SP-4218 To See the Unseen


- Chapter Two -

Fickle Venus



[27] In 1958, MIT's Lincoln Laboratory announced that it had bounced radar waves off Venus. That apparent success was followed by another, but in England, during Venus' next inferior conjunction. In September 1959, investigators at Jodrell Bank announced that they had validated the 1958 results, yet Lincoln Laboratory failed to duplicate them. All uncertainty was swept aside, when the Jet Propulsion Laboratory (JPL) obtained the first unambiguous detection of echoes from Venus in 1961.

As we saw in the case of radar studies of meteors and the Moon in the 1940s and 1950s, planetary radar astronomy was driven by technology. The availability of military apparatus made possible the rise of radar astronomy in Britain in the 1940s. Just as the threat of airborne invasion gave rise to the Chain Home radar, the Cold War and its scientific counterpart, the Space Race, demanded the creation of a new generation of defensive radars, and those radars made possible the first planetary radar experiments. Even British and Soviet planetary radar astronomy were not free of the sway of military and space efforts. Thus, the Big Science efforts brought into being by the Cold War and the Space Race provided the material resources necessary for the emergence of planetary radar astronomy.

The initial radar detections of Venus signaled a benchmark in radar capacity that separated a new generation of radars from their predecessors. High-speed digital computers linked to more powerful transmitters and more sensitive receivers utilizing state-of-the-art masers and parametric amplifiers provided the new capacity. As we saw in Chapter One, initial radar astronomy targets were either ionospheric phenomena, like meteors and auroras, or the Moon, whose mean distance from Earth is about 384,000 kilometers. The new radars reached beyond the Moon to Venus, about 42 million kilometers distant at its closest approach to Earth.

Radar detections of the planets, while sterling technical achievements, were incapable of demonstrating the value of planetary radar as an ongoing scientific activity. As radar astronomy already had achieved with meteor studies, planetary radar became a scientific activity by solving problems left unsolved or unsatisfactorily solved by optical means.

As they made their first detections of Venus, planetary radar astronomers found and solved two such problems. One was the rotation of Venus, the determination of which was prevented by the planet's optically impenetrable atmosphere. The other problem was the astronomical unit, the mean radius of the Earth's orbit around the Sun. Astronomers express the distances of the planets from the Sun in terms of the astronomical unit, but agreement on its exact value was lacking. Radar observations of Venus provided an exact value, which the International Astronomical Union adopted, and revealed the planet's retrograde rotation.

While the astronomical unit and the rotation of Venus interested astronomers, they also held potential benefit for the nascent space program. In many respects, the problems solved by the first planetary radar experiments needed solutions because of the Space Race. By February 1958, when Lincoln Laboratory first tried to bounce radar waves off Venus, Sputnik 1 and the Earth-orbiting dog Laika were yesterday's news. The Space Race was hot, and so was the competition between the United States and the Soviet Union. [28] Planetary radar astronomy rode the cresting waves of Big Science (the Space Race) and the Cold War well into the 1970s.


From the Rad Lab to Millstone Hill


Scientists and engineers at MIT's Lincoln Laboratory attempted to reach Venus by radar in 1958, because they had access to a radar of unprecedented capability. The radar existed because MIT, as it had since the days of the Radiation Laboratory, conducted military electronics research. Lincoln Laboratory did not emerge directly from the Radiation Laboratory but through its direct descendant, the Research Laboratory of Electronics (RLE).

The RLE, a joint laboratory of the Physics and Electrical Engineering Departments, continued much of the fundamental electronic research of the Radiation Laboratory. The Signal Corps, Air Force, and the Office of Naval Research jointly funded the new laboratory, with the Signal Corps overseeing the arrangement. Former Radiation Laboratory employees filled research positions at the RLE, which occupied a temporary structure on the MIT campus erected earlier for the Radiation Laboratory. The two leaders of the Lincoln Laboratory Venus radar experiment, Robert Price and Paul E. Green, Jr., were both student employees of the RLE. Price also had an Industrial Fellowship in Electronics from Sperry. Among the other early RLE fellowship sponsors were the General Radio Company, RCA, IT&T, and the Socony-Vacuum Oil Company.

In September 1949, the Soviet Union detonated its first nuclear bomb; within months civil war exploded in Korea. The need for a United States air defense capable of coping with a nuclear attack was urgent. Project Charles, a group of military and civilian experts, studied the problems of air defense. Its findings led directly to the creation of Lincoln Laboratory in the Autumn of 1951.1

MIT was, in the words of Hoyt S. Vandenberg, U.S. Air Force chief of staff, "uniquely qualified to serve as contractor to the Air Force for the establishment of the proposed [Lincoln] laboratory. Its experience in managing the Radiation Laboratory of World War II, the participation in the work of ADSEC [Air Defense Systems Engineering Committee] by Professor [George E.] Valley and other members of the MIT staff, its proximity to AFCRL [Air Force Cambridge Research Laboratories], and its demonstrated competence in this sort of activity have convinced us that we should be fortunate to secure the services of MIT in the present connection."2

Lincoln Laboratory was to design and develop what became known as SAGE (Semi-Automatic Ground Environment), a digital, integrated computerized North-American network of air defense. SAGE involved a diversity of applied research in digital computing and data processing, long-range radar, and digital communications. The Army, Navy and Air Force jointly underwrote Lincoln Laboratory through an Air Force prime contract. The Air Force provided nearly 90 percent of the funding. In 1954, Lincoln Laboratory moved out of its Radiation Laboratory buildings on the MIT campus and into a newly constructed facility at Hanscom Field, in Lexington, Massachusetts, next to the Air Force Cambridge Research Center.

[29] Lincoln Laboratory quickly began work on the Distant Early Warning (DEW) Line in the arctic region of North America. The first experimental DEW-line radar units were in place near Barter Island, Alaska, by the end of 1953. The radar antennas were enclosed by a special structure called a radome, which protected them from arctic winds and cold.

InterContinental Ballistic Missiles (ICBMs) challenged the DEW Line and the North American coordinated defense network, which had been designed to warn against airplane attacks. ICBMs could carry nuclear warheads above the ionosphere, higher than any pilot could fly; existing warning radars were useless. In order to detect and track ICBMs, radars would have to recognize targets smaller than airplanes at altitudes several hundred kilometers above the Earth and at ranges of several thousand kilometers. The new radars would have to distinguish between targets and auroras, meteors, and other ionospheric disturbances, which experience already had shown were capable of crippling military communications and radars.3

In 1954, Lincoln Laboratory began initial studies of Anti-InterContinental Ballistic Missile (AICBM) systems and the creation of the Ballistic Missile Early Warning System (BMEWS). By the spring of 1956, the construction of an experimental prototype BMEWS radar was underway. Its location, atop Millstone Hill in Westford, Massachusetts, was well away from air routes and television transmitters and close to MIT and Lincoln Laboratory. The Air Force owned and financed the radar, while Lincoln Laboratory managed it under Air Force contract through the adjacent Air Force Cambridge Research Center.

Herbert G. Weiss was in charge of designing and building Millstone. After graduating from MIT in 1936 with a BS in electrical engineering, Weiss conducted microwave research for the Civil Aviation Authority in Indianapolis and worked in the MIT Radiation Laboratory. After the war, Weiss worked at Los Alamos, then at Raytheon, before returning to MIT to work on the DEW radars.

Millstone embodied a new generation of radars capable of detecting smaller objects at farther ranges. Thanks to specially designed, 3-meter-tall (11-feet-tall) klystron tubes, Millstone was intended to have an unprecedented amount of peak transmitting power, 1.25 megawatts from each klystron (2.5 megawatts total). Its frequency was 440 MHz (68 cm). The antenna, a steerable parabolic dish 26 meters (84 feet) from rim to rim, stood on a 27-meter-high (88-foot-high) tower of concrete and steel. Millstone began operating in October 1957, just in time to skin track the first Sputnik.



Figure 4. The Lincoln Laboratory Millstone Hill Radar Observatory, ca. 1958.

Figure 4. The Lincoln Laboratory Millstone Hill Radar Observatory, ca. 1958. (Courtesy of MIT Lincoln Laboratory, Lexington, Massachusetts, photo no. P489-128.)


Millstone furnished valuable scientific and technological information to the military, while advancing ionospheric and lunar radar research. In addition to testing and evaluating new defense radar techniques and components, its scientific missions included measuring the ionosphere and its influence on radar signals (such as Faraday rotation), observing satellites and missiles, and performing radar studies of auroras, meteors, and the Moon, all of which were potential sources of false alarm for BMEWS radars.4


The Lunchtime Conversazione


The idea of using the Millstone Hill radar to bounce signals off Venus arose during one of the customary lunchtime discussions between Bob Price and Paul Green. As MIT doctoral students and later as Lincoln Laboratory engineers, Price and Green worked closely together under Wilbur B. Davenport, Jr., their laboratory supervisor and dissertation director. They worked on different aspects of NOMAC (NOise Modulation And Correlation), a high-frequency communication system (known by the Army Signal Corps production name F9C) that used pseudonoise sequences, and on Rake, a receiver that [31] solved NOMAC multipath propagation problems. Later, what Lincoln Laboratory called NOMAC came to be called spread spectrum.

Their work was vital to maintaining military communications in the face of enemy jamming. One of their units went to Berlin in 1959 in anticipation of a blockade to provide essential communications in case of jamming. The Soviet Union already had demonstrated its jamming expertise against the Voice of America. Conceivably, all NATO communications could be jammed in time of war. The Lincoln Laboratory anti-jamming project was a direct response to that threat.5

Radio astronomy, which influenced the rise of planetary radar astronomy during the 1960s, played a small role in the Lincoln Laboratory Venus experiment. Price actually had worked at the University of Sydney under radio astronomer Gordon Stanley and met such pioneers as Pawsey, Taffy Bowen, Paul Wild, Bernie Mills, and Chris Christiansen. A recently published book on radio astronomy by the Australian scientists J. L. Pawsey and Ronald N. Bracewell was the subject of lunch conversation between Green and Price in the Lincoln Laboratory cafeteria. The chapter on radar astronomy predicted that one day man would bounce radar waves off the planets. But radio astronomy did not give rise to the decision to attempt a radar detection of Venus.6

What did trigger the decision was the completion of the Millstone facility. Green and Price wondered if it was powerful enough to bounce radar signals off Venus. Gordon Pettengill, a junior member of the team, joined the lunchtime discussions. Trained in physics at MIT and an alumnus of Los Alamos, Pettengill had an office at Millstone. After making calculations on a paper napkin, though, they estimated that Millstone did not have enough detectability for the experiment, even if one assumed that Venus was perfectly reflective.

The lunchtime conversazione went nowhere, until Robert H. Kingston, who had a joint MIT and Lincoln Laboratory appointment, joined the discussions. Kingston had just built a maser. "Within an hour," Green recalled, "we had the whole damn thing mapped out."7 The maser gave the radar receiver the sensitivity necessary to carry out the experiment.

