原创 1946: Project Diana bounces radio signals off moon

The United States Army Signal Corps' first attempt to "touch" another celestial body was on January 10, 1946, when it bounced radio signals off the moon and received the reflected signals.

Dubbed "Project Diana" for the Roman moon goddess, the effort led to what is today known as EME (Earth-Moon-Earth) communications, used for ham radio.

Project Diana is often noted as the birth of the US space program, as well as that of radar astronomy. The project was the first demonstration that artificially created signals could penetrate the ionosphere, opening the possibility of radio communications beyond the Earth for space probes and human explorers.

Project Diana also established the practice of naming space projects after Roman gods and goddesses, like Mercury and Apollo.

Project Diana's first successful echo detection came on at 11:58 am by John H DeWitt and his chief scientist E King Stodola from a lab at Camp Evans, in Wall Township, NJ.

A large transmitter, receiver, and antenna array were constructed at the lab for the project. The transmitter, a highly modified World War II SCR-271 radar set, provided 3,000 watts at 111.5MHz in quarter-second pulses, while the "bedspring" dipole array antenna provided 24 dB of gain.

Reflected signals were received about 2.5 seconds later, with the receiver compensating for Doppler modulation of the reflected signal.

Attempts could be made only as the moon passed through the 15-degree-wide beam at moonrise and moonset, as the antenna's elevation angle was horizontal. About 40 minutes of observation was available on each pass as the moon transited the various lobes of the antenna pattern.

The Project Diana site is today maintained by the Infoage Science/History Learning Center.

Suzanne Deffree is EDN's executive editor. She is an award-winning journalist who manages several blogs and sections of EDN.com and EDN’s e-newsletters including its daily newsletter, EDN Today, and EDN Fun Friday. She also heads EDN’s social media and community efforts.