The U.S. Air Force's X-37B space plane has now been circling Earth for more than 600 days on its latest mystery mission.
The reusable robotic vehicle, which looks like a miniature version of NASA's space shuttle orbiters, launched atop a SpaceX Falcon 9 rocket from NASA's Kennedy Space Center in Florida on Sept. 7, 2017.
https://www.space.com/x-37b-military-space-plane-otv5-600-days.html