Clayton Jones of Webb Research in East Falmouth, Massachusetts, is a lead developer of the Slocum Glider, which uses an innovative thermal engine to power its undersea journeys. Instead of motoring back up to the surface after a dive, which eats up battery life, the thermal glider powers itself by capitalizing on the drastic temperature and density changes between deep ocean and surface water.
When the glider reaches a preset depth, a preloaded spring pumps mineral oil into an external bladder, increasing the buoyancy of the glider and causing it to rise. On the way to the surface, gradually warming water slowly melts the solid wax inside the engine. The wax expands, pushing more mineral oil against the spring and reloading it for its next dive.
Years spent developing the Slocum robotic sub seem to have blurred the boundary between scientist and device: Jones often refers to the sub as "we" instead of "it."
Popular Science: Why does the expanded bladder cause the glider to float?
Clayton Jones: This whole glider concept is driven by buoyancy. We're neutrally buoyant compared to the water around us. We're either just floating or just sinking. By changing the volume of the instrument-we don't change the weight-by pushing the mineral oil out into an external bladder, we suddenly take up more space for the same weight. We become lighter than the water around us, and we float.
PS: What about the next dive?
CJ: When we want to go down, we kind of take the oil back into the hull and shrink the bladder. For the same amount of weight, we shrink our volume. We become denser than the water around us, and we sink.
PS: The glider needs the huge range in temperature from the surface to the deep ocean in order to recharge the engine. Does this limit its capabilities?
CJ: Yes, it has limits. You wouldn't use it in shallow or coastal water applications, where the water is mostly warm. Yet if you look at those constraints in a global sense, we can fly in about 80 percent of the world's oceans.