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X-37B landing
Workers in protective suits check out the Air Force’s X-37B Orbital Test Vehcile after its touchdown at NASA’s Kennedy Space Center Shuttle Landing Facility. (U.S. Air Force Photo)

After nearly two years in orbit, the U.S. Air Force’s X-37B robotic space plane landed at NASA’s Kennedy Space Center in Florida today with a loud sonic boom, but nary a word about what exactly it was doing up there all this time.

This was the fourth and longest classified mission for the Boeing-built craft, which was launched from Florida 718 days earlier in 2015 atop a United Launch Alliance Atlas 5 rocket. The three earlier missions were flown in 2010, 2011-2012 and 2012-2014, with landings at Vandenberg Air Force Base in California.

The Air Force’s fleet of X-37B Orbital Test Vehicles has now spent a total of 2,085 days to gauge the reusable winged plane’s ability to conduct on-orbit operations and return for airplane-style horizontal landings.

“The landing of OTV-4 marks another success for the X-37B program and the nation,” Lt. Col. Ron Fehlen, X-37B program manager, said in an Air Force news release. “This mission once again set an on-orbit endurance record and marks the vehicle’s first landing in the state of Florida. We are incredibly pleased with the performance of the space vehicle and are excited about the data gathered to support the scientific and space communities.”

The purpose of the X-37B program has been a mystery for well more than a decade. Precursor prototypes were rumored to be designed as “space bombers,” but more recent speculation has downplayed the plane’s potential use against terrestrial targets.

Instead, the plane is seen as an experimental test bed for military space technologies.

“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 says in its X-37B fact sheet.

Such experiments are thought to include a new type of rocket thruster built by Aerojet Rocketdyne, new sensors for intelligence gathering, and new tools for deploying and retrieving payloads in space.

Randy Walden, director of the Air Force Rapid Capabilities Office, took special note of the first-ever Florida landing. “The ability to land, refurbish and launch from the same location further enhances the OTV’s ability to rapidly integrate and qualify new space technologies,” he said.

The Air Force says it’s preparing to launch its fifth top-secret X-37B mission from Cape Canaveral Air Force Station in Florida later this year.

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