July 18, 2001 The sky is black 100,000 feet above ground, and you can clearly see the curvature of the Earth. The air is so thin it is incapable of supporting life. It is also incapable of supporting sustained horizontal flight of an aircraft -- until now.
It is into that hostile environment 19 miles above ground that a small group of engineers from NASA's Dryden Flight Research Center, Edwards, CA, and AeroVironment, Inc., Monrovia, CA, plan to fly the unique unmanned solar-powered Helios Prototype.
The giant yet ultralight flying wing could soar into the stratosphere on its quest as early as the second week in August, after successfully completing an 18-hour functional checkout flight on July 15. The flights are being conducted from the U.S. Navy's Pacific Missile Range Facility on the Hawaiian island of Kauai.
Should the Helios Prototype reach its objective, it would set a new world's altitude record for propeller-driven aircraft, surpassing the 80,201-foot record of its predecessor, the solar-electric Pathfinder-Plus, set in August, 1998. It would also exceed the highest reported altitude achieved in sustained horizontal flight by jet-powered aircraft as well, 85,068 feet by a SR-71 aircraft in July, 1976. Only short- duration rocket-powered aircraft have flown higher.
The Helios Prototype is one of the unique remotely operated, uninhabited aerial vehicles (UAV) being developed for high- altitude, long-duration earth science imaging and atmospheric sampling missions under the Environmental Research Aircraft and Sensor Technology (ERAST) project at Dryden.
John Del Frate, project manager for solar-powered aircraft at Dryden, noted that setting an altitude record is only one of several goals for this summer's flight tests. "A 100,000-foot altitude record would be the icing on the cake," he said. "Our primary interest in testing this new aircraft is for taking sophisticated lightweight science instruments to greater heights."
"Another added bonus for NASA is the fact that flight at 100,000 feet would be very similar to flight in the Martian atmosphere," Del Frate added. "In a way, we are going to school on these flights to learn what the aerodynamics are like in these conditions."
AeroVironment vice-president Robert Curtin noted that production versions of the Helios could also serve as long- endurance commercial telecommunications relay platforms, orbiting over major population centers at 55,000 to 70,000 feet altitude for months at a time. Disaster recovery agencies might one day be able to move a Helios over the scene of a catastrophe where the normal communications infrastructure has been destroyed.
"AeroVironment's goal is to develop an airplane that is the equivalent of an 11-mile-high tower in the sky," he added.
The primary objective of Helios' recent checkout flight was to expand the flight envelope of the aircraft and verify proper operation of aircraft systems at high altitudes. Reaching an altitude of 76,271 feet was considered necessary in order to reduce risk for the upcoming effort to achieve sustained horizontal flight at 100,000 feet altitude.
The 247-foot-span ultralight flying wing flew six low- altitude initial airworthiness validation flights on battery power at NASA Dryden in the fall of 1999.
Since then, the Helios Prototype has undergone major upgrades, including the installation of approximately 65,000 high-efficiency solar cells across the wing, which can produce more than 35 kilowatts of electricity.
The 100,000-foot altitude flight is one of two major flight milestones set for the craft by NASA, the other being a four- day non-stop long-endurance demonstration flight above 50,000 feet planned for 2003.
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