Tethys is about two meters long and weighs 110 kilograms. MBARI researchers designed the vehicle’s tube-like shape to minimize drag and optimize propulsion. The design also allows the researchers to lengthen or shorten the body to accommodate a range of payload sizes. The researchers increased the robot’s performance over previous designs by building a propeller that works at two speeds: one meter per second and half a meter per second. To make Tethys consume little power, the MBARI researchers custom-built most of the onboard electronics. They also built a system to monitor the instrumentation and turn devices on and off every fraction of a second they are not being used.
Using Tethys is like putting a laboratory in the ocean, says Bellingham. During its autonomous journeys through the water, it occasionally surfaces to send data back to the researchers via satellite. MBARI researchers have tested the robot in California’s Monterey Bay, tracking algal blooms and phytoplankton, and measuring the physical and chemical properties of the surrounding water. Eventually, the system could do much more, says Eric D’Asaro, a professor of oceanography at the University of Washington. “This could be the first vehicle to take sample materials in the water and bring them back to the lab,” he says.