The maser, an acronym for Microwave Amplification by Stimulated Emission of Radiation, was a new type of solid-state microwave amplifying device vaunted by one author as "the greatest single technological step in radio physics for many years, with the possible exception of the transistor, comparable say with the development of the cavity magnetron during the Second World War." The maser was at the heart of the low-noise microwave amplifiers used in radio astronomy. The first radio-astronomy maser application, a joint effort by Columbia University and the Naval Research Laboratory, occurred in April 1958. The first use of a maser in radar astronomy, however, preceded that application by two months, in February 1958, at Millstone. While most masers [32] functioned above 1,000 MHz, Kingston's operated in the UHF region, around 440 MHz, and reduced overall system noise temperature to an impressive 170 K.8

Despite the maser's low noise level, Price and Green knew that they would have to raise the level of the Venus echoes above that of the noise. Their NOMAC anti-jamming work had prepared them for this problem. They chose to integrate the return pulses over time, as Zoltán Bay had done in 1946. In theory, the signals buried in the noise reinforced each other through addition, while the noise averaged out by reason of its random nature.9

A digital computer, as well as additional digital data processing equipment, linked to the Millstone radar system performed the integration and analysis of the Venusian echoes. An analog-to-digital convertor, initially developed for ionospheric research by William B. Smith, digitized information on each radar echo. That information simultaneously was recorded on magnetic tape and fed to a solid-state digital computer. The experiment was innovative in digital-signal processing and marked one of the earliest uses of digital tape recorders.10


Venus or Bust


Kingston's maser was installed at Millstone Hill just in time for the inferior conjunction of Venus. However, a klystron failure left only 265 kilowatts of transmitter power available for the experiment. On 10 and 12 February 1958, the radar was pointed to detect Venus, then some 45 million kilometers (28 million miles) away. The radar signals took about five minutes to travel the round-trip distance. In contrast, John DeWitt's signals went to the Moon and back to Fort Monmouth, NJ, in only about 2.5 seconds.

Of the five runs made, only four of the digital recordings had few enough tape blemishes that they could be easily edited and run through the computer. Two of the four runs, one from each day, showed no evidence of radar returns. The others had one peak each. Price recalled, "When we saw the peaks, we felt very blessed."11 It was not absolutely clear, however, that the two peaks were really echoes.

Green explained: "We looked into our soul about whether we dared to go public with this news. Bob was the only guy who really stayed with it to the end. He had convinced himself that he had seen it, and he had convinced me that he had seen it. Management asked us to have a consultant look at our results, and we did." Thomas Gold of Cornell University looked at the peaks and said "Yes, I think you should publish this." Green and Price then published their findings in the 20 March 1959 issue of Science, the journal of [33] the American Association for the Advancement of Science, 13 months after their observations in February 1958.12

By then, despite the unsuccessful Lunik I Moon shot, the Soviet Union had achieved a number of successful satellite launches. The United States space effort still was marked by repeated failures. All of the four Pioneer Moon launches of 1958 ended in failure. There was a desperate need for good news; the Lincoln Laboratory publicity department gave the Venus radar experiment full treatment. In addition to a press conference, Green and Price quickly found themselves on national television and on the front page of the New York Times. President Eisenhower sent a special congratulatory telegram calling the experiment a "notable achievement in our peaceful ventures into outer space."13

Once Price and Green accepted the validity of the two peaks, the next step was to determine the distance the radar waves travelled to Venus and to calculate a value for the astronomical unit. They estimated a value of 149,467,000 kilometers and concluded, moreover, that it did not differ enough from those found in the astronomical literature to warrant a re-evaluation of the astronomical unit.14

The Lincoln Laboratory 1958 Venus experiment launched planetary radar astronomy; Millstone Hill was the prototype planetary radar. Its digital electronics, recording of data on magnetic tape for subsequent analysis, use of a maser (or other low-noise microwave amplifier) and a digital computer, and long-period integration all became standard equipment and practice. As with any experiment, scientists must be able to duplicate results. The next inferior conjunction provided an opportunity for scientists at Jodrell Bank to attempt Venus, too.

Jodrell Bank had a new, 76-meter (250-foot) radio telescope, the largest of its type in the world. Although planned as early as 1951, the telescope did not detect its first radio waves until 1957 as a consequence of a long, nightmarish struggle with financial and construction difficulties. The civilian Department of Scientific and Industrial Research and the Nuffield Foundation underwrote its design and construction. Success in detecting Soviet and American rocket launches brought visits from Prince Philip and Princess Margaret and fame. Fame in turn brought solvency and a name (the Nuffield Radio Astronomy Laboratories, Jodrell Bank).

Although the design and construction of the large dish was unquestionably an enterprise carried out with civilian funding, radar research at Jodrell Bank owed a debt to the United States armed forces; however, that military research was limited to meteor studies carried out with the smaller antennas, not the 76-meter (250-foot) dish. The U.S. Air Force and the Office of Naval Research supplied additional money for tracking rocket launches, while the European Office of the U.S. Air Force Research and Development Command (EOARDC) funded general electronics research at a modest level. During the Cuban missile crisis, the 76-meter (250-foot) radio telescope served to detect missiles that might be launched from the Soviet Union. From intelligence sources, the locations of such missiles directed against London were known, and the telescope was aimed accordingly. No U.S. equipment or funding were engaged in this effort, though.15



Figure 5. The Jodrell Bank 250-foot (76-meter) telescope in June 1961.

Figure 5. The Jodrell Bank 250-foot (76-meter) telescope in June 1961. The control room is partially visible bottom left. The 1962 and 1964 Jodrell Bank Venus radar experiments were carried out using a U.S.-supplied continuous-wave radar mounted on this telescope. (Courtesy of the Director of the Nuffield Radio Astronomy Laboratories, Jodrell Bank.)


Preparation for the 1959 Venus experiment began in 1957, as the dish was reaching completion. The telescope, however, was not yet ready for radar work. John Evans recognized that its transmitter power and operating frequency would have to be raised in order to achieve critical extra gain for the Venus experiment. The 100-MHz (3-meter), 10-kilowatt Moon radar was not powerful enough. The University of Manchester Physics Department had developed a 400-MHz (75 cm), 100-kilowatt klystron. "It was a real kludge," Evans later recalled, "because it was basically a Physics Department experiment. It was continuously pumped; it sat on top of vacuum pumps, which required liquid nitrogen for cooling."16

Lovell had the General Electric Company of Britain supply a modulator for the klystron. Evans was responsible for designing and building the rest of the equipment. As the 1958 Venus inferior conjunction approached, "we simply were not ready, and Lovell was quite upset," Evans explained. Out of desperation, Evans employed the 100-MHz Moon radar enhanced with a computer integration scheme, but the equipment failed to detect echoes. When Lincoln Laboratory announced its success, Evans recalled, "We shrugged and felt we were beaten to the punch."

The 1958 Jodrell Bank failure put all that much more pressure on Evans to produce results during the next inferior conjunction of September 1959. The transmitter was more [35] or less ready. The klystron was mounted in one of the telescope towers. "It was a royal pain," Evans remembered, "because we had to take liquid nitrogen up the elevator and then a vertical ladder to get to this darn thing." As if that were not enough, a water pump burned up, and the connectors on the coaxial cable carrying power to the dish burned out every ten or fifteen minutes. While still struggling with the connector problem, Evans made several runs on Venus.

Evans was a junior scientist, having just received his Ph.D. in 1957. He felt he was under great pressure to produce positive results. Lovell was anxious to know if they had found an echo; the Duke of Edinburgh was about to visit. Evans looked at his data, taken from the first few minutes of each run, when he thought the apparatus was working. He had what looked like a return, but it could have been noise. Evans decided, "Well, I think we have an echo." The Venus detection was announced in the 31 October 1959 issue of Nature. The Duke of Edinburgh visited Jodrell Bank on 11 November 1959; he received an explanation and a demonstration of the technique, using the Moon as a target.

Despite the patchwork equipment, the 50-kilowatt, 408-MHz (74-cm) radar obtained a total of fifty-eight and three quarters hours of useful operating data, before Venus passed beyond its range. As expected, none of the echoes were stronger than the receiver noise level; integration techniques increased the strength of the echoes. The Jodrell Bank signal processing equipment was rather limited in its ability to search. Without accurate range or Doppler correction information, Evans had to make assumptions; he chose the Lincoln Laboratory 1958 published value. Not surprisingly, the value Jodrell Bank derived for the astronomical unit agreed with that determined at Lincoln Laboratory.17 The Jodrell Bank confirmation of the Lincoln Laboratory results placed them on solid scientific ground, that is, until Lincoln Laboratory repeated the experiment.


Fickle Venus


Bob Price and his fellow Lincoln Laboratory investigators were highly optimistic about verifying their 1958 results. Millstone now had a peak transmitter power of 500 kilowatts, almost twice the 1958 level. In addition to using a higher pulse repetition rate, which improved signal detectability, Price's team replaced the maser with a parametric amplifier. Like the maser, the parametric amplifier was a solid-state microwave amplifier. Parametric amplifiers were simpler, smaller, cheaper, and lighter than masers, and they did not require cryogenic fluids to keep them cool. Although masers generally were less noisy, the Millstone parametric amplifier was, Pettengill and Price reported, "gratifyingly stable and reliable in its operation." 18 Over a four-week period around the inferior conjunction of Venus, the Lincoln Laboratory team made two types of radar observations. On 66 runs, they recorded the echoes digitally for subsequent computer processing, as they had done in 1958. The second approach, used on 117 runs, involved initial analog processing in a series of electronic circuits, followed by digitization and integration in real time by the site's computer. It was their first attempt at a real-time planetary detection by radar. Of all the runs, only one displayed a peak sufficiently above the noise level to be statistically significant. When subjected to detailed analysis, though, the peak turned out to be only noise. Price and [36] Pettengill concluded that "none of the individual runs show strong evidence of Venus echoes."19

Jodrell Bank had corroborated the 1958 results; yet with an improved radar, Lincoln Laboratory could not confirm them. The disparity between the results was perplexing--and bothersome. "It is difficult to explain the disparity between the results obtained at the two Venus conjunctions. Our current feeling," wrote Green and Pettengill, "is that the planet's reflectivity may be highly variable with time, and that the two successes in 1958 were observations made on very favorable occasions."20

At the Jet Propulsion Laboratory (JPL), the Lincoln Laboratory and Jodrell Bank experiments were viewed with disbelief. As an internal report stated in 1961, "It is not known at the present time with certainty that a radio signal has ever been reflected from the surface of Venus and successfully detected."21 JPL investigators intended to obtain the first unambiguous detection of radar echoes from the Venusian surface.


The Jet Propulsion Laboratory


JPL began modestly in Pasadena, California, in 1936 as the Guggenheim Aeronautical Laboratory, California Institute of Technology (GALCIT), rocket project, led by Hungarian-born professor Theodore von Kármán and financed by Harry Guggenheim. Starting in 1940, with backing from the Army Air Corps, the GALCIT group turned into a vital rocket research, development, and testing facility. A 1944 contract signed by GALCIT, the Army Air Force, and the California Institute of Technology (Caltech) transformed it into a large permanent laboratory called the Jet Propulsion Laboratory, whose major responsibility was research, development, and testing of missile technology, including the country's first tactical nuclear missiles, the Corporal and Sergeant, for the Army.

JPL electronics arose out of the need for missile guidance and tracking systems. William Pickering, a Caltech electrical engineering professor with a Ph.D. in physics, became the director of JPL in 1954 and remained in that position until 1976. His specialization was electronics, not propulsion. Under Pickering's aegis, electronics grew in prominence at JPL and came to the forefront in 1958, when JPL became a NASA laboratory and started work on a worldwide, civilian satellite communications network known today as the Deep Space Network (DSN).22

The communications network, known originally as the Deep Space Instrumentation Facility (DSIF), was the home of planetary radar at JPL. The three leaders of the Venus radar experiment were engineers involved in its design, Eberhardt Rechtin, Robertson Stevens, and Walter K. Victor. Rechtin, the architect of the DSIF, had a Ph.D. in electrical engineering from Caltech. He also was an inventor, with Richard Jaffe (also at JPL), of CODORAC (COded DOppler, Ranging, And Command), a radio communication system that [37] detected and tracked narrow band signals in the presence of wideband noise. CODORAC, whose electronics in many ways resembled Lincoln Laboratory's NOMAC, became the basis for much of the DSIF's electronics. Bob Stevens had an M.S. in electrical engineering from the University of California at Berkeley, and Walt Victor, who assisted Rechtin in developing CODORAC, had a B.S. in mechanical engineering from the University of Texas.

