Earth–Moon–Earth communication

Earth–Moon–Earth communication (EME), also known as moon bounce, is a radio communications technique that relies on the propagation of radio waves from an Earth-based transmitter directed via reflection from the surface of the Moon back to an Earth-based receiver.

The use of the Moon as a passive communications satellite was proposed by W.J. Bray of the British General Post Office in 1940. It was calculated that with the available microwave transmission powers and low noise receivers, it would be possible to beam microwave signals up from Earth and reflect off the Moon. It was thought that at least one voice channel would be possible.

The "moon bounce" technique was developed in parallel by the United States military and the Hungarian group lead by Zoltán Bay in the years after World War II. The first successful reception of echoes off the Moon being carried out at Fort Monmouth, New Jersey on January 10, 1946 by John H. DeWitt as part of Project Diana. It was followed by Zoltan Bay's group on February 6, 1946. The Communication Moon Relay project that followed led to more practical uses, including a teletype link between the naval base at Pearl Harbor, Hawaii and United States Navy headquarters in Washington, DC. In the days before communications satellites, a link free of the of ionospheric propagation was revolutionary.