Last week President Obama signed a sweeping aviation bill that, among other things, will open the skies to “unmanned aircraft systems,” more commonly known as drones. Much of the discussion regarding the coming era of domestic drones has been focused on the many important questions regarding their use at low altitudes. To what extent will it be legal, for example, for drones to hover 300 feet above residential neighborhoods snapping pictures into backyards and windows? What level of human-in-the-loop control is needed to ensure safety in a crowded airspace? And how can we stop terrorists from piloting drones at treetop level towards a target?
But there is another portion of the airspace—the stratosphere—that while mostly empty today, will in the coming years will become increasingly populated by gossamer-like, solar-powered drones turning silent, lazy circles in the sky. These drones will stay aloft for years at a time, running on energy collected during the day using solar panels mounted on paper-thin wings. As their slowly turning propellers push them along at bicycle speeds, arrays of high-resolution cameras on their undersides will record the daily comings and goings of the population of entire cities.