The U.S. Air Force’s secretive X-37B space plane returned to terra firma on Sunday after spending 780 days in low-Earth orbit.

It was the unmanned spacecraft’s longest mission to date, beating its previous record, set in 2017, by 63 days.

“The X-37B continues to demonstrate the importance of a reusable space plane,” Barbara Barrett, secretary of the Air Force, said in a statement after it landed at the Kennedy Space Center in Florida. Barrett added that each successive mission undertaken by the X-37B “advances our nation’s space capabilities.”

The latest outing, named Orbital Test Vehicle-5 (OTV-5), began aboard a Space X Falcon 9 rocket that launched in September 2017

The Boeing-built X-37B resembles the now-decommissioned Space Shuttle but at 8.8 meters (29 feet) is about a quarter the length. It’s described as being part of “an experimental test program” aimed at demonstrating various technologies “for a reliable, reusable, unmanned space test platform for the U.S. Air Force.” It has two main goals: To develop “reusable spacecraft technologies for America’s future in space, and operating experiments which can be returned to, and examined, on Earth.”

Many of the X-37B’s activities are classified, though the Air Force has released some information about its most recent mission. For example, it spent its time testing a broad range of technologies that included advanced guidance, navigation and control, thermal protection systems, avionics, high temperature structures and seals, conformal reusable insulation, lightweight electromechanical flight systems, advanced propulsion systems, advanced materials, and autonomous orbital flight, re-entry, and landing.

In the past, the U.S. has been accused of using the X-37B to spy on China’s Tiangong-1 space station module when it was in operation, though some experts have disputed this, claiming that their respective orbits were out of sync to such an extent that any such mission objective would have been virtually impossible to achieve.

Each X-37B outing has seen the vehicle set a new record for mission length. The first one, OTV-1, launched in April 2010 and lasted 224 days, while OTV-2 spent 468 days in space between March 2011 and June 2012.

OTV-3’s mission lasted for 674 days from December 2012 to October 2014, and OTV-4 spent 717 days in space in a mission that launched in May 2015. The latest mission lasted a total of 780 days.

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