The Boeing X-37, which is also known as the X-37 Orbital Test Vehicle, is a reusable unmanned spacecraft. It is boosted into space by a rocket, then re-enters Earth's atmosphere and lands as a spaceplane. The X-37 is operated by the United States Air Force for orbital spaceflight missions intended to demonstrate reusable space technologies. Originally a joint research effort beginning in 1999 by NASA, Defense Advanced Research Projects Agency and Boeing, the program was transferred to the Air Force in 2004. With a length of 29 feet, 3 inches (about 8.9 meters), height of 9 feet, 6 inches and a wingspan of 14 feet, 11 inches, the X-37B is about one-fourth the size of the recently retired space shuttles, Boeing said in a previous release. The vehicles were designed to stay in orbit for 270 days.