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| Echo 1 launch cover with Sarzin cachet, postmarked on August 12, 1960, Port Canaveral. |
1960-08-12 USA Echo 1
Project Echo was the inaugural passive communications satellite experiment. Both American spacecraft, launched in 1960 and 1964, were metalized balloon satellites that served as passive reflectors of microwave signals. Communication signals were transmitted from one point on Earth, reflected off the satellite's surface, and directed to another location on Earth.
(Reference from Project Echo)
