Some of the latest consumer drones, such as the DJI Phantom 4, come with an obstacle avoidance system. They're designed for stationary and slow-moving objects, however, like trees and cyclists, rather than aircraft ripping through the sky at 550mph. That poses a problem if we ever want manned and unmanned aircraft playing nicely in the sky. To help, the Defense Advanced Research Projects Agency (DARPA) is working on a new sense-and-avoid (SAA) system. The group recently conducted its first test flight, demonstrating that a shoebox-sized prototype can effectively detect and track a Cessna 172G aircraft approaching from different angles.