A rocket has been launched into space by the US military - but details of what it is being used for are top secret.
The unmanned shuttle was sent into orbit yesterday as part of a secretive military research programme.
The US Air Force won't reveal how long the mission with last or where it will end, but said it was the fourth flight sent into space for the programme.
The last X-37B mission returned in 2014 after 674 days in space while the first three flights spanned 1,367 days.
The research programme was initiated by NASA but was handed to the military seven years later, prompting concerns over the militarization of space.
Some have speculated that it is a drone spy ship used to monitor Chinese satellites, meanwhile Iran believes it is a space warplane carrying weapons - which the Air Force denied.
Another theory is the plane will be used as a surveillance plane for sensitive regions like the Middle East.
While the US military won't say anything about the purpose of the mission, it has revealed a number of experiments that are on board.
It is using the aircraft to test the reaction of almost 100 materials to space exposure, radiation and temperature swings