Maj. Benjamin Calhoon, the chief of the Positioning, Navigation and Timing Branch within the Space Operations Division of Headquarters Air Force, gives a GPS lecture at the Smithsonian’s National Air and Space Museum in Washington D.C., July 17, 2015. The GPS was invented by the Department of Defense; it’s a constellation of orbiting satellites that provides navigation data to military and civilian users all over the world. (U.S. Air force photo/Staff Sgt. Whitney Stanfield)
Staff Sgt. Whitney Stanfield
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