A mysterious, top secret aircraft called “X-37B”, belong to the US Air Force landed on a base in California after 674 days in space, on a mission covered by a veil of secrecy.

For about two years, the next-gen aircraft, the mission of which involves several federal agencies of the United States, most of which are unknown to the public, performed “experiments” in space.

According to The Guardian British newspaper, the secrecy surrounding the vehicle has captured the imagination of scientists and dozens of conspiracy theorists.

Some of these theories are the monitoring of satellites of other countries, such as Russia, China and the EU, and to monitor the “secret space station” supposedly created by China in space.

The only certainty is that the mission of the mysterious X-37B spacecraft will not be its last, as American federal agencies are planning the fourth launch from Cape Canaveral, next year.