Facebook's Connectivity Lab announced today that the company has for the first time test-flown a full-scale version of Aquila, the solar-powered high-altitude drone that Facebook hopes to use to deliver Internet connectivity to the remotest populated corners of the Earth. The test flight took place June 28 but was only announced today by Facebook.

The low-altitude test flight was originally intended only as a 30-minute “functional check” flight. "It was so successful that we ended up flying Aquila for more than 90 minutes—three times longer than originally planned," wrote Jay Parikh, Facebook's vice president of infrastructure engineering, in a post to Facebook's Newsroom blog published today.

The initial test goals were simply to ensure that the huge Aquila drone—with a wingspan comparable to a Boeing 737 and mass more like an automobile—could even get airborne. To minimize its weight, Aquila doesn't have "traditional landing gear," according to Martin Gomez and Andy Cox of the Aquila team. "We attached the airplane to a dolly structure using four straps, then accelerated the dolly to takeoff speed. Once the autopilot sensed that the plane had reached the right speed, the straps were cut simultaneously by pyrotechnic cable cutters known as 'squibs.'"

The entire takeoff sequence is driven by the drone's autopilot. But despite testing with a scaled-down (1/5-size) drone previously, this was the first time the computer modeling for the take-off attitude and speed had been tested. "The specifications based on our simulations resulted in a successful takeoff," Cox and Gomez reported on Facebook's Engineering Blog today.

The test also collected data on Aquila's aerodynamic performance at low altitude, its battery and power usage, and the effectiveness of the autopilot system. Like other autonomous drones, Aquila can be remotely commanded to fly by GPS waypoints, but all of the actual flying is done by the autopilot without direct human control. And this flight was the first opportunity to test the performance of the autopilot on a full-sized drone under real-world atmospheric conditions.

Parikh said the flight was a test of the Aquila drone's performance characteristics and components, including its batteries and control system, as well as a verification of the Aquila's crew training. "In our next tests," he said, "we will fly Aquila faster, higher, and longer, eventually taking it above 60,000 feet."

The goal of Aquila is to provide what has been described as an "atmospheric satellite" capability—the drones will fly for up to three months at a time, orbiting over remote areas and providing connectivity for a circle as much as 60 miles in diameter, using a laser-based network "backbone" and radio signals for local bandwidth. Because of its lift-to-weight ratio, Aquila can fly as slowly as 25 miles per hour in level flight.

But to achieve that goal, the Aquila team is going to have to significantly push forward solar-powered aircraft technology. "We will need to break the world record for solar-powered [uncrewed] flight, which currently stands at two weeks," Parikh noted. "This will require significant advancements in science and engineering to achieve."

Among the biggest challenges facing the Aquila team is getting enough sunlight to continually recharge the drone's batteries so it can stay aloft at night. That will be a challenge during winter months—while the drone's motors will only require about 5,000 watts of power to stay aloft at high altitude, it will have to fully recharge batteries with as little as 10 hours a day of sunlight in the expected range for Aquila's operation. And those batteries will have to be as light as possible to allow Aquila to perform its mission. "Given current and projected battery performance," Cox and Gomez noted, "that means batteries will account for roughly half the mass of the airplane. We’re pushing the edge of high energy-density batteries while exploring the best designs to ensure we have enough resilience in the system."

There are additional challenges that have less to do with getting into the air and more to do with Aquila being allowed to get there in the first place. In addition to making Aquila financially sustainable—by reducing how much it costs to operate and maintain—Facebook will have to convince network operators and other partners to help them get the broadband links they need. They will also need to convince governments to allow them to fly over their territory. Given the friction Facebook has faced with its free broadband efforts so far—such as India's ban on Facebook's Free Basics on network neutrality grounds—the company and its Internet.org effort will have to navigate carefully.