PETERSON AIR FORCE BASE, CO - DECEMBER 9: A bus enters a tunnel for a half-mile trip to the command center of the Northern Command December 9, 2002 located deep within Cheyenne Mountain at the foot of the Rocky Mountains near Colorado Springs, Colorado. Built in the 1960s to withstand a direct nuclear strike, the station sits stop springs and behind a pair of giant blast doors that can seal out contamination.The station now monitors homeland security as well as foreign nuclear threats. Every commercial plane in U.S. air space is monitored from the center. Crews reporting unruly passengers or planes that drop from radio contact are given special attention since the September 11, 2001 terrorist attacks. (Photo by Kevin Moloney/Getty Images)
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