NASA Demonstrates Novel Ocean-Powered Underwater Vehicle
NASA, U.S. Navy and university researchers have successfully demonstrated
the first robotic underwater vehicle to be powered entirely by natural, renewable, ocean thermal
energy.
The Sounding Oceanographic Lagrangrian Observer Thermal RECharging (SOLO-TREC)
autonomous underwater vehicle uses a novel thermal recharging engine powered by the natural
temperature differences found at different ocean depths. Scalable for use on most robotic
NASA, U.S. Navy and university researchers have successfully demonstrated
the first robotic underwater vehicle to be powered entirely by natural, renewable, ocean thermal
energy.
The Sounding Oceanographic Lagrangrian Observer Thermal RECharging (SOLO-TREC)
autonomous underwater vehicle uses a novel thermal recharging engine powered by the natural
temperature differences found at different ocean depths. Scalable for use on most robotic
oceanographic vehicles, this technology breakthrough could usher in a new generation of autonomous
underwater vehicles capable of virtually indefinite ocean monitoring for climate and marine animal
studies, exploration and surveillance.
Researchers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.; and the Scripps Institution of
Oceanography, University of California, San Diego, completed the first three months of an ocean
endurance test of the prototype vehicle off the coast of Hawaii in March.
“People have long dreamed of a machine that produces more energy than it consumes and runs
indefinitely,” said Jack Jones, a JPL principal engineer and SOLO-TREC co-principal investigator.
“While not a true perpetual motion machine, since we actually consume some environmental energy,
the prototype system demonstrated by JPL and its partners can continuously monitor the ocean
without a limit on its lifetime imposed by energy supply.”
“Most of Earth is covered by ocean, yet we know less about the ocean than we do about the surface
of some planets,” said Yi Chao, a JPL principal scientist and SOLO-TREC principal investigator.
“This technology to harvest energy from the ocean will have huge implications for how we can
measure and monitor the ocean and its influence on climate.”
SOLO-TREC draws upon the ocean’s thermal energy as it alternately encounters warm surface water
and colder conditions at depth. Key to its operation are the carefully selected waxy substances known
as phase-change materials that are contained in 10 external tubes, which house enough material to
allow net power generation. As the float surfaces and encounters warm temperatures, the material
melts and expands; when it dives and enters cooler waters, the material solidifies and contracts. The
expansion of the wax pressurizes oil stored inside the float. This oil periodically drives a hydraulic
motor that generates electricity and recharges the vehicle’s batteries. Energy from the rechargeable
batteries powers the float’s hydraulic system, which changes the float’s volume (and hence
buoyancy), allowing it to move vertically.
So far, SOLO-TREC has completed more than 300 dives from the ocean surface to a depth of 500
meters (1,640 feet). Its thermal recharging engine produced about 1.7 watt-hours, or 6,100 joules, of
energy per dive, enough electricity to operate the vehicle’s science instruments, GPS receiver,
communications device and buoyancy-control pump.
The SOLO-TREC demonstration culminates five years of research and technology development by
JPL and Scripps and is funded by the Office of Naval Research. JPL developed the thermal
recharging engine, building on the buoyancy engine developed for the Slocum glider by Teledyne
Webb Research, Falmouth, Mass. Scripps redesigned the SOLO profiling float and performed the
integration. The 84-kilogram (183-pound) SOLO-TREC prototype was tested and deployed by the
JPL/Scripps team on Nov. 30, 2009, about 161 kilometers (100 miles) southwest of Honolulu.
The performance of underwater robotic vehicles has traditionally been limited by power
considerations. “Energy harvesting from the natural environment opens the door for a tremendous
expansion in the use of autonomous systems for naval and civilian applications,” said Thomas Swean,
the Office of Naval Research program manager for SOLO-TREC. “This is particularly true for
systems that spend most of their time submerged below the sea surface, where mechanisms for
converting energy are not as readily available. The JPL/Scripps concept is unique in that its stored
energy gets renewed naturally as the platform traverses ocean thermal gradients, so, in theory, the
system has unlimited range and endurance. This is a very significant advance.”
SOLO-TREC is now in an extended mission. The JPL/Scripps team plans to operate SOLO-TREC
for many more months, if not years. “The present thermal engine shows the great promise in
harvesting ocean thermal energy,” said Russ Davis, a Scripps oceanographer. “With further
engineering refinement, SOLO-TREC has the potential to augment ocean monitoring currently done
by the 3,200 battery-powered Argo floats.” The international Argo array, supported in part by the
National Oceanic and Atmospheric Administration, measures temperature, salinity and velocity across
the world’s ocean. NASA and the U.S. Navy also plan to apply this thermal recharging technology to
the next generation of submersible vehicles.
To learn more about SOLO-TREC, visit http://solo-trec.jpl.nasa.gov .
For more information about NASA and agency programs, visit: http://www.nasa.gov .
JPL is managed for NASA by the California Institute of Technology in Pasadena.
