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April 24, 2002

Release: 02-24

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In a major breakthrough which met a NASA performance requirement,engineers from AeroVironment, Inc., and NASA have successfullycompleted functional tests of a prototype regenerative Energy StorageSystem for the Helios Prototype solar-powered aircraft.

The prototype system, housed within a pod that is designed to replace oneof the existing landing gear pods, contains a hydrogen-oxygen regenerativefuel cell system that could be used to power the Helios aircraft through thenight in future flight demonstrations. The energy storage system is thecrucial element required to enable a solar-powered aircraft to fly longerthan a single day and potentially for unlimited duration.

The energy storage system is based on proton exchange membrane (alsoknown as polymer electrolyte membrane) fuel cell technology now rapidlyemerging in automotive applications. The system is designed to captureexcess electric power produced by the Helios Prototype's solar arraysduring daytime flight and use it to electrolyze water into its constituentgases, hydrogen and oxygen. These gases would be stored under pressureand recombined in a fuel cell, producing electricity as a byproduct to enablenight flight.

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The recently completed tests, conducted at National Technical Systems inSaugus, Calif., climaxed more than two years of development work anddemonstrated the viability of a flight-configured, hydrogen-oxygen aerospaceregenerative fuel cell energy storage system. During the simulated dayportion of the test, the prototype system absorbed 16 kilowatts of electricalenergy for a period of about 5.5 hours until the storage tanks were fullycharged by the electrolyzer. During the simulated night phase of testing, gaswas discharged from the tanks over a period of about five hours into the fuelcell stack, producing up to 4.6 kW.

The prototype tests were conducted at sea level conditions with a system that,although not yet as light as will be required for flight on the Helios Prototype,has the essential attributes to fulfill the form, fit and function requirements ofa flightworthy energy storage system.

"The significance of this system cannot be overstated," said John Del Frate,solar aircraft project manager at NASA Dryden Flight Research Center. "Aflight-weight energy storage system not only gives Helios the ability to flythrough the night, but eventually the capability to fly continuously as a stratospheric platform with its duration limited only by thereliability of onboard systems."

"The Helios project office believes this may be the first demonstration of aportable high power regenerative energy storage device based onenvironmentally friendly fuel cell technology," Del Frate commented. "Thenew technology demonstrates an energy storage density better than doublethe most advanced secondary battery systems yet devised.

"This lightweight portable regenerative energy storage technology can alsobe configured and scaled for non-aircraft applications," he added. "Some ofthose applications include NASA space exploration and planetary surfacepower, electric vehicles, and both fixed and portable solar power on Earth."

The completion of this effort successfully fulfilled a milestone establishedunder NASA's Environmental Research Aircraft and Sensor Technology(ERAST) project, which is managed at NASA Dryden. The HeliosPrototype met another ERAST milestone last August when it flew to anunofficial world altitude record for non-rocket-powered aircraft of 96,863feet near Hawaii and maintained stable horizontal flight above 96,000 feet for more than 40 minutes.

The energy storage system design team was led by AeroVironment, with technical assistance from NASA Dryden Flight ResearchCenter at Edwards, Calif., and NASA Glenn Research Center, Cleveland, Ohio.


Note to Editors: Still photos and video footage of the Helios Prototype solar aircraft and graphic illustrations of the Helios' energy storage system are available from the Dryden Public Affairs Office to support this release. Still photos of the aircraft are available on the NASA Dryden Flight Research Center Internet web site, URL: /centers/dfrc/Gallery/Photo/Helios/index.html

For photo prints, graphic illustrations or video dubs, please call (661) 276-2665 or (661) 276-3449.

NASA Dryden news releases are also available on the Internet at: /centers/dfrc/Newsroom/NewsReleases/index.html

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