Development of Fuel Cell AUV"URASHIMA"TOSHIO MAEDA* 1
SHINJI ISHIGURO* 1
KAZUHISA YOKOYAMA* 1
KIYOSHI HIROKAWA* 1
AKIRA HASHIMOTO* 2
YUKIHITO OKUDA* 3
TOSHIHIRO TANI* 4

Urashima, the world's first autonomous underwater vehicle powered by fuel cells, recorded a continuous cruising
distance of 220 km off the shore of Suruga basin in June 2004. A closed cycle fuel cell system developed by Mitsubishi
Heavy Industries, Ltd. (MHI) is installed in the unmanned underwater vehicle, which incorporates various newideas and technologies. This latest underwater vehicle features a number of novel functions, including acoustic
remote control, weight and trim control system, and investigating and observing functions. At the sea trials, thesefunctions have been confirmed together with a power supplying function by fuel cells, autonomous navigation control, and many other outstanding functions.
Communication between the vehicle and the mothership is realized by optical or acoustic means under water, long-distance radio at the surface, and radio wave
LAN communication on board.
Urashima has three navigation modes: autonomous
navigation mode, acoustic remote control mode, and optical communication control mode by optical fiber cable(called untethered remotely operated vehicle mode or UROV mode).
The acoustic remote control mode and U-ROV mode
are modes of navigation by remote control command fromthe mother ship, and the means of command of communication in each case is optical communication by opticalfiber of small diameter (1 mm in outside diameter) or
acoustic means. For acoustic communication, the vehicle
must be located within a conical area of ± 30 degrees
directly below the acoustic transmitter and receiver ofthe mother ship. The U-ROV mode is mostly used during the period from start of underwater navigation until
acoustic communication with the mother ship has been
established. This wide variety of communication monitoring functions is one of the special features ofUrashima.

1. Introduction
In order to investigate the causes of global warming,
it is indispensable to gather and analyze ocean dataaround the north pole. As an effective means of investigating the Arctic Ocean, access to which is difficult, there
has been a demand for development of an autonomous
underwater vehicle (AUV) capable of cruising long distances.
Urashima, which is a test vehicle for development ofAUV, was delivered to the Japan Marine Science andTechnology Center (now Japan Agency for Marine-EarthScience and Technology) in March 2000, and MHI has
been promoting ocean cruising tests jointly with theAgency. The vehicle, powered by lithium ion rechargeable batteries, recorded the world’s deepest dive for anAUV of 3 500 m in August 2001, and marked a cruising
distance of 132.5 km in June 2002. In order to enable itto cruise longer distances, the power source was changed
to fuel cells. The new “Urashima” was completed inMarch 2003 as a cruising vehicle having a maximum
range of 300 km.
This paper gives an outline and reports on the seagoing test results of the world’s first fuel cell-powered
AUV Urashima.

3. Main composition of the vehicle
The principal specifications of the vehicle are given
e 1 , and its general arrangement is shown inin Tablable
Fig
Fig.. 1 .
(1) Structure
The vehicle consists of pure titanium frames, necessary devices and buoyancy materials, and theoutside is covered with FRP fairing covers. The buoyancy materials are syntactic foams of specific gravityof 0.5, and are made of tiny hollow glass microballoonsof 40 to 100 μ m in diameter solidified with resin.

2. Construction and application of Urashima system
Urashima is an AUV, and basically does not require
support from a mother ship during navigation, but canbe accompanied by a mother ship when carrying out observations. The Urashima system is composed of thevehicle and the on-board facilities.
The on-board facilities include the control container
accommodating control and monitor panels, power source
container, and fuel cell on-board equipment.
*1 Kobe Shipyard & Machinery Works*2 Nagasaki Research & Development Center, Technical Headquarters*3 Takasago Research & Development Center, Technical Headquarters*4 Nagasaki Shipyard & Machinery Works

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)

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Emergency transponder

Acoustic telemetry transmitter

Vertical rudder

GPS antenna Fuel cell pressure vessel

Main pressure vessel

Oxygengas tank

Horizontal plane

Metal hydride pressure vessel

Pressure vessel
for buoyancy
control system

Acoustic telemetry receiver
Acoustic homing sonar

Main thruster

Color TV camera
Forward altitude sonar
Vertical rudder

Oil bladder

Vertical thruster (aft)Side scan sonar

Trim controller
Snapshot digital camera

Vertical thruster (fore)

Lithium ion
rechargeable battery

Emergency ballast releaser
Doppler velocity log.

