The solar-powered Helios Prototype is nearly ready for a summertime attempt at a never-before-achieved milestone in the annals of flight - sustaining horizontal flight at 100,000 feet above the Earth.
The Helios Prototype was shipped to Hawaii in late March, and engineers and technicians for AeroVironment, Inc., the giant flying wing's manufacturer, began the process of reassembly and checkout of the craft at the Navy's Pacific Missile Range Facility on the island of Kaua'i in April. A full-scale combined systems test took place April 28, and according to Dryden's solar-aircraft project manager John Del Frate, the test went well, with no major anomalies or issues.
The first flight under solar power, covering functional checkout and flight envelope expansion, is targeted for late May to early June. Depending on the results of that flight, the first attempt to reach and sustain flight at 100,000 feet altitude could come as early as late June or early July.
AeroVironment technicians had completed installation of high-efficiency solar cell arrays on all six of the Helios Prototype's wing sections early this year. They also completed upgrades to the ground control station, the tracking antennas, and updated operational procedures. More recently, AeroVironment has developed a new propeller design, which is both stronger and more efficient than the propellers, which drove the Helios Prototype during its earlier test flights.
The 247-foot-span ultralight flying wing, whose development is being funded and managed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) project, flew six low-altitude airworthiness validation flights on battery power at NASA Dryden in the fall of 1999.
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 endurance demonstration flight above 50,000 feet planned for 2003. Development of a regenerative hydrogen-oxygen energy storage system, which would make the multi-day continuous flight possible, is progressing at AeroVironment. The system uses excess power generated by the solar arrays during the daytime to run an electrolyzer that separates water into its component parts, hydrogen and oxygen, which are then stored under pressure in specially-designed tanks. At night, the hydrogen and oxygen are recombined by the fuel cells, with electricity produced as a by-product, providing power to Helios' motors.
Two subcontractors, Giner and Lynntech, have developed prototype "short-stack" fuel cells and electrolyzers that have undergone rigorous testing. Lynntech has now built full-size units, which will undergo high-pressure testing before being installed in a prototype energy storage system at AeroVironment. The completed system will then be subject to both sea-level and high-altitude testing in an altitude chamber. Further testing of Giner's intermediate and full-size fuel cell and electrolyzer components will also be conducted. In addition, another subcontractor, Kaiser Compositek, is developing and testing composite pressure tanks for storing the hydrogen and oxygen.
