A mysterious robotic ‘space plane’ has stayed in orbit for nearly two years - and few people know what it’s really up to.
The Boeing X-37B craft - also known as Orbital Test Vehicle 4 - has now been in orbit for 700 days.
It launched on its latest mission on September 7, 2017, Space.com reports, and is now just a few days short of its all-time record for remaining in space.
Observers have speculated that the Space Shuttle-esque vehicle might be designed to destroy satellites - or work as a ‘movable’ satellite itself.
When it landed from a previous mission, it was greeted by ground crew in biohazard suits - sparking gossip that there was something radioactive on board.
The aircraft has a wingspan of less than 15ft - and is taken into space on a rocket, but glides back to Earth like a space shuttle.
NASA has said that there is a materials experiment on board - but its main payload remains a mystery.
During the aircraft’s previous missions, amateur astronomers were able to detect the orbital pattern of the first X-37B which included flyovers of North Korea, Iraq, Iran, Pakistan and Afghanistan, heightening the suspicion that the vehicle was being used for surveillance.