1960-08-12 USA Echo 1

Project Echo was the first passive communications satellite experiment. Each of the two American spacecraft, launched in 1960 and 1964, were metalized balloon satellites acting as passive reflectors of microwave signals. Communication signals were transmitted from one location on Earth and bounced off the surface of the satellite to another Earth location.

Echo 1 launch cover with Sarzin cachet, postmarked on August 12, 1960, Port Canaveral.

(Reference from Project Echo)