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Project Diana, named for the Roman moon goddessDiana, was an experimental project of theUS Army Signal Corps in 1946 to bounceradar signals off theMoon and receive the reflected signals.[1] This was the first experiment inradar astronomy and the first active attempt to probe anothercelestial body. It was the inspiration for laterEarth–Moon–Earth communication (EME) techniques.
Following the end of World War II, Col.John H. DeWitt Jr., Director of the Evans Signal Laboratory atCamp Evans (part ofFort Monmouth), inWall Township, New Jersey, was directed by the Pentagon to determine whether the ionosphere could be penetrated by radar, in order to detect and track enemy ballistic missiles that might enter the ionosphere. He decided to address this charge by attempting to bounce radar waves off the Moon. For this task he assembled a team of engineers that included Chief ScientistE. King Stodola, Herbert Kauffman, Jacob Mofenson, and Harold Webb. Input from other Camp Evans units was sought on various issues, including most notably the mathematicianWalter McAfee, who made the required mathematical calculations.[2][3][4]
On the Laboratory site, a largetransmitter,receiver andantenna array were constructed for this purpose.[1] The transmitter, a highly modified SCR-271radar set fromWorld War II,[1] provided 3kilowatts (later upgraded to 50 kilowatts) at111.5 MHz in1⁄4-second pulses, applied to the antenna, a "bedspring"reflective array antenna composed of an 8x8 array ofhalf wave dipoles and reflectors that provided24 dB of gain. Return signals were received about 2.5 seconds later, the time required for the radio waves to make the 768,000-kilometre (477,000 mi) round-trip journey from the Earth to the Moon and back.[1] The receiver had to compensate for theDoppler shift in frequency of the reflected signal due to the Moon's orbital motion relative to the Earth's surface, which was different each day, so this motion had to be carefully calculated for each trial.[1] The antenna could be rotated inazimuth 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'selevation angle was horizontal. About 40 minutes of observation was available on each pass as the Moon transited the various lobes of theantenna pattern.
The first successful echo detection came on 10 January 1946 at 11:58am local time by Harold Webb and Herbert Kauffman.[5]
Project Diana marked the birth ofradar astronomy later used to map Venus and other nearby planets, and was a necessary precursor to theUS space program. It was the first demonstration that terrestrial radio signals could penetrate theionosphere,[1] opening the possibility of radio communications beyond the Earth forspace probes and human explorers. It also established the practice of naming space projects after Roman gods, e.g.,Mercury andApollo.
Project Diana demonstrated the feasibility of using the Moon as a passive reflector to transmit radio signals from one point on the Earth to the other, around the curve of the Earth. ThisEarth-Moon-Earth (EME) or "moonbounce" path has been used in a few communication systems. One of the first was the secret USmilitary espionagePAMOR (Passive Moon Relay) program in 1950, which sought to eavesdrop on Soviet Russian military radio communication by picking up stray signals reflected from the Moon. The return signals were extremely faint, and the US began secret construction of the largestparabolic antenna in the world atSugar Grove, West Virginia, until the project was abandoned in 1962 as too expensive. A more successful spinoff was the US NavyCommunication Moon Relay or Operation Moonbounce communication system, which used the EME path for US military communication. In January, 1960 the system was inaugurated with a lunar relay link between Hawaii and Washington DC. Moonbounce communication was abandoned by the military with the advent ofcommunications satellites in the early 1960s. Since then it has been used byamateur radio operators.
Today, the Project Diana site is part of theCamp Evans Historic District, InfoAge Science History Learning Center and Museum, and is maintained by the Infoage Space Exploration Center,[6] and previously by the Ocean-Monmouth Amateur Radio Club.[7] The antenna array was removed earlier and is now presumably lost.