Cape Canaveral, FL -- An unmanned Atlas 5 rocket carrying a small robotic space shuttle lifted off from Cape Canaveral Air Force Station in Florida on Tuesday for the third flight in a classified military test program.

The 196-foot rocket blasted off at 1:03 p.m. ET carrying the military's original X-37B experimental space plane, also known as an Orbital Test Vehicle, or OTV.

The unmanned, reusable space shuttle, one of two operated by the U.S. Air Force, spent 224 days circling Earth during its debut mission in 2010. A sister ship blasted off in 2011 and landed itself after 469 days in space, completing the second orbital test flight.

The military is not saying how long the third X-37B mission will last, nor what the vehicle will be doing in orbit.
      
While launching from Florida, the military has been landing the robotic space planes at Vandenberg Air Force Base in California. The agency is considering landing and refurbishing its X-37B spaceships at NASA and Air Force bases in Florida, which has been courting new customers since the retirement of NASA's space shuttles last year.

The vehicles, which were built by Boeing, are about one-fourth the size of a NASA shuttle and use solar panels to generate power, rather than chemical fuel cells that limited the space shuttles' time in orbit.   Neither NASA nor the Air Force has plans to upgrade the X-37B to carry people.

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