A miniature robotic space shuttle wrapped up a 224-day classified military mission and made an unannounced landing in darkness on a California runway on Friday, Air Force officials said.
The Orbital Test Vehicle, or X-37B, touched down at 1:16 a.m. PST at Vandenberg Air Force Base, becoming the first U.S. spaceship to land itself on a runaway.
The former Soviet Union's Buran space shuttle accomplished a similar feat in 1988.
"We are very pleased that the program completed all the on-orbit objectives for the first mission," program manager Lt. Col. Troy Giese said in a statement.
The project, which was started by NASA in the late 1990s and later adopted by the military, is intended to test technologies for a next-generational space shuttle.
Rather than carry people, however, the military is looking at the spaceplane as a way to test new equipment, sensors and material in space, with the intention of incorporating successful technologies into satellites and other operational systems.
Another key point of the project is to see if the costs and turnaround time between flights can be reduced from months to days.
The Air Force imposed a news blackout on the X-37B's activities while in orbit, though it was tracked by amateur satellite-watchers throughout its nine-month mission.
The X-37B looks like a space shuttle orbiter, but is smaller, with a similar shape and payload bay for cargo and experiments. But it measures 29 feet, 3 inches in length (8.9 metres) and has a 15-foot (4.5-metres) wing span, compared to the 122-foot (37-metres) orbiters with wing spans of 78 feet (23.8 metres).
Unlike NASA's space shuttles which can stay in orbit about two weeks, X-37B is designed to spend as long as nine months in space, then land itself on a runway.
The Air Force plans to fly its second X-37B vehicle this spring. The spaceplanes were built by Boeing's advanced research lab, Phantom Works.