https://techcrunch.com/2019/08/26/experimental-u-s-air-force-space-plane-breaks-previous-record-for-orbital-spaceflight/

The Boeing-built X-37B space plane commissioned and operated by the U.S. Air Force has now broken its own record for time spent in space. Its latest mission has lasted 719 days as of today, which is one day longer than its last mission which ended in 2017, as noted by Space.com. It’s not an overall record, since geocommunications satellites typically have life spans of five years or more, but it’s nonetheless an impressive milestone for this secretive Air Force vehicle, which is all about testing and developing U.S. technologies related to reusable spaceflight and more.

The X-37B began its current mission in September 2018, when it launched atop a SpaceX Falcon 9 rocket. The specific details of the spacecraft’s missions are classified, but in addition to apparently spending ever increasing amounts of time up in space (each successive mission of the space plane has lasted longer), it’s also “operating experiments which can be returned to, and examined, on Earth.” These tests involve tech related to guidance, navigation, thermal protection, high-temperature materials and durability, flight and propulsion systems and more, which is basically not saying much since that’s just everything involved in space flight.