THE INSTITUTEOn 10 January 1946 four standard-array antennae at Camp Evans, on the grounds of Fort Monmouth in New Jersey, sent a radar pulse toward the moon as it rose above the horizon. Just 2.5 seconds later, the signal had bounced off the lunar surface, its echo appearing clearly on an oscilloscope.
That seemingly modest demonstration, called Project Diana, had a lasting impact, marking the birth of radar astronomy, which has been used to map other planets. It also set the stage for the space race in the United States.
Project Diana was dedicated as an IEEE Milestone on 17 May. The IEEE New Jersey Coast Section sponsored it. Administered by the IEEE History Center and supported by donors, the Milestone program recognizes outstanding technical developments around the world.
DOING THE IMPROBABLE
During World War II, scientists emitted short bursts of microwave signals from one point on the Earth to another by bouncing them off the ionosphere. The so-called skywave-communication technique, which reached up nearly 400 kilometers, was used mainly to detect enemy aircraft.
The Camp Evans laboratory, called Site Diana, built a large transmitter, receiver, and reflective-array antenna to bounce radar signals off the moon. The transmitter, a modified SCR-271 radar set from the war, was connected to the antenna, composed of an 8-by-8 array of half-wave dipoles and reflectors.
The receiver compensated for the shift in frequency of the reflected signal because the motion toward or away from the line of sight differed each day. The receiver’s rotation angles were carefully calculated for each trial. The antenna could be rotated only in azimuth, meaning it could be turned only from side to side, not up and down. The attempt could be made only as the moon passed through the 12-degree-wide patch in the sky the antenna was aimed at during moonrise and moonset, because the antenna’s elevation angle was fixed. Scientists could observe for only about 40 minutes due to the transition of the moon and the lobes of the antenna pattern.
Engineer John H. DeWitt Jr. and chief scientist E. King Stodola received the first reflected signals at 11:58 a.m. EDT on 10 January. It took a little more than 2 seconds for the signals to be reflected, the same amount of time required for light to travel to the moon and back. The experiment demonstrated that radio communication could be conducted through the ionosphere.
Since 1946, mapping of astronomical objects has been done with radar, although it’s more sophisticated than what the Project Diana crew did. But the basic technique of bouncing radio signals off distant bodies that was developed for the project has been used to gather data about the geological and dynamic properties of many of the solar system’s planets and other heavenly bodies. Additionally, the technique has been used to determine the distance from the earth to the sun and the scale of the solar system itself.
Project Diana was honored on 17 May on the former grounds of Fort Monmouth, in Wall Township, N.J. The post was selected for closure in 2005 by the U.S. Defense Department’s Base Realignment and Closure Commission and officially closed in 2011. The site is now being redeveloped.
“Project Diana brought promise of a coming golden age of science and technology arising from the aftermath of World War II,” IEEE Life Member Albert Kerecman said at the plaque’s unveiling ceremony. “It refocused engineers and scientists to establish new goals centered on benefiting humanity, and created a need for developing solid-state technologies capable of surviving space launch and environments.”
The plaque, mounted near the entrance of the building that housed the laboratory, reads:
On 10 January 1946, a team of military and civilian personnel at Camp Evans, Fort Monmouth, New Jersey, USA, reflected the first radar signals off the moon using modified SCR-270/1 radar. The signals took 2.5 seconds to travel to the moon and back to the Earth. This achievement, Project Diana, marked the beginning of radar astronomy and space communications.