As of 6:43am ET today, the X-37B spaceplane's fifth mission, dubbed the Orbital Test Vehicle (OTV-5), will have spent 719 days in orbit—just 11 days shy of a full two years circling the globe. The previous record was 717 days, 20 hours and 42 minutes, achieved just a few years earlier with OTV-4

All we know about the 29-foot long spaceplane's mission comes from the Air Force description, which is light on details, to say the least:

The X-37B Orbital Test Vehicle, or OTV, is an experimental test program to demonstrate technologies for a reliable, reusable, unmanned space test platform for the U.S. Air Force. 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.

The Air Force notes that the vehicle is able to "return experiments to Earth," but we have no idea what those experiments might be:

Upon command from the ground, the OTV autonomously re-enters the atmosphere, descends, and lands horizontally on a runway. The X-37B is the first vehicle since NASA's Shuttle Orbiter with the ability to return experiments to Earth for further inspection and analysis,