Worker applies solar panels to Pathfinder.

Almost twenty years after MacCready's human-powered plane, the Gossamer Condor, flew into history, its direct descendants are reaching new heights.

In 1995, Scientific American Frontiers was there for the first high- altitude test flight of the Pathfinder, a 100-foot flying wing designed by MacCready's company, AeroVironment. Fueled by a layer of wafer-thin solar cells with the power equivalent of just four hair dryers, the Pathfinder reached an astounding 50,000 feet.

Helios in flight

In "The Eternal Wing," Frontiers checks in again with Bob Curtin and the AeroVironment team. The next generation of flying wings, the 250-foot Helios, has been designed by engineers to reach an altitude of 100,000 feet.

NASA is funding the flying wing project in the hopes that the solar-powered planes might soon replace more expensive, higher maintenance satellites. Circling high above commercial airlines, Helios may one day relay voice, television or Internet signals.

Though AeroVironment engineers are still tinkering with its control system, so far the Helios has performed flawlessly.

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