File:Contrail-af.jpg

Summary
http://commons.wikimedia.org/wiki/File:Contrail-af.jpg The E-3 Sentry is a modified Boeing 707/320 commercial airframe with a rotating radar dome. The dome is 30 feet in diameter, 6 feet thick and is held 11 feet above the fuselage by two struts. It contains a radar subsystem that permits surveillance from the Earth's surface up into the stratosphere, over land or water. The radar has a range of more than 200 miles for low-flying targets and farther for aerospace vehicles flying at medium to high altitudes.