**2.8. Energy sources for MCM UUVs**

maneuverable platform. MCM expert system has the capability to perceive the object of interest from multiple perspectives, which then increases the probability of classification for the mine targets. A key concept in data fusions of expert system includes the employment of heuristic knowledge, which incorporates constraint knowledge associated with target characteristics,

This provides basis for interaction with the object of interest, and dynamic perceptions that provide active sensor management and vehicle path planning in the navigation and guidance [16]. A second unique aspect of the AI expert system architecture is the implementation of sensing, evaluation and action encapsulated as subordinate tasks under the integrated mission control system. It optimizes machine-generated direction of task-organized approach and initiates signal for the course of action [6]. The MCM AI expert system architecture and its relationships between the executors, and the data/signal processing are shown in **Figure 2**.

The system capability of precise navigation and operational data collection is critical to ensure safe navigation of the vehicle and in the achievement of system objectives. To resolve the vehicle position at the submeter level, a compact low-power solid state inertial measurement

environment and attitude of vehicle.

134 Autonomous Vehicle

**Figure 2.** Operations of MCM mission management expert system.

**2.6. Vehicle management system**

Power system considerations dominate the design of UUVs, due to the fact that usually the energy source is the most limiting factor for mission operations of autonomous vehicles. The energy system of UUVs has been a major issue due to its impact on the ultimate performance and extension of UUV missions [24]. There are strong desires to minimize the size, cost and energy consumption rate for all aspects of UUV operations. In the operation of unmanned vehicles, missions with high speed and longer endurance, such as mine countermeasure (MCM), antisubmarine warfare (ASW), and intelligence, surveillance, and reconnaissance (ISR), need more powerful and sophisticated energy systems, such as fuel cells and hybrid systems in addition to battery power [23].

Since the power required to propel an underwater vehicle is roughly proportional to its surface area, and cubic of forward velocity, the stored energy capacity is proportional to its volume, the mission duration or range achievable at a given velocity varies directly with vehicles. The information of the UUV energy source gained via analysis of the batteries, fuel cells, internal combustion engines or other available energy sources is found in Jane's Underwater Technol‐ ogy Information. Important UUV power system performance metrics consist of energy and power, specific energy and power, usable state of charge, voltage response under load, calendar life and charge acceptance specifically, power and energy density and physical volume are critical to UUV system design. **Figure 3** [24] shows the specific power and energy properties of major UUV energy sources.

**Figure 3.** Energy source characteristics, Ragone Chart [24].

Based on current technology development of battery systems, high-performance battery is the most favorable choice for the autonomous vehicles based on performance, availability and cost-effectiveness. With battery applications, to facilitate the addition of battery packs to the vehicle, the hull shape should be redesigned to be longer or wider. Such hull reshaping reduces the overall vehicle drag coefficient and increases energy to UUV's propulsion power. As UUV energy systems are characterized by specific energy or power density per unit volume or weight, adding additional energy to the system increases the vehicle length [23]. When the battery packs are added, the midsection (*D*) must be longer (*L*) in order to house additional battery packs. This changes the aspect ratio, and increases the vehicle drag coefficient. Increased vehicle drag requires more propulsion power, which is a portion of added energy. The sensitivity to added battery packs is compensated for by changing the axial drag coeffi‐ cients as and other conditions, including hotel loads, are unchanged.

Based on the Ragone Chart characteristics [23], the preferred long-term approach to using hydrogen is the fuel cell. Fuel cells use a process that is essentially the reverse of electrolysis to combine hydrogen and oxygen in the presence of a catalyst to generate electricity. Fuel cells are much more efficient than ICEs often topping 70% [24, 25]. The main problem with fuel cells is the cost, and the other primary issue with fuel cells is durability. Both of these renewable fuels have lower heating values (Btu/gallon) than their counterpart gasoline and diesel fuel, resulting in higher fuel consumption when measured on a volume basis. Diesel engine offer better fuel savings over gasoline engines, battery and fuel cells on specific energy containment and gives good gas mileage on fuel consumption (gallon/mile) and load-specific fuel con‐ sumption (gallon per ton-moles), defending on the engines and operating conditions, diesel engine can provide up to 25% lower fuel consumption than gasoline engines.

Considering more than 50 days of field operation of MCM UUV and current technology development of battery systems, it could be a realistic combination for larger diameter long endurance MCM UUV system with diesel internal combustion engine (ICE) and effective battery systems. Internal combustion system gives relatively high specific power and is proven as a convenient technology, whereas battery systems give operational conveniences. We tried to integrate a small diesel engine connected to battery system, as well as to modify the hull of the UUV for a snorkeling operation [25]. This is for both recharging and the propulsion of the MCM UUV. This diesel battery hybrid power system is designed to be controlled by vehicle management computers and the main AI expert mission management system. In this power option, we consider appropriate snorkeling systems and structural accommodations.
