Submarine juice bar

Advanced Battery Technology, Sep 2001

An underwater service station that can recharge robotic submarines so they never have to surface has been successfully tested in Germany, reports New Scientist.

Robotic submarines, used in commercial oil exploration and marine biology, need to recharge their batteries and download data they have collected during a mission. Normally they surface to do this, but this takes time and risks accidental damage to the subs as they are lifted aboard their mother ship. Now the Eurodocker project, backed by the European Union, has shown that this can be done underwater.

The Eurodocker garage is a metal frame anchored to the sea floor. The challenge has been to ensure the "autonomous underwater" vehicle (AUV) can find its way back to the garage, despite the shifting currents. "The trick of homing is combining data from several sensors so the AUV knows by dead reckoning where it is in relation to home all the time," says Ander Bjerrum, technology manager at the company Maridan of Hosholm in Denmark, one of the partners in the project.

The 4.5-meter-long sub has sensors in its nose and tail that enable a Doppler sonar to measure its speed over the sea floor. At the same time, a laser gyroscope continuously records the direction of travel.

"The AUV can tell where it is to within one meter," says Bjerrum. "This is accurate enough because the entrance to the garage is three meters across." Once in the funnel-shaped entrance, rails guide the robot into the docking station, where it plugs into power and data sockets. Cables link these sockets to a ship on the surface.