Two Roads that Crossed in the Wood: Growth of US Radio Astronomy in the 1950s and 1960s
Historically, Defense Department activities tend to drive improvements in instrument technology. Defense Dept investment in instrument technology and the instrument technology needs of radio astronomy are Two Roads that began to cross in the wood quite frequently in the 1950s and 1960s.
In 1894, six years after Hertz discovered radio waves, Sir Oliver Lodge announced that he hoped to detect radio waves from the sun. He apparently tried during 1897-1900, but experienced "instrumentation problems" similar to those familiar to the users of radio telescopes. About 45 years later, in 1945, George Southworth of Bell Laboratories detected the solar radio waves that Lodge had suggested. (See: G.C. Southworth, "Microwave radiation from the sun", J. Franklin Inst. 239: 285, 1945; reprinted in W.T. Sullivan III, Classics in Radio Astronomy, Dordrecht, D. Reidel Publishing Co, 1982, p.168.) In 1932, 13 years prior to Southworthís work, and also at Bell Labs, Karl Jansky detected extraterrestrial radiation at 20 MHz. (See: K. Jansky: "Directional studies of atmospherics at high frequencies", Proc.IRE 20: 1920, 1932, and "Electrical disturbances apparently of extraterrestrial origin", Proc.IRE 21: 1387, 1933.) In 1938, Grote Reber confirmed Jansky's discovery when he detected radio emission from the Milky Way at 160 MHz. (See: G. Reber, "Cosmic Static", Proc. IRE 28: 68, 1940, and "Cosmic Static", Astrophys. J. 91: 621, 1940.)
Radio astronomy proceeded from these early beginnings along two paths, one exploring the radio characteristics of sources in the solar system, and the other, the radio properties of galactic and extragalactic sources. There was a common need for improved spatial resolution and low noise amplification. The Department of Defense helped to satisfy that need.
During the war years in the early 1940s the characteristics of solar radiation and burst activity influenced the performance of radar surveillance of the horizon. Defense Department interest sparked an immediate need for further knowledge concerning solar radio noise characteristics. Solar radio astronomers were suddenly able to pursue their "hobby" with the support of the Defense Department. The Two Roads crossed in the wood.
The pursuit of extragalactic sources of radio noise was less fortunate. Progress along this path in the 1930s through the mid-1940s was due to the determination of one man, Grote Reber. I had the pleasure of working with Reber in 1948 at Naval Research Laboratory (NRL) during my annual two week active duty service as a member of the Naval Reserve. Captain Howard Menzel, Commanding Officer of the Naval Reserve Group at Harvard, arranged this unique opportunity. Menzel wanted to build a solar radio telescope at Harvard using a Wurtzberg antenna. He reasoned that two weeks with Reber would provide all of the smarts needed concerning the design of a solar telescope. On my arrival at "Reberís Observatory" at NRL, I asked Reber what he wanted me to do during my two week tour of duty. He told me there were only two things that he wanted me to do: 1) do not wear a Navy uniform, and 2) donít park my car closer than 1000 feet from his radio observatory, to minimize the detection of ignition noise. My prompt and affirmative response to both requests led to a fruitful scientific and engineering experience. Reberís advice concerning the Harvard Solar Telescope was a typical one sentence response, "Mount your elevation over azimuth Wurtzberg on a latitude wedge and use a stable, high gain, low noise receiver."
Texas Towers, Radio Telescopes, and Sputnik in the 1950s
The drivers of Defense Department activities in the early 1950s were the Cold War with Russia and China and the Korean conflict, beginning in 1952. Two major program efforts by the Defense Department at that time had a major impact on radio astronomy. The first was the radar perimeter fence, located in Alaska, known as White Alice. The Semi-Automatic Ground Environment (SAGE) system was continued about 100 miles off the coast of New England, on the continental shelf, where it was called the Texas Towers. The second major effort was the construction of a 600 foot fully steerable antenna located in the hills of West Virginia in a quiet town called Sugar Grove. The timely product of White Alice for the radio astronomy community was low noise receiver technology and affordable computers. For TV viewers, the high power transmitter developments for the Texas Towers opened up the UHF TV spectrum. The Sugar Grove antenna project, though never completed, provided an invaluable fund of data concerning the design of large steerable antennas. The activities and interests of the Defense Department were very timely, as Associated Universities Inc. initiated its study in 1954 to select a site and assemble a 140 foot radio telescope for the National Radio Astronomy Observatory initiative.
