Sea glider takes flight

Researchers from the Woods Hole Oceanographic Institution (WHOI) and Webb Research Corporation of Falmouth, Massachusetts have successfully flown the first thermally powered robotic vehicle through the sea.

Gliders propel themselves through the sea by changing their buoyancy to dive and surface. Wings generate lift, while a vertical tail fin and rudder allow the vehicles to be steered horizontally.

Most gliders rely on battery-powered motors and mechanical pumps to move ballast water or oil from inside the vehicle’s pressure hull to outside, increasing or decreasing the displacement of the glider without changing its mass.

The new thermal glider draws its energy for propulsion from the differences in temperature (thermal stratification) between warm surface waters and colder, deeper layers of the ocean. The heat content of the ocean warms wax-filled tubes inside the engine. The expansion of the warming wax converts heat to mechanical energy, which is stored and used to push oil from a bladder inside the vehicle’s hull to one outside, changing its buoyancy. Cooling of the wax at depth completes the cycle.