Unmanned space vehicle lands at Vandenberg Air Force Base
A statement on the base's website said the craft conducted experiments during its more than 220 days in orbit on its maiden flight.
There has been speculation that it could be used for military purposes.
A second launch is planned in spring.
Boeing Co.'s Phantom Works in Huntington Beach built the spacecraft, which is about 29 feet long.
Photo: The X-37 sits in its encapsulation cell before it was launched at Cape Canaveral, Fla., atop an Atlas V rocket on April 22. Credit: U.S. Air Force