For 908 days, the US military's mysterious X-37B space plane has been orbiting Earth for unknown reasons. On Friday, the spacecraft landed at NASA's Kennedy Space Center. From Space.com:
The X-37B resembles NASA's now-retired space shuttle but is much smaller, measuring just 29 feet (8.8 meters) from nose to tail. The space shuttle was 122 feet (37 m) long and was piloted — another key difference, as the X-37B is autonomous[…]
Space Force and Boeing describe the X-37B as chiefly a testing platform; the vehicle allows researchers to see how payloads work in the space environment and then examine them afterward on the ground[…
Many of these payloads are classified, as are most of the X-37B's activities; the Space Force doesn't announce details of the vehicle's orbit, for example, or tell us in advance when each OTV mission is going to end.