This artist's rendition of the X 37 B shows it gliding back to earth by remote control, as it is unmanned. It is 29 feet long, 15 feet wide, and about 22% the size of the space shuttle. It is much less expensive to build, operate, and maintain and much safer. The X 37 project was initiated by NASA in 1999. Both prototypes were designed by NASA and built by Boeing. The spacecraft are owned and operated by the US Air Force and launched into orbit atop NASA's Atlas V Rocket. It's longest mission so far was 469 days in orbit.