Both White Alice and Sugar Grove were in the process of major installation efforts in 1957 when the Sputnik passed overhead, and perimeter surveillance, along with eavesdropping over the horizon, became obsolete. White Alice was scrapped, the Texas Towers were brought back to shore, and Sugar Grove became a memory marked by a huge foundation on the side of a mountain in West Virginia. Defense activities moved from the land and sea perimeters to space. Here again, radio astronomy reaped huge benefits as the common needs of the Two Roads once again crossed in the wood.
Early space defense activities involved the Polaris Program, the Minuteman in its silos, and the Strategic Air Command, linked by SAGE. Technology requirements were fierce. The Department of Defense and Massachusetts Institute of Technology formed Lincoln Laboratory as a high power version of the Radiation Laboratory that was at MIT during World War II. NASA was formed to provide a non-military contingent for space exploration. Man in space became a momentary battle ground between the Manned Orbiting Laboratory (MOL) to be operated by DoD and the Apollo Program proposed by NASA. The need for a global communications capability to support space activities in near earth orbit led to the installation of ground stations around the world to provide continuous coverage. The steerable antennas were 85 to 210 feet in diameter. Radio astronomy said thank you by purchasing several of the 85 foot antennas. Harvard traded in its 60 foot reflector for an 85 foot reflector. NRAO installed the 85 foot Tatel telescope at Green Bank WV while waiting for the 140 foot telescope to come on line. The Two Roads had crossed once again and as a result radio telescope antennas from 85 to 210 feet in diameter became affordable.
The Needham Telescope
Polaris had a unique celestial navigation requirement. As the Director of Polaris, Rear Admiral Red Rayburn described the requirement as follows: "When the red phone rings, I have four minutes to launch my missiles. I need to know my azimuth and my location." This was a 24/7 requirement independent of weather conditions. Rayburnís solution was to use radio stars as celestial sources to assure an all-weather capability. Radio star research was in its infancy. The precise location of the stars was essential to their use for navigation. Developing a reliable "radio sextant" was an equally important requirement. Initially, the Polaris was based on the launch of Jupiter missiles from light cruisers. For this configuration, the radio sextant would be an el/az mounted 28 foot antenna on a gyro-stabilized platform. The prototype was assembled in Needham, MA. The initial priority was the development of a radio star catalog. That was a classified effort that enjoyed a unique opportunity to compare radio star positions measured at Needham with those measured in England and Australia. The Two Roads had crossed in an arena of basic and applied research.
The use of "sky horns" and rf noise balancing techniques developed under the Polaris Sextant program were early benefits made available to radio astronomy telescopes. The instantaneous bandwidth of the Sextant was 7.5-8.5 GHz obtained by cascading three low noise traveling wave tubes. Elevation and azimuth tracking of a radio star was accomplished by sequential lobing of orthogonal pairs of antenna feeds, one pair in elevation and the other in azimuth. A broadband four-port Faraday ferrite switch was developed for the sequential lobing function. Automatic rf noise injection was developed for the elevation coordinate to offset the atmospheric "secant effect".
The need to remain informed concerning the radio phenomenology of space opened a radio astronomy charter at many government laboratories, such as NRL, Lincoln Lab, Air Force Research Lab (AFRL) and the Redstone Arsenal. When it became apparent that putting a man on the moon might coincide with the time of maximum solar radio activity, AFRL was assigned the task of developing and validating a Radio Solar Telescope Network (RSTN). The prototype was assembled and operated at the Sagamore Hill Observatory in Ipswich, MA during the first half of the decade of the 1960s. Near the end of the decade, AFRL began the installation of five stations in a global network designed to observe the sun at all times. A D.S. Kennedy equatorially mounted 28 foot antenna was one of the telescopes included in the RSTN configuration at each station. The Needham telescope had completed its lunar work and was made available to RSTN for assignment to one of the five stations. The solid dish was removed and scraped. The original mesh dish was shipped with the mount to Sagamore Hill and then on to the RSTN station in Oahu. In 1977, I was assigned to the validation team at Oahu, where I saw the Needham Telescope for the last time as she majestically looked toward Cas A at an observing frequency of 240 MHz and obtained a beautiful drift scan while I visited Pearl Harbor. The last time I had operated the telescope was in Needham, when the observing frequency was 95 GHz, certain proof that what goes around comes around. The occasion coincided with the celebration of my Harvard Service Award for 25 years of faithful service. The Harvard Chair with monogram awaited my return to Cambridge.
