Meeting the Energy Needs of Future Warriors (2004)

Soldier power requirements are changing as fast as new electronics are being developed. In addition to soldier communications and computers, there are a myriad of other applications for the dismounted soldier of the future that will require portable energy, including such things as laser-designators, chemical-biological sensors, uniform ventilators, and exoskeletal enhancements.

This report assesses power/energy sources, low-power electronics, and power management technologies and provides recommendations on energy solutions for the future soldier. It also evaluates the progress that is being made toward countering increasing energy demands.

This chapter provides background information on soldier power/energy issues and the origin of the study. It presents the statement of task that was used to guide the study and the approach that was taken by the committee to complete its work. It reviews findings from other studies and workshops that are relevant to soldier power/energy issues and clarifies the characteristics of the regimes that are considered by the study.

Electronics are essential to the Army’s success on the battlefield. Computers, displays, radios, sensors, and other electronics applications are keys to soldier combat effectiveness. Energy to power soldier systems, while always important, must now be viewed on a par with the other critical logistics commodities—ammunition, fuel, food, and water.

Batteries are now the mainstay of soldier-portable electronics, but the acquisition, storage, distribution, and disposal of over a hundred different battery types introduces layers of logistics management and uncertainty and adds to the risks already inherent to combat. The intense demand for batteries during Operation Iraqi Freedom, for example, exceeded manufacturing capacity, and supplies would have been exhausted if combat operations in Iraq had lasted another 30 days (Fein, 2003).

In the early 1980s, the Army recognized that the practice of equipping dismounted soldiers with items of equipment developed discretely, without an integrated view of the overall impact on the soldier, was no longer acceptable. The concept of the soldier as a system evolved from this recognition and led to a prototype for the first Land Warrior (LW) system, which was described in a previous NRC report, Energy-Efficient Technologies for the Dismounted Soldier (NRC, 1997), 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. Night-vision and infrared sights extend the reach of personal weapons, computer displays provide maps and locations of friendly and enemy troops, communications send and receive information on prospective targets as well as available sources of fire beyond rifle range. Suitably equipped soldiers can relay details about local targets and bring to bear virtually unlimited firepower, a capability that would have been inconceivable as recently as the first Gulf War.

The needs for electronics that use less power and for improved power sources are further driven by the fact that the Army is undergoing a major battlefield communications revolution with the transition from platform-centric warfare to network-centric warfare. This new paradigm calls for the vast amounts of information available from many and various battlefield sensors (including the soldier as a sensor) to be sent directly to an overall battlefield network rather than just to another platform (soldier, vehicle, plane, tank,

etc.). The information is thus instantly available to all battlefield elements. This possible order-of-magnitude increase in information transfer, as well as the greater use of soldier-carried sensors, could easily increase the power needs of the future LW.

The LW ensemble for dismounted soldiers is designed to satisfy requirements for regular infantry, special operations forces (SOF), and Rangers, as well as airborne, air assault, and mechanized infantry. To account for different mission requirements, the Army is also developing separate ensembles for mounted soldiers, such as the Air Warrior system for helicopter crews.

But these capabilities come at a cost. Even without LW, the soldier’s physical load can exceed 100 pounds for certain missions. The weight of the ensemble may add 30 pounds or more, not counting extra batteries that might be needed to guarantee power for the mission.

The Objective Force Warrior-Advanced Technology Demonstration (OFW-ATD) program will integrate LW electronics using advanced concepts and demonstrate an OFW prototype in 2004.¹ Technologies and concepts demonstrated may then serve as the basis for a future generation of LW, referred to as the Land Warrior-Advanced Capability (LW-AC), to be fielded in 2007. Land Warrior-Stryker Interoperable (LW-SI) will be the first version of the LW ensemble fielded to an Army unit of soldiers. The LW acquisition program and the selection of a lead technology integrator (LTI) for the OFW-ATD in 2003 now provide the Army with an opportunity to make improvements on the design of LW from a system perspective. At least initially, the LTI focus is on relatively near-term technologies that can be used for LW-AC, but the intention is to provide a longer-term means for upgrading LW capabilities by the successive demonstration and insertion of new technology.

The Army Program Executive Office-Soldier (PEO), responsible for both the LW-SI and OFW-ATD programs, greatly assisted the study by providing access to the LTI as well as information on soldier power requirements and issues.