Ballast releaser

Fig. 1 General arrangement of vehicle
Configuration and layout of the vehicle (side view)
Table 1 Principal specifications of the vehicle
ItemSpecification

Type

Autonomous underwater vehicle (AUV)

Overall dimensions(m)

Weight in air(t)Length x width x height: approx. 10.7 x 1.3 x 1.5
approx. 10

Maximum operating depth (m)3 500

Maximum cruising range (km)300
approx. 3Cruising speed(kt)Hull system

Trim controller, buoyancy control system, ballast releaser, emergency ballast releaser

Power sources

Fuel cell system- Fuel cell: Polymer electrolyte fuel cell (PEFC), rating 4 kW, 120 V- Oxygen gas tank: internal pressure 14.7 MPa- Metal hydride system
Auxiliary power source: lithium ion rechargeable battery for hybrid use

Maneuvering systems

Observation systems

Navigation instruments

1.8 kW x 1Main thruster
Vertical thruster
0.6 kW x 2Horizontal thruster
0.6 kW x 1
Vertical rudder, horizontal plane
TV camera, underwater light, side scan sonar, snapshot digital camera,
CTDO, multipoint water sampling device (installed when using lithium ion
rechargeable battery as main power source)
Inertial navigation system, inclination meter, Doppler sonar, depth meter,
altitude sonar, GPS, acoustic homing sonar, forward altitude sonar,
acoustic transponder, emergency transponder(2) Maneuvering systems
Urashima is a cruising vehicle, and is basically designed for straight forward movement. Steering iscontrolled by the vertical rudder and horizontal planeat the stern. The vertical thruster is used for verticalmovement when stopping (hovering).
(3) Weight and trim control system and ballast devices
It is a distinctive feature of Urashima that it has
vehicle weight and trim adjusting systems for use
during underwater navigation. When Urashima isnavigating over long distances, buoyancy balancevariation are predicted due to changes in seawatertemperature and density. Although the vehicle can beexpected to cruise stably even in such conditions byusing this system. The fore-aft inclination angle (trim)
is adjusted by the trim adjusting device that moves aweight of about 50 kgf by one meter forward or backward. By controlling the oil level contained in the oilbladder, the buoyancy control system can adjust thebuoyancy by about 60 kgf. When the mission has been
completed for the dive, the vehicle ascend to the surface by dropping the ascent ballasts.
(4) Observation systems
For sea bottom investigations, the vehicle isequipped with a TV camera, a snapshot digital camera, and a side scan sonar. For ocean observation whilecruising, various instruments are mounted includinga CTDO sensor for continuous measurement of salt
concentration, water temperature and dissolved oxygen, and a multipoint water sampling device. The
multipoint water sampling device can sample 250 ccof seawater per cell in a total of 200 cells.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)2

