TABLE 2-2 Devices in 20-W Regime Planned for Objective Force Warrior (OFW)-Advanced Technology Demonstration


Power Demanda (W)


Soldier radio


Squad radio


UAW/robotic vehicle


Computer displays

Handheld flat panel




Integrated sight—module display








aBreakdown of OFW numbers:

• Soldier radio, 7.80 W (JTRS numbers are not available; assumed the same as Stryker MBITR radio);

• Squad radio, 4.40 W (communications processor card) + 0.60 W (WLAN card) + 0.60 W (VoIP processor) + 0.60 W (WLAN antenna);

• UAW/robotic vehicle, 3 to 10 W for como-crypto interface (Brower, 2003);

• Handheld flat panel, 6.30 W + 0.75 W (handheld keyboard and cable);

• Helmet-mounted display, 0.50 W;

• Integrated sight display, 3 W (HIA module including breakaway connection to body PAN);

• Sensors, 2.15 W (thermal weapons sight) + 1.10 W (daylight video sight) + 4.00 W (multifunction laser) + 1.50 W (GPS) + 0.25 W (dead reckoning module) + 0.50 W (microphone/speaker assembly); and

• Computer, 2.10 W (computer assembly) + 10.9 W (computer processing card) + 3.42 W (PAN body hub) + 1.00 W (PAN weapon hub).

NOTE: UAW, universal access workstation; JTRS, Joint Tactical Radio System; MBITR, multiband intra/inter team radio; WLAN, wireless local area network; VoIP, Voice over Internet Protocol; HIA, high integration actuator; PAN, primary area network; and GPS, Global Positioning System.

SOURCE: Adapted from Erb, 2003, and Brower, 2003.

need to make the final decision based on trade-offs to suit specific mission requirements.

The statement of task includes peak power requirements for two of the three power regimes of interest. How peak power is handled by the energy source will depend on the duty cycle. In general, hybrid systems can enable high-efficiency operation over an entire power spectrum of operation provided that the requirement for a separate peak power source warrants the additional weight and volume. If a separate battery is chosen to meet the minimum and peak power demands, it must be capable of delivering the desired power and part of the total energy. The energy converter portion of the hybrid must provide the average power and all of the balance of the total energy. This includes energy sufficient to fully recharge the battery during the nonpeak or low-power operating portion of the duty cycle.

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. Reasonable comparisons can be made if, and only if, the total energy content, including converter, fuel, and fuel tank, of the energy conversion device is compared with an energy storage device, such as a battery pack, having an equal amount of stored energy. In other words, the total energy produced by each system must be measured under the identical load conditions (power profile) to obtain an accurate comparison between the two.

A second issue is related to technology maturity. For many emerging technologies, fully packaged systems are not available. The system dry weight, including the fuel tank, the quantity of fuel, the energy content of the fuel, and the energy conversion efficiency, are all needed to compute performance metrics. Efficiency data are available for some emerging technologies. If the quantity and energy content of the fuel are known, all that is needed is the dry weight of the optimized system for a specific mission requirement. Reasonable estimates of system dry weights can be inferred from breadboards, brassboards, prototypes, and commercial products. In the latter case, allowances need to be made to account for differences between commercial and military priorities, e.g., the weight may be unimportant to a commercial customer whereas it is critical to the soldier. Hence, the commercial product is not optimized for weight, and the specific energy of the technology may be underestimated. To make meaningful comparisons among alternatives, energy conversion system dry weights were estimated based on assumptions that are explained in Appendix D with references.

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