JPL located its share of the DSIF antennas in the Mojave Desert, about 160 kilometers from JPL, on the Fort Irwin firing range near Goldstone Dry Lake, where GALCIT earlier had tested Army rockets.23 The two antennas on which JPL investigators performed their Venus experiment in 1961 were artifacts of the funding and research agendas of both the military and NASA. The first was a 26-meter-diameter (85-feet-diameter) dish named the HA-DEC antenna, because its axes were arranged to measure angles in terms of local hour angle (HA) and declination (DEC). JPL installed it at Goldstone during the second half of 1958 to track and receive telemetry from the military's Pioneer probes.24


Figure 6. JPL Goldstone 26-meter HA-DEC antenna erected in late 1958 to track and receive telemetry from the military's Pioneer probes.

Figure 6. JPL Goldstone 26-meter HA-DEC antenna erected in late 1958 to track and receive telemetry from the military's Pioneer probes. It was used with the 26-meter AZ-EL antenna to detect radar echoes from Venus in 1961. (Courtesy of Jet Propulsion Laboratory, photo no. 333-5968AC.)


[38] JPL erected the second antenna for Project Echo. Echo, a large balloon in Earth orbit, tested the feasibility of long-range satellite communications. As such, it was heir to the lunar-repeater communication tests discussed in Chapter One. Originally funded by NASA's predecessor, the National Advisory Committee for Aeronautics (NACA), and the Defense Department's space research organization, the Advanced Research Projects Agency (ARPA), Project Echo became a JPL, NASA, and Bell Telephone Laboratories undertaking in an agreement signed in January 1959.

The Echo experiments used the existing HA-DEC antenna to receive as part of a satellite circuit running from east to west. The west-to-east circuit, however, required the construction of an antenna capable of transmitting. Therefore, JPL installed a second 26-meter-diameter (85-feet-diameter) dish at Goldstone about a year after the HA-DEC antenna for Project Echo. The axes of the second antenna measured angles in terms of azimuth (AZ) and elevation (EL); hence, it was referred to as the AZ-EL antenna.25


Figure 7. Jet Propulsion Laboratory Goldstone 26-meter AZ-EL antenna built for Project Echo and used with the 26-meter HA-DEC antenna to detect echoes from Venus in 1961.

Figure 7. Jet Propulsion Laboratory Goldstone 26-meter AZ-EL antenna built for Project Echo and used with the 26-meter HA-DEC antenna to detect echoes from Venus in 1961. (Courtesy of Jet Propulsion Laboratory, photo no. 332-168.)


[39] By August 1960, as Goldstone prepared to participate in Project Echo, the Lincoln Laboratory and Jodrell Bank Venus experiments already had taken place. Solomon Golomb, assistant chief of Communications System Research Section under Walt Victor, asked his employee, Richard Goldstein, to design a space experiment to feed the rivalry between Eb Rechtin, JPL program director for the DSIF, and Al Hibbs, who was in charge of space science at JPL. Goldstein suggested the Venus radar experiment. Victor, JPL project engineer for the Echo program and recently promoted to chief of the Communications System Research Section, and Bob Stevens, head of the Communications Elements Research Section, became the project managers.26

Rechtin, Victor, and Stevens organized the Venus experiment as a drill of the DSIF and its technical staff. The functional, organizational, and budgetary status of planetary radar astronomy as a test of the DSIF originated in their conception of the 1961 Venus experiment and defined planetary radar at JPL for over two decades. At the time, the laboratory was preparing for the first Mariner missions. Consequently, as Rechtin pointed out, JPL had "a particular interest in an accurate determination of the distance to Venus in order that we might guide our space probes to that target."27

The NASA Office of Space Science approved the Mariner 1 and 2 missions in July 1960. Goldstone was to provide communications with them. The task would be more challenging than communicating with a Ranger Moon probe. While a Ranger mission required three days, the Mariner missions would involve months of round-the-clock, high-level technical performance. In June 1960, even before final approval of the Mariner probes, Rechtin proposed the radar experiment to NASA, emphasizing not its scientific value, but the "practical, purely project point of view."28

In order to perform the Venus experiment, JPL had to modify the Echo equipment. Venus was a much farther object than the Earth-orbiting Echo balloon, and both differed radically as radar targets. Victor and Stevens, moreover, wanted to avoid long-term integration and after-the-fact data reduction and analysis, that is, the Lincoln Laboratory and Jodrell Bank approach. Instead, JPL attempted a real-time radar detection of Venus.

The JPL antennas were unlike those of Lincoln Laboratory and Jodrell Bank in many ways. They operated in tandem, the AZ-EL transmitting and the HA-DEC receiving. This bistatic mode, as it is called, offered advantages over the Millstone and Jodrell Bank monostatic mode, in which a single instrument both sent and received. Monostatic radars have to stop transmitting half the time in order to receive, while bistatic radars can operate continuously, gathering twice the data in the same period of time. The Goldstone radars also operated at a higher frequency (S-band v. UHF) and sent a continuous wave, whereas the Lincoln Laboratory and Jodrell Bank radars transmitted discrete pulses.

JPL also boosted the transmitting power and receiver sensitivity of the two radars. The normal output of the AZ-EL transmitter klystron tube was 10 kilowatts at 2388 MHz (12.6 cm), but engineers coaxed a nominal average power output of 13 kilowatts out of it. [40] Raising the sensitivity of the HA-DEC receiver was a daunting challenge; the total receiver system noise temperature on Project Echo had been 1570 K!29

The technical solution was a maser and a parametric amplifier in tandem on the HA-DEC antenna. Charles T. Stelzried and Takoshi Sato created a 2388-MHz maser specifically for the Venus radar experiment and suitable for Goldstone's tough desert ambient temperatures (from -12° to 43°C; 10° to 110°F) and climate (rain, dust, and snow). The maser and 2388-MHz parametric amplifier combined gave an overall average system noise temperature of about 64 K during the two months of the Venus experiment, considerably lower than the best achieved at Millstone in 1958 (170 K). As Victor and Stevens proclaimed, "This is believed to be the most sensitive operational receiving system in the world."30


"No Echo, No Thesis"


Besides testing the personnel and materiel of the Goldstone facility, the JPL Venus experiment also was the doctoral thesis topic of two employees in Walt Victor's section, Duane Muhleman and Richard Goldstein. Muhleman graduated from the University of Toledo with a BS in physics in 1953, then worked two years at the NACA Edwards Air Force Base High-Speed Flight Station as an aeronautical research engineer, before joining JPL. As part of his duties at JPL, Muhleman tested the Venus radar system and its components during January, February, and March 1961, using the Moon as a target. For the Venus experiment, Muhleman contributed an instrument to measure Doppler spreading.31

Goldstein was a Caltech graduate student in electrical engineering. His task on the Venus radar experiment was to build a spectrum measuring instrument. It recorded what the spectrum looked like during reception of an echo and what it looked like when the receiver saw only noise. JPL hired his brother, Samuel Goldstein, a JPL alumnus and radio astronomer at Harvard College Observatory, as a consultant on the Venus experiment; Samuel also helped his brother with some of the radio techniques.

Dick Goldstein wanted to use the Venus radar experiment as his thesis topic at Caltech, but his advisor, Hardy Martel, was highly skeptical. The inability of Lincoln Laboratory to detect Venus was widely known. Although he thought the task indisputably impossible, Martel finally agreed to accept the topic, but with a firm admonition: "No echo, no thesis."32

[41] On 10 March 1961, a month before inferior conjunction, the Goldstone radars were pointed at Venus. The first signals completed the round-trip of 113 million kilometers in about six and a half minutes. During the 68 seconds of electronic signal integration time, 1 of 7 recording styluses on Goldstein's instrument deviated significantly from its zero level and remained at the new level.

To verify that the deflection came from Venus and was not leakage from the transmitter or an instability in the receiver, the transmitter antenna was deliberately allowed to drift off target. Six and a half minutes later, the recording stylus on Goldstein's instrument returned to its zero setting. The experiment was immediately repeated with the same result. JPL had achieved the first real-time detection of a radar signal from Venus. And Dick Goldstein had his dissertation topic.33


Following the initial contact, JPL conducted additional radar experiments almost daily from 10 March to 10 May 1961, collecting 238 hours of recorded radar data about Venus.35 No previous Venus radar experiment, nor any others carried out in 1961, collected as many hours of data as the JPL experiment.

The JPL experiment succeeded, because it did not depend on knowing the range to Venus, specifically; it did not depend on prior knowledge of the precise value of the astronomical unit. On the other hand, Lincoln Laboratory, as well as Jodrell Bank, had based its experiment on an assumed, yet commonly accepted, value for the astronomical unit, and, consequently, for the distance between Earth and Venus during inferior conjunction.


"We Were Wrong."


The results obtained by Lincoln and other laboratories in 1961 agreed with those obtained by JPL. That agreement led Gordon Pettengill to discern the error of the 1958 Lincoln Laboratory observations. "In view of the generally excellent agreement among the various observations made at several wavelengths [in 1961]," Pettengill and his colleagues concluded, "it seems likely that the results reported from observations of the 1958 inferior conjunction are in error, although no explanation has been found."36

Green recalled: "It was sort of devastating, when the next conjunction of Venus came around, and we learned that we were wrong. We had the wrong value of the astronomical unit. It wasn't over here; it was way over there someplace. In fact, it wasn't even easy to go back and look at the original data and conclude that it was really over there. The original [42] data just had turned out to be too noisy....It was a chastening experience for us."37 Price remembered someone entering his office with "a rather long look on his face" and saying, "Bob, I think we've been found to be wrong." It was an embarrassing moment.

Price re-examined the Lincoln Laboratory 1958 tapes. "I wanted to be sure that we hadn't detected it. I really mean that. I wanted to make sure that we had a negative result and that by accident we didn't have two wrongs making a right, that is, false processing of the 1958 data led to a false result, so the proper processing of the 1958 data would agree with JPL. I wanted to prove that that was not the case. So I went back and found the peaks, just as I had done before. I made a meticulous measurement of their position, which is the whole thing that the false echo hinged on. I developed with magnetic powder over and over again those tapes, and I inspected them until my eyes were sore. I reran the Fortran programs and checked all the programs, because you could create a timing error in the program."

The experience reminded Price of his work in Australia. Every day, his group had made ink-pen recordings of the radio sky over the antenna, usually recording only random lines, but a peak appeared on two successive days. Did the peak mean a detection of deuterium? They decided that it was a fluke and published their negative results. "If we had behaved the same way at Millstone," Price reflected, "we might have saved ourselves some embarrassment. But that is hindsight." The two Venus pulses arrived 2.2 milliseconds apart. "We just turned our back on it," Price admitted, "did a little wishful thinking, and said, 'That's the same pulse.'...I just pulled them together, ignored the 2.2-millisecond difference, and sat one on top of the other."38

Whatever the cause of the 1958 false readings, JPL was unquestionably the first to detect radar waves reflected off Venus. The literature contains two earlier, but after-the-fact detections. Only months after acknowledging JPL's priority, Lincoln Laboratory found on their data tapes a detection of Venus on 6 March 1961, a few days prior to that of JPL. Later, in 1963, Lincoln Laboratory electrical engineer Bill Smith re-examined the 1959 data tapes and found that an echo had been recorded on 14 September 1959.39 Such after-the-fact discoveries are not uncommon in the history of science, and radar astronomers from both JPL and MIT thirty years later commemorated JPL's uncontested priority in detecting radar waves reflected off Venus.

