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The U.S. Air Force's unmanned X-37B space plane has now circled Earth for more than 400 days on a hush-hush mission that is creeping closer and closer to the vehicle's orbital longevity record.

The X-37B spacecraft launched on Dec. 11, 2012, meaning that it has been aloft for 413 days as of Tuesday (Jan. 28) on the third mission for the program, which is known as OTV-3 (short for Orbital Test Vehicle-3). The endurance record is 469 days, set during OTV-2, which blasted off in 2011.

OTV-2 and OTV-3 have utilized different X-37B vehicle (the Air Force currently has two vehicles). The space plane currently zipping around Earth also flew the program's inaugural OTV-1 mission, which stayed in space for 225 days after launching in 2010. [See photos from the X-37B space plane's OTV-3 mission]

OTV-1 and OTV-2 both touched down at California's Vandenberg Air Force Base. But the Air Force and Boeing, which builds the X-37B, are eyeing NASA's Kennedy Space Center (KSC) in Florida as a landing site for future missions.

Coming home to FloridaBoeing announced this month that it will expand its presence in Florida by adding technology, engineering and support jobs at KSC.

As part of that package, investments will be made to convert the former space shuttle facility, Orbiter Processing Facility (OPF-1), to a structure that would enable the U.S. Air Force "to efficiently land, recover, refurbish, and re-launch the X-37B Orbital Test Vehicle (OTV), a 29-foot-long, reusable unmanned spacecraft," according to Boeing.

Construction will be completed by the second quarter of 2015, said Boeing spokeswoman Diana Ball.

The X-37B vehicles are being provided to the Air Force by Boeing's Space & Intelligence Systems. What payloads the robotic space planes carry on their confidential cruises remains classified. [Space Planes: Evolution of the Winged Spaceship (Infographic)]

This is a condensed version of a report that appeared on Read the full report.

- Leonard David,'s Space Insider Columnist

Leonard David has been reporting on the space industry for more than five decades. He is former director of research for the National Commission on Space and is co-author of Buzz Aldrin's new book "Mission to Mars – My Vision for Space Exploration" published by National Geographic. Follow us @Spacedotcom, Facebook or Google+. Originally published on

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