Northrop Grumman Planning First UAV-to-UAV Aerial Refueling

At Northrop Grumman’s unmanned systems development center in suburban San Diego, some folks are describing a $33 million contract that was announced today as “DARPA hard.”

DARPA is an acronym for the Pentagon’s Defense Advanced Research Projects Agency, and the two-year contract awarded to Northrop Grumman calls for demonstrating the feasibility of using one high-altitude unmanned Global Hawk aircraft to refuel another. The UAV-to-UAV in-flight refueling is to be completely autonomous, with the robotic aircraft using GPS navigation and optical tracking systems to approach, link up, and complete the refueling procedure. If successful, the first unmanned aerial vehicle (UAV) air-to-air refueling will mark a historic milestone—for both aviation and robotics.

UAV-UAV aerial refueling (photo illustration)

UAV-UAV aerial refueling (photo illustration)

While mid-air refueling has been done with piloted aircraft since 1923, it remains a tricky and hazardous maneuver that requires extensive pilot training. In the case of two robotic aircraft, both UAVs must automatically adjust to turbulence and other environmental uncertainties while maneuvering in the thin air of high altitude (the Global Hawk’s cruising altitude is 65,000 feet).

“So this one definitely fits” the category of DARPA hard, says Mark Gamache, the San Diego-based director of advanced concepts for Northrop Grumman Aerospace Systems. In a telephone interview, Gamache tells me DARPA hard “means they only like to work on projects that nobody else would do.”

The Global Hawk was itself the product of DARPA-funded development during the 1990s, with the first seven aircraft built in San Diego under the agency’s Advanced Concept Technology Demonstration program. The first flight was on Feb. 28, 1998. Conceived as the robotic equivalent of Lockheed’s U-2 spy plane, the current Global Hawk design is powered by a single jet engine, and was designed with a nearly 131-foot wingspan to intelligence-gathering surveillance missions for up to 40 hours. Images and data are relayed by satellite.

But not everyone at the Pentagon is a Global Hawk fan. Earlier this week, Ashton Carter, the Defense Department’s undersecretary of acquisition technology and logistics, told reporters the Global Hawk is “on a path to be non-affordable.” The program has been plagued with cost overruns, and while the Global Hawk officially costs about $35 million for each aircraft, it’s more like $123 million apiece when development costs are added to the mix.

The refueling mission will be flown in reverse order, Gamache says, with the tanker UAV following behind the UAV that needs refueling. “We want the aircraft with the smarts and the maneuvering capabilities in the rear,” Gamache says. The development schedule calls for the first UAV-UAV refueling flight sometime during the first half of 2012.

The core innovation requires the integration of a GPS navigation system (developed by Sierra Nevada of Sparks, NV) and optical tracking system with the computerized mission management system that Northrop Grumman developed to operate the flight controls—and “achieving the precision required to maneuver the aircraft,” Gamache says. “Really, it’s an integration of several technologies to achieve that precision tolerance.”

Bruce V. Bigelow is the editor of Xconomy San Diego. You can e-mail him at or call (619) 669-8788 Follow @bvbigelow

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  • C Butts

    Qinetiq flew the ‘Eternal’ Zephyr UAV for two weeks without landing, one year ago.

    It carried two army Combat-Net field radios. The UAV was covered with PV solar cell skin to power the radios and electric motors.