9

Findings, Conclusions, and Recommendations

OVERALL SUMMARY

The committee found many opportunities to enable a more capable Army within a very challenging and a somewhat uncertain future multi-domain environment. As in any study of multiple alternatives, there are some trade-offs. For example, if silent mobility and low thermal signatures are mandatory with an extended range, there may be a need to deploy a limited number of hydrogen proton exchange membrane (PEM) fuel cells, albeit with penalties in the number of convoy transport trucks. Some of these trade-offs for the major recommended technologies are summarized in the trade-off/decision matrix in Table 9.1.

CHAPTER 1—THE MULTI-DOMAIN OPERATIONS AND THE 2035 OPERATIONAL AND TECHNOLOGY ENVIRONMENT

Recommendation: For future studies, the Army should make available a clearer view of how multi-domain operations would be conducted, such as through detailed scenarios that describe science and technology needs for multi-domain operations in 2035.

CHAPTER 3—ENERGY SOURCES, CONVERSION DEVICES, AND STORAGE

Finding: Biodiesel may be a preferred fuel source during peacetime, given the growing need to address climate change. Certification for acceptability

TABLE 9.1 Decision/Trade-Off Matrix

of the various sources would be needed to ensure any reliability concerns are addressed. (Tier 1, Lead)

Finding: JP8, diesel, and/or biodiesel are all potential fuels to be supplied to the battlefield, particularly for high power–use applications such as armored ground combat vehicles. The complexity impact of using multiple fuels on the logistics chain needs to be compared to the benefits discussed. (Tier 1, Lead)

Conclusion: Alternative liquid hydrocarbon fuels are compositionally variable and may introduce new durability concerns and, in the case of ATJ fuels, may not provide the cetane ratings needed to run properly in internal combustion engines. Although alternative fuels may be suitable for use on an ad hoc basis during combat operations, their suitability as a more permanent staple of the fuel supply system will require a careful cost benefit analysis on a case-by-case basis over a variety of environmental conditions. (Tier 1, Follow)

Conclusion: A logistics distribution network for propane, natural gas, or hydrogen is unlikely to effectively replace hydrocarbon fuels on the battlefield because of their lower volumetric energy density (requiring more fuel transport trucks or convoys) and increased storage complexity versus JP8.

Conclusion: Generating hydrogen from water using aluminum near the point of use offers potential advantages vis-à-vis transporting hydrogen in a supply convoy. However, a number of critical questions remain, including definition of the complete process to be used for each application.

Recommendation: The Army should continue to explore the potential use of aluminum for onsite generation of hydrogen for use in proton exchange membrane fuel cells, not only for use in vehicles, but also for potential use in dismounted and base-camp applications. The latter may leverage ongoing Navy efforts. (Tier 2, Watch [U.S. Marine Corps and Office of Naval Research-led effort])

Conclusion: Given that fuel-cell technology may serve as a key enabling technology for near-silent operation, low thermal signature, and long-endurance UAVs/UGVs, combined with the prevalence of JP8 on the battlefield through 2035, the committee supports continued investment by the U.S. Army to fund the technology and economic analysis of the reformation process with diesel and JP8 fuels for use in SOFC power systems. (Tier 2, Lead)

Conclusion: Similar to the 2016 Defense Science Board report,¹ the committee concludes that solar, wind, and geothermal power sources present significant environmental benefits and are worthy of consideration for domestic and permanent overseas facilities. However, current and near-future iterations provide far less utility for mobile forces in multi-domain operations (MDO) and are unlikely to meet the power needs of a brigade combat team. As demonstrated in recent operations in Southwest Asia and elsewhere, such technologies can help reduce logistical requirements, especially in remote and dismounted operations. (Tier 1, Follow)

Finding: Battery technology will be a part of Army operations for the foreseeable future. However, traditional Li-ion batteries present certain limitations that will not meet all of the Army’s emerging needs. However, redesigning electrode structures as 3D architectures may permit greater performance with retention of battery-effective energy density and can improve the performance of both primary and rechargeable batteries.

Conclusion: Zn-based batteries, once moved to a new performance curve, may bypass the safety issues associated with Li-ion and the low-energy limitations of lead-acid while providing the following critical

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¹ M. Anastasio, P. Kern, F. Bowman, J. Edmunds, G. Galloway, W. Madia, and W. Schneider, 2016, “Task Force on Energy Systems for Forward/Remote Operating Bases,” Defense Science Board, Under Secretary of Defense for Acquisition, Technology, and Logistics, pp. 26–28, https://dsb.cto.mil/reports/2010s/Energy_Systems_for_Forward_Remote_Operating_Bases.pdf.

functions: (1) extended mission life for a given battery weight or volume; (2) platform simplification, because less balance-of-plant is required for safe, aqueous-based cell chemistry; and (3) simultaneous energy and power delivery from a single device. (Tier 2, Lead)

