by combining an air-breathing system (e.g., metal/air battery, fuel cell, small engine) with a rechargeable battery.

To be acceptable for soldier use, a power/energy source must be impervious to dust and moisture. An acceptable fueled hybrid must be smart; that is, it must be capable of sensing and reacting to its environments so as to allow the unit to operate under water and to protect it from destruction. Modeling is critical to the design of acceptable hybrid systems.

Recommendation 5: The Army should refine duty-cycle estimates for the Land Warrior suite of electronics so as to enable the development of high-fidelity models incorporating soldier usage patterns and other details of interactions between power sources and soldier electronics. These estimates are essential for developing smart hybrid systems that can react to the environment for the future LW as well as for developing energy-efficient systems to meet unforeseen Army mission requirements.

While many commercial energy sources exist, they are driven by the consumer market and are not developed in sizes commensurate with the broad spectrum of Army needs. The committee was specifically requested in the task statement to select and prioritize power source alternatives in each of the three target regimes. Recommendations 6 through 8 are consistent with the previous recommendations and the S&T objectives set for the Army in Table ES-1.

Recommendation 6a: As its first priority in the 20-W target regime, the Army should support development of batteries with specific energies greater than 300 Wh/kg (e.g., Li/(CF)_x, Li/S, Li/air, C/air) in sizes commensurate with LW requirements.

Recommendation 6b: The Army should develop smart hybrid systems capable of air-independent operation and the 50-W peak load. These hybrid systems must be developed with the aid of duty-cycle analysis and modeling. Key to this is an evaluation of the limits of battery-battery hybrid system performance as well as methods for packaging or sealing air-breathing hybrid systems.

Recommendation 6c: If the Army determines that a nonstandard fuel source is acceptable for battlefield use by dismounted soldiers (see Recommendation 2 above), it should develop PEM and SOFCs as complete systems with the hydrogen storage or generation subsystem yielding at least 6 percent by weight hydrogen, including all components. In this context the Army should investigate methods of reforming methanol, ammonia, butane, and liquid hydrocarbon fuels and should evaluate whether the development of direct methanol fuel cell (DMFC) systems would be less complex than fuel-processing approaches.

Recommendation 6d: As a final priority in the 20-W regime, and for the far term, the Army should develop and evaluate small engines that operate on standard logistics fuels.

Recommendation 7a: As its first priority in the 100-W target regime, the Army should develop smart hybrid systems capable of air-independent operation that can accommodate total energy requirements. The emphasis should be placed on fueled systems (small engines, fuel cells) capable of operating on standard logistics fuels.

Recommendation 7b: The Army should support development of high-specific-energy batteries for niche applications, such as laser designators.

Recommendation 8a: As its top priority in the 1- to 5-kW regime, the Army should continue to develop lightweight engines with high specific power that operate on standard logistics fuels. It should investigate Stirling engines, as they are fuel-versatile and offer significant acoustic signature reduction.

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.

Correctly matching power source technologies (sources) with particular electronics applications (sinks) can greatly affect energy efficiency. System developers must also consider how Army logistics and operations impact the selection of power solutions for the soldier. The duty cycle is extremely important when considering a hybrid power solution. Also, dismounted soldiers who are accompanied in combat by a robotic vehicle, as envisioned by the Army for the future, will have a possible means for recharging batteries or fuel supplies that soldiers operating alone do not have.

Considering the OFW prototype as a possible third generation of LW electronics, the average power has been estimated at 20 W and the peak power at 60 W, for all three generations. The committee observed that power savings made possible by technology improvements in later elec-