Developing a Sediment Sampling ROV for the Deepest Ocean

Sea Technology, Mar 2008 by Ishibashi, Shojiro, Yoshida, Hiroshi

A Challenge to Dive to Depths of More Than 10,000 Meters in the Mariana Trench

In 1995, the Japan Agency for MarineEarth Science and Technology GAMSTEC) developed a 10,000-meter-class remotely operated vehicle (ROV), Kaiko, and until five years ago operated it for deep-sea research.

Kaiko was composed of a launcher and a vehicle. The launcher was connected to the support ship by a primary cable, and the vehicle was connected to the launcher by a secondary cable.

On May 29, 2003, the vehicle was lost when the secondary cable snapped in Nankai Trough off Cape Muroto in Japan. JAMSTEC searched frantically for the lost vehicle, but it could not be found. As a result of this incident, JAMSTEC lost the world's only vehicle capable of researching the deepest areas of the ocean at that time.

Unfortunately, there was still unfinished business at the bottom of Earth's deepest ocean trench. Several years before Kaiko was lost, the presence of a number of different bacteria was discovered in the sedimentary layers of Challenger Deep in Mariana Trench. Many scientists hoped to explore there and get useful mud samples, so in April 2005 JAMSTEC began developing a new ROV to try to address this need, the Automatic Bottom Inspection and Sampling Mobile (ABISMO).

The major goal of ABISMO is to dive to Challenger Deep, survey the seafloor and obtain mud samples from the sedimentary layers.

ABISMO Specifications

Like Kaiko, ABISMO is composed of a launcher and a vehicle. The lower part of the launcher is constructed of a framework made from stainless steel, and the vehicle is stored within it. Pressure hulls for electronic devices, a rope winch, a secondary cable drum and two electric transformers are set into the upper part of the launcher. The cable drum can wind the secondary cable with a force of more than four kilonewtons and hold it with a force of 10 kilonewtons. The rope winds another rope connected to the samplers. Its winding force is 10 kilonewtons, and it can hold with a force of 20 kilonewtons. The samplers include a gravity core sampler and a bottom grab sampler, and one sampler is set between the two. The length and internal diameter of its inner tube are 1,000 millimeters and 76 millimeters, respectively. There are two thrusters, a docking system, the vehicle, a transponder and an acoustic positioning system applying the short baseline method in the lower part of the launcher. The vehicle is hung in the launcher by the docking system. When the system detaches it and the cable drum feeds the secondary cable, the vehicle can dive down, and its position is measured by the acoustic positioning system. The position of the launcher is measured by the support ship, which has a super-short baseline positioning system. The launcher also has a high-definition television (HDTV) camera and a National Television System Committee (NTSC) television with pan/tilt function.

The vehicle is mainly composed of aluminum frames; buoyancy materials, which are covered with a fiber reinforced plastics fairing; two crawlers; and pressure hulls for electronic devices. It is very small and has the ability to turn in a small radius because it has four thrusters with a thrust force of 150 newtons. Its weight in air and water is 330 and 100 kilograms, respectively.

The vehicle is used for the preliminary surveying of the sediment surface in a planned area where the launcher drops the samplers. It is equipped with crawlers that are triangle-type and made from stainless steel and monomercast nylon. They can be detached in advance depending on the mission or the environment of the landing point. It has an NTSC television camera with pan/tilt function.

The secondary cable connected to Kaiko was made of Kevlar fiber, so a new secondary cable, made of aramid fiber, was developed for ABISMO. This fiber has a tensile strength of 350 kilograms per square millimeter.

The secondary cable consists of the aramid fiber, two coaxial cables for signal lines, four single cables for power lines, cable sheath and resin. The signal lines and the power lines are its cable core, and they are covered with the rod-type aramid fiber. It was made to prevent stress concentration. The configuration of the buoyancy materials is syntactic form, and its specific gravity is 0.63.

Onboard Equipment

The onboard equipment for ABISMO includes a man-machine interface (MMI) system to operate it, a power supply and a launch-recovery implement. The latter two items are already mounted on the support ship that Kaiko used, and they can be integrated with ABISMO. The power supply supplies high-voltage power to the launcher through the primary cable, and the primary cable is rolled by a drum which is mounted on the hanger deck of the support ship. A part of the operation console for Kaiko is used to control the power supply.

However, the MMI system for ABISMO had to be newly developed. Set on the rear section of the navigation bridge, the MMI system was designed with a compact size and mobile type in order to allow set up on any support ship. It is composed of five computers, an optical communication system and several monitors. One computer is used as the downlink interface to control ABISMO, and three computers are used as the uplink interface to observe its status. Another computer is used as the format converter for the up/downlink via the optical communication system. Programs with graphical user interface (GUI) are installed into each computer, and there are eight GUI windows. The MMI system has an automatic control function to keep its own heading with the ship's because the primary cable is twisted thickly and quickly.