Engineers at NASA's Dryden Flight Research Center say that the initial low-altitude flight tests of the remotely piloted Centurion airplane were an unqualified success, following the conclusion of the series with a third and final flight Dec. 3.

Project officials noted that all of the objectives of the series were met ahead of schedule. Four to seven missions had originally been planned, but the test series was completed in only three flights.

Although Centurion did its initial test flights with batteries, the upper surface of the 206-foot-long Centurion will eventually be covered with solar cells to support program officials' plans to achieve high-altitude flight tests to 90,000 to 100,000 feet.

An earlier version of the plane, the Pathfinder Plus, achieved a world record height for a propeller-driven airplane of 80,000 feet in tests at the Pacific Missile Range Facility (PMRF) in Hawaii in August of this year. That plane flew entirely on solar power.

Last Thursday's flight represented the 43rd consecutive successful flight of this type of solar aircraft. NASA has sponsored development of the Pathfinder under the Environmental Research Aircraft and Sensor Technology (ERAST) program.

The Centurion is the latest evolution of AeroVironment's solar aircraft platform, refined and proven over more than a decade. Centurion is a production prototype designed to validate the technology for the next and ultimate step, Helios, a long-endurance derivative of the Centurion design.

Helios will incorporate energy storage for nighttime flight and be capable of continuous flight for six months at a time at altitudes of over 60,000 feet on telecommunications or science missions. The ERAST program is working to develop the technology base for a future fleet of such remotely piloted aircraft.

For its final flight the Centurion carried a simulated payload of more than 600 pounds -- approximately half the lightweight aircraft's empty weight. John Del Frate, the NASA program manager, noted the airframe "really has the muscle to do big jobs."

Bill Parks of AeroVironment, Centurion's chief engineer and flight test director, noted the high gross-weight payload was a major objective of the flight test program: "We verified the performance of the aircraft while flying in a high gross-weight configuration.

"We came here with a new variant of our proven platform and it performed exactly as expected; there were no aircraft systems failures that had to be corrected. It doesn't get any better than that," Parks added.

Ray Morgan, vice president of AeroVironment's Design and Development Center, noted that the Centurion altitude and payload targets are significantly higher than those of eventual Helios telecommunications applications (100,000 feet versus 50,000-70,000 feet, and 600 lbs versus about 200 lbs payload). "We've purposely overdesigned the plane versus its likely commercial missions."

The successful record flight is one more milestone on the way to commercial solar-powered aircraft becoming low-cost complements to satellites.

According to Tim Conver, president of AeroVironment: "Until now, there has been only one sort of high-altitude, long-duration platform available -- satellites. High-altitude solar planes will be cost-effective as a substitute or complement for many applications currently performed by satellites.

"They can relay communications signals. They can take photos. They can track hurricanes. They can do exactly what a satellite does, but more flexibly and with less investment. We are looking at telecommunications applications as a major possible avenue of growth for AeroVironment," Conver concluded.

For some communications applications, Helios will have critical advantages over satellites: distance, location and recovery. At under 15 miles altitude, solar airplanes are much closer to the ground than any satellite, allowing use of much cheaper transmitters and reuse of scarce frequency spectrum. Because solar airplanes can land and take off as needed, their payloads can incorporate the latest technology and avoid obsolescence.

At well under $10 million each in production, solar airplanes can also be significantly less expensive than satellites, which can cost up to $100 million or more to build and launch. Given these advantages and the success of the plane's development program, the commercial future for solar airplanes looks very promising.

Morgan believes "It's inevitable that, in the future, solar-powered aircraft will be operating routinely as stratospheric satellites."

David Nufer, chief marketing executive of AeroVironment, noted that there has been significant interest among aerospace and telecommunications firms in the Helios solar platform and that "we are pursuing these potential opportunities aggressively."

AeroVironment has long been known as the leader in solar flight.

Other pioneering air vehicles produced by AeroVironment have included the human-powered "Gossamer Albatross," and the solar-powered "Gossamer Penguin" and "Solar Challenger." In 1981, the Solar Challenger flew 163 miles from Paris to London, at altitudes up to 11,000 feet, powered only by the sun.

The Solar Challenger is now owned by the Smithsonian Institute's National Air and Space Museum. Ground-breaking land vehicles have included the "Sunraycer" solar-powered car and the "Impact" electric car, forerunner of the General Motors EV1.