A secret mission came to a public end this morning as the US Air Force’s top secret X-37B spaceplane landed at Vandenberg Air Force Base in California. The unmanned reusable spacecraft touched down on the runway like a conventional aircraft this morning at 9:24 am EDT after a record-breaking 674 days in orbit. According to the Air Force, the automatic landing was monitored by the 30th Space Wing and occurred without incident.

The X-37B Orbital Test Vehicle mission 3 (OTV-3) launched on October 25, 2012 atop an Atlas/Centaur rocket from Cape Canaveral, Florida, and has achieved the longest time in orbit by a reusable spacecraft; breaking the record set by OTV-2 in 2012, which launched on March 5, 2011 and returned to Earth on June 16, 2012. With Friday’s landing, the program has so far clocked up a total of 1,367 days in orbit.

The exact nature of the OTV-3 mission is still a closely guarded secret, though the Air Force says that the Boeing-built X-37B is designed for “risk reduction, experimentation, and concept of operations development.” Since the program began, some have speculated that the orbital missions have been for the purposes of technology or materials testing, reconnaissance, or space weapons testing, though the Air Force denies the latter.

"The landing of OTV-3 marks a hallmark event for the program" said the X-37B program manager, whose name was not revealed in the statement. "The mission is our longest to date and we're pleased with the incremental progress we've seen in our testing of the reusable space plane. The dedication and hard work by the entire team has made us extremely proud."

According to the Air Force, OTV-4 is currently preparing for launch from Cape Canaveral some time next year.

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