Once JPL unambiguously detected echoes from Venus, the key question planetary radar astronomers addressed was the size of the astronomical unit. In order to determine more precisely the Earth-to-Venus distance, JPL ran ranging experiments between 18 April and 5 May 1961. In the July 1961 issue of Science, Victor and Stevens announced a preliminary value for the astronomical unit of 149,599,000 kilometers with an accuracy of ± 1500 kilometers.40 That value was over 100,000 kilometers larger than the false radar value determined by Lincoln Laboratory in 1958 and confirmed by Jodrell Bank in 1959, 149,467,000 kilometers. Values obtained from preliminary analyses of radar data at Lincoln Laboratory and elsewhere in 1961 agreed closely with that of JPL (Table 1).

When Lincoln Laboratory undertook its 1961 Venus radar experiment, Gordon Pettengill, joined by John Evans, took over Bob Price's leadership role. Evans had left Jodrell Bank for Lincoln Laboratory during the previous summer, after being courted by the National Bureau of Standards and Stanford. At Jodrell Bank, Evans had had one....



Table 1. Radar Values for the Astronomical Unit, 1961-1964.


Error of measurement (in kilometers)

Value of astronomical unit (in kilometers)


Optical values.

Spencer Jones



Eugene Rabe




1961 Conjunction.

Jet Propulsion Laboratory

July 1961 (1)



August 1961 (2)



Muhleman (3)



Lincoln Laboratory

May 1961 (4)



Corrected value (5)



Jodrell Bank (6)



RCA/Flower and Cook Observatory (7)



Soviet Union

Pravda value (8)



November 1961 (9)



Revised value (10)



Space Technology Laboratories (11)




1962 Conjunction.

Jodrell Bank (12)



Soviet Union (13)



Jet Propulsion Laboratory Muhleman (14)




1964 Conjunction.

Lincoln Laboratory (15)



Jet Propulsion Laboratory (16)



Soviet Union (17)



IAU value





1. W. K. Victor and R. Stevens, "Exploration of Venus by Radar," Science 134 (July 1961): 46-48.

2. D. O. Muhleman, D. B. Holdridge, and N. Block, "Determination of the Astronomical Unit from Velocity, Range, and Integrated Velocity Data, and the Venus-Earth Ephemeris," pp. 83-92 in W. K. Victor, R. Stevens, and S. W. Golomb, eds., Radar Exploration of Venus: Goldstone Observatory Report for March-May 1961, Technical Report 32-132 (Pasadena: Jet Propulsion Laboratory, 1 August 1961).

3. D. O. Muhleman, D. B. Holdridge, and N. Block, "The Astronomical Unit Determined by Radar Reflections from Venus," The Astronomical Journal 67 (1962): 191-203.

4. Staff, Millstone Radar Observatory, Lincoln Laboratory, "The Scale of the Solar System," Nature 190 (13 May 1961): 592.

5. G. H. Pettengill, H. W. Briscoe, J. V. Evans, E. Gehrels, G. M. Hyde, L. G. Kraft, R. Price, and W. B. Smith, "A Radar Investigation of Venus," The Astronomical Journal 67 (1962): 181-190.

6. J. H. Thomson, J. E. B. Ponsonby, G. N. Taylor, and R. S. Roger, "A New Determination of the Solar Parallax by Means of Radar Echoes from Venus," Nature 190 (1961): 519-520.

7. I. Maron, G. Luchak, and W. Blitzstein, "Radar Observation of Venus," Science 134 (1961): 1419-1421.

8. V. A. Kotelnikov, "Radar Contact with Venus," Journal of the British Institution of Radio Engineers 22 (1961): 293-295.

9. V. A. Kotelnikov, V. M. Dubrovin, V. A. Morozov, G. M. Petrov, O. N. Rzhiga, Z. G. Trunova, and A. M. Shakhovoskoy, "Results of Radar Contact with Venus in 1961," Radio Engineering and Electronics Physics 11 (November 1961): 1722-1733.

10. V. A. Kotelnikov, B. A. Dubinskiy, M. D. Kislik, and D. M. Tsvetkov, "Refinement of the Astronomical Unit on the Basis of the Results of Radar Observations of the Planet Venus in 1961," NASA TT F-8532, October 1963.

11. J. B. McGuire, E. R. Spangler, and L. Wong, "The Size of the Solar System," Scientific American vol. 204, no. 4 (1961): 64-72.

12. J. E. B. Ponsonby, J. H. Thomson, and K. S. Imrie, "Radar Observations of Venus and a Determination of the Astronomical Unit," Monthly Notices of the Royal Astronomical Society 128 (1964): 1-17.

13. V. A. Kotelnikov, V. M. Dubrovin, V. A. Dubinskii, M. D. Kislik, B. I. Kusnetsov, I. V. Lishin, V. A. Morosov, G. M. Petrov, O. N. Rzhiga, G. A. Sytsko, and A. M. Shakhovskoi, "Radar Observations of Venus in the Soviet Union in 1962," Soviet Physics - Doklady 8 (1964): 642-645.

14. D. O. Muhleman, Relationship Between the system of Astronomical Constants and the Radar determinations of the Astronomical Unit, Technical Report 32-477 (Pasadena: Jet Propulsion Laboratory, 15 January 1964).

15. J. C. Pecker, ed., Proceedings of the Twelfth General Assembly (New York: Academic Press, 1966), p. 602.

16. J. C. Pecker, ed., Proceedings of the Twelfth General Assembly (New York: Academic Press, 1966), p. 603.

17. V. A. Kotelnikov, Yu. N. Aleksandrov, L. V. Apraksin, V. M. Dubrovin, M. D. Kislik, B. I. Kuznetsov, G. M. Petrov, O. N. Rzhiga, A. V. Frantsesson, and A. M. Shakhovskoi, "Radar Observations of Venus in the Soviet Union in 1964," Soviet Physics - Doklady 10 (1966): 578-580.


[44] ....technical assistant; but at Lincoln Laboratory, as Bernard Lovell pointed out, he had "an army of engineers and technicians together with a transmitter vastly superior to the one at Jodrell Bank."

Evans' departure from Jodrell Bank could not have come at a worse time, in the opinion of Lovell. "For me it was the beginning of a distressing series of losses of the brilliant young men who had been with me throughout the crisis of the telescope and whose devotion and skill had been a determining factor in the immediate success of the instrument. But who could expect a young man to resist a lavish red carpet reception and an offer of a salary many times greater than any sum which we could possibly offer him?"41

During the 1961 Venus experiment, the Millstone Hill radar ran at peak transmitting power, 2.5 megawatts. The increased transmitter power overcame the higher overall receiver noise temperature (240 K) to make the telescope a far more capable instrument. Pettengill and his colleagues aimed their radar at Venus on 6 March 1961, again using a technique to provide real-time detection. No echoes appeared until 24 March. Preliminary analysis yielded a value for the astronomical unit of 149,597,700 ± 1,500 kilometers in May 1961.42 That agreed closely with JPL's preliminary value, 149,599,000 kilometers. Despite considerable obstacles, and chastened by their 1959 false detection, Jodrell Bank investigators also found a value for the astronomical unit that agreed with the JPL value.

In 1959, John H. Thomson took over the planetary radar program, and in the autumn of 1960, Lovell added John E. B. Ponsonby, who had come to Jodrell Bank to work on a doctorate after graduating in electrical engineering from Imperial College, London. Ponsonby had experience in meteor radar through his high school teacher and one-time member of the Jodrell Bank group, Ian C. Browne.43

Working from notes and memoranda left by Evans, the new team, which included G. N. Taylor and R. S. Roger, put together a radar system that "yielded a clear-cut and decisive answer after only a few 5 minute integration periods."44 The first thing they did, however, was to abandon the atrocious klystron. With most of the problems that plagued the 1959 experiment overcome, with a more sensitive receiver, and with peak power output boosted from 50 to 60 kilowatts, the 76-meter (250-foot) Jodrell Bank telescope detected Venus beginning 8 April 1961, a few weeks after both JPL and Lincoln Laboratory had started their experiments, and ending 25 April 1961.

Jodrell Bank calculated a value for the astronomical unit, 149,600,000 ± 5000 kilometers,45 close to the preliminary values of JPL (149,599,000 kilometers) and Lincoln [45] Laboratory (149,597,700 kilometers), but with a far greater possible error of measurement. Similar results came from an unexpected source. RCA's Missile and Surface Radar Division in Moorestown, New Jersey, carried out its first and last planetary radar experiment in 1961. The Division performed radar research for the Army Signal Corps and the Navy, and in 1960, the Division performed solar radio experiments using a missile-tracking radar. On their Venus radar experiment, RCA investigators collaborated with the Flower and Cook Observatory of the University of Pennsylvania. Between 12 March and 8 April 1961, RCA tracked Venus with a BMEWS experimental radar in order to measure the astronomical unit. In over six hours of transmitted signals, they found only four peaks from which they calculated a value for the astronomical unit of 149,596,000 ± 200 kilometers,46 only 3,000 kilometers less than the JPL value. Not all Venus radar results agreed with those of JPL, however.

In the Soviet Union, planetary radar was fundamental to the space program. One of the main objectives of the Crimean Venus experiment was to calculate a more precise value for the astronomical unit for use in launching planetary probes. The calculation of the orbit of the Mars-1 probe, in November 1962, utilized a radar-based value for the astronomical unit. The Institute of Radio Engineering and Electronics (IREE) of the U.S.S.R. Academy of Sciences, in association with other unnamed (but presumably military and intelligence) organizations and under the direction of Vladimir A. Kotelnikov, of the Soviet Academy of Sciences, designed and built planetary radar equipment that was installed at the Long-Distance Space Communication Center, located near Yevpatoriya in the Crimea. The IREE installation had nothing to do with the radar work carried out in the Soviet Union in 1946 on meteors or between 1954 and 1957 on the Moon.

The IREE planetary radar was a monostatic pulse 700-MHz (43-cm) system. For the receiver, the IREE expressly designed both a parametric and a paramagnetic amplifier, another form of solid-state, low-noise microwave amplifier. The noise temperature of the entire receiver (without antenna) was claimed to be 20 ± 10 K. The antenna was an array of eight 16-meter dishes, unlike any design ever used in the United States or Britain for planetary radar astronomy.47

Kotelnikov and his colleagues observed Venus between 18 and 26 April 1961. Their preliminary analysis of the data yielded an estimate of the astronomical unit, 149,457,000 kilometers, which appeared in the newspapers Pravda and Izvestiia on 12 May 1961. Over 100,000 kilometers less than the JPL and other values, the Soviet astronomical unit measurement was so incredibly incongruous, that Solomon Golomb told a conference of astronomers, "we should congratulate our Russian colleagues on the discovery of a new [46] planet. It surely wasn't Venus!" Retrospectively, Kotelnikov explained that "random realizations of noise were taken for reflected signals."48

The cause of the Soviet error might have been rooted in Cold War competition, which placed Soviet scientists under great pressure to produce results quickly for political reasons. The Pravda and Izvestiia announcements appeared on 12 May 1961, six days after the Jodrell Bank, but before the Lincoln Laboratory, announcements. If published sources had guided Kotelnikov and his colleagues, they would have been the erroneous Lincoln Laboratory and Jodrell Bank results of 1958 and 1959, with which the Izvestiia value agreed closely (within 10,000 kilometers).

