After the event, it was hailed as "a milestone in the history of aviation," but as the sleek black-winged, white-bodied plane rolled down the runway at an airshow at Laupheim airport outside Stuttgart, Germany, last week, 30,000 spectators held their breath. Then came the cheers and thunderous applause: Icare was up and flying.

The name gives some clue to the achievement: Icare derives in part from Icarus of Greek mythology, whose hubris led him to fly too close to the sun on waxen wings--which melted with fatal results. More appropriate was the Re, from the Egyptian sun god, for it was solar power alone that kept the German plane aloft for 15 minutes and propelled it into the history books. Flying at an altitude of about 400 m, pilot Werner Scholz executed some lazy figure-eight turns before bringing Icare smoothly back to earth.

What was the big deal? Didn't American Paul MacCready hop from London to Paris flying without fossil fuel way back in 1981? And didn't Eric Raymond cross America the same way in 1990? Yes, but they were record seekers flying improvised lightweights that required intrepid pilots and a lot of luck. Icare is a conventional plane that had to meet airworthiness requirements from roll-out to landing, such as structural sturdiness and crash capability. Both criteria bring with them weight penalties that make solar flight a major engineering challenge.

How tough that test is was demonstrated by the dropout rate in the competition for a $66,000 prize offered by the city of Ulm, located 72 km southeast of Stuttgart, for the most impressive flight by a solar-powered plane. There were 46 expressions of interest from universities, research centers and private firms. That number fell to 17 entrants, and on the big day only Icare and four other planes were in the hangar at Laupheim. The other four had equally ambitious names, such as Solair II and even O Sole Mio, but only Icare took to the cloudy sky.

The rules required a climb after take-off of not less than 2 m a second. What's more, the aircraft flew with a solar energy of only 540 watts per sq m. On a cloudless day the sun can generate up to 900 watts.

Professor Rudolf Voit-Nitschmann and a team from the University of Stuttgart were among those who originally took up the challenge. Two years and $1 million later, they were polishing the cockpit of Icare. The 260-kg plane has an 8-m fuselage and a wingspan of 25 m. The wings and tail surfaces are covered by 3,000 superefficient photo-voltaic cells, each 10 cm square, providing a total surface area of 21 sq m.

The solar energy captured by Icare's surface powers an electrical engine that in turn drives the plane's single propeller. Designed by Braunschweig professor Herbert Weh, the motor can deliver 12 kw of power but weighs only about 11 kg--about a fifth the weight of a normal motor with that output.

Among the crowd watching Icare lift off was Manfred Reinhardt, president of the International Scientific and Technical Gliding Organization, the international technical body for gliders. Said Reinhardt: "I'm amazed. I didn't think it was possible." Christoph Eitner, who heads the department of solar technology in Bonn's federal Ministry of Education, Science, Research and Technology, was also ecstatic, "This team pushed every bit of technology to the limits. The flight was a solar spectacular." Added Ulm's mayor, Ivo Gonner: "A dream has been realized. This day will go down in aviation history."

Though solar-powered passenger plane flights across continents remain science fiction, Icare's success is important for solar-assisted gliders, and perhaps for remote-controlled flying platforms used to monitor traffic or report weather conditions.

Rudiger Rosenberg, an energy specialist with Greenpeace Germany, said of Icare's brief flight, "Every bit of progress in solar energy brings us closer to the day when it will be a competitive alternative to fossil fuel."

How did it feel for pilot Scholz? On landing he recalled a phrase used by a test pilot after taking up the first jet-engine plane back in 1944, "It's as if you're being pushed by angels." A half-century later Icare provided a heavenly bonus: no pollution.

--Reported by Bruce van Voorst/Bonn