Hydrogen-powered high flier

The Global Observer, an unmanned airborne vehicle (UAV) that is designed to stay aloft for up to 7 days at an altitude of up to 65,000 feet while carrying a 400-pound payload, had its first flight last month. The launch from Edwards Air Force Base in California marked the beginning of a test program that will result in a week-long flight in the stratosphere using liquid-hydrogen fuel.

"We successfully completed Global Observer's historic first flight on August 5 and its second flight on August 19,” Bob Curtin, AeroVironment’s vice president of business development, told TechNewsDaily.

“In both flights [the aircraft] employed batteries to fly for more than one hour at a maximum altitude of approximately 4,000 feet above mean sea level. These first two flights satisfied the team's objectives for demonstrating and gathering data on aircraft control, handling, communications and structural performance."

Unmanned platforms like the Global Observer that operate above 50,000 feet combine the capabilities of satellites with the flexibility of aircraft for persistent intelligence, surveillance and reconnaissance (ISR) missions. The aircraft is being developed by AeroVironment under a joint concept technology demonstration (JCTD) sponsored by several U.S. agencies under the direction of the Special Operations Command.

Hydrogen powered

Ultimately, the Global observer will be powered by a liquid-hydrogen-fueled propulsion system. AeroVironment had explored the use of solar power for the aircraft , but determined that liquid hydrogen propulsion was the best solution for a high-altitude, long-endurance UAV. Solar power today is not sufficient to support continuous operation beyond the tropics during winter.

The Global Observer has a 175-foot wingspan and weighs less than 10,000 pounds. It has a modular composite airframe, which enables it be transported by a cargo aircraft, and an internal-combustion engine modified to burn hydrogen that drives a generator to produce electricity to power the UAV’s four propellers. Hydrogen was chosen because it has three times the energy of conventional fuel. When in operation, the aircraft produces no carbon emissions.

"Global Observer is being developed to address the need for an affordable, persistent platform that can provide seamless communications and ISR over any spot on the globe for as long as required,” Curtin said. “Swapping orbits every 5 to 7 days, a two-air vehicle system would maintain uninterrupted coverage in a manner similar to a geosynchronous satellite, but about 2,000 times closer to the earth's surface."

A new frontier

Compared to conventional aircraft, the Global Observer requires fewer takeoffs and landings, which translates into lower cost. And unlike satellites, it can easily be repositioned, the technology can be upgraded and the payload can be switched.

Aerovironment Chairman and CEO Tim Conver believes that the Global Observer can open the stratosphere for practical use just as airplanes opened up the lower atmosphere for use and satellites made operating in space possible.

AeroVironment is best known for small, unmanned aircraft such as the RQ-11 Raven . The Raven, which weighs 4.2 pounds and can stay aloft for 90 minutes, has been used extensively by U.S. troops in Afghanistan for surveillance.