50th anniversary of the opening of the North American Aerospace Defense Command Combat Operations Center inside Cheyenne Mountain. 1/3rd mile inside the main access tunnel are a pair of steel blast doors leading to the main complex. Each is 25 tons, is 11 ft high by 13 ft wide, 3 1/2 ft thick, and are spaced 50 ft apart. They are encased in reinforced concrete collars 17 ft thick, and can be closed &amp; locked by a hydraulic pump within 30 to 45 seconds. Or can be manually closed in 4 1/2…