China also is looking at taking its drone swarms into near space, alongside a planned arsenal of anti-stealth drones, hypersonic spy planes and high-altitude airships. In fall 2017, the Chinese Academy of Sciences used high-altitude balloons to release two shoebox-sized, flying-wing drones that flew downward from a height of 15 miles, and flew a distance of more than 60 miles. Those high-altitude micro UAVs have passive sensors for detecting electromagnetic activity and can map terrain. Similarly to the Perdix system drone swarm showed off by the Pentagon's Strategic Capabilities Office, the Chinese Academy of Science's flock could be released by fighters, bombers, and other drones.