WASHINGTON (CBSDC) — A Defense Department agency successfully refueled drones while they were 45,000 feet in the air.

The Defense Advanced Research Projects Agency concluded its two-year Autonomous High-Altitude Refueling program Sept. 30 after two RQ-4 Global Hawks were able to safely refuel in-flight.

According to DARPA’s press release, the tests proved for the first time that High Altitude Long Endurance class drones can refuel tens of thousands of feet up.

“The goal of this demonstration was to create the expectation that future HALE aircraft will be refueled in flight,” Jim McCormick, DARPA Program Manager, said in a statement. “Such designs should be more affordable to own and operate across a range of mission profiles than systems built to satisfy the most stressing case without refueling.”

The testing found that 60 percent of attempts to refuel drones in-flight were successful, after initially believing only 17 percent would make positive contact. Previous refueling tests for drones required a pilot.

The final test lasted two and a half hours with the drones being navigated 100 feet apart for the refueling process. The refueling can take place during turns and up to wind gusts of 20 knots.