Differing from the land-use system, the fuel cell system
mounted on Urashima is a completely closed cycle fuel cellsystem. Fuel cells are contained in pressure vessels madeof titanium alloy, oxygen gas is supplied from a high-pressure (14.7 MPa) oxygen gas tank, and hydrogen gas issupplied as fuel from metal hydride contained in a pressure vessel. Instead of air, pure oxygen is used as theoxidizer, which is also one of the distinctive features of theclosed cycle system. The unreacted gas passing throughthe fuel cell stack is recirculated in the system, and reacted water is collected in a reaction water tank in the fuelcell pressure vessel.
Temperature and humidity control is very important for
the PEFC. In the fuel cell stack, circulation water at constant temperature circulates to maintain the operating
temperature, and temperature and humidity of the gas line
are controlled by heat insulation and heating. In the circulating water line, cooling pipes are provided for releasingheat to the outside of the pressure vessel, and the temperature is kept constant by controlling its flow.
4.2 Metal hydride
To consider safety, hydrogen gas is stored by a storage
method using metal hydride. As the metal hydride, AB5
type rare-earth-based alloy is used on account of its excellent absorbing efficiency, and it is capable of absorbing anddesorbing in the normal temperature range (20 to 60oC).
Desorbing of hydrogen from the metal hydride is an heatabsorbing reaction, and the desportion is controlled by using the waste heat from the fuel cell as the heat source.
Fig. 4 shows an example of gas pressure control of metalhydride in the seawater. As hydrogen gas is consumed, thepressure of the metal hydride drops, but when the pressure drops, the circulating water is passed to raise thetemperature of metal hydride, which in turn raises thepressure of the metal hydride. When elevated to the specified pressure, passing of circulating water is stopped. Bymeans of this temperature control, the pressure of the metal
hydride is maintained in a range of 0.85 to 0.95 MPaG.

4.1 Fuel cell
The power source used in an underwater vehicle is required to be small in size, light in weight and easy tohandle. Urashima uses polymer electrolyte fuel cell(PEFC) system as a power source. As compared with otherfuel cells, the PEFC is characterized by a low operating
temperature of about 60 to 80oC. Since the temperature
is close to normal temperature, it is easy to start and stop,heat insulation measures are possible, and it can be assembled in a small and lightweight system. This fuel cellsystem and fuel cell stack have been newly developed by
MHI to serve as the power source of Urashima. Two stacks
are connected in series, and the rated output is 120 V,
4 kW. An outline of the fuel cell system is given in Fig
Fig.. 2and a photograph is shown in Fig.3
Fig.3.

Metal hydridepressure vessel
Fuel cellstack
Metal hydride
Coolingpipes

Heat exchanger
Oxygengastank: Hydrogen: Oxygen: MH circulation water: FC circulation water

Hydrogen humidifier

Reaction water tank
Fuel cell pressure vessel

Fig. 2 Block diagram of fuel cell system
Outline and composition of system for gas and circulating water in thefuel cell system of Urashima.

Temperature (oC), current (A)60: 0.9 MPaG (pressure control target): Metal hydride temperature: Metal hydride pressure

1.250

1.040

0.830

0.620
1000.4: Hydrogen flow rate
: Fuel cell current: Seawater temperature
12Pressure (MPaG)

4. Fuel cell system0.23450.0

Time (h)Fig. 3 Fuel cell
Fuel cell system mounted on vehicle's fuel cellpressure vessel

Fig. 4 Pressure control of metal hydride
Gas pressure is kept within a specific range by controlling temperatureof metal hydride by means of circulating water.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)3

5.2 Autonomous navigation function
Autonomous navigation of Urashima is executed according to a predetermined scenario. It is carried out infour hierarchical tasks: (a) supervisory control task, (b)navigation pattern execution task, (c) motion control
processing task, and (d) actuator control task.
In the supervisory control task, the execution andprogress of the scenario are managed, while in the navigation pattern execution task, execution of the navigation
pattern is managed, including change or hold of course,change or hold of depth, etc.
In the motion control processing task, the control command values of the actuators are determined forexecuting the navigation pattern, and the actuator control task is to drive actuators such as thruster, rudder
and trim adjusting devices.
The scenario is written in the sequence of navigation commands, and navigation commands include “Goto specified point,” “Correct position by transponder signal,” “Cruise at specified depth (altitude), course,”“Observe at specified position,” and others.

