Boeing’s [BA] liquid hydrogen-powered Phantom Eye unmanned aerial vehicle (UAV) completed its second flight Feb. 25, demonstrating capabilities that could allow it to perform intelligence, surveillance and reconnaissance (ISR) missions for up to four days without refueling.

The 150-foot wingspan Phantom Eye climbed above an altitude of 8,000 feet and remained aloft for 66 minutes at a cruising speed of 62 knots before landing. The aircraft exceeded what it achieved last year during its first flight when it flew at an altitude of 4,080 feet and remained aloft for 28 minutes, according to a company statement.

“We’re going to slowly expand the envelope of Phantom Eye with the eventual goal of getting up to 65,000 feet at pretty much the same speeds as the first flight in the 62 knots region,” Boeing Phantom Eye Program Manager Drew Mallow said last week in an interview.

Mallow said two other significant achievements in Phantom Eye’s second flight were flight testing new landing gear and improving the UAV’s software. Mallow said Boeing brought over people from its military aircraft division working on F-15 and F-18 landing gear and immersed them in the Phantom Works prototyping approach. Mallow said the additional expertise helped Boeing quickly design, build, and test the landing gear while landing.

The purpose of the company-funded Phantom Eye development is to prove the endurance capability of the hydrogen propulsion and fuel system as well as the high altitude capability, Mallow said. Boeing Chief Program Engineer Brad Shaw said last week hydrogen has three times the energy content of normal aviation fuel.

Now that Boeing has the landing gear working properly, Mallow said the company will have much more minor changes, such as fine tuning some control systems, as the program moves forward. But despite the successful test flights, Mallow said he didn’t know when Boeing would be ready for a third test flight.

Boeing will continue to push Phantom Eye’s horizons with each subsequent flight, Mallow said.

“What we’re going to keep doing is slowly expanding the envelope and as we get more and more confident, we’ll go up to 65,000 feet,” Mallow said. “But we haven’t decided what the next flight window will be yet and I don’t think it will be up to 65,000 feet.”

Mallow said not only does Boeing eventually want Phantom Eye to reach a four-day endurance, but he said the company has been in discussion with interested customers who want a 10-day endurance capability.

“You can take the same propulsion system with different fuel tanks on a larger air vehicle and it would have 10-day endurance capability,” Mallow said. “We envision a lot of need for a vehicle, eventually, that would be in the 10-day endurance capability and that would allow you with basically three vehicles to basically cover almost the entire globe from a surveillance-type capability.”

Mallow said when Boeing originally designed Phantom Eye, it allocated that the vehicle would be capable of carrying 450 pounds worth of payload. He said there was no payload on this Phantom Eye flight and there will be no payload until its high altitude capability is proven.

Phantom Eye’s first flight took place last summer, climbing to an altitude of 4,080 feet and cruising at 62 knots (Defense Daily, June 6). Boeing envisions Phantom Eye competing with Northrop Grumman’s [NOC] Global Hawk UAV (Defense Daily, April 12).