First Commercially Available Receiver for NRAO
The sextant technique was classified but the components were quickly reconfigured in an unclassified configuration to perform radio astronomy research at the Needham Telescope. With the aid of this sensitive receiver, Frank Drake made radio brightness measurements of several celestial radio sources. The measured antenna temperature of Saturn was 0.04K, Jupiter 0.15K, M17 3K, the antenna temperature of the planetary nebula NGC 7293 was 0.25K, and NGC 6853 was 0.10K. The TWT radiometer in the configuration used by Drake at Needham was named the HII X2C. This became the first commercially available radio telescope receiver purchased by NRAO. The Roads had crossed and Polaris gave a present to NRAO.
Polaris Submarine Sextant Supports Solar and Lunar Research
As the triad of land, sea and air defense evolved during the 1950s with Minuteman, Polaris, and SAC, the role of Polaris was redefined as an undetectable platform. When Sputnik passed overhead, the ship-borne configuration was abandoned. Polaris went underwater as a submarine fleet. There was inadequate room for a 28í antenna. The maximum antenna size for the submarine was 3 feet. Radio stars were abandoned and the sun and moon became the all weather celestial sources for the Polaris submarine. The stability of the thermal centroid for both sources became a major concern. The effect of sun spot activity on the radio centroid of the sun was a significant concern, since it might be necessary to set up a global network to provide a continuous measure of the solar centroid and communicate the position to the fleet. Concern with the location of the lunar centroid was based on inadequate knowledge about the heating and cooling characteristics of the lunar surface at microwave frequencies. As a result, the Polaris Office supported several solar and lunar research studies at government, university and industrial research centers.
Another concern was the attenuation of the rf waveguide between the antenna and the input to the traveling-wave tube (TWT) receiver chain. The proposed solution was to replace the input TWT with a maser and cool the waveguide with a closed cycle liquid nitrogen system. There was a problem: neither the maser nor the closed cooling system existed. Polaris funded and fielded the first commercially available X-Band maser within 90 days following the Lincoln Lab announcement of success with the first maser in 1957.
The first radio sextant was installed on the 610 Boat (submarine) and underwent extensive sea trials. There was good and bad news. The good news was that the demonstrated all weather capability of the radio sextant exceeded expectations. The bad news was a motion picture of the three foot diameter ball supported on a cylindrical mast, steaming along at 20 knots and laying down an easily detectable wake. This did not meet the requirement of "underwater-undetectable". Polaris abandoned the use of radio sextants in 1959.
During the decade of the 1950s, the Polaris program interest in radio sextants enhanced the knowledge and capabilities of radio astronomy. Contributions included improved knowledge of solar, lunar, and radio star phenomenology. The Polaris initiative also contributed to advancements in the associated instrument technology such as maser amplifiers, low noise broadband traveling wave tubes, closed cycle cooling systems, and techniques like the sky horn and rf input noise balancing. Polaris was one of the more memorable times that the Two Roads crossed in the wood.