5. Autonomous control
5.1 System configuration and functions
The configuration of the control system used in autonomous control is shown in Fig. 5
5. The vehicle control
system consists of a CPU for calculation and control anda CPU for IO, and is installed in the main pressure vessel. Actuators and sensors of the vehicle are all controlled
by the vehicle control system, but the fuel cells and metal
hydride are controlled by a dispersal control system having individual control devices in each pressure vessel.
During autonomous navigation, the vehicle is controlled by a predetermined scenario, but optical or
acoustic commands from the mother ship can be received
whenever necessary. The vehicle is constantly sending
data to the mother ship. The vehicle conditions (depth,course, velocity, attitude angle, position, etc.), running
conditions of devices and TV image and side scan image
can be monitored at all times. At the surface, two-way
communication between the vehicle and mother ship is
capable by long-distance radio.

Communication with mother ship

Radiowave LANLong-distanceradio wave
communicationsystem

Acoustic
telemtrytransmitter

Optical fibertransmitter

Satellite
communicationsystem

HubCPU for
calculation and control
MC 68060
CPU for IO
MC 68040

Flash memory
64 MB
Vehicle control
deviceRAS board

DIO board
64/64 chAI board
16 ch

Digital signal
for sensor

Rudder andtrim controller

SIO board
Total 32 ch

Maneuveringsystems

Navigation system,
observationinstruments

Fig. 5 Control system configuration
Composition and external interface of vehicle control system.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)

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In autonomous navigation, two transponders were located in the north and south, and the vehicle traveledback and forth between the two reference points. Usually, a vehicle navigates while ascertaining its positionby the inertial navigation system. In case of long-distance cruising under external disturbances of small
acceleration components such as tidal currents, the inertial navigation system has dislocation from the actual
position by accumulation of errors. To avoid such errors,in Urashima, on the basis of the acoustic transponders
preliminarily calculating (calibrating) the location of installation, the position is corrected autonomously byacoustic positioning.

6. Sea trial

45040

100

35200

30300

25400

20: Hydrogen desportion: Fuel cell current: Depth: Vehicle speed

1510500
600

800

0900
2004/6/9
23 : 00

2004/6/10
11: 00We consider it had been sufficiently confirmed thatthe fuel cells are useful as an underwater power sourceat the sea trial in June. During continuous navigationfor 43 hours, the autonomous control system operated
normally, and the vehicle cruised exactly according tothe scenario.
In concluding this paper, we express our deep gratitude
to the staff members of the Japan Agency for Marine-Earth
Science and Technology for their kind support and advice
from the initial stage of development of Urashima and fuelcells system for the underwater vehicle.

7005
2004/6/9
11: 00

7. Conclusions

Depth (m)Fuel cell current (A), Flow rate
(NL/min), vehicle speed (kt)

A long-distance autonomous cruising test was executed during the period from 9 to 11 June, 2004, to travelback and forth between two points 25 km apart northand south off the shore of Suruga basin. After continuous autonomous navigation of 43 hours at a depth of 800
m and average velocity of about 2.8, the trial was suspended due to an approaching typhoon, but a continuous
cruising distance of 220 km was recorded.
During navigation, the fuel cells followed up smoothly
to load changes such as variations in vehicle velocity,and operated stably. Supply of hydrogen from the metal
hydride was normal, and good overall performance as afuel cell system was confirmed. Fig. 6 shows the operation data of fuel cells during the trial.

References(1) Hyakutome, D., Deep Cruising AUV URASHIMA 's Now andFuture, Japan Marine Engneering Journal Vol.37 No.9 (2002)
p.23(2) Aoki, T. et al., PEFC Deep Cruising AUV "URASHIMA", FuelCell Synposium Proceedings (2003) p.90
(3)Aoki, T. et al., Fuel Cell Underwater Vehicle "URASHIMA",ISOPE-2004 Conference Proceedings (2004)

2004/6/10
23 : 00TimeFig. 6 Operation record of fuel cell
Sea trial data of fuel cell.

Toshio Maeda

Shinji Ishiguro

Kazuhisa Yokoyama Kiyoshi Hirokawa

Akira Hashimoto

Yukihito Okuda

Toshihiro Tani

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)

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