This X-37B flight is a 2-year secret military mission with an unmanned mini-space shuttle that orbited the Earth.
The reusable, unmanned X-37B Orbital Test Vehicle landed at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida, an airport used by the United States space agency's Space Shuttle for landing until the programme's end in 2011.
Some Brevard County residents may have heard sonic booms before the touchdown at the three-mile Shuttle Landing Facility, similar to when much larger space shuttle orbiters returned home.
After circling Earth for an unprecedented 718 days, the X-37B touched down Sunday (May 7) at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida - the first landing at the SLF since the final space shuttle mission came back to Earth in July 2011. The first three missions all landed successfully at Vandenberg Air Force Base in Lompoc, California.
In a statement, officials said the X37B shuttle is "an experimental test program to demonstrate technologies for a reliable, reusable, unmanned space test platform for the U.S. Air Force".
The vehicles are 29 feet (9 meters) long and have a wingspan of 15 feet, making them about one quarter of the size of the National Aeronautics and Space Administration's now-retired space shuttles.
"Today marks an incredibly exciting day for the 45th Space Wing as we continue to break barriers", Brig. But no one flies on them; they are operated robotically. "Our team has been preparing for this event for several years, and I am extremely proud to see our hard work and dedication culminate in today's safe and successful landing". Gen. Wayne Monteith, commander of the Air Force's 45th Space Wing.
It's the fourth and longest-running mission for the X-37B program, run by the U.S. Air Force's Rapid Capabilities Office. However, then the program was relocated in the Pentagon's Defense Advanced Research Projects Agency, or DARPA, in 2004. The first X-37B took off on the program's initial orbital test flight April 22, 2010. The third flight, the second for the original OTV-1, took off on December 11, 2012 and landed in California on October 17, 2014, after logging almost 675 days aloft.
Most X-37B payloads and vehicles are considered classified, so it's not completely clear what the Air Force is doing with these space planes.