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The Boeing Phantom Eye is a high-tech surveillance and communications drone that runs on liquid hydrogen. [Image courtesy Boeing]

Even as debate continues over the ethical use of drones in foreign and domestic airspace, two new drone designs are nearing full airworthiness—and pushing the boundaries of their respective technologies. Boeing’s Phantom Eye boasts, among other features, a liquid-hydrogen-powered internal combustion propulsion system. The Northrop Grumman MQ-4C Triton carries highly advanced surveillance and communications equipment. Each offers long-range, high-altitude reconnaissance support and long-term flight capability. Both feature relatively long wingspans, and neither is designed to carry weaponry.

The Boeing Phantom Eye propulsion system went through its second flight test in February, when the aircraft achieved an altitude of 8,000 feet and flew for more than an hour without incident. The drone is propelled by two 2.3-liter engines (similar to those used in a Ford Fusion automobile), modified to run on hydrogen. “The only byproduct of the engine is water, so it’s also an environmentally responsible aircraft,” program manager Andrew Mallow said. (In its first test in 2012, the prototype’s landing gear was damaged when it dug into the lakebed upon landing at Edwards Air Force Base; the gear was redesigned for the latest test).

With an initial payload of 450 pounds, and weighing in at about 9,800 pounds, the Phantom Eye is designed primarily for surveillance and can operate at 65,000 feet for up to four days. There are plans for a larger version, featuring a 250-foot wingspan, which will reportedly stay aloft for up to 10 days. According to Boeing, it would take only three such drones to cover operations across the globe.

The Northrop Grumman MQ-4C Triton is designed for naval air operations and carries sophisticated 360-degree sensors that allow it to identify different types of ships and other targets. The drone is intended to play a major role in the military’s surveillance strategy, particularly in the areas surrounding the South China Sea, according to a statement by Rear Adm. Sean Buck, commander of the Navy Patrol and Reconnaissance Group. “Triton will bring an unprecedented ISR [intelligence, surveillance and reconnaissance] capability to the warfighter,” he said.

The MQ-4C weighs about 16 tons and is powered by two Rolls-Royce turbofans. The drone is designed to stay in the air for at least 24 hours at altitudes above 55,000 feet before it needs to be refueled. Tests will continue throughout the year, with operational capability anticipated by late 2015.