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NASA News
National Aeronautics and
Space Administration
Dryden Flight Research Center
P.O. Box 273
Edwards, California 93523
Phone   (661) 276-3449
FAX (661) 276-3566 
                        __
May 29, 2003


Alan Brown
NASA Dryden Flight Research Center
(661) 276-2665
alan.brown{at}dfrc.nasa.gov

RELEASE: 03-27

HELIOS PROTOTYPE SET FOR LONG-ENDURANCE FLIGHT DEMONSTRATION

    The solar-powered flying wing that set a world altitude 
record two years ago is poised for another milestone flight this 
summer - a long-endurance mission of almost two days and nights in 
the stratosphere.

    This year's mission for NASA's Helios Prototype will be 
powered with high-efficiency solar arrays by day and a newly 
developed fuel cell-based electrical energy system at night. 
Developed by Helios' manufacturer, AeroVironment, Inc., of Monrovia, 
Calif., the system combines advanced automotive fuel cell components 
with proprietary control technology designed for the harsh 
environment above 50,000 feet altitude.

    The two-day endurance flight demonstration will be the 
crowning achievement in NASA's 10-year Environmental Research 
Aircraft and Sensor Technology (ERAST) project, under which the 
Helios Prototype and several other remotely operated unmanned aerial 
vehicles (UAV) were developed. The ERAST project will conclude this 
September.

    "The Helios Prototype has proven its capabilities to conquer 
the day on solar power," said John Del Frate, Helios project manager 
at NASA's Dryden Flight Research Center. "Now to fulfill the 
long-term vision for it to fly routinely for extreme duration, the 
next challenge is to conquer the night. The key to that is 
development of the fuel cell system. It's the necessary next step to 
extreme endurance."

    Depending on technical and scheduling issues, the 
long-endurance demonstration flight could occur as early as mid-July 
from the U.S.  Navy's Pacific Missile Range Facility (PMRF) on the 
Hawaiian island of Kaua'i. A preliminary liftoff test May 15 on the 
PMRF runway showed the craft was stable despite the increased weight 
and load distribution of the fuel cell system. A 20-hour checkout 
flight to operate the system at altitudes above 50,000 feet is 
tentatively scheduled for early June. 

    Del Frate noted that the Helios Prototype will be the first 
large airplane to fly on fuel cell power, and the first to do so at 
night. The AeroVironment system consumes no fossil fuels, emits no 
atmospheric pollutants, and has a power-to-weight ratio about twice 
that of the best battery systems.

    The fuel cell system being flight tested this summer combines 
gaseous hydrogen from two pressurized tanks mounted on Helios' 
outboard wing sections with oxygen from the atmosphere. The hydrogen 
and oxygen are fed to a series of proton-exchange membrane fuel cell 
"stacks" mounted in the central landing gear pod. The system produces 
more than 15 kW of direct-current electricity to power Helios' motors 
and operating systems, with the only by-product being water vapor and 
heat.

    "The challenge is to operate the fuel cell system in a 
high-altitude flight environment," said AeroVironment engineer Bill 
Parks, who led the development effort. "We had to learn a lot about 
operating in that environment. There were a number of tradeoffs, in 
terms of weight vs. efficiency, all of which were optimized for this 
(high-altitude flight) application."

    In August 2001, flying on electrical power generated solely 
by the 62,000 silicon solar cells mounted across the upper surface if 
its 247-foot long wing, Helios soared to an altitude of 96,863 feet, 
maintaining stable horizontal flight above 96,000 feet for more than 
40 minutes. It was a world record for all winged aircraft except 
those powered by rockets. 

    Although the ERAST project will end this year, further 
development of the fuel cell system is likely to continue under a 
follow-on NASA project to perfect a regenerative version of the 
system.

"A mature non-regenerative system similar to the one we are flying 
this summer has the potential to fly continuously for two weeks in 
the stratosphere," Del Frate explained. "It can give the Helios 
year-around global coverage, not limited to temperate or equatorial 
climes or latitudes.

"After testing on this system is finished this summer, we will focus 
on development of a fully regenerative system that could fly up to 
six months or more," he added.

Del Frate said a production version of the Helios with the 
regenerative fuel cell system is of interest to NASA for 
environmental science, the military and AeroVironment for various 
roles, primarily as a stratospheric telecommunications relay platform.

The latter role will be the focus of a flight demonstration planned 
for September at PMRF, in which the Helios Prototype will carry 
advanced broadband Internet connectivity and antenna systems 
developed by Japan's Communication Research Laboratory and the 
Telecommunications Advancement Organization of the Japanese Ministry 
of Public Management, Home Affairs, Post and Telecommunications.

"These are payloads designed to be carried aboard a proposed high 
altitude stratospheric airship," Del Frate explained. "We are 
providing a mechanism to test these technologies under operating 
conditions - flying slow, fairly stationary orbits at 65,000 feet 
altitude - conditions currently impossible for other aircraft."

- NASA -

    Still photos and video footage of prior flights are available 
to support this release. Photos are available on the NASA Dryden 
Flight Research Center internet website at:

http://www.dfrc.nasa.gov/Gallery/Photo/Helios/index.html

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