The Cold War prevented communication and cooperation among planetary radar investigators. The Space Race in 1961 was still an extension of the Cold War; informal communications did not exist. Lincoln Laboratory did secret military research; JPL was a sensitive space research center with connections to ARPA, a military research agency. Jodrell Bank did not yet have ties with their Soviet counterparts. While Lincoln Laboratory, JPL, and Jodrell Bank personnel exchanged data, such informal links with Soviet scientists did not and could not exist.

Kotelnikov and his associates at the IREE, after realizing their error, turned their attention to a complete analysis of the raw radar data recorded on magnetic tape with the help of a special analyzer. Their new value, 149,598,000 ± 3300 kilometers, agreed closely with those of the United States and Britain.49 Although the Soviet and British errors of measurement were greater than those of the American laboratories, they were far less than the values obtained by optical methods. The accuracy of the radar over the optical method and the general agreement among the preliminary results obtained in the United States, Britain, and the Soviet Union were the basis for a re-evaluation of the astronomical unit by the International Astronomical Union (IAU).


Redefining the Astronomical Unit


The re-evaluation of the astronomical unit was part of a general movement within the IAU to reform the entire system of astronomical constants conventionally used to compute ephemerides. On 21 August 1961, shortly after JPL, Lincoln Laboratory, and Jodrell Bank announced their first estimations of the astronomical unit, the IAU executive committee decided to organize a symposium on the system of astronomical constants. That system rested upon observations made in the nineteenth century and values adopted at international conferences held in Paris in 1896 and 1911.50

By 1950, two competing optical methods provided more accurate values for the astronomical unit. Harold Spencer Jones, Astronomer Royal of Great Britain from 1933 to 1955, used a trigonometric approach based on the triangulation of Eros. The orbit of the [47] asteroid, discovered in 1898 by Berlin astronomer Gustav Witt, approaches Earth at regular intervals. As president of the IAU Solar Parallax Commission, Spencer Jones oversaw a worldwide operation to record photographic observations of Eros during its closest approach to Earth in 1930 and 1931. Through a complicated analysis of nearly 3,000 photographs, Spencer Jones estimated the astronomical unit to be 149,675,000 ± 17,000 kilometers. Eugene Rabe, an astronomer at the Cincinnati Observatory, applied the so-called dynamic method to observations of Eros between 1926 and 1945. He took into account the gravitational effects of the Earth, Mars, Mercury, and Venus on the orbit of Eros, and arrived at a value of 149,530,000 ± 10,000 kilometers.51

In addition, investigators at the Space Technology Laboratories (STL), a wholly-owned subsidiary of Ramo-Wooldridge (later TRW), computed a value from data acquired during the Pioneer 5 mission. In figuring the probe's trajectory, STL chose Rabe's value over that of Lincoln Laboratory in 1958. Not surprisingly, STL found a value for the astronomical unit, 149,544,360 ± 13,700 kilometers, in agreement with Rabe, but with a greater error of measurement. The STL value hardly challenged the more accurate ground-based radar measurements. Its "published accuracy," Walter Fricke, astronomer and professor at the Heidelberg Astronomisches Rechen-Institut, judged, "does not yet indicate any advantage over the traditional methods."52 The Pioneer 5 value did not play any part in the IAU's revision of the astronomical unit.

The organizing committee of the IAU symposium on astronomical constants brought together astronomers from the United States and Europe who were responsible for drawing up the ephemerides. COSPAR (the Committee on Space Research) named an ad hoc committee to participate in the symposium, and additional astronomers from the United States, Britain, France, West Germany, Portugal, the Soviet Union, and South Africa took part. The members of the organizing committee included Eb Rechtin, the JPL manager of the DSIF; Dirk Brouwer, director of the Yale Observatory; and Gerald M. Clemence, scientific director of the U.S. Naval Observatory in Washington. Both Brouwer and Clemence had helped JPL with the Venus radar experiment ephemerides. Among the additional astronomers participating in organizing committee activities were two radar astronomers, Dewey Muhleman and Irwin I. Shapiro.53

Soon after the 1961 Venus experiment, Muhleman left JPL for the Harvard Astronomy Department. There, under Fred Whipple, A. Edward Lilley, and William Liller, he completed a doctoral dissertation based on Venus radar data collected at Goldstone in June 1963. After returning to JPL, Muhleman took a teaching position in the Cornell Astronomy Department in 1965. Shapiro had a Ph.D. in physics from Harvard and had worked on the detection of objects with radar in a clutter environment and on ballistic missile defense systems, before joining the team conducting radar experiments on Venus as the "guru" who calculated the ephemerides for Lincoln Laboratory planetary radar research.54

[48] The IAU symposium took place at the Paris Observatory between 27 and 31 May 1963. By then, Lincoln Laboratory and JPL had refined the accuracy of their calculations even further, to ± 400 and ± 250 kilometers respectively. In his inaugural address, Walter Fricke lauded the accuracy and general agreement of the radar measurements. As far as Fricke and other symposium participants were concerned, the real debate was between the radar and dynamic methods. Spencer Jones' trigonometric method contained too many inherent sources of systematic error. In an attempt to reconcile the dynamic and radar methods, Brian G. Marsden, an astronomer at the Yale University Observatory, concluded in favor of the radar measurements. Rabe defended his method in person, arguing that the radar observations were inconsistent with the observed orbit of Eros and with gravitational theory.55

Muhleman and Shapiro supported the radar method and explained the basis on which JPL and Lincoln Laboratory had obtained their results. Additional support for the radar method came from Britain. D. H. Sadler, Superintendent of H. M. Nautical Almanac Office at the Royal Greenwich Observatory, read a paper on the results of the Jodrell Bank 1962 Venus experiment.

Lest it appear that there was unanimous approval of the radar method, COSPAR raised the question of the discrepancy between the radar observations of 1958 and 1959 and those of 1961. Both Muhleman and Shapiro insisted that a discussion of the 1958 data, which they both labelled "manifestly wrong," would be too difficult and serve no purpose. They explained that the 1958 technology was highly inadequate and stressed the harmonious agreement among the 1961 measurements.56

The participants unanimously adopted Resolution Six, which recommended that the astronomical constants be studied by both existing and new methods, so that the results might be compared. The IAU Executive Committee then translated Resolution Six into Resolution Four, which recommended that a working group study the system of astronomical constants, including the astronomical unit expressed in meters. Next, the IAU Executive Committee named the Working Group on astronomical constants: Dirk Brouwer, Jean Kovalevsky (Bureau of Longitudes, Paris), Walter Fricke (chairman), Aleksandr A. Mikhailov (director of the Pulkovo Observatory, Soviet Union), and George A. Wilkins (Royal Observatory of Greenwich; Secretary). The Working Group sent a circular letter and copies of the Paris resolutions to all persons, some 80 in number, who were thought to be likely to be able to help the Group or who might be affected by the introduction of new constants. The Working Group met in January 1964, at the Royal Greenwich Observatory, Herstmonceux Castle, and drew up a list of constants, including the astronomical unit, for consideration by the IAU general assembly, which met in Hamburg later that year.57

The Working Group met again during the Hamburg meeting on 27 August. Muhleman and Pettengill, who read Shapiro's paper in his place, reviewed the latest radar determinations of the astronomical unit by JPL and Lincoln Laboratory from new observations made in 1964. Pettengill reported that preliminary analysis of the new data confirmed a value of 149,598,000 kilometers, while Muhleman disclosed the JPL value of [49] 149,598,500 kilometers. The error of measurement reported by both laboratories, ± 100 kilometers, was the smallest yet.58

Walter Fricke, chair of the Working Group, had misgivings about the radar method: "One could argue that the radar results are still too fresh to deserve full confidence. My personal distrust of them in so far as it originates in their newness has a counterpart in my distrust of the dynamical [Rabe] result obtained from the discussion of the observations of Eros." 59

Without any discussion of the dynamic method, however, the Working Group recommended adoption of a value expressed in meters and based on radar observations. The IAU general assembly then adopted the recommended value, 149,600 X 106 meters (149,600,000 kilometers).60 It was now a matter of incorporating the new value into the various national almanacs and ephemerides.


The Rotation of Venus


The establishment of a highly accurate value for the astronomical unit and its adoption by the IAU was but one way that planetary radar demonstrated its value as a problem-solving scientific activity. The distance from Earth to Venus as measured by JPL radar also proved essential in keeping the 1962 Mariner 2 Venus probe on target. Early in its flight, Mariner 2 went off course. The Pioneer and Echo antennas sent midcourse commands, and a 34-minute maneuver put Mariner 2 on course. Had Rabe's value for the astronomical unit been used in place of the radar value, Mariner 2 would have passed Venus without acquiring any useful data.61

Valuable insight into the rotation of Venus further demonstrated the problem-solving scientific merit of planetary radar. Optical and spectrographic methods failed to reveal the planet's period or direction of rotation, because Venus' thick, opaque cloud layer hid all evidence of its motion. Astronomers could only infer and imagine. Radar waves, on the other hand, were quite capable of penetrating the Venusian atmosphere; yet determining the planet's rotation by radar was still not easy. The key was methodical and meticulous attention to the shape of the echo spectra. Although JPL, Lincoln Laboratory, Jodrell Bank, and the Soviet Yevpatoriya facility calculated rotational rates for Venus, only JPL and Lincoln Laboratory found its "locked" orbit and retrograde motion.62

Evans and Taylor at Jodrell Bank published the first estimate of the planet's rotational period, about 20 days, using their erroneous 1959 data. In 1964, John Thomson reckoned a slow rotational rate, "probably" somewhere between 225 days and a similar retrograde period. After seeming to be on the brink of discovery, Thomson pulled back, concluding, "Future observations of the change of spectral width with time should enable the rotation rate and rotation axis to be determined." "Retrograde rotation," he held, was "physically unlikely."63

[50] As close as Jodrell Bank came to discovering Venus' retrograde motion, the Soviets were that far away. Looking at frequency shifts in their 1961 data, Kotelnikov's group persistently estimated the planet's rotational period as 11 days, if not 9 or 10 days. They entirely missed the planet's retrograde motion. The Soviet error arose from their finding that the spectrum had a wide base, at least 400 hertz wide, indicating rapid motion. All British and United States workers agreed that the spectrum was far narrower. Lincoln Laboratory, for example, found a narrow spectrum of only 0.6 hertz. After their 1962 radar study of Venus, Kotelnikov and his colleagues re-evaluated their data and concluded a retrograde rotational period of 200 to 300 days.64

By then, though, JPL and Lincoln Laboratory already had discovered Venus' retrograde motion. Finding it was not easy. Along the way, both laboratories concluded that the Venusian day was as long as its year, about 225 days. Venus was "locked" in its orbit, turning one face always toward the Earth at the moment of inferior conjunction. However, these initial reports failed to note the planet's retrograde motion.65

The investigators who found it did not follow the same path of discovery. Just as the availability of technology had made planetary radar astronomy possible, the limits of that technology shaped the paths of discovery. JPL harvested the benefits of a powerful, low-noise continuous-wave radar in their 1962 and 1964 Venus experiment, while Lincoln Laboratory reaped the rewards of their computer and signal processing skills.

