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Complementing the work on the Cape Cod System was an extensive radar development effort to increase response times through early-warning radars. Radar systems were developed for use in the air, over water, and in the Arctic. Although these radar developments were not formally part of the SAGE project, they were necessary to make the overall nation-wide air defense system work, and Lincoln Laboratory had a large role in their development.
In the summer of 1952, a group of scientists, engineers, and military personnel met at Lincoln Laboratory to consider ways to improve the air defense of North America. Headed by Jerrold Zacharias, the group included Albert Hill, director of Lincoln Laboratory, Herbert Weiss and Malcolm Hubbard, among others from the Laboratory, and a number of distinguished scientists, including J. Robert Oppenheimer, Isidor Rabi, and Robert Pound.
The 1952 Summer Study undertook the tasks of assessing the vulnerability of the United States to surprise air attack and of recommending ways to lessen that vulnerability. Since the greatest threat appeared to be an air attack by the Soviet Union via the North Pole, the study group focused its attention on the airspace above the 55th parallel, where Soviet bombers, having passed over the Pole, could fly undetected nearly to the border of the United States.
The plan for SAGE, already under way, was to detect, identify, track, and intercept just such aircraft. However, without early warning of an approaching attack, the readiness of interceptors and depth of airspace in which interception could take place would be drastically limited.
The Summer Study concluded it would be feasible to install a network of surveillance radars and communication links across northernmost North America from Alaska to Greenland that could give three to six hours' early warning against the threat envisioned. The results and recommendations of the study were briefed to key personnel of the Department of Defense (DoD) in late August 1952 and were well received.
The DEW Line
The DoD approved the 1952 Summer Study configuration for what would soon become known as the Distant Early Warning (DEW) Line and directed the Air Force to take immediate action to implement such a system. By December, the Air Force had awarded a contract to Western Electric for the construction and operation of a radar and communications network across northern Canada. The difficulties of installing, operating, and maintaining radars in the Arctic environment were immense, and the DEW Line, which became operational in 1957, remains an extraordinary feat of engineering.
Lincoln Laboratory provided numerous technical contributions to the DEW Line. One of the first issues the Summer Study had to resolve concerned the feasibility of long-distance communications in the Arctic. The frequent occurrence of solar disturbances in the far north ruled out the then standard forms of ionospheric-reflection HF communications. Fortunately, researchers at Lincoln Laboratory and MIT had already developed a better form of long-range communication—VHF ionospheric scatter propagation, which was not susceptible to solar disturbances.
VHF scatter propagation used the inhomogeneities of the ionosphere to provide a reliable method of long-distance communications, even in the Arctic. Solar disturbances did not disrupt this form of communications; in fact, they often improved it. Moreover, VHF scatter propagation required only moderate-power transmitters—10 to 50 kW. Until the advent of satellite communications, therefore, VHF scatter communications was able to provide a reliable method of rearward communications for the DEW Line. In addition, tropospheric scatter propagation, also investigated in large part by Lincoln Laboratory, was adopted for multichannel lateral communication between stations along the DEW Line.
Another issue discussed at meetings of the Summer Study was the staffing of the installations. It was clearly desirable to post as few technicians as possible at each site, and the automatic alerting radar developed by Lincoln Laboratory provided a way to reduce personnel requirements. An automatic alerting radar sounds an alarm whenever an aircraft enters the area of surveillance, thus freeing site technicians from 24-hour vigilance at the display scopes. This radar was especially useful in the far northern regions, because the display scopes were generally empty. With reasonably well-trained personnel, a typical site could be maintained with fewer than 20 technicians.
The X-1 automatic alerting radar was designed and fabricated in a five-month crash program at Lincoln Laboratory. Following the completion of this program, models X-2 through X-6 were designed and assembled in rapid succession for installation by Western Electric at test sites in Illinois and the Arctic. The design of the X-3 automatic alerting radar was turned over to Raytheon, and production models were installed along the DEW Line. This radar was designated the AN/FPS-19. This approach of prototyping first-of-a-kind articles, and then transitioning the design to industry for production, was established at Lincoln Laboratory during the SAGE era and is still in practice today.
Lincoln Laboratory also had a hand in developing a continuous-wave bistatic fence radar that was used as a gapfiller between AN/FPS-19 radars to detect low-flying aircraft. In the design of these radars, later designated AN/FPS-23, and in the improvement of large search radars, new techniques and components were introduced to decrease false-alarm rates and enhance automatic operation.
Lincoln Laboratory's efforts in radar design focused primarily on electrical engineering issues, but the high winds and extreme temperatures of the Arctic environment compelled Lincoln Laboratory to advance the mechanical engineering aspects of radars as well. Antenna shelters had to offer sufficient structural strength to withstand Arctic windstorms and still cause minimal attenuation of the radar beam. Before the development of the DEW Line, inflatable radomes had been occasionally used as antenna shelters, but inflatable radomes had great difficulty surviving Arctic conditions. Lincoln Laboratory solved this problem by developing rigid, electromagnetically transparent radomes. These radomes made possible not only uninterrupted operation of the DEW Line, but also a new generation of very large, precisely steerable antennas for long-range surveillance. This kind of rigid radome continues to be manufactured for many purposes.
Personnel in the newly formed Engineering Group approached Buckminster Fuller, inventor of the geodesic dome, and asked him for assistance in designing a rigid radome. Fuller suggested a three-quarter-sphere design and recommended polyester-bonded fiberglass, which offered a high strength-to-weight ratio, excellent weather resistance, and reasonable cost.
The concept of the geodesic dome seemed feasible, so the Engineering Group at Lincoln Laboratory procured a series of prototype rigid radomes. The first one (31 ft equatorial diameter) was erected on the roof of Building C. It was unexpectedly pummeled by Hurricane Carol in August 1954, with winds estimated up to 110 mph, and no damage was inflicted. The radome was then disassembled and erected on Mount Washington in New Hampshire, and it successfully survived that mountain's fierce environment, where the highest wind speeds on the face of the earth have been recorded. A second 31 ft diameter radome was erected over an AN/FPS-8 antenna on the roof of Building C. Tests demonstrated that the radome's effect on radar performance was negligible.
Lincoln Laboratory designed and procured a series of 50 ft diameter rigid radomes that were installed in Thule, Greenland; Saglek Bay, Newfoundland; and Truro, Massachusetts. A second radome was also erected on the roof of Building C, where it sheltered the Sentinel antenna. The program culminated with the installation of a 150 ft diameter radome at the Haystack Observatory.
Western Electric carried out the immense and highly successful project of installing the DEW Line radars. The DEW Line was completed in October 1962 with an extension to Iceland, giving the Air Force a 6000 mi radar surveillance chain from the Aleutians to Iceland.
|Two of the DEW Line installations. The installation below was in Point Lay, Alaska.|
Adapted from E.C. Freeman, ed., Technology in the National Interest, Lexington, Mass.: MIT Lincoln Laboratory, 1995.top of page