Space.com By Mike Wall 4/30/2019
Exactly what it's doing up there is unclear.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.
As of today (April 30), the space plane has been aloft for 601 days, on a mission known as Orbital Test Vehicle 5 (OTV-5) because it's the fifth flight of the X-37B program.
It's unclear what exactly the spacecraft is doing up there. X-37B missions are classified, and Air Force officials tend to speak of project goals in general terms, as this excerpt from the X-37B fact sheet shows: "The primary objectives of the X-37B are twofold: reusable spacecraft technologies for America's future in space and operating experiments which can be returned to, and examined, on Earth."
More:
https://www.space.com/x-37b-military-space-plane-otv5-600-days.html
