Connecting the entire world to the internet by way of solar-powered drones with fricking laser beams attached to their heads sounds more like an Austin Powers plotline than an actual business strategy, but for the folks at Facebook's Connectivity Lab it isn't so far-fetched. In its quest to provide remote regions with affordable internet access, the team recently conducted its first successful full-scale testing of a critical piece of the puzzle, an internet-broadcasting drone called Aquila that will eventually stay airborne for 90 days at a time.
Facebook first revealed a full-scale version of Aquila in July last year. The solar-powered drone has a wingspan of 42 m (138 ft), which is greater than that of a Boeing 737, yet it weighs around a third as much as an electric car, with around half of this accounted for by batteries. Built with a carbon fiber frame and wings coated in solar panels, Aquila is designed to draw all of its power from the sun and stay aloft for months at altitudes ranging from 60,000 to 90,000 ft.
The social media giant has been flying scale models of Aquila as far back as March last year, but hasn't been so forthcoming with details of these tests, other than to describe them as successful. Today the company has given a decent rundown of the initial testing of a full-scale Aquila, which launched into its first flight on June 28.
Because Aquila is designed to be as light as possible, it doesn't carry typical takeoff and landing gear. The flight gave the team the opportunity to test out an unconventional takeoff method, which sees Aquila strapped into a dolly structure that propels it along the runway until it hits takeoff speed. Once it has built up enough momentum, Aqula's autopilot takes over, cutting the straps with pyrotechnic cable cutters and releasing the craft into the air. This played out as the team hoped.
With Aquila in the air, the team were able to observe how their flight modeling stacked up against the real thing. They had built computer models designed to predict the amount of power the drone would need to fly in response to changing aerodynamics, at low altitudes, for example, where the air is warmer and thicker, compared to higher altitudes where it is colder and thinner. Facebook says Aquila's climb rate and battery usage were in line with its modeling.
At its nighttime cruising altitude of 60,000 ft, the drone will require 5,000 W of power, collected by its solar cells during the daytime. But the team is relying purely on batteries for its first tests as it learns about the drone's performance. Its debut saw Aquila float along at only 25 mph (40 km/h). This is a much slower speed than is typically possible with aircraft of the same size, but is made possible by the craft's unique weight-to-surface area ratio. The drone used less than 2,000 W during this first flight, which the team says is indicative of the propellor efficiency, motor efficiency and drag also lining up with the its predictions.
Aquila flew for a total of 96 minutes controlled by its autopilot software, which the team says also performed well. This flight time was more than three times longer than the planned mission length, which allowed the team to gather extra data on the drone's performance to pore over over the coming months. The next stages of testing will involve the Connectivity Lab team adding more Aquilas to the fleet that will be flown to higher altitudes to answer a few key questions Facebook sees as integral to the project's success.
How to gather enough energy from the sun during the day to power not just propulsion, but the drone's payloads, electronics and communications gear over dark stretches as long as 14 hours through the night is one. How to develop high density batteries to store this energy, all while keeping costs low and making Aquila an economically practical way of usurping current network infrastructure, such as expensive cables and cell towers, are a couple of others.
And then of course there is the ambitious idea of using flying lasers to wirelessly transmit information, a technique that promises very high bandwidth and data capacity but comes with more than a few challenges. Facebook imagines that fleets of Aquila's equipped with lasers will receive a ground-based internet signal and daisy-chain it amongst themselves to spread it far and wide, in turn beaming their own broadband coverage down to the ground across an area with a 60-mile (96.5 km) diameter.
This week the company made a promising advance in its pursuit of such a laser-based communication system by revealing a design for a lightbulb-shaped light collector made from fluorescent plastic fibers that could be used to receive the signals being carried by the lasers. This system achieved impressive speeds of up to 2 Gbps, but the team says that speeds of up to 10 Gbps may be possible with further development. So while the company is still a long way from its dream of drone-based internet, it is making some tangible progress towards this goal.
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