January 10
10 January 1946
 |
| Project Diana radar antenna at Fort Monmouth, New Jersey, USA. Credit: InfoAge Science History Learning Center and Museum |
On January 10, 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 a specially 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. The effort resolved doubts about whether electromagnetic waves suitable for long-range communication and radar could penetrate the Earth’s ionosphere. It was the first documented experiment in radar astronomy and in actively probing another celestial body, and was the dawn of the space age.
Following the end of World War II, Col. John H. DeWitt Jr. (1906–1999), Director of the Evans Signal Laboratory at Camp Evans (part of Fort Monmouth), in Wall 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 Scientist E. King Stodola (1914–1992), Herbert Kauffman (1914–1980), Jacob Mofenson (1914–1969), and Harold Webb (1909–1989). Input from other Camp Evans units was sought on various issues, including most notably the mathematician Walter McAfee (1914–1995), who made the required mathematical calculations.
 |
| Project Diana staff from left: Jacob Mofenson, Harold D. Webb, John H. DeWitt, Jr., E. King Stodola, and Herbert P. Kauffman. Credit: US Army Communications Electronics Museum |
The reflective array antenna consisted of 64 half-wavelength dipoles in an 8x8 array in front of a flat reflective screen, and had a gain of 24 dB and a main lobe beamwidth of about 15°. It was driven by a 50 kW modified SCR-271 radar set that produced quarter-second pulses. The whole assembly was mounted atop a 100-foot reinforced tower. The signals had a frequency of 115.5 MHz, the peak power was 15 kW. The echoes took about 2.5 seconds to return. The receiver had to compensate for the Doppler 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. The antenna could be rotated in azimuth only so the experiment could only be done at moonrise and moonset as the moon passed through the antenna's horizontal beam.
The first successful echo detection came on January 10, 1946 at 11:58 am local time by Harold Webb and Herbert Kauffman. The experiment was concluded at 12:09 pm, when the Moon moved out of the radar's range. The experiment was repeated daily over the next three days and on eight additional occasions during the month.
Although the possibility of reflecting radar signals off the Moon had been discussed in the scientific literature, there are no prior documented similar achievements. Zoltán Bay (1900–1992) and a Hungarian team achieved a similar result on February 6, 1946. Because their receiver did not have the sensitivity required, and their antenna did not have the gain needed to directly detect the reflected signal, they used an accumulating coulometer to acquire a 30 fold increase in the signal to noise ratio, producing a signal, post processing, 4% above the noise floor.
Demonstrating that signals could travel from the Earth to the Moon and back was proof of concept for the idea of what is known as Earth-Moon-Earth (EME), or “moonbounce” communication. Following the success of the project, the US Navy set out to explore the implications and applications of this form of communication - the idea of a reliable, secure EME scheme. The system in its completed state began seeing use in 1960 and was expanded to accommodate ship-to-shore transmissions. In the later 1960s it became obsolete due to the advent of artificial satellites in orbit to serve the same purpose.
 |
| Oscilloscope display showing the Project Diana radar signal. The large pulse on the left is the transmitted signal, the small pulse on the right is the return signal from the Moon. The horizontal axis is time, but is calibrated in miles. It can be seen that the measured range is 238,000 mi (383,000 km), the distance from the Earth to the Moon. Credit: Radio News Magazine |
10 January 1968
 |
| Engineering model, S-10, of the Surveyor lunar lander at the Smithsonian's National Air and Space Museum. It was reconfigured to represent a flight model of Surveyor III or later, since it was the first to have a scoop and claw surface sampler. Credit: Mark Avino. Smithsonian's National Air and Space Museum |
 |
A Surveyor VII landing site panorama, using newly digitized data. Credit: NASA/JPL-Caltech/University of Arizona Lunar and Planetary Laboratory/Gary Rennilson |
Approximately 66 hours of alpha-scattering data were obtained during the first lunar day on three samples: the undisturbed lunar surface, a lunar rock, and an area dug up by the surface sampler. An additional 34 hours of data were obtained on the third sample during the second lunar day. The surface sampler dug a number of trenches and conducted static and dynamic bearing strengths of the lunar material. The performance of the instrument and its controllers was outstanding.
In addition to acquiring a wide variety of lunar surface data, Surveyor VII also obtained pictures of the Earth and performed star surveys. Laser beams from the Earth were successfully detected by the spacecraft's television camera in a special test of laser-pointing techniques.
 |
The
scoop of the surface sampler, shown in the middle of the photograph,
being used to help deploy the sensor head of the Alpha Scattering
Experiment (on the left) on January 12, 1968. Credit: NASA (from Andrew LePage. Surveyor 7: The Mission to Tycho. Drew Ex Machina) |
 | ||||
The
Surveyor photograph of the partially sunlit Earth, taken by Surveyor
VII at 09:06 UT on January 20, 1968, shows two narrow laser beams sent
to the Moon from the Kitt Peak National Observatory, near Tucson, Ariz.,
and the Table Mountain Observatory, near Los Angeles. The blue-green
argon-ion laser beams seen within the white circle on the photograph
each contained only about 1 watt of power. This was an engineering test
to gain experience for the Apollo laser-ranging retroreflector
experiment. Credit: NASA (from Andrew LePage. Surveyor 7: The Mission to Tycho. Drew Ex Machina)
|
Komentarze
Prześlij komentarz