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

The prototype system, housed within a pod that is designed to replace
one of the existing landing gear pods, contains a hydrogen-oxygen
regenerative fuel cell system that could be used to power the Helios
aircraft through the night in future flight demonstrations. The
energy storage system is the crucial element required to enable a
solar-powered aircraft to fly longer than a single day and
potentially for unlimited duration.

The energy storage system is based on proton exchange membrane (also
known as polymer electrolyte membrane) fuel cell technology now
rapidly emerging in automotive applications. The system is designed
to capture excess electric power produced by the Helios Prototype’s
solar arrays during daytime flight and use it to electrolyze water
into its constituent gases, hydrogen and oxygen. These gases would
be stored under pressure and recombined in a fuel cell, producing
electricity as a byproduct to enable night flight.

The recently completed tests, conducted at National Technical Systems
in Saugus, Calif., climaxed more than two years of development work
and demonstrated the viability of a flight-configured,
hydrogen-oxygen aerospace regenerative fuel cell energy storage
system. During the simulated day portion of the test, the prototype
system absorbed 16 kilowatts of electrical energy for a period of
about 5.5 hours until the storage tanks were fully charged by the
electrolyzer. During the simulated night phase of testing, gas was
discharged from the tanks over a period of about five hours into the
fuel cell 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 of a flightworthy energy storage

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

“The Helios project office believes this may be the first
demonstration of a portable high power regenerative energy storage
device based on environmentally friendly fuel cell technology,” Del
Frate commented. “The new technology demonstrates an energy storage
density better than double the most advanced secondary battery
systems yet devised.

“This lightweight portable regenerative energy storage technology can
also be configured and scaled for non-aircraft applications,” he
added. “Some of those applications include NASA space exploration and
planetary surface power, electric vehicles, and both fixed and
portable solar power on Earth.”

The completion of this effort successfully fulfilled a milestone
established under NASA’s Environmental Research Aircraft and Sensor
Technology (ERAST) project, which is managed at NASA Dryden. The
Helios Prototype met another ERAST milestone last August when it flew
to an unofficial world altitude record for non-rocket-powered
aircraft of 96,863 feet 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 Research Center at
Edwards, Calif., and NASA Glenn Research Center, Cleveland, Ohio.


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:

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