The computer subsystems evolved in a different way. As opposed to the single processor in the earliest LW system, the OFW design includes a number of processors that are interconnected through multiple high-speed local area networks (body LAN). To assure longevity, the OFW design has gone to an open architecture with several standardized buses (e.g., Firewire, gigabit Ethernet). While a variety of buses enhances the number of modules that could connect to the OFW electronics, it does exact a premium for power to keep all the buses energized, even if there is only one transaction type per bus. The result has been that computer power demands of the three generations of LW are about constant in spite of the significant improvement in energy efficiency of the underlying computer system technologies.
Power demand estimates for the sensor suite have increased slightly over the three generations. The number and types of sensors are similar, but there have been significant improvements in functionality.
The OFW-ATD is working to develop power-aware applications and an intelligent middleware layer that will efficiently manage bandwidth usage. It will use a radio (Joint Tactical Radio System (JTRS) Cluster 5 SLICE radio) that creates a peer-to-peer network architecture, but the software-based design solution for JTRS may not allow for reductions in power demand. Initial OFW estimates take an optimistic approach to what will be available in 2007 by using power numbers no worse than those for the MBITR radio with LW-SI, thus enabling a complete high-level comparison of the overall power demands of LW electronics. The importance of soldier communications-electronics to reductions in power demand is discussed further below.
The Army Program Executive Office (PEO-Soldier) and the LTI provided briefings on facets of the OFW-ATD relating to power, including power sink technologies, system design, doctrine, networking, and power sources. For each recommendation derived from the five conclusions in Energy-Efficient Technologies (NRC, 1997), the LTI provided specific examples of how the OFW-ATD would improve the energy effectiveness of the LW system.
Efficient power usage is understood to be critical to the success of the OFW-ATD and has been identified as a key performance metric. Every energy-consuming capability must earn its way onto the system. The OFW-ATD is using state-of-the-art technology developed by both commercial entities (for main computers) and government programs (for radios) to reduce system power demand. The OFW-ATD system architecture is intended to be flexible enough to incorporate new technology as it is developed.
The OFW-ATD is also using computer-aided design, simulation, and profiling tools to perform power analysis on proposed designs. All applications to be developed will be power-aware. A custom Linux kernel is being created, tuned for power and security.
To synchronize doctrine with technology and minimize soldier communications transmissions, the OFW-ATD software team is working closely with the operational effectiveness team to analyze and prioritize the data that need to be transmitted across the Army force structure. The OFW-ATD is also studying the operational utility of unmanned vehicles, both air and ground, as nodes in the peer-to-peer network architecture that would have more powerful reach-back capabilities.
In response to the 1997 recommendation for research and development in rechargeable batteries, the OFW-ATD is working with a commercial battery supplier to devise a rechargeable battery with a specific energy on the order of 200 Wh/kg. The OFW-ATD is also tracking advances in energy sources and is exploring hybrid systems. It also supports continued research into advanced energy sources and is particularly interested in direct methanol fuel cells.
The assumption that future soldiers will be resupplied every 24 hr does not necessarily modify the goal of 72-hr self-sufficiency. To justify the 24-hr assumption, OFW makes the further assumption that each unit will use a vehicle for resupply (such as a robotic Mule). This assumption, endorsed by the Army, is important because it has substantial logistical implications, for including procurement and transportation of Mules, spare parts, and fuel.
The A123Systems battery technology is high payoff/ high risk. The high power capability of this approach is based on doped LiFePO4 as extrapolated from laboratory experiments. The chemistry is inherently safe, and the raw material is not expensive. Nevertheless, there are other rechargeable alternatives, and the OFW-ATD will probably need to pursue these concurrently to ensure success.
OFW plans to embed data-logging capability in the system to track energy and power demand. This is an excellent idea that could provide an initial basis for subsequent development of needed models. Actual power usage profiles can also be used to evaluate future design trade-offs. This should provide substantially more accuracy for power modeling than the current estimates of subsystem duty cycles.
The committee notes that hybrid techniques, such as