Radar Makes Round Trip To Moon 1946-01-31 Universal Newsreel Project Diana Earth-Moon-Earth
more at
“Fort Monmouth, New Jersey where army engineers sent radar to moon, closeup of screen shows radar signal, Col. DeWitt speaks, many future possibilities appear if allow imagination to reign.”
Public domain film from the National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
Project Diana, named for the Roman moon goddess Diana — goddess of the hunt, wild animals and the moon — was a project of the US Army Signal Corps to bounce radio signals off the moon and receive the reflected signals. Today called EME (Earth-Moon-Earth), this was the first attempt to “touch” another celestial body.
From a laboratory at Camp Evans (part of Fort Monmouth), in Wall Township, New Jersey, a large transmitter, receiver and antenna array were constructed for this purpose. The transmitter, a highly modified SCR-271 radar set from World War II, provided 3,000 watts at 111.5 MHz in 1/4 second pulses, and the antenna (a “bedspring” dipole array) 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. The antenna could be rotated in azimuth only, so the attempt 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 first successful echo detection came on 10 January 1946 at 1158am local time by John H. DeWitt and his chief scientist E. King Stodola.
Project Diana marked the birth of the US space program, as well as that of radar astronomy. It 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. It also established the practice of naming space projects after Roman gods, e.g., Mercury and Apollo.
Today, the Project Diana site is maintained by the Infoage Science/History Learning Center.
Earth-Moon-Earth, also known as moon bounce, is a radio communications technique which 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…
History
The use of the Moon as a passive communications satellite was proposed by Mr. 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 by the United States Military in the years after World War II, with 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. 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 vagaries of ionospheric propagation was revolutionary.
Later, the technique was used by non-military commercial users, and the first amateur detection of signals from the Moon took place in 1953.
EME communications technical details
As the albedo of the Moon is very low (maximally 12% but usually closer to 7%), and the path loss over the 770,000 kilometre return distance is extreme (around 250 to 310 dB depending on VHF-UHF band used, modulation format and Doppler shift effects), high power (more than 100 watts) and high-gain antennas (more than 20 dB) must be used.
In practice, this limits the use of this technique to the spectrum at VHF and above.
The Moon must be above the horizon in order for EME communications to be possible…
Current EME communications
Amateur radio (ham) operators utilize EME for two-way communications…
Amateur operations use VHF, UHF and microwave frequencies. All amateur frequency bands from 50 MHz to 47 GHz have been used successfully, but most EME communications are on the 2 meter, 70-centimeter, or 23-centimeter bands…
Recent advances in digital signal processing have allowed EME contacts, admittedly with low data rate, to take place with powers in the order of 100 Watts and a single Yagi antenna…
