Facebook’s Connectivity Lab announced today that the company has for the first time tested a full version of Aquila, the high-altitude solar-powered drone that Facebook hopes to use to deliver Internet connectivity to the most remote corners of the Earth. The test flight took place on June 28, but was only announced today by Facebook.
The low-altitude test flight was originally intended to be a 30-minute “functional check” flight only. “It was so successful that we ended up flying Aquila for more than 90 minutes — three times longer than originally planned,” Jay Parikh, Facebook’s vice president of infrastructure engineering, wrote in a post on Facebook’s Newsroom blog published today.
The initial test goals were simply to ensure that the huge Aquila drone – with a wingspan similar to that of a Boeing 737 and mass more like that of a car – could even take to the skies. To minimize weight, Aquila does not have “traditional landing gear,” according to Martin Gomez and Andy Cox of the Aquila team. “We attached the aircraft to a dolly structure with four belts and then accelerated the dolly to takeoff speed. Once the autopilot sensed the aircraft had reached the correct speed, the belts were simultaneously cut by pyrotechnic cable cutters known as ‘squib’.”
The entire takeoff sequence is driven by the drone’s autopilot. But despite testing with a scaled-down (1/5 size) drone before, this was the first time the computer modeling for takeoff attitude and speed had been tested. “The specifications based on our simulations resulted in a successful start,” Cox and Gomez reported today on Facebook’s Engineering Blog.
The test also collected data on Aquila’s aerodynamic performance at low altitudes, battery and power consumption, and the effectiveness of the autopilot system. Like other autonomous drones, Aquila can be remotely controlled to fly via GPS waypoints, but all flying is done by autopilot without direct human control. And this flight was the first opportunity to test autopilot performance on a full-size drone under real atmospheric conditions.
Parikh said the flight was a test of the performance characteristics and components of the Aquila drone, including the batteries and control system, as well as a verification of the training of the Aquila’s crew. “In our next tests,” he said, “we’ll fly Aquila faster, higher, longer, and eventually get above 60,000 feet.”
Aquila’s goal is to provide what has been described as an “atmospheric satellite” capability – the drones will fly for up to three months at a time, orbit over remote areas and provide connectivity for a circle as large as 60 in diameter. miles. using a laser based network “backbone” and radio signals for local bandwidth. Due to its lift-to-weight ratio, Aquila can fly as slow as 25 miles per hour in level flight.
But to achieve that goal, the Aquila team will need to significantly improve solar-powered aircraft technology. “We will have to beat the solar energy world record [uncrewed] flight, which currently stands at two weeks,” Parikh noted. “This requires significant advancements in science and engineering.”
One of the biggest challenges the Aquila team faces is getting enough sunlight to continuously charge the drone’s batteries so it can stay aloft at night. That will be a challenge during the winter months – while the drone’s motors only need about 5,000 watts of power to stay aloft at high altitude, it will need to fully charge its batteries with only 10 hours of sunlight a day in the expected range for Aquila’s operation. And those batteries will have to be as light as possible to enable Aquila to carry out its mission. “Given current and projected battery performance,” Cox and Gomez noted, “that means batteries will account for about half the mass of the aircraft. We are pushing the boundaries of high energy density batteries as we explore the best designs to ensure to make sure we have enough resilience in the system.”
There are additional challenges that have less to do with getting airborne and more to do with Aquila getting there in the first place. In addition to making Aquila financially sustainable – by reducing operating and maintenance costs – Facebook will need to convince network operators and other partners to help them get the broadband connections they need. They will also have to convince governments to fly over their territory. Given the friction Facebook has experienced so far with its free broadband efforts — such as India’s ban on Facebook’s Free Basics on the grounds of network neutrality — the company and its Internet.org efforts will have to navigate with caution.