Venus Fly-by in 1962: Space and Millimeter Wave Astronomy
Sputnik accelerated the formation of NASA and the need to demonstrate that the U.S. was ready for the space challenge. In response to JPLís request for innovative proposals, a group of Harvard and MIT radio astronomers proposed a fly-by of the planet Venus. The four observing frequencies were 15, 22, 35 and 75 GHz. The goal was to look through the clouds at 15 GHz, look for water at 22 GHz, look partially into the clouds at 35 GHz, and view the cloud tops at 75 GHz. This intriguing combination of planetary atmospheric measurements with surface temperature characteristics led to the NASA decision to proceed with the Venus fly-by as the Mariner A Program. It also stimulated an early interest in radio meteorology of the terrestrial atmosphere observed from space. Water vapor, oxygen, and ozone distributions are now routinely monitored from orbit at millimeter wavelengths. Today, the development of millimeter and submillimeter wavelength components and systems needed for radio telescopes like ALMA will be aided by the product of the research and development associated with meteorological programs like National Polar-Orbiting Operational Environmental Satellite System (NPOESS). Here again the Roads will cross in the wood and radio astronomy will be a beneficiary.
The Centaur rocket was originally scheduled to send the Mariner A payload to Venus. It was a no-show at launch time. JPL did a heroic job reconfiguring the Mariner A into what became known as Mariner R. Mariner R was about one half the payload weight of the A-configuration. The launch went off on schedule with an Atlas-Agena rocket vehicle configuration. The fly-by surprise was a Venus surface temperature of 750 K.
Lunar Landing Sites and the Radio Phases of the Moon
Putting a man on the moon during the 1960s was a major technological goal of the decade. It seemed as far-fetched as the thought in the 1950s that one could fire a rocket into space from a submerged submarine. The man-on-the-moon initiative generated numerous technology spin-off benefits. For radio astronomy, it provided the large steerable antennas that were developed for the Deep Space Network, low noise receivers, and an affordable computer capability.
The determination of lunar surface material characteristics based on measurements of the heating and cooling characteristics of the surface became a major program effort under the direction of Jack Copeland and Warren Tyler. Copeland and Tyler were members of the scientific team selected by JPL for the Mariner fly-by. They arranged for resurfacing of the 28' parabolic reflector of the Needham Telescope to support observations at frequencies up to 95 GHz. In addition to observing Venus from Earth during the fly-by of Mariner R, Copeland and Tyler performed a series of measurements with the Needham Telescope to determine the heating and cooling characteristics of various parts of the lunar surface. From these measurements they deduced that the lunar surface had the characteristics of pulverized concrete, easily able to support the safe landing of a space craft and a walk on the moon. The Needham Telescope supported the trend toward large millimeter wave telescopes, for the ground-based observation of space phenomena. The Telescope was loaned by the Polaris program to the NASA-supported measurement of the lunar surface characteristics. This was an interesting example of the Two Roads crossing.
The Boston Marching and Chowder Society
During the 1950s and 1960s NSF, AUI, and ultimately the NRAO organization itself, developed the National Radio Astronomy Observatory with the combined help of many representing various regional and national interests. With excellent leadership and effort, NRAO became a center of excellence. The trip was bumpy at times, but worth the effort.
As an aid in smoothing the bumps, Ewen Knight formed a Science Committee comprised of leaders in radio astronomy and chaired by Fred Whipple, the Director of the Harvard-Smithsonian Center for Astrophysics. Charter members included Ed Lilley, Frank Drake, Al Barrett, Harold Weaver, Jack Copeland, Sandy Weinreb, Jack Campbell, G. Richard Huguenin, Paul Coyne, Warren Tyler, Paul Kalaghan, and Doc Ewen. Meetings were informal and held when some event was deemed important or worthy of joint discussion. Visitors from major international observatories were frequent guests of the Committee.
It soon became evident that the membership should be expanded to include others in the scientific community who were not available as consultants, such as members of the technical staff at Lincoln Lab and AFRL. Jim Meyers, the Assistant Director of Lincoln Lab, made the original suggestion to expand the membership under the name, "The Marching and Chowder Society of Boston". The idea was accepted, and we began to discuss common interests, common denominators, and how we could arrange that the Two Roads meet more frequently in the wood, to the benefit of all.
Though Two Roads diverged in a yellow wood, as in Robert Frost's famous poem, it has been the crossing of Two Roads in a wood that has characterized the historical growth of radio astronomy and the NRAO. Iím sure that my Amherst College English Professor Bob Frost would agree: that has made all the difference.
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