The US Air Force’s secretive X-37B reusable unmanned space vehicle has surpassed a year in orbit.

The unmanned X-37B spacecraft — flying a mission known as Orbital Test Vehicle 3 (OTV-3) — launched into space atop an Atlas 5 rocket from Florida’s Cape Canaveral Air Force Station on Dec. 11, 2012. What payloads the space plane is toting and the overall mission goals on its confidential cruise are classified.

The Space.com article notes that “skywatchers” have been constantly monitoring the X-37’s orbit and altitude changes. What it is actually doing remains a mystery.

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