The six-foot-long glider was launched from a point about 100 miles south of Nantucket Island, Mass. on September 11 of this year. It traveled slowly at an average speed of about 12 miles per day and was recovered last week just north of Bermuda. It has no outside moving parts - at all. It moves forward by using battery-powered hydraulic pumps to vary its air volume by a few hundred cubic centimeters (using oil-filled bladders); this generates the buoyancy changes that power its forward gliding (see path diagram below).

(From Spray Autonomous Underwater Vehicle)

The batteries also power on-board instruments to measure temperature, salinity, pressure and the turbidity of the water (a measure that relates to biological productivity). Spray records its surface position at each point; it rolls 90 degrees to allow the GPS antenna embedded in the right wingtip to gather that data. Every seven hours it spends fifteen minutes on the surface to send data back to scientists Breck Owens from Woods Hole Oceanographic Institution, and Russ Davis and Jeff Sherman of Scripps Institution of Oceanography at the University of California, San Diego, using the satellite phone in its left wing.

(From Spray Autonomous Underwater Vehicle)

Spray is capable of maintaining its course autonomously, but operators on shore can send new commands to change course or alter the data gathering parameters at any time. "The key," said Davis, "is that Spray can stay at sea for months at relatively low cost, allowing us to observe large-scale changes under the ocean surface that might otherwise go unobserved."

Spray has a potential range of up to 3,500 miles - it could someday cross the Atlantic Ocean or explore other ocean basins. "We envision having fleets of gliders in operation in a few years," Owens said. "It could change the very nature of the kinds of questions we can ask about how the ocean works."

Future missions planned for 2005 include a round trip from Woods Hole, Mass to Bermuda; an Acoustic Doppler current Profiler will be used to give vertical profiles of current speed and velocity. Other sensors could be added to measure dissolved oxygen, carbon dioxide, alkalinity and nutrients in the ocean water.

"Oceanographic gliders are now at the stage similar to the start of aviation," Sherman said. Today's autonomous buoyancy-driven vehicles owe their existence to a visionary article published in 1989 by Henry Stommel.