The solar-powered drones were intended to fly continuously for months in 3-mile circles at an altitude of 11 to 16 miles while relaying satellite service to within a 30-mile radius on the ground. Facebook’s intent with the initiative, called Aquila and started in 2015, was to provide Internet service to an estimated 4 billion people who lack access.

IEEE Spectrum reported that the engineer hired in 2014 to build Facebook’s drones left quietly earlier this year along with the company’s head of aeronautical platforms. Of the company’s two completed test drones, one was damaged badly in its first flight, IEEE Spectrum noted, and the FCC registration for both has lapsed. The first full-scale test flight was in 2016.

Google’s parent, Alphabet, shuttered a similar drone-based project called Titan in 2017.

The company cited successes in making more spectrum available useful to ground-to-air transmissions, and will continue to promote efforts to get governments to allocate even more. In a test with equipment on a conventional Cesna plane circling 4 miles above the ground, Facebook said it could transmit and receive data at rates up to 40 gigabits per second.

Facebook isn’t alone in trying to create the equivalent of floating cellular towers or relays. Separately, Google and a company called Altaeros are testing blimps. Google’s Project Loon blimps would be elevated to 11 miles above ground, while Altaeros’s are tethered to the Earth and hover at just hundreds of feet.

As part of the Aquila shutdown, Facebook also halted its work developing areas appropriate for its craft’s specific needs to take off and land at Spaceport America in New Mexico.

The company said it would continue to support expanding Internet access, such as through its investment in Terragraph, which focuses on dense urban areas with underserved people. Facebook said in February that carriers in Europe were evaluating the technology, and Norwegian carrier Telenor planned a field trial in Kuala Lumpur.