While batteries are clearly the best solution for many soldier applications, Army research has focused on technology alternatives that might reduce soldier dependence on batteries. The Army Research Laboratory/Army Communications Electronics Command (ARL/CECOM) workshop held in October 2002 reviewed known power/energy solutions and determined that there are multiple technology solutions depending on the specific technical requirements. The solutions most relevant to future Army applications reside in three separate regimes: 20-W average with 50-W peak; 100-W average with 200-W peak; and, 1- to 5-kW high-power-draw applications (Green et al., 2002).

The 2-day workshop recommended that the Army focus on developing specific power sources for the near to mid-term and the mid- to long term. The near- to mid-term focus should be on rechargeable/disposable batteries for short missions and battery-battery hybrids for long missions. The mid- to long-term focus should be on multiple-technology hybrid systems in which a “battery” is the key component.

In addition to the ARL/CECOM workshop, three studies were conducted to analyze aspects of the growing problem of soldier power/energy sufficiency. Along with the workshop, these studies provided points of departure for the committee’s work.

The NRC Committee on Electric Power for the Dismounted Soldier completed a study on soldier power in 1997 (NRC, 1997). The resulting report, Energy-Efficient Technologies for the Dismounted Soldier, assessed technologies in all areas and contained five overall conclusions:

• Lack of power will limit the combat effectiveness of dismounted soldiers.

• Both fueled power/energy systems and energy-efficient designs will be necessary to achieve energy sufficiency on the battlefield.

• Access to the commercial electronics world must be improved.

• 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.

The Army Science Board (ASB) completed a summer study The Objective Force Soldier/Soldier Team, in November 2001, which included several relevant findings on soldier power (ASB, 2001). The mission of the study’s panel on power was to identify, assess, and recommend advanced power system technologies for the soldier system of the future. The panel concluded that power management affords the highest payoff and is the critical technology for enabling increases in mission duration comparable to what has been achieved in commercial systems: 2× improvement would be achieved by careful implementation of software to manage existing subsystems (e.g., power on/off devices) and by

Army energy conservation and signature management; 5× to 10× improvements would be realized by considering power and power management in the design cycle.

The ASB study recommended a power source roadmap leading from enhanced disposable/rechargeable batteries in the near term (2004), to rechargeable batteries (better than 2× improvement in power management) in the mid-term (2007), to a hybrid power system (rechargeable battery with a wearable, refuelable, and disposable source) in the far term (2012).

The JASONs completed a study, Portable Energy for the Dismounted Soldier, for the Office of Defense Research and Engineering in 2003 (JASON, 2003). Among other things, its charter was to assess fuel cell technologies and to provide insights on whether alternative energy generation technologies would be more appropriate for investment. Findings included the following:

• Several technologies have legitimate potential, at 20 W for long missions, to significantly outperform existing battery packs. All such systems are hybrids with secondary batteries or electrochemical capacitors. Existing hybrid battery/battery systems can significantly reduce soldier battery pack mass (from 20 kg to 6 or 7 kg) for certain missions.

• Engineering considerations, as opposed to fundamental physical constraints, dictate the performance of fielded systems. The application space is unique to the military.

• PEM/H₂ fuel cells (with tankage for pressurized hydrogen gas) can provide significant improvement over current primary batteries. Direct methanol fuel cell (DMFC) systems look especially promising for this application, having demonstrated output energy densities from fuel 10 times greater than current batteries.

• Microdiesel engines producing 100 to 500 W seem well suited for rapid multibattery charging using JP-8. Engineering trade-offs become severe as overall system volume and mass decrease or as power capacity per unit increases.

The three studies and the ARL/CECOM workshop had different task statements (terms of reference) and varied significantly in depth. Each study effort included evaluations of some technologies to be used for soldier power, and more than one assessed the state of the art. The ARL/CECOM workshop was only 2 days long, but benefited from many of the findings of the studies.

Table 1-1 provides a quick overview of technologies that were considered in past study efforts. The committee used information in Appendix C of Energy-Efficient Technologies (NRC, 1997) and assessments of technology readiness documented in Appendix D of the present study as the bases for its findings in this report.

The ARL/CECOM Energy and Power Workshop for the Soldier held on 15-17 October 2002 provided the foundation for this study effort. 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

approved a statement of task for a study to be implemented by the National Research Council Board on Army Science and Technology.

