The Aqulia aircraft has the wingspan of a Boeing 737 but weighs about the same as a car. Its wings are covered in solar panels that provide enough energy to keep it aloft for three to six months at an altitude of 60,000 to 90,000 feet, well above aircraft.
It's one of Facebook's answers to the problem of extending low-cost Internet access to parts of the world that don't currently receive it. It's also something of an engineering marvel.
"The idea is you can send it out to a place where it might be too expensive to deploy infrastructure otherwise," Zuckerberg said. "It will just fly and stay up there and can beam down Internet access."
Facebook unveiled the project in June 2015 and has been working on perfecting the aircraft and the laser communications system that will be used to link drones together and to ground stations.
Internet users will receive WiFi or LTE signals from the drone.
"We’re going to do our first trials at full scale a bit later this year," said Zuckerberg, speaking at Mobile World Congress in Barcelona.
Engineers are currently flying a scale model every week in tests ahead of the flight of the full-size craft, he said.
If the project goes according to plan, Facebook will be in a position to take the idea to telecommunications carriers. Like Google, which is proposing using balloons, Facebook will offer the service to existing mobile networks rather than direct to users.
"Hopefully in the next year or so, we’ll be able to incorporate this into what we come and talk to our operator partners about, to help extend all the networks to regions where it might not have been previously economical to build out traditional terrestrial networks," Zuckerberg said.