Zephyr– high-altitude “pseudo-satellite” ( HAPS) — is actually an unmanned, ultra-light, solar-powered, propeller-driven aircraft. But it is designed, just as some satellites are, to hover indefinitely over the same part of the world. With a 23-metre wingspan and a weight of only 50kg, it is fragile and must remain above the ravages of the weather and the jet stream both by day and by night. It therefore flies at an altitude of around 21km (70,000 feet) during daylight hours, and then glides slowly down to around 15km when the sun is unavailable to keep it aloft….
The main uses for satellites are observation and communication. Both are appealing markets for HAPS. Hovering drones could act as relays for telephone calls and internet traffic in places that do not have good enough infrastructure on the ground. And there is never a shortage of customers who would like to snoop on various parts of the Earth’s surface, whether for commercial or military reasons.
By satellite, such snooping is done from an altitude of about 800km. Zephyr flies at one-fortieth of that, so the optics its needs to take pictures are far less demanding. (Just as well, of course, for it is unlikely to be able to carry a huge payload.)
Airbus is not alone in the HAPS game. Google and Facebook are involved as well—and with similar customers in mind—though Google will also be its own customer, since keeping its Google Earth imagery up to date is a demanding task. Paul Brooks, spokesman for Airbus’s HAPS programme, says he does not see these firms as competitors, but rather as collaborators in proving the idea of endurance flight and promoting the changes in regulations needed to permit its safe use. Once this has happened, and the world’s aviation authorities have agreed common operating standards, HAPS should prove a cheap and reliable alternative to blasting things into orbit.
Excerpts, Pseudo-satellites: The west wind blows afresh, Economist, Aug. 30, 2014