Recommendation: Since the Army and Navy have many of the same battery safety concerns, close cooperation between the two services is encouraged. For the Army, fast rechargeability is an important objective that enables expeditious tapping into the vast supply of electricity available from generators and microgrids, as well as unmanned and manned combat vehicles. (Tier 1, 2, Lead)

CHAPTER 4—SYSTEM-WIDE COMMUNICATION ISSUES IN SUPPORT OF MDO

Finding: 5G implementation on the battlefield offers significant bandwidth opportunities but presents some serious technical challenges, including P&E requirements on vehicles and for the dismounted soldier. 5G technologies should not be viewed as a “do it all” stand-alone solution but rather an opportunity to combine with other communications systems when appropriate.

Recommendation: To realize the benefits associated with a significant bandwidth increase, the Network Science Research Laboratory’s MANET (mobile ad hoc network) predictive model of network performance needs to be updated for 5G technologies and other emerging communication technologies (e.g., Internet of Things, 6G, and short-range, directed, and secure communications across a variety of devices) complemented with subsequent testing and field experimentation. (Tier 1, Lead)

CHAPTER 5—DISMOUNTED SOLDIER POWER AND LIGHT UAV/UGVS

Conclusion: The demands of the future operating environment (smaller formations supported by logistical and fire support) indicate that the Army’s power and energy (P&E) efforts should be focused less on heaviest power draw and more how P&E will support a distributed force structure.

Finding: Thermophotovoltaic processes represent a promising opportunity in support of the dismounted soldier, while an upsized version might prove attractive for other applications, such as unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs).² (Tier 2, Lead)

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² See Appendix I for a summary of possible technical challenges.

Finding: Extensive use of “mule vehicles” from the Army’s SMET program provides an opportunity to recharge soldier batteries on the battlefield while lightening their weight burden, carrying ammunition, fuel, and water as well as batteries. (Tier 1, Lead)

Conclusion: Further studies of dismounted soldier SOFC fuel cells utilizing propane, methanol, and other non-JP8 hydrocarbon fuels are not recommended beyond the work presently under way. This position might change under two scenarios. The first is that the field-implementable batch processing to desulfurize JP8 proves feasible to the 1 ppm level necessary for SOFCs. The second is that the point-of-use generation of hydrogen using activated aluminum or from hydrides such as alane (aluminum hydride) proves to be viable and practical, making possible the use of PEM fuel cells. (Tier 2, Watch)

Conclusion: The current level of study and development is appropriate to identify applications where a lightweight radioisotope decay system possibly coupled with a rechargeable battery could provide adequate power for present and future demands of the dismounted soldier. (Tier 2, Lead).

CHAPTER 6—VEHICLE POWER AND LARGE WEAPON SYSTEMS

Recommendation: The Army has undertaken a number of internal vehicle power plant programs (Advanced Powertrain Demonstrator, Projected Propulsion System, Advanced Mobility Experimental Prototype, and Platform Electrification Mobility) that will significantly enhance the Army’s operational capabilities in a multi-domain operations environment. The committee recommends that their funding and timing continue as presently planned.

Conclusion: The use of DF2 in lieu of JP8 could reduce the fuel supply line due to its higher energy density, which would decrease the number resupply missions required to sustain the operational units. Although this violates the Army’s present “single fuel policy” and will present some added logistics complexity challenges, further consideration by the Army is warranted. (Tier 1, Lead)

Recommendation: The Army should consider using closed-loop combustion control in all new engine designs as these engines, properly calibrated, could allow seamless operation between jet propellant 8 (JP8), diesel, and biodiesel while simultaneously increasing fuel efficiency while using JP8. (Tier 1, Lead)

Conclusion: It is possible with substantial changes to design an engine that can run gasoline or diesel fuel interchangeability, however, the operational advantages such a capability would provide are judged to be small.

Conclusion: Although technically possible, given the lower energy density of gaseous fuels and associated transport concerns, it is not recommended that mobile JP8/gaseous dual fuel engines be pursued.

Recommendation: Free-piston engine technology is a rapidly developing field that offers some significant efficiency benefits versus other internal combustion engine mechanisms. The committee anticipates further improvements in the future. It is highly recommended that the Army monitor progress in this technology, in particular keeping track of work at Toyota and SWEngin. (Tier 2, Watch)

Conclusion: Gas turbines continue to be the power pack of choice for most Army helicopters due to their power-to-weight advantages. On the other hand, diesel engines will continue to be the power pack of choice for most ground combat and tactical vehicles due to their fuel efficiency advantages. Continued monitoring of the Air Force Research Laboratory’s Advanced Turbine Technologies for Affordable Mission-Capability (ATTAM) work is appropriate to assess whether this comparison between the two competing technologies changes in the future. (Tier 2, Lead)

Conclusion: The power requirements to recharge the batteries of an all-electric armored ground combat vehicle make an all-electric design impractical. Because of lengthy recharging requirements and the requirement for extremely large electrical power sources, extensive use of battery electric tactical vehicles (including those in a supply convoy) also have limited practicality in a battlefield environment. The battery space requirements and additional weight limit all-battery vehicle use to select missions where silent operations are paramount and lengthy recharging times can be accommodated.

