HELIOS: The Ultimate Aerial EV
By Bill Moore
It is propelled by 14 electric motors spinning stubby propellers spaced along a transparent wing that is 8 feet wide, but 246 feet long, longer that a 747-400.
It's called Helios and it just set the altitude record for not only a propeller driven aircraft, but for a non-rocket aircraft, surpassing the official record of the secretive SR-71 Blackbird spy plane. And it did it all on the electric power supplied by sunlight!
During its record breaking flight, which lasted a total of just under 17 hours, the 1,557 pound, remote-controlled, pilot-less aircraft climbed to a record 96,500 feet, besting the SR-71 record by 11,500. It ascended from a surface temperature at the Pacific Range Missile Facility at Barking Sands on the Hawaiian island of Kauai of 80 degrees F to minus 85 degrees F at the very edge of the earth's atmosphere. It accelerated from a take-off speed of 21 mph to 170 mph at its peak altitude or Mach 0.25!
This ultimate electric aerial vehicle, which costs $15 million dollars, was designed and built by EV-pioneers AeroVironment, of Monrovia, California. Under the guidance of Dr. Paul McCready, AeroVironment has designed a long series of unusual aircraft from the human-powered Gossamer Albatross and Condor to the Solar Challenger to the Pathfinder, predecessor of the Helios. The company also designed the developed the prototype of the GM EV1 battery electric car.
The Helios is powered by the electricity supplied from 62,000 photovoltaic solar cells glued to the top of the vehicle's wing, which is constructed of Kevlar, Styrofoam and Mylar. At full-power, the cells generate 41kW of electricity. During the August 13th flight, they were still producing 24kW of energy at 96,500 feet. So close was Helios to the edge of space that AeroVironment engineers said several stars were visible in a special, fish-eye video camera mounted on top of the wing.
Currently the Helios relies on battery back-up to keep it aloft during the day as the sun appears to move across the sky and the Helios gradually orbits at altitude. Sometime in 2003, small combination hydrogen electrolyzer/fuel cells will be incorporated into the design to store excess solar energy during the day. At night, the stored hydrogen will be used to produce electricity to power the aircraft. The "waste" water will be recycled to produce more hydrogen during the day.
The climb to the record books took some seven hours as the Helios climbed at between 200 and 300 feet per minute. The atmosphere is so thin at 96,000 feet (about 0.000038 slugs per cubic foot compare to 0.0023 slugs at sea level) that it took 36 minutes to climb the last 1,200 feet. Four different pilots, working in shifts, guided the Helios during its record climb, which was delayed some 36 minutes due to low cloud cover at Barking Sands.
The Helios team, consisting of people from AeroVironment, NASA, PMRF, ITT, SunPower, HTS, KAS, Niihau Ranch Company, AmTech, and Kauai Community College, spent another anxious hour while the Helios steered clear of clouds, finally climbing above them at 5,000. From there up to 77,000 feet the flight was described as uneventful. Once Helios reached its maximum altitude at 4:10 PM local time, it remained above 96,000 feet for some 40 minutes.
In order to not deplete the onboard batteries, controllers began the long descent back to earth, a descent that took nearly ten hours. The aircraft landed smoothly and uneventfully well after midnight under starry Hawaiian skies.
With the Helios, AeroVironment has clearly set a new benchmark for electric-powered vehicle performance. While unmanned vehicles like Pathfinder and Helios will never carry passengers, it is envisioned that they will fill other commercial niches, one being a low-cost replacement for expensive communications satellites.
NASA, who funded the Helios project as part of its ERAST program, estimates that eventually communication's companies will be able to launch a recoverable Helios-like aircraft that will remain aloft 6 months at a time. Skytower Communications, a newly formed subsidiary of AeroVironment estimates that a Helios-based communications platform operating at "station-keeping" mode at 65,000 feet could be flown for about $20 million, including two aircraft and the associated communications gear. This is about one-tenth the price of launching a low earth orbit communications satellite.
NASA is also looking at the Helios concept for future exploration of Mars where the atmosphere is equivalent to that of the Earth's in the region where the Helios operators. An unmanned, solar-powered flying wing like the Helios could explore and map far more of the surface of the Red Planet than land-based robotic vehicles.
Interestingly, another electric vehicle -- this one built by GM -- was the first passenger-carrying vehicle to drive across another world when Apollo astronauts explored the moon using the Lunar Rover.
Let's see someone try these feats with a gasoline internal combustion engine.
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