The mysterious US X-37B space plane has landed after over two years in space.

The secretive, unpiloted X-37B, built by Boeing, touched down on an air strip at NASA's Kennedy Space Center on Sunday after 780 days orbiting Earth, the US Air Force said.

The space plane, which is roughly the size of a small bus, shares many design features with NASA's Space Shuttle, and was sent into orbit in 2017 atop a SpaceX Falcon 9 rocket.

Its mission was to test classified technology in a long-duration space environment.

“The X-37B continues to demonstrate the importance of a reusable spaceplane,” Barbara Barrett, the newly appointed Air Force secretary, said in a statement.

“Each successive mission advances our nation's space capabilities.”

The latest landing tallies marks 2,865 total days in space for the program, the Air Force said.

It comes at a time that the Pentagon pushes Congress to approve funding for a proposed Space Force, which would serve as a new branch of the military.

“The sky is no longer the limit for the Air Force and, if Congress approves, the US Space Force,” General David L. Goldfein, Chief of Staff of the Air Force, said.