Recommendation: The majority of planned funding for the All Electric Combat Powertrain and any anticipated funding for battery electric tactical vehicles should be reallocated to work on series hybrid, parallel hybrid, and/or other partial vehicle electrification concepts. (Tier 2, Lead)

Recommendation: Continued engineering work on both series and parallel hybrids for the full complement of Army ground combat vehicles is strongly recommended because of the multiple benefits they provide. Although these studies can leverage work in the automotive industry,

the specific needs of the Army (e.g., much heavier armored vehicles, less stringent emission standards) will result in significant differences. (Tier 2, Watch)

Recommendation: The Army should conduct a modeling and simulation analysis of different battlefield scenarios to define the optimal silent mobility range that is required for ground combat vehicles. The results will influence the size of the battery storage required and inform the optimum mix of research and development for parallel and series hybrid configurations. (Tier 1, Lead)

Recommendation: Given the importance of power and energy on overall operational capabilities, it is strongly recommended that the scope of future warfare computer simulations (i.e., tactical exercises without troops) be expanded to include power and energy considerations. These simulations should include identification of the quantity and form of energy to be transported to the battlefield, how much of this could be replaced with local sources, where it would be stored, any set-up or takedown times, at what rate (i.e., power) that energy could be released, and how the energy needs of operating bases, vehicles, and dismounted soldiers would be replenished, including any refueling or recharging time requirements. When wargames are undertaken without computer simulation, a power and energy expert should be part of the evaluation team.

CHAPTER 7—FORWARD OPERATING BASE POWER

Conclusion: SOFC power systems would offer the same advantages and disadvantages in semi-permanent operating bases as in the commercial market. Their use could facilitate use of local fuel sources. (Tier 1, Watch)

Conclusion: The Pele nuclear power plant program now under way may prove appropriate for domestic and permanent overseas bases. It will not, however, adequately meet the needs of expeditionary and defensive operations due to its limited power rating and mobility concerns. The committee also found disparate views as to the level of effort needed to comply with regulatory and safety requirements.³

Recommendation: It is recommended that the detailed safety and regulatory requirements of a nuclear power plant be clearly defined and agreed to by all appropriate government agencies before prototype definition proceeds further. Furthermore, use cases for these reactors need to be carefully defined given the limited power and mobility of the envisioned systems.

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³ See Appendix M for additional information.

Additional safety and regulatory considerations of micro-nuclear power plants are summarized in Appendix M. (Tier 1, Lead)

Conclusion: Given their high net electric thermal efficiency, a wheel-mounted linear generator running on JP8 fuel could be as mobile as the Army’s present MEP-PU-810 DPGDS Prime Power Unit (PPU). Development of the fuel system substituting JP8 for CNG would be required. (Tier 2, Lead)

Conclusion: Cutting-edge commercial chargers and auxiliary batteries automatically adapt to charge or deliver power at the appropriate voltage, current, and duty cycle. Implementing similar concepts among military systems, such as the STAMP microgrid, could build upon the Tactical Microgrid Standard effort to develop collateral standards and hardware/software technologies that provide “plug and play” functionality and intelligent control of all connected power devices. (Tier 1, Watch)

Conclusion: In the future, the ability to use onboard vehicle electricity from a variety of mobile platforms, both tactical and tracked, will enable microgrids for mobile command centers to be quickly set up under a variety of terrain conditions, including soft ground, where trailer towed Mobile Electric Power Solution (MEPS) systems cannot reach. (Tier 1, Lead)

CHAPTER 8—FUEL CONVERSION EFFICIENCY AND OTHER MATERIAL DRIVEN OPPORTUNITIES

Finding: Although SiC semiconductor devices can operate at higher temperatures than conventional Si devices, the operating temperature limits of passive components such as capacitors and inductors still establish the upper temperature limit of power electronic systems.

Recommendation: To increase the temperature in which electronic energy conversion systems can operate, the Army should engage in research to develop higher temperature passive electrical components.

Conclusion: The pursuit of higher performance nuclear reactors for the operational Army could benefit from Army S&T investments in the research and development of SiC-SiC materials to advance the safety of future deployed MNRs. (Tier 2/3, Lead)⁴

Finding: As new material opportunities are identified, the countries to which they are sourced need to be considered.

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⁴ See Appendix M and Chapter 7 for additional information.

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