts should require contractors to adopt improved technology automatically as it becomes available.

Recommendation 3b. The Army should support efforts to maintain the pace set by the National Technology Roadmap for Semiconductors. The road map is a key means of ensuring continued superiority in electronics technology by defining critical technology areas and research gaps that may stand in the way of needed breakthroughs. The Army should:

• Use the road map to project technology availability in specifying new systems.

• Support research and development in industry and universities in areas identified as critical in the road map.

• Contribute to the road map, either directly through U.S. Department of Defense representation on the road map committee, or indirectly, through other members, such as representatives of the national laboratories.  

Recommendation 3c. The Army should develop an effective strategy for keeping abreast of state of the art consumer product development and for specifying low power performance criteria in its solicitations. The Army should emphasize participation in consumer-oriented electronics industry activities that focus on low power electronics, such as conferences, symposia, and focus centers, as a way of raising awareness and expectations of energy-efficient performance. Only through participation can the Army keep abreast of technology development and, more important, influence industry priorities.

Recommendation 3d. The Army must experiment continuously to keep pace with the development of commercial equipment. Simulations should be used to determine the value of trade-offs between improvements in energy consumption and less essential equipment characteristics.

Conclusion 4. Wireless transmission will dominate energy demand in future dismounted soldier systems.

If the Army can take advantage of trends in commercial consumer electronics, the power requirements of computers, sensors, and displays for the dismounted soldier will fall to nearly negligible levels. Subsystems that perform these functions could consume less than 1 W of electricity by the year 2015. Energy needed for radio transmission will then dominate the power requirements for successor Land Warrior systems.

Recommendation 4a. The Army should refine its requirements for high-resolution images and video communications to the minimum necessary to meet battlefield needs.

Recommendations 4b. The Army should minimize wireless data transmission by reducing the time required to convey a given amount of information. Relevant technologies include speech and image compression, database caching, and information science technologies that reduce, eliminate, or automate the energy inefficient natural language (read message) transmissions that are currently used.

Recommendation 4c. The Army should adapt the hierarchical network architecture of cellular telephones to create a "virtual peer-to-peer" network, which would improve the distribution of computational resources while taking advantage of commercial cellular technologies.

Recommendation 4d. The Army should modify and synchronize operational doctrine with emerging systems to minimize soldier transmissions. For example, data collection and reduction should be performed as close to the data collector as possible, and computational components should be distributed across the network of soldier communicators. The Army should exploit energy saving communications protocols, such as the protocols used to alert radio receivers to incoming data in pagers and cellular phones. Other commercial techniques should be incorporated doctrinally to reduce or eliminate the operational demands on transmit energy.

Recommendation 4e. The Army should study alternatives for the military network design to optimize power consumption. For example, it should investigate the use of commercial low-orbit satellite systems and unmanned aerial vehicles as relatively energy-efficient alternatives that may also provide high-bandwidth capabilities.

Conclusion 5. Research to improve energy source must continue.

Improved energy sources, with higher specific energies and better performance characteristics, will be important to the dismounted soldier because the

proliferation of new electronics-based systems will continue. Unlike commercial investments in microelectronics and communications technologies, commercial investments in power sources and systems technologies will probably not be sufficient because the military market is small. Therefore, military research and development will still be needed.

In the near term, the dismounted soldier must rely on both nonrechargeable and chargeable batteries for power. But batteries will not suffice for missions that require more than a kilowatt-hour (about 20 hours using the initial Land Warrior system). For high energy (long mission time) requirements, fueled systems (generally, combinations of rechargeable batteries or capacitors charged by fuel cells or other fueled energy sources) can offer specific energy an order of magnitude higher than the best battery at relatively small development risk. Hybrid systems will make it possible to optimize performance for both high power and high energy requirements.

Recommendation 5a. For the near term, the Army should continue to support research and development on rechargeable batteries with specific energy higher than 200 watt hours per kilogram.

Recommendation 5b. The Army should continue research into fueled energy sources and high-performance capacitors for use in hybrid energy supply systems for the dismounted soldier. It should develop prototypes of the most promising ones for field trials within the next decade.

Recommendation 5c. The Army should continue research for the far future across a broad range of technologies, including advanced fuel cells, microturbines, and thermophotovoltaic converters.

Doney, M. 1996. Land Warrior System. Briefing by Michael Doney, U.S. Army, Project Manager-Soldier, to the Committee on Electric Power for the Dismounted Soldier, Washington, D.C. August 15, 1996.