The Aquila UAV was designed and built in the UK by Ascenta, and was acquired by Facebook in 2014 to provide a platform to deliver Internet access in remote areas of the world, The test flight, using purely lithium ion batteries, lasted for 90 minutes at a speed of 25 mph and showed a 2kW requirement. Operating at 60,000 to 90,000 feet at 80 mph will require 5kW of power, says Facebook.
The wingspan of the 300 kg craft is 142 m, providing up to 280 sq m for solar cells. US supplier Alta Devices this month demonstrated an aerial basestation design at the Farnborough Air Show in the UK using its single and dual-junction GaAs-based cells that have efficiencies of 28% and 31%. A dual junction cell can provide up to 300 W/m 2 which would make up to 84kW available. This leaves plenty of power for the basestation and for the communications links between the craft and to the ground station, while adding just 47 kg to the weight of the aircraft.
The challenge of the commmunications link has been addressed with new research at the Facebook Connectivity Labs, where plastic fibre doped with fluourescent material acts a a receiver for a laser signal from another craft.