Odysseus, scheduled for its first test flight in 2019, is just one of a number of High Altitude Pseudo Satellites (HAPS) currently under development.
HAPS are designed to occupy that sweet spot between conventional UAVs and traditional satellites. In theory, these completely autonomous aircraft will be able to fly for an indefinite period of time, powered by solar energy and traveling at altitudes of about 20 km (12 mi), above clouds, jet streams and winds in general, and commercial airliners.
Aurora Flight Sciences first revealed its intention to produce a HAPS back in 2008 when the Odysseus was revealed as part of DARPA's Vulture program. Back then, Odysseus was presented in concept form, with a radical Z wing configuration.