The US military's experimental X-37B space plane has landed at NASA's Kennedy Space Center in Florida, completing a classified mission that lasted nearly two years, the Air Force says.
The unmanned X-37B, which resembles a miniature space shuttle, touched down on Sunday morning on a runway formerly used for landings of the now-mothballed space shuttles, the Air Force said in an email.
The Boeing-built space plane blasted off in May 2015 from nearby Cape Canaveral Air Force Station aboard an Atlas 5 rocket built by United Launch Alliance, a partnership between Lockheed Martin Corp and Boeing Co.
The X-37B, one of two in the Air Force fleet, conducted unspecified experiments for more than 700 days while in orbit. It was the fourth and lengthiest mission so far for the secretive program, managed by the Air Force Rapid Capabilities Office.
The orbiters "perform risk reduction, experimentation and concept-of-operations development for reusable space vehicle technologies", the Air Force has said without providing details. The cost of the program is also classified.
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The Secure World Foundation, a nonprofit group promoting the peaceful exploration of space, says the secrecy surrounding the X-37B suggests the presence of intelligence-related hardware being tested or evaluated aboard the craft.
The Air Force intends to launch the fifth X-37B mission from Cape Canaveral Air Force Station, located just south of the Kennedy Space Center, later this year.
