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

The 60-meter 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.

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