The new energy storage system – MK8 MOD1 SEAL Delivery Vehicle (SDV) – was one of more than one hundred projects reviewed at the recent Joint Defense Manufacturing Technology Panel (JDMTP). The technical review panel examined projects for many criteria, including “jointness”, or opportunities for teaming.

The JDMTP works to gain insight that will:

1. Aid the joint planning process
2. Identify progress in promoting jointness in project planning and execution
3. Identify Defense Technology Objectives and measure progress towards stated goals and objectives
4. Identify levels of effectiveness in program execution
5. Provide feedback to project engineers and JDMTP Principals

Technical issue
Navy SEALs currently need more than 36 hours to recharge the silver zinc (AgZn) energy storage system for the SDV, which does not support their mission turnaround time of 12 hours. To accomplish mission turnaround, they currently deploy with two to three AgZn battery sets to support each SDV, so that a fully charged battery system remains available. The primary insertion platform for the SDV is the Dry Deck Shelter (DDS) configured SSN. The DDS is an extremely cramped and humid environment for opening battery canisters during battery removal and installation. Additionally, the batteries have to be passed through numerous hatches and ladder-wells between the vehicle and the charging station. There are 24 battery trays per AgZn system, weighing 53 pounds each. Throughout the handling process, personnel must wear Personal Protective Equipment (PPE) and keep the batteries upright to protect from electrolyte exposure. AgZn batteries cannot be charged in place, and batteries must be fully charged prior to all missions. The current process involves over 46 man hours to charge, remove, and install over 2,500 pounds of AgZn batteries. The project’s primary goals are to retain mission turnaround time while increasing capability and safety at a decreased life cycle cost (Table 4-1).

Technical solution
The solution is to use lithium-ion battery technology. The lithium-ion energy system has a charge-in-place feature that requires less than 12 hours to recharge. This is possible because lithium-ion (Li-ion) technology can be driven at higher charge rates, whereas AgZn has no more than a C/20 charge rate. AgZn also requires a balance charge every cycle and gas handling.

The AgZn batteries have a rated capacity of 60 kWh. It is higher during initial discharges but lower towards the end of life. These batteries require a balance at every charge and teardown during deployments to support turnaround requirements. The Li-ion battery has an expected capacity of 100 kWh and a uniform fade rate. The AgZn energy system of the MK8 MOD1 SDV has single point failure, having only a single series string. This means that if one cell on the string shorts or opens, the boat will have no power.

In the event of string failure, the higher Li-ion cell voltage with 10 parallel strings facilitates a redundant capability to continue mission execution at a slightly reduced capability. The Li-ion cells are very low maintenance. The AgZn batteries require balancing every cycle, whereas, the Li-ion system only needs cell capacity balancing after 100 cycles. The Li-ion cells require no activation, clean-up, or purge, and the cells arrive activated and ready for charge.

Benefits
Following are the immediate tangible benefits of the new Li-ion technology:

1. Extended battery cycle-life – 17 times (plus) that of the existing AgZn battery
2. A one-time installation of a Li-ion battery system during Fiscal Year ’08/ ’09 matches ideally with the expected service-life of the MK8 MOD1 SDV (Fiscal Year ’15).
3. Elimination of separate storage areas for non-activated AgZn and electrolyte
4. Elimination of chilled areas for wet activated AgZn batteries
5. Reduced life cycle costs (mainly associated with maintenance)
6. Significant reduction in man hours.

Transition
The JDMTP considers the final customer and their involvement in transition planning, questioning whether funding sources have been identified for transition (i.e., qualification). The SDV teams are the final customer, and in-water testing is ongoing (November 2005 through November 2006) at NSWC Panama City. The prototype Li-ion system has been installed in the MK8 MOD1 SDV prototype and is undergoing rigorous evaluation. Transition to SDV Li-ion is a top priority of Naval Special Warfare (NSW), and it is a planned NSW POM ’08 submission to USSOCOM for possible acquisition during Fiscal Year ’08-’09, for a complete SDV fleet retrofit. The transition is a form, fit, and function replacement, which will be transparent to the user.

Jointness
The JDMTP categorizes a program based on whether it is jointly funded, whether it has implementations benefiting more than one service, or whether it is managed with joint decision-making. The project may also be of interest or potential benefit to more than one service. The SDV Battery Project is service-specific but has a technology that is beneficial to all of the services. Some other systems that Saft America, the vendor of the program, is working on include a Navy Unmanned Aerial Vehicle (UAV), the Army Improved Target Acquisition System (ITAS), and an Air Force Autonomous Underwater Vehicle (AUV). Any other system that requires a high energy density battery system will benefit. Information is being shared with other Navy activities such as NAVSEA, PEO LMW, PMS 403 (UUV). They are looking at what this program has accomplished, for possible integration into large diameter Unmanned Undersea Vehicles (UUVs) which are close to the size of the SDV.

Leveraging
Leveraging is an important aspect, and the ONR and USSOCOM (PMS-NSW) have each contributed to the program. Saft America has also contributed internal engineering dollars and hours towards the program. The project participants are USSOCOM, PMS NSW, NSWC Crane, NSWC Panama City, the EMPF, and Saft America.