The Assistant Secretary of the Army (Acquisition, Logistics, and Technology) requested the National Research Council to determine suitable alternatives for powering future soldiers on the battlefield by accomplishing a study on portable power sources, power management, and low-power electronics technologies as follows:

1. Expand upon the conclusions from the ARL/CECOM Energy and Power Workshop for the Soldier, held on 15-17 October 2002, through the specification of both impact and feasibility of incorporating power management components, techniques and procedures for powering low-power electronic devices. The specific regimes from the workshop were: 20-watt average with 50-watt peak and 100-watt average with a 200-watt peak for up to 72-hour missions. Address power for high-power draw applications such as exoskeleton applications (1-5 kW average).

2. Assess electric power technologies to support soldier applications associated with future power and energy demands on the battlefield, e.g. expected OFW operational capabilities for the 2005-2025 timeframe, with emphasis on alternative compact high-power and energy-dense sources, power management and distribution techniques, and low-power electronics such as asynchronous microchips, smart dust, etc. Assess technical risks and feasibility associated with each of the technologies and make recommendations pertaining to their potential efficacy and utility within the context of future OFW operational capabilities. Consider risks associated with technology development, integration of hybrid generators and sources, adaptation of commercial technologies, and battlefield logistics. Systems concepts involving appropriate power sources, power management and low-power electronics are to be specified and delineated.

3. Update the technologies evaluated in the 1997 NRC report on Energy-Efficient Technologies for the Dismounted Soldier including changes in individual technology development trends. Determine advantages and disadvantages for appropriate technologies in prospective application areas. Develop standard measures to facilitate comparison.

4. Prepare a consensus report documenting the study results and containing findings and recommendations to assist the Army in its development program. Prioritize the energy source alternatives appropriate to each application. Propose S&T objectives leading to the future incorporation in the Objective Force Warrior program. The report will include:

   1. Recommendations for examined technologies with high benefit for target regimes with detailed justification for technology selection or rejection.

   2. Recommendations for power distribution techniques for soldier systems. Applicability of low-power electronics, such as asynchronous microchips, smart dust, etc., to soldier device loads.

   3. Recommendations for centralized vs. distributed power management for soldier systems including software/hardware techniques for control and conversion.

   4. Applicability of examined technologies to single type sources vs. hybrid sources considering logistics, versatility, utility, environmental factors, safety, reliability, logistic infrastructure, manufacturability and availability.

   5. Recommendation for recharging from soldier carried sources, robots (or vehicle) or fixed platforms.

   6. Recommendations for predictive models and modeling techniques that would elucidate power use and management.

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.

The chair determined that to accomplish its primary task, the study should rely on the expertise of the members to make realistic assessments of the possible solutions in each of the regimes and to focus on technologies that can enable systems within the near, medium, and far terms. Technologies that can enable viable power/energy systems were then compared and ranked. The assessments also provided the basis for identifying suitable Army research objectives.

The committee evaluated Army progress toward resolving soldier power issues by reviewing the LW-SI acquisition program and the OFW-ATD. It received briefings on anticipated soldier applications in the higher power regimes from both the Army and the Defense Advanced Research Projects Agency (DARPA).

The committee assessed advances in low-power electronics and investigated applicable areas of power distribution and management. It updated earlier assessments of trends in commercial electronics contained in NRC (1997) and developed future warrior design concepts. It then reached consensus on its specific recommendations for the Army.

This report documents the study findings and recommendations and is organized in accord with the task statement and the study approach described above. The report is organized in chapters as follows.

Chapter 1 (Introduction) provides background information and the statement of task for the study. Chapter 2 (Technology Alternatives) describes the most realistic power/energy technology solutions in each of the three regimes of prime concern for present and future Army applications. Chapter 3 (Power System Design) discusses guidelines for the efficient integration of power source technology. Chapter 4 (Soldier Energy Sinks) discusses the range of power demands of soldier applications and the key role played by logistics in determining the viability of energy solutions.

Chapter 5 (Progress) summarizes committee observations on the progress made by the Army since the 1997 NRC study report and on recent commercial trends in technology. 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. Chapter 7 (Recommendations) summarizes the findings and presents the study recommendations. Appendix C (Measures of Performance) describes the methods used to classify the power sources and provides means for evaluating new power sources. Finally, Appendix D (Source Technologies) describes the characteristics of the power sources considered and reports on advances in technology since Energy Efficient Technologies (NRC, 1997).