BACKGROUND:
The MK8 Mod 1 SEAL Delivery Vehicle [SDV] project was undertaken by the U.S. Navy Seals to support various missions. The SDV was initially developed to utilize silver-zinc (AgZn) batteries. These batteries had the highest energy storage capacity of rechargeable batteries at that time. With the advancement of Lithium- Ion in consumer electronics and commercial energy storage, the U.S. Navy and Special Operations Command funded in partnership with the US Navy ManTech Program to pursue a replacement battery program that would result in higher energy density, less maintenance, and a lower life cycle cost system.

DARPA DEVELOPMENT:
A DARPA contract was undertaken in FY99 to develop a lithium-ion battery for the MK30 Underwater Target, SDV and Advanced SEAL Delivery Vehicle [ASDS]. The Commercial-Off-the-Shelf-Savings-Initiative [COSSI] was let to examine what type of commercial batteries could meet the needs of the US Navy. The controlling agency in the DARPA/COSSI contract was Naval Sea Systems [NAVSEA] Program Office, PMS-395 Deep Submergence. This initial effort was completed by Alliant Techsystems, PMS-395, Coastal Systems Station-Panama City and Naval Surface Warfare Center Crane in FY01. The ManTech challenge is to safely and economically package Li-Ion batteries and battery monitoring electronics to withstand the rugged environmental conditions encountered in Special Operations missions.

ACQUISITION COST VERSUS TOTAL COST OF OWNERSHIP:
While the acquisition cost of a lithium-ion energy storage system is higher than that of the silver-zinc, the cycle life [the number of cycles an energy storage system can be used before disposing] greatly overcomes the higher cost. This is shown in chart1 below. Batteries are replaced when their stored energy potential drops below 400 Amp-Hours. The red line, the silver-zinc battery, from chart 1 indicates a battery life of approximately 35 cycles, while the blue line , Li-Ion, shows a cycle life in excess of 135 cycles. Further testing has shown a battery cycle life of approximately 600 cycles. This is reflected in the equation reflecting the fade of each battery. Silver-zinc having a loss of 5.133 Amp-Hours per cycle, while Li-Ion has a loss of 0.1419 Amp-Hours per cycle, a ratio of 36:1.

The EMPF, in partnership the Office of Naval Research ManTech Program and US Special Operations Command has initiated a manufacturing technology program that will improve the following issues presently encountered with Silver-Zinc [AgZn] Energy Storage System:

Battery Life: Wet (Activation) Life of 12 to 28 months

Recharging: Requires battery disassembly and slow recharge, approximately 36 hours.

Maintenance: The current AgZn battery requires operator maintenance, separate storage facilities for non-activated batteries and electrolyte; chilled storage areas for activated batteries. Maintenance costs to clean, repair and refurbish the battery container in the event of electrolyte leakage is a driver in the total cost of ownership of the current system.

The specific tasks within the ManTech Program that will be worked on during this contract are:

High Cost of Energy Storage - Develop manufacturing processes that reduces the cost of packaging large scale high energy storage Li-Ion batteries.

High Cost Battery Chargers - The current recharging system is a custom designed power supply and control unit. The recharging system acquisition cost is approximately $300K per charger. Each deployment requires 6 charging systems aboard the host submarine. A commercial-of-the-shelf, COTS, solution will be approximately 20 to 50% of the cost and would meet the recharging needs of various unmanned underwater systems, UUVs, in addition to manned submersibles. Commercial charging systems have already been verified at shore installation, the packaging and controls of a commercial system to meet shipboard requirements needs to be accomplished.

Battery Monitoring Electronics - The current battery has no battery monitoring circuitry and due to this the operator of the vehicle cannot be informed of a loss in power, due to a cell failure. Taking advantage of commercial battery monitoring circuitry the goal is package these COTS devices to withstand the underwater environment that the SDV operates in. Commercial battery monitoring electronics already exist. The effort is to transition this technology.

Power Distribution System - The power distribution system needs to be upgraded to allow for use of new sensors and equipment that the US Navy SEALs will use with the SDV. The packaging of COTS devices to withstand the rigors of the SDV environment is required to install a low acquisition cost, low maintenance cost system that supports the needs of the US Navy SEALS. The proposed power distribution system for the SDV will be composed of two parallel strings, eliminating one single point of failure, and will support recharging the battery while assembled in the SDV.

Power Monitoring System - (The current SDV does not have a battery monitoring system.) The operator "judges" the remaining energy based on amp-hours consumed. The proposed SDV battery monitoring system, envisioned to be located within each of the battery canisters, will interface directly to the operator panel. It will provide the vehicle pilot with an accurate indication of remaining energy.

Battery Charging System - The proposed Lithium-Ion battery will require a new battery charging system that must be qualified for operation aboard submarines. It must also interface with the battery monitoring systems and be compatible with the safety designed hull penetrators. The SDV system will be charged to approximately 185 volts for the propulsion strings and 36 volts for the electronics strings. As part of the SDV project, an additional goal is to design a commercial charging system that will meet requirements for operation on submarines, and be utilized for battery charging on various systems; SDV, ASDS, SeaHorse, Lelfass, etc. It will provide a low life cycle cost.

IPT Team Members:
An Integrated Product Team [IPT] has been established that will survey, analyze, monitor and provide the US Navy Special Warfare Command [SPECWARCOM] and US Special Operations Command [US SOCOM] an energy storage system that enhances the mission capabilities and reduces the life cycle cost of the vehicle.

Team members of the IPT are from the EMPF (US Navy Center of Excellence for Electronics), Office of Naval Research (ONR), NSWC Crane, CSS Panama City, PMS-Naval Special Warfare. Additional participation from the Portsmouth Naval Shipyard, Ocean Engineering Inc. and the US Navy Submarine Safety Program Office will be provided to the IPT as required.

Benefits to the US Navy:
The benefits to the US Navy are both in a life-cycle-cost reduction and in operational capabilities through the transition of manufacturing technologies, and integration of commercial technologies into undersea special warfare applications. The cost benefits, in Return on Investment to the US Navy show a total return on investment in slightly over two years after completion of the program. The operational benefits will probably never be published but will be heard throughout the Special Warfare community.