The Goldstone radar permitted Roland L. Carpenter to find the retrograde motion of Venus in a rather novel fashion. Carpenter actually had a BA in psychology from California State University at Los Angeles, but he had been interested in astronomy since childhood, and he had worked at Griffith Observatory as a guide. Finding very little work available in psychology, Carpenter found a job at Collins Radio as an electrician thanks to his friend, astronomer George Abell (known for Abell's clusters of galaxies), who had a summer job there. Carpenter gradually worked his way up to electronics engineer, simply through his work experience at Collins Radio. Then, when JPL began hiring people with experience in radio communications for the Deep Space Network, Carpenter jumped at the opportunity. Carpenter worked with Dewey Muhleman in Walt Victor's group and took advantage of JPL's employee benefits program by pursuing an advanced degree in astronomy at UCLA, while working full-time at JPL. His doctoral dissertation, "The Study of Venus by CW Radar," written under Lawrence Aller and completed in 1966, used data from the 1964 JPL Venus radar experiment.66 By then, however, Carpenter already had published his discovery of the retrograde rotation of Venus.

[51] His first announcement of the planet's retrograde motion appeared in a JPL internal report dated 1 May 1962 and was based on the 1961 Venus experiment. Carpenter suggested a retrograde rotational period of about 150 days, but backed off from insisting on his discovery. "Unfortunately," Carpenter concluded, "a definitive answer cannot be given for the rotation period of Venus based on the present data."67

Carpenter hesitated until he had the results of the Goldstone 1962 Venus experiment. Between 1 October and 17 December 1962, when Venus was closest to Earth, Goldstone made nearly daily radar observations of the planet with a 13-kilowatt continuous-wave transmitter operating at 2388 MHz (12.6 cm). Equipped with a maser and a parametric amplifier, the system's total noise temperature was only 40 K, better than the 64 K achieved in 1961.68

The Goldstone radar was sufficiently powerful and sensitive that a large feature on the planet's surface showed up as an irregularity or "detail" on the power spectrum. The surface feature scattered back to the radar antenna more energy than the surrounding area. Normally, most spectral irregularities resulted from random fluctuations produced by noise. The power and sensitivity of the Goldstone radar made all the difference.

"On close examination," Carpenter wrote, "one irregularity was found to persist from day to day and to change its position slowly....The relative permanence of the detail strongly suggests that it was caused by an actual physiographic feature on the surface of Venus and that its motion was the result of the planet's rotation. The true nature of the feature can only be guessed at; however, it is not unreasonable to assume that it is a particularly rough region of rather large extent."


Figure 8. Lower portion of the spectra obtained by Roland Carpenter during the week prior to the 1962 conjunction of Venus.

Figure 8. Lower portion of the spectra obtained by Roland Carpenter during the week prior to the 1962 conjunction of Venus. Note the persistent detail on the left side of each spectrum. Carpenter followed that detail to determine the retrograde motion of Venus. (Courtesy of Jet Propulsion Laboratory.)


[52] Carpenter then followed the movement of this "detail" in order to deduce the planet's rotational period. He calculated that Venus had either a forward period of about 1200 days or a retrograde period of 230 days from one conjunction to the other. Next, he measured the bandwidth of the lower portion of the spectra; their widths were incompatible with a 1200-day forward rotation. The base bandwidth measurements, however, did "strongly suggest that the sidereal rotation period of Venus is not synchronous, but rather 250 ± 40 days retrograde."69

Millstone lacked the power and sensitivity of Goldstone. The discovery of Venus' retrograde motion at Lincoln Laboratory by William B. Smith relied instead on his computer and signal analyzing skills. Although Smith preceded Carpenter in announcing the retrograde motion of Venus in a publication, he did not achieve recognition as its discoverer.

Smith looked at the spectral bandwidths of radar returns on 11 separate days between 2 April and 8 June 1961. Like Carpenter, he failed to verify a synchronous rotation; however, Smith came to realize that the way the signal bandwidth changed over time could be explained only by retrograde motion. He wrote up his findings and submitted them to his supervisor, Paul Green, for approval. Smith wanted to feature the planet's retrograde motion in his paper, but Green remembered an earlier episode, when "we had been badly burned." That was the embarrassment of 1958.

Green hesitated. Uranus was the only planet then known to have a retrograde period, "but that one is way the hell out, and who would have thought that the next planet to the Earth would have had that kind of anomalous behavior?" Green admitted, "I guess I was working more on psychological factors than on anything else. So I had Bill tone it down." The published article's abstract read: "The (relatively weak) result implies a very slow or possibly retrograde rotation of the planet." The article itself contained no statement of the planet's retrograde motion.70

The watered down version made all the difference. Carpenter published his explicit and unequivocal results jointly with fellow JPL radar astronomer Dick Goldstein in the 8 March 1963 issue of Science, while the February 1963 issue of The Astronomical Journal carried Smith's suggestive abstract.71

Green regretted his decision. "Bill Smith is the man who discovered that Venus has retrograde spin, and he should go down in the history books. Due to me he didn't, because his paper didn't feature it the way it should have. If I hadn't sat on it, it would have featured it, but as it came out, it didn't. The people that look at the fine print realize that he had that message, that that was what his data showed, but it didn't make the big splash and give him the career achievement that he deserved."72 Fellow Lincoln Laboratory radar astronomer Irwin Shapiro concurred: "I felt he [Smith] got a raw deal, because he made a major discovery for which he never got credit."73

The detection of Venus, the measurement of the size of the astronomical unit, and the determination of the rotational period and direction of Venus formed the foundation on which planetary radar astronomy was laid. Planetary radar advanced by solving problems left unresolved or at best unsatisfactorily resolved by optical methods. Deliberately or not, the problems solved supported the NASA mission to explore the solar system. Driving the new scientific activity was the availability of a new generation of radars built for military defense (at Lincoln Laboratory) and for space exploration (at JPL). The limits of that technology shaped the paths of discovery.

[53] Without technology and without funding, planetary radar astronomy was impossible. The emergence of planetary radar coincided with the creation of a national, civilian space agency, NASA, a national, civilian agency to fund scientific research, the National Science Foundation (NSF), and a national, military space research agency, ARPA. It also paralleled the rise of American radio astronomy and the age of the Big Dish. Standing at the intersection of civilian and military research into space, the ionosphere, the Moon, and the Sun, planetary radar offered much to potential patrons. It was a wonderful and unique time to organize a new scientific activity.



1. "President's Report Issue," MIT Bulletin vol. 82, no. 1 (1946): 133-136; ibid., vol. 83, no. 1 (1947): 154-157; ibid., vol. 86, no. 1 (1950): 209; "Government Supported Research at MIT: An Historical Survey Beginning with World War II: The Origins of the Instrumentation and Lincoln Laboratories," May, 1969, typed manuscript, pp. 15-19 & 30-31, MITA; George E. Valley, Jr., rough draft, untitled 4-page manuscript, 13 October 1953, 6/135/AC 4, and MIT Review Panel on Special Laboratories, "Final Report," pp. 132-133, MITA. James R. Killian, Jr., The Education of a College President: A Memoir (Cambridge: The MIT Press, 1985), pp. 71-76, recounts the founding of Lincoln Laboratory, too.

2. Vandenberg to James R. Killian, Jr., 15 December 1950, 3/136/AC 4, MITA. A portion of the quote also appears in Killian, p. 71.

3. Valley; "Final Report," pp. 133-137; "Government Supported," p. 33; C. L. Strong, Information Department, Western Electric Company, press release, 1 October 1953, 6/135/AC 4, MITA; Carl F. J. Overhage to Lt. Gen. Roscoe C. Wilson, 15 October 1959, and brochure, "Haystack Family Day, 10 October 1964," 1/24/AC 134, MITA; F. W. Loomis to Killian, 17 April 1952, 4/135/AC 4, MITA; various documents in 2/136/AC 4 and 7/135/AC 4, MITA; Overhage, "Reaching into Space with Radar," paper read at MIT Club of Rochester, 25 February 1960, pp. 6-7, LLLA. For a popular introduction to the DEW Line, see Richard Morenus, Dew Line: Distant Early Warning, The Miracle of America's First Line of Defense (New York: Rand McNally, 1957).

4. Weiss 29/9/93; "Final Report," pp. 136 & 138; Overhage, "Reaching into Space," p. 2; Overhage to Wilson, 30 June 1961, 1/24/AC 134, MITA; Allen S. Richmond, "Background Information on Millstone Hill Radar of MIT Lincoln Laboratory," 5 November 1958, typed manuscript, LLLA; Weiss, Space Radar Trackers and Radar Astronomy Systems, JA-1740-22 (Lexington: Lincoln Laboratory, June 1961), pp. 21-23, 29, 44 & 64; Price, "The Venus Radar Experiment," in E. D. Johann, ed., Data Handling Seminar, Aachen, Germany, September 21, 1959 (London: Pergamon Press, 1960), p. 81; Price, P. Green, Thomas J. Goblick, Jr., Robert H. Kingston, Leon G. Kraft, Jr., Gordon H. Pettengill, Roland Silver, William B. Smith, "Radar Echoes from Venus," Science 129 (1959): 753; "Missile Radar Probes Arctic," Electronics 30 (1957): 19; Pettengill 28/9/93.

5. William W. Ward, "The NOMAC and Rake Systems," The Lincoln Laboratory Journal vol. 5, no. 3 (1992): 351-365; Green 20/9/93; Price 27/9/93. Green and Price acknowledged each other in their dissertations. Green, "Correlation Detection using Stored Signals" D.Sc. diss., MIT, 1953, and Price, "Statistical Theory Applied to Communication through Multipath Disturbances," D.Sc. diss., MIT, 1953.

A history of the subject, R. A. Scholtz, "The Origins of Spread-Spectrum Communications," IEEE Transactions on Communications COM-30 (1982): 822-854, is reproduced in Marvin K. Simon, Jim K. Omura, Scholtz, and Barry K. Levitt, eds., Spread Spectrum Communications (Rockville, Md.: Computer Science Press, Inc., 1985), Volume 1, Chapter 2, "The Historical Origins of Spread-Spectrum Communications," pp. 39-134. Price, "Further Notes and Anecdotes on Spread-Spectrum Origins," IEEE Transactions on Communications COM-31 (January 1983): 85-97, provides an absorbing anecdotal sequel to Scholtz.

6. Pawsey and Bracewell, Radio Astronomy (Oxford: Clarendon Press, 1955); Green 20/9/93; Price 27/9/93.

7. Green 20/9/93; Pettengill 28/9/93. For a description of the maser, see Kingston, A UHF Solid State Maser, Group Report M35-79 (Lexington: Lincoln Laboratory, 1957); and Kingston, A UHF Solid State Maser, Group Report M35-84A (Lexington: Lincoln Laboratory, 1958).

8. J. V. Jelley, "The Potentialities and Present Status of Masers and Parametric Amplifiers in Radio Astronomy," Proceedings of the IEEE 51 (1963): 31 & 36, esp. 30; J. W. Meyer, The Solid State Maser - Principles, Applications, and Potential, Technical Report ESD-TR-68-261 (Lexington: Lincoln Laboratory, 1960), pp. 14-16; Jelley, pp. 31 & 36; J. A. Giordmaine, L. E. Alsop, C. H. Mayer, and C. H. Townes, "A Maser Amplifier for Radio Astronomy at X-band," Proceedings of the IRE 47 (1959): 1062-1070; Pettengill and Price, "Radar Echoes from Venus and a New Determination of the Solar Parallax," Planetary and Space Science 5 (1961): 73. For Townes and the invention of the maser, see Paul Forman, "Inventing the Maser in Postwar America," Osiris ser. 2, vol. 7 (1992): 105-134.

