Following an initial hour-long, battery-powered flight, AeroVironment’s Global Observer unmanned aircraft is beginning a test program planned to culminate in a week-long flight in the stratosphere using liquid-hydrogen fuel. The flight debuts an innovative approach to persistent surveillance and marks a dramatic departure for a company that dominates the market for small, hand-launched UAVs.

The Global Observer (GO) is flying from Edwards AFB, Calif., where it will undergo an operational utility assessment under a joint concept technology demonstration (JCTD) sponsored by several U.S. agencies and led by Special Operations Command. The initial GO-1 aircraft is designed to stay aloft for seven days at up to 65,000 ft. carrying a 400-lb. payload.

The aircraft reached almost 4,000 ft. on its Aug. 5 first flight and conducted a series of maneuvers, including climbs and turns. After battery-powered flights to expand the envelope, the Global Observer will begin using hydrogen fuel.

Unmanned platforms orbiting in the stratosphere for extended periods could allow operators to combine the capabilities of satellites with the flexibility of aircraft. But endurance measured in days not hours requires a different approach to design and propulsion.

After experimenting with solar power, AeroVironment selected hydrogen propulsion as the most practical solution for a high-altitude, long-endurance UAV that can be launched at short notice to maintain a continuous presence at low cost for persistent surveillance, communications relay, border security, remote sensing and other missions.

“In the same way that airplanes opened the lower atmosphere to practical use, and satellites did for space, we believe that the stratosphere can be opened for practical use by Global Observer,” says Chairman and CEO Tim Conver. Covering an area 600 mi. in diameter from the vantage point of the stratosphere with an affordable, persistent platform “translates into more coverage for fewer dollars,” he says.

“Compared to conventional aircraft, GO requires fewer takeoffs and landings, which translates into lower cost,” he says. “Compared to satellites, it will be easy to reposition GO, to upgrade technology and change out payloads.” The company calculates that the GO system requires up to two times fewer aircraft and eight times fewer takeoffs and landings to maintain year-round coverage compared with conventional UAVs.

AeroVironment is better known for its small unmanned aircraft, particularly the RQ-11 Raven, thousands of which have been produced. The hand-launched, battery-powered Raven weighs 4.2 lb. and flies for 90 min. The Wasp is even smaller, and the company is developing the Switchblade, a tube-launched lethal UAV, and the Shrike, a vertical-takeoff-and-landing “perch-and-stare” micro-UAV.

The Global Observer is a return to AeroVironment’s origins in designing large, lightweight aircraft. The company was founded by Paul MacCready, whose Gossamer Condor made the first sustained, controlled, human-powered flight in 1977. This led to the development of solar-powered aircraft—the Solar Challenger crossed the English Channel in 1981.

As part of NASA’s Environmental Research Aircraft and Sensor Technology (Erast) program, AeroVironment then developed a series of high-altitude, solar-powered unmanned aircraft. The 100-ft.-span Pathfinder reached 71,500 ft. in 1977, the 120-ft. Pathfinder-Plus exceeded 80,000 ft. and the 247-ft. Helios reached 96,860 ft. in 2001. All these aircraft were flying wings sheathed with photovoltaic cells.