Somewhere in the U.K., Facebook has completed the first flight of a prototype of the solar-powered stratospheric unmanned aircraft the social media giant is developing to provide Internet infrastructure in remote parts of the world.

CEO Mark Zuckerberg unveiled the aircraft’s design and announced the first test flight on his Facebook page on March 25 and, on March 26 at a Facebook developer’s conference in San Francisco, Chief Technology Officer Mike Schroepfer showed a photograph of the subscale prototype in flight.

The Aquila is an early prototype for aerodynamic testing, said Schroepfer, but he also showed time-lapse video of a composite wing-skin section for the full-scale aircraft being produced robotically.

Facebook acquired small U.K. consultancy Ascenta in March 2014, bringing on board some of the people responsible for designing early versions of the Qinetiq Zephyr solar-powered unmanned aircraft. In 2010, the Zephyr 7 set a world endurance record of 336 hr., 22 min., reaching 70,740 ft. altitude.

By comparison, Northrop Grumman’s RQ-4B Global Hawk jet-engined unmanned aircraft has stayed aloft for 34.3 hr., and Aurora Flight Sciences’ twin-diesel-powered Orion flew for 80 hr. in December, setting a record only bested by the Zephyr.

Both Facebook and Google, which acquired U.S. unmanned-aircraft developer Titan Aerospace in April 2014, have rekindled interest in using solar-powered high-altitude, long-endurance UAVs as “atmospheric satellites” able to stay aloft for week and months to provide communications service.

Qinetiq sold the Zeyphr to Airbus Defense & Space, which in 2014 completed an 11-day Zephyr flight in Australia to prove its capabilities during the shorter days and longer nights of winter. The UAV then made its first civil flight, in the United Arab Emirates, reaching 61,696 ft.

Schroepfer says the final design of Facebook’s solar-powered UAV “will have a wingspan greater than a [Boeing] 737 [which is just under 120 ft.], but will weigh less than a small car” and be able to stay aloft at 60,000-90,000 ft. altitude for months at a time, providing backbone Internet access.

This is significantly larger than the latest Zephyr 8 “high-altitude pseudo-satellite” developed by Airbus. This has a wingspan increased to 92 ft. from 75.5 ft. for the Zephyr 7, to increase the wing area covered with solar cells and weight with payload increased to 130 lb. from 120 lb.

Google, meanwhile, says trials of its solar-powered UAV will begin this year under Project Titan. The search giant has received permission for broadcast transmission testing in an area around Titan’s base at Moriarty, New Mexico.

Before it was acquired by Google, startup Titan was developing the Solara family of “solar atmospheric satellites,” designed to stay aloft up to five years. The initial Solara 50 was to have a 164-ft. span and 70-lb. payload.

A solar-electric unmanned communications and surveillance aircraft able to stay aloft in the stratosphere for more than five years was envisioned by the U.S. Defense Advanced Research Projects Agency (Darpa) under its Vulture program.

Boeing, with Qinetiq, was awarded a contract in 2010 to build the SolarEagle demonstrator for Vulture. This would have had an almost 400-ft. wingspan and one-year endurance, but construction and flight testing were canceled in 2012.

But where Darpa leads, the world tends to follow, eventually, and Facebook and Google seem intent on bringing the concept of ultra-long-endurance stratospheric UAVs to fruition to meet the need to deliver affordable Internet connectivity to parts of the world that lack communications infrastructure.