9. Price, p. 70; Price et al, p. 751. Later, Price acknowledged the pioneering integration work of Zoltán Bay in 1946. Price, p. 73. Kerr, "On the Possibility of Obtaining Radar Echoes from the Sun and Planets," Proceedings of the IRE 40 (1952): 660-666, specifically recommended long-period integration for radar observation of Venus.

10. Smith graduated MIT in 1955 with a master's degree in electrical engineering and worked with Price and Green on the F9C in Davenport's group. Smith 29/9/93; Green 20/9/93; Price 27/9/93; Price, p. 72; Price et al, p. 751; Scholtz, p. 838; Weiss, Space Radar Trackers, pp. 53, 59, 61 & 63-64; "Biographical data, MIT Lincoln Laboratory," 18 March 1959, LLLA.

11. Price 27/9/93; Weiss, Space Radar Trackers, pp. 29 & 44; Price, pp. 71 & 76; Price et al, p. 751.

12. Green 20/9/93; Gold 14/12/93; Price et al, pp. 751-753.

13. Green 20/9/93; Price 27/9/93; Pettengill 28/9/93; Overhage to Wilson, 24 March 1959, 1/24/AC 134, MITA; "Venus is Reached by Radar Signals," New York Times, vol. 108 (20 March 1959), pp. 1 & 11.

14. For their calculation of the astronomical unit, see Pettengill and Price, "Radar Echoes from Venus and a New Determination of the Solar Parallax," Planetary and Space Science 5 (1961): 71-74.

15. Lovell, 11/1/94; Lovell, Jodrell Bank, passim, but especially pp. 220-222, 224, 242, 225. On the Foundation, see Ronald William Clark, A Biography of the Nuffield Foundation (London: Longman, 1972). Created in 1962, EOARDC was essentially a military operation headquartered in Brussels. It underwrote a wide range of European scientific research, though more money went into electronics research than any other field. Howard J. Lewis, "How our Air Force Supports Basic Research in Europe," Science 131 (1960): 15-20. From August 1957, when Jodrell Bank began preliminary calibration measurements to August 1970, the telescope gathered results for 68,538 hours. Of those, 4,877 hours (7.1% of operational time) represented "miscellaneous use." Of that "miscellaneous use," 2,498 hours (3.6% of operational time) were directly concerned with the space programs of the United States and the Soviet Union. Lovell, Out of the Zenith: Jodrell Bank, 1957-1970 (New York: Harper & Row, 1973), p. 2.

16. Evans 9/9/93.

17. Evans 9/9/93; Jodrell Bank, Moon and Venus Radar Passive Satellite Observations: Technical (Final) Report, October 1958 - December 1960, AFCRL Report 1129 (Macclesfield: Nuffield Radio Astronomy Laboratories, 1961), p. 22; Evans and G. N. Taylor, "Radio Echo Observations of Venus," Nature 184 (1959): 1358-1359; Lovell, Out of the Zenith, p. 193. The noise figure was 4.6 db. The frequency of the lunar radar was lowered from 120 MHz to 100 MHz, when it was found to interfere with operations at nearby Manchester Airport.

18. Pettengill and Price, p. 73.

19. Pettengill and Price, p. 73; Green and Pettengill, "Exploring the Solar System by Radar," Sky and Telescope 20 (1960): 12-13; Jelley, pp. 30 & 35. During the 1959 Lincoln Laboratory Venus experiment, over 150 runs were made, yet no echoes as strong as those of 1958 were observed. Overall system noise temperature rose from 170 Kelvins in 1958 to 185 Kelvins with the parametric amplifier. For a discussion of parametric amplifiers, see Karl Heinz Locherer, Parametric Electronics: An Introduction (New York: Springer-Verlag, 1981), pp. 276-286.

20. Green and Pettengill, p. 13.

21. JPL, Research Summary No. 36-7, Volume 1, for the period December 1, 1960 to February 1, 1961 (Pasadena: JPL, 1961), pp. 68 & 70.

22. "Jet" was a broader term than rocket and avoided any stigma still attached to that word. Clayton R. Koppes, JPL and the American Space Program: A History of the Jet Propulsion Laboratory (New Haven: Yale University Press, 1982), pp. ix, 4-5, 10-17, 20, 38, 45 & 65.

23. Rechtin, telephone conversation with author, 13 September 1993; Stevens 14/9/93; Nicholas A. Renzetti, ed., A History of the Deep Space Network from Inception to January 1, 1969, vol. 1, Technical Report 32-1533 (Pasadena: JPL, 1 September 1971), pp. 6-7 & 11; William R. Corliss, A History of the Deep Space Network, CR-151915 (Washington: NASA, 1976), pp. 3-4 & 16; Craig B. Waff, "The Road to the Deep Space Network," IEEE Spectrum (April 1993): 53; Scholtz, pp. 841-843; additional background material supplied from oral history collection, JPLA.

24. Dish diameters have been expressed in meters only recently. Initially, they were measured in feet. For the sake of consistency, diameters are given in both feet and meters throughout the text. Victor, "General System Description," p. 6 in Victor, Stevens, and Solomon W. Golomb, eds., Radar Exploration of Venus: Goldstone Observatory Report for March-May 1961, Technical Report No. 32-132 (Pasadena: JPL, 1961); Corliss, Deep Space Network, pp. 16-17 & 20-25.

25. Victor, "General System Description," in Victor, Stevens, and Golomb, p. 6; Corliss, Deep Space Network, pp. 25-27; Donald C. Elder, III, "Out From Behind the Eight Ball: Echo I and the Emergence of the American Space Program, 1957-1960," Ph.D. diss., University of California at San Diego, 1989, passim. For a history of ARPA, see Richard J. Barber Associates, Inc., The Advanced Research Projects Agency, 1958-1974 (Washington, D.C.: National Technical Information Service, 1975). For the story of JPL and Project Echo, see Stevens and Victor, eds., The Goldstone Station Communications and Tracking System for Project Echo, Technical Report 32-59 (Pasadena: JPL, 1960); Victor and Stevens, "The Role of the Jet Propulsion Laboratory in Project Echo," IRE Transactions on Space Electronics and Telemetry SET-7 (1961): 20-28.

26. Golomb, "The First Touch of Venus," paper presented at the Symposium Celebrating the Thirtieth Anniversary of Planetary Radar Astronomy, Pasadena, October 1991, Renzetti materials; Goldstein 7/4/93; Goldstein 14/9/93; Goldstein 19/9/91; Stevens 14/9/93; biographical material and JPL Press Release, 23 May 1961, 3-15, Historical File, JPLA.

27. Rechtin, "Informal Remarks on the Venus Radar Experiment," in Armin J. Deutsch and Wolfgang B. Klemperer, eds., Space Age Astronomy (New York: Academic Press, 1962), p. 365; Golomb, "Introduction," in Victor, Stevens, and Golomb, pp. 1-2; Rechtin, telephone conversation, 13 September 1993; Goldstein 19/9/91.

28. Golomb, "Introduction," p. 1; JPL, Research Summary No. 36-7, p. 70; Rechtin, telephone conversation, 13 September 1993; Waff, "A History of the Deep Space Network," manuscript furnished to author, ch. 6, pp. 22 & 24. Because the manuscript is not paginated sequentially, both chapter and page references are provided.

29. Rechtin, p. 366; Victor, "General System Description," pp. 6-7; Stevens and Victor, "Summary and Conclusions," p. 95; Victor and Stevens, "The 1961 JPL Venus Radar Experiment," IRE Transactions on Space Electronics and Telemetry SET-8 (1962): 85-90; Charles T. Stelzried, "System Capability and Critical Components: System Temperature Results," in Victor, Stevens, and Golomb, pp. 28-29. For a general description of the radar system, see M. H. Brockman, Leonard R. Malling, and H. R. Buchanan, "Venus Radar Experiment," in JPL, Research Summary No. 36-8, Volume 1, for the period February 1, 1961 to April 1, 1961 (Pasadena: JPL, 1961), pp. 65-73; Victor and Stevens, "Exploration of Venus by Radar," Science 134 (1961): 46. The Jodrell Bank transmitter had a peak power of 50 kilowatts; Millstone's peak power was 265 kilowatts in 1958 and 500 kilowatts in 1959. However, comparing the peak power ratings of pulse and continuous-wave radars is the electronic equivalent of comparing apples and oranges. One must compare their average power outputs.

30. Stevens and Victor, "Summary and Conclusions," p. 95; Sato, "System Capability and Critical Components: Maser Amplifier," in Victor, Stevens, and Golomb, p. 17; Stelzried, "System Capability and Critical Components: System Temperature Results," pp. 28-29; H. R. Buchanan, "System Capability and Critical Components: Parametric Amplifier," in Victor, Stevens, and Golomb, pp. 22-25; Walter H. Higa, A Maser System for Radar Astronomy, Technical Report 32-103 (Pasadena: JPL, 1961); Higa, "A Maser System for Radar Astronomy," in K. Endresen, Low Noise Electronics (New York: Pergamon Press, 1962), pp. 296-304.

31. Muhleman 8/4/93; Muhleman 19/5/94; Muhleman 27/5/94; Goldstein 19/9/91; Stevens 14/9/93; Golomb, "Introduction," p. 3; Stevens, "Additional Experiments: Resume," in Victor, Stevens, and Golomb, p. 70. Muhleman's dissertation was "Radar Investigations of Venus," Ph.D. diss., Harvard University, 1963.

32. Goldstein 7/4/93; Goldstein 19/9/91; Goldstein 14/9/93.

33. JPL Press Release, 23 May 1961, 3-15, Historical File, JPLA; Malling and Golomb, "Radar Measurements of the Planet Venus," Journal of the British Institution of Radio Engineers 22 (1961): 298; Victor and Stevens, "The 1961 JPL Venus Radar Experiment," IRE Transactions on Space Electronics and Telemetry SET-8 (1962): 90-91. Goldstein's dissertation was "Radar Exploration of Venus," Ph.D. diss., California Institute of Technology, 1962.

34. 3-15, Historical File, JPLA.

35. Victor and Stevens, "1961 JPL Venus Radar Experiment," p. 91.

36. Pettengill, Briscoe, Evans, Gehrels, Hyde, Kraft, Price, and Smith, "A Radar Investigation of Venus," The Astronomical Journal 67 (1962): 186.

37. Green 20/9/93.

38. Price 27/9/93.

39. Smith 29/9/93; Smith, "Radar Observations of Venus, 1961 and 1959," The Astronomical Journal 68 (1963): 17; Pettengill et al, "A Radar Investigation of Venus," p. 183.

40. Rechtin, p. 367; Victor, "General System Description," p. 7; Victor and Stevens, "1961 JPL Venus Radar Experiment," p. 88; Victor and Stevens, "Exploration of Venus by Radar," p. 46.

