A robotic miniature space shuttle on a classified mission for the U.S. Air Force marked its 500th day in orbit on Friday, with no word about when and where the space plane will land.
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The X-37B, one of two vehicles comprising the Orbital Test Vehicle, or OTV, program, blasted off aboard an unmanned Atlas 5 rocket from Cape Canaveral Air Force Station on Dec. 11, 2012.
Five hundred days later, it's still in orbit, eclipsing by wide margin the 244-day flight of the last X-37B mission.
The Air Force did not immediately respond to a request for comment about the milestone, nor how much longer it planned to keep OTV-3 in space.
By the time it returns, the program may have a new home base.
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Boeing is investing in a mothballed space shuttle processing hangar at the Kennedy Space Center to refurbish the 29-foot long X-37B vehicles in Florida. Previously, the vehicles launched from Florida but landed and were prepared for flight at Vandenberg Air Force Base in California.
The move to the shuttle processing hangar will "enable the U.S. Air Force to efficiently land, recover, refurbish and re-launch" the spacecraft, Boeing said in a statement in January.
Under the plan, the X-37B would use the shuttle's runway at the Kennedy Space Center for landing. Space Florida, the state's aerospace economic development agency, is negotiating to lease the landing strip, among other facilities, from NASA.
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The hangar earmarked for the X-37B program, which Boeing is subleasing from Space Florida, is one of three previously used to prepare NASA's now-retired space shuttles for launch. It has been vacant since June 2012, following the return of shuttle Atlantis from the program's final flight in July 2011.
Boeing already subleases another shuttle hangar for its planned CST-100 capsules, which are being developed in partnership with NASA to fly astronauts to the International Space Station. The CST-100 also is designed to fly on United Launch Alliance Atlas rockets.
The X-37B currently in orbit had a debut flight in April 2010 that lasted 7.5 months. Its sister craft launched in March 2011 and returned to Earth in June 2012.
The Air Force says it is using the experimental space plane to test technologies, but provides no details.