The US Army Signal Corps made the first attempt to “touch” another celestial body when on January 10, 1946, 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.

This 111.5 MHz reflective array antenna at Fort Monmouth, NJ was used by the US Army Signal Corps to bounce a radar signal off the Moon.

Project Diana’s first successful echo was detected by engineer John H. DeWitt and chief scientist E. King Stodola from a lab at Camp Evans, in Wall Township, NJ.

The team there built a large transmitter, receiver, and reflective-array antenna for the project. The transmitter was a modified World War II SCR-271 radar set, which provided 3,000 watts at 111.5 MHz in quarter-second pulses, while the “bedspring” dipole array antenna provided 24 dB of gain.

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.

Reflected signals were received about 2.5 seconds later, with the receiver compensating for Doppler modulation of the reflected signal. The radar pulse sent toward the Moon bounced off the lunar surface, and its echo appeared on an oscilloscope.

The Project Diana site is today maintained by the InfoAge Science & History Learning Center. In May of 2019, Project Diana was dedicated as an IEEE Milestone.

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Editor’s note: This article was originally posted on January 10, 2013 and edited on January 10, 2019.