41. Lovell, Out of the Zenith, pp. 192 & 195; Evans 9/9/93; Green 20/9/93; Smith 29/9/93; Pettengill 28/9/93.

42. The Staff, Millstone Radar Observatory, Lincoln Laboratory, "The Scale of the Solar System," Nature 190 (1961): 592; Pettengill et al, "A Radar Investigation of Venus," pp. 182-183; Pettengill and Price, p. 73; Pettengill, "Radar Measurements of Venus," in Wolfgang Priester, ed., Space Research III, Proceedings of the Third International Space Science Symposium (New York: Interscience Publishers Division, John Wiley and Sons, 1963), p. 874; Overhage to Wilson, 22 May 1961, 1/24/AC 134, MITA.

43. Ponsonby 11/1/94; I. C. Browne and T. R. Kaiser, "The Radio Echo from the Head of Meteor Trails," Journal of Atmospheric and Terrestrial Physics 4 (1953): 1-4.

44. Evans 9/9/93; Lovell, Out of the Zenith, pp. 198-199; Thomson, Ponsonby, Taylor, and Roger, "A New Determination of the Solar Parallax by Means of Radar Echoes from Venus," Nature 190 (1961): 519-520. The Jodrell Bank experiment was funded by Air Force contract no. AF61(052)-172. John Evans, then of Lincoln Laboratory, privately had communicated the laboratory's results to Thomson at Jodrell Bank.

45. I have calculated this value from the information provided in Thomson, Ponsonby, Taylor, and Roger, pp. 519-520. While the authors concern themselves with the solar parallax, they also provide a figure for the light-time of the astronomical unit, 499,011 ±0.017 seconds, which represents the time taken by radar waves to travel the distance of one astronomical unit, and another for the speed of light, 299,792.5 kilometers per second, which is the same as the speed of electromagnetic waves. By multiplying the two figures, I obtained a product of 149,599,750 kilometers.

The first published value of the astronomical unit I have found was in the comments given by Thomson following a presentation by Malling and Golomb at a convention in Oxford that took place 5-8 July 1961. The date of publication was October 1961. Malling and Golomb, p. 302.

46. W. O. Mehuron, "Passive Radar Measurements at C-Band using the Sun as a Noise Source," The Microwave Journal 5 (April, 1962): 87-94; David K. Barton, "The Future of Pulse Radar for Missile and Space Range Instrumentation," IRE Transactions on Military Electronics MIL-5, no. 4 (October, 1961): 330-351; Irving Maron, George Luchak, and William Blitzstein, "Radar Observation of Venus," Science 134 (1961): 1419-1420.

47. B. I. Kuznetsov and I. V. Lishin, "Radar Investigations of the Solar System Planets," in Air Force Systems Command, Radio Seventy Years (Wright-Patterson AFB, Ohio: Air Force Systems Command, 1967), pp. 187-188, 190 & 201; Vladimir A. Kotelnikov, "Radar Contact with Venus," Journal of the British Institution of Radio Engineers 22 (1961): 293; Kotelnikov, L. V. Apraksin, V. O. Voytov, M. G. Golubtsov, V. M. Dubrovin, N. M. Zaytsev, E. B. Korenberg, V. P. Minashin, V. A. Morozov, N. I. Nikitskiy, G. M. Petrov, O. N. Rzhiga, and A. M. Shakhovskoy, "Radar System Employed during Radar Contact with Venus in 1961," Radio Engineering and Electronic Physics 11 (1962): 1715-1716. For a brief history of the IREE, see Y. V. Gulyaev, "40 Years of the Institute of Radioengineering and Electronics of Russian Academy of Sciences," Radiotekhnika Elektronika vol. 38, no. 10 (October 1993): 1729-1733. Soviet investigators performed radar studies of meteors in 1946 and of the Moon in 1954-1957, according to A. E. Solomonovich, "The First Steps of Soviet Radio Astronomy," pp. 284-285 in Sullivan. Although radar astronomers recently have used the arrayed dishes of the Very Large Array in bistatic experiments, dish arrays have not been used as transmitting antennas.

48. Kotelnikov et al, "Radar System," pp. 1715 & 1721; Kotelnikov, "Radar Contact," p. 294; Malling and Golomb, p. 300; Kotelnikov, "Radar Observations of the Planet Venus in the Soviet Union in April, 1961," typed manuscript, 27 February 1963, anonymous translation of a technical report of the Soviet Institute of Radio Engineering and Electronics, DTIC report number AD-401137, pp. 41-42, Renzetti materials. The Soviet publication venue and aberrant astronomical unit value raise serious doubts about the veracity of their announcement.

49. Kotelnikov et al, "Radar System," p. 1721; Kuznetsov and Lishin, p. 188; Kotelnikov, "Radar Observations," p. 2; Kotelnikov, Dubrovin, Morozov, Petrov, Rzhiga, Z. G. Trunova, and Shakhovoskoy, "Results of Radar Contact with Venus in 1961," Radio Engineering and Electronics Physics 11 (1962): 1722 & 1725. For a discussion of the integration technique, see V. I. Bunimovich and Morozov, "Small-Signal Reception by the Method of Binary Integration," ibid., pp. 1734-1740.

50. Jean Kovalevsky, ed., The System of Astronomical Constants (Paris: Gauthier-Villars & Cie., 1965), p. 1; Walter Fricke, "Arguments in Favor of the Revision of the Conventional System of Astronomical Constants," in J. C. Pecker, ed., Proceedings of the Twelfth General Assembly (New York: Academic Press, 1966), p. 604.

51. Spencer Jones, "The Solar Parallax and the Mass of the Moon from Observations of Eros at the Opposition of 1931," Memoirs of the Royal Astronomical Society 66 (1938-1941): 11-66; Rabe, "Derivation of Fundamental Astronomical Constants from the Observations of Eros during 1926-1945," The Astronomical Journal 55 (1950): 112-126; Fricke, "Inaugural Address Delivered at the IAU-Symposium No. 21," in Kovalevsky, pp. 12-13.

52. Fricke, "Inaugural Address," p. 13; James B. McGuire, Eugene R. Spangler, and Lem Wong, "The Size of the Solar System," Scientific American vol. 204, no. 4 (1961): 64-72. The value given in the article is 92,925,100 ±8,500 miles, which I have converted into kilometers for consistency.

53. Rechtin, p. 368; Muhleman, D. Holdridge, and N. Block, "Determination of the Astronomical Unit from Velocity, Range and Integrated Velocity Data, and the Venus-Earth Ephemeris," in Victor, Stevens, and Golomb, pp. 83-92. Kovalevsky, p. 1, provides a list of their names.

54. Muhleman 8/4/93; Muhleman 19/5/94; Shapiro 30/9/93; Evans 9/9/93.

55. Kovalevsky, p. 3; Fricke, "Inaugural Address," pp. 12-13; Fricke, "Arguments in Favor of the Revision of the Conventional System of Astronomical Constants," in Pecker, p. 606; Marsden, "An Attempt to Reconcile the Dynamical and Radar Determinations of the Astronomical Unit," in Kovalevsky, pp. 225-236; Rabe, "On the compatibility of the Recent Solar Parallax Results from radar Echoes of Venus with the Motion of Eros," in Kovalevsky, pp. 219-223.

56. Shapiro, "Radar Determination of the Astronomical Unit," in Kovalevsky, pp. 177-215, and Muhleman, "Relationship between the System of Astronomical Constants and the Radar Determinations of the Astronomical Unit," in ibid., pp. 153-175; Kovalevsky, pp. 298 & 311.

57. Kovalevsky, pp. 314 & 323; "Joint Discussion on the Report of the Working Group on the IAU System of Astronomical Constants," in Pecker, p. 600.

58. "Joint Discussion," pp. 591, 599 & 602-603; Shapiro, "Radar Determinations," in Pecker, pp. 615-623.

59. "Joint Discussion," p. 606.

60. Ibid., p. 606; "Report to the Executive Committee of the Working Group on the System of Astronomical Constants," in Pecker, p. 594.

61. Renzetti 17/4/92; Renzetti, A History, pp. 20 & 31; Renzetti, Tracking and Data Acquisition Support for the Mariner Venus 1962 Mission, Technical Memorandum 33-212 (Pasadena: JPL, 1 July 1965), pp. 9, 17 & 75-76.

62. RCA did not hesitate a guess on the rotation rate or direction. Maron, Luchak, and Blitzstein, pp. 1419-1421.

63. Evans and Taylor, p. 1359; Ponsonby, Thomson, and Imrie, "Radar Observations of Venus and a Determination of the Astronomical Unit," Monthly Notices of the Royal Astronomical Society 128 (1964): 14-16.

64. Kuznetsov and Lishin, pp. 199-201; Kotelnikov, "Radar Contact with Venus," Journal of the British Institution of Radio Engineers 22 (1961): 295; Kotelnikov et al, "Results of Radar Contact," p. 1732; Kotelnikov, Dubrovin, M. D. Kislik, Korenberg, Minashin, Morozov, Nikitskiy, Petrov, Rzhiga, and Shakhovskoy, "Radar Observations of the Planet Venus," Soviet Physics - Doklady 7 (1963): 728-731; Kotelnikov, Dubrovin, V. A. Dubinskii, Kislik, Kusnetsov, Lishin, Morozov, Petrov, Rzhiga, G. A. Sytsko, and Shakhovskoy, "Radar Observations of Venus in the Soviet Union in 1962," Soviet Physics -Doklady 8 (1964): 644; Smith, p. 15. Rzhiga, "Radar Observations of Venus in the Soviet Union in 1962," in M. Florkin and A. Dollfus, eds. Life Sciences and Space Research II (New York: Interscience Publishers, 1964), pp. 178-189, states 300 days but still misses the retrograde motion.

65. Pettengill et al, "A Radar Investigation of Venus," pp. 189-190; Pettengill, "Radar Measurement of Venus," in Priester, pp. 880-883. The range given was between 115 to 500 days, that is, 225 (+275, -110) days. The first JPL external announcement of that finding was made in a paper read by Solomon Golomb and Leonard R. Malling at a convention on radio techniques and space research held at Oxford in July 1961. Malling and Golomb, pp. 297-303. The paper was not published until October 1961 and was preceded in print by the internal report, Victor and Stevens, "Summary and Conclusions," pp. 94-95. See also Victor and Stevens, "Exploration of Venus by Radar," pp. 46-47; Muhleman, "Early Results of the 1961 JPL Venus Radar Experiment," The Astronomical Journal 66 (1961): 292; Victor and Stevens, "The 1961 JPL Venus Radar Experiment," p. 94.

66. Carpenter, telephone conversation, 14 September 1993.

67. Carpenter, "An Analysis of the Narrow-Band Spectra of Venus," in JPL Research Summary No. 36-14 for the Period February 1, 1962 to April 1, 1962 (Pasadena: JPL, 1 May 1962), pp. 56-59.

68. Carpenter, telephone conversation, 14 September 1993; Goldstein and Carpenter, "Rotation of Venus: Period Estimated from Radar Measurements," Science 139 (1963): 910; Carpenter, "Study of Venus by CW Radar," The Astronomical Journal 69 (1964): 2. Details of the 1962 JPL Venus radar experiment are given in Goldstein, Stevens, and Victor, eds., Radar Exploration of Venus: Goldstone Observatory Report for October-December 1962, Technical Report 32-396 (Pasadena: JPL, 1 March 1965).

69. Carpenter, "Study of Venus by CW Radar," pp. 4-6; Carpenter, telephone conversation, 14 September 1993.

70. Green 20/9/93; Smith 29/9/93; Smith, pp. 15-21.

71. Goldstein and Carpenter, pp. 910-911; Smith, pp. 15-21. Internal evidence indicates that Science received the paper on 15 January 1963.

72. Green 20/9/93.

73. Shapiro 30/9/93.