KENNEDY SPACE CENTER, Fla. – Two months after a sister ship successfully concluded a demo flight, the U.S. military's second robotic X-37B space plane is in Florida preparing for blastoff March 4 on another secret mission, according to an Air Force official.

The 29-foot-long, 14-foot-wide X-37B space plane is being readied for flight in a processing facility near its launch site at Cape Canaveral, Fla., according to Lt. Col. Troy Giese, the X-37B program manager in the Air Force Rapid Capabilities Office.

Like its predecessor last year, the X-37B will lift off inside the nose cone of an Atlas 5 rocket. The flight is scheduled for March 4, but the Air Force has not released a time for the blastoff. [Gallery: Photos of the X-37B Space Plane]