The US Air Force's not-so-secret secret spaceplane, the X-37B, set a new orbital endurance record for a reusable unmanned spacecraft as it set down today at the Kennedy Space Center in Florida. Orbital Test Vehicle mission 4 (OTV-4) came to an end at about 8:00 AM EDT as the aircraft made an autonomous touchdown on the runway of the Shuttle Landing Facility after spending 718 days in orbit.

The X-37B is used by the Air Force for studies in spaceflight risk reduction, orbital experiments, and operations development for reusable space vehicles.

The fourth of the X-37B missions, OTV-4 lifted off from Cape Canaveral Air Force Station, Florida on May 20, 2015 atop an Atlas V rocket. The mini-shuttle was tasked with testing the Aerojet Rocketdyne XR-5A Hall-effect thruster as part of the Advanced Extremely High Frequency communications satellite program, as well as carrying out prolonged material tests for NASA.

Today's landing after 718 days brings the total for OTV missions to 2,085 flight-days. The previous record was set by OTV-3. This was the first X-37B landing in Florida.

"The hard work of the X-37B OTV team and the 45th Space Wing successfully demonstrated the flexibility and resolve necessary to continue the nation's advancement in space," says Randy Walden, the director of the Air Force Rapid Capabilities Office. "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."

The Air Force says a fifth OTV mission will launch from Cape Canaveral later this year.

Here's a look at the X-37B landing to complete the marathon OTV-4 mission, plus footage of the launch back in 2015:

Source: US Air Force

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