The U.S. Air Force's secretive X-37B mini-shuttle was launched on March 4, 2011, for a second mission but the purpose for which it was built is yet to be unveiled.
The robotic X-37B mini-shuttle l lifted off from Cape Canaveral, Fla., atop an Atlas 5 rocket. Rocket launch provider United Launch Alliance is overseeing the flight operations. According to the launch provider, the robotic X-37B space plane’s launch window opened at 3:39 p.m. EST.
Boeing designed and built the X-37B spacecraft, called Orbital Test Vehicle 2 (OTV-2), for the Air Force. The unmanned X-37B spacecraft, which is 29 feet long and 14 feet wide, features a blunt nose and stubby wings.
The payload bay of the spacecraft takes the size of a pickup truck bed. The X-37B spacecraft is capable of landing horizontally on a runway and staying for months together in orbit. The X-37B spacecraft is designed to launch vertically inside the nose cone of a rocket.
The autonomously controlled X-37B space plane comes equipped with a solar array for generating power while staying in its orbit.
Source: http://www.boeing.com/