[ I ] The 1958 and 1959 attempts to bounce radar waves off the planet Venus were made at the Massachusetts Institute of Technology's Lincoln Laboratory in Lexington, Mass. Spherical radomes on the laboratory's roof housed radar antennas that were used for the

designing, testing, and building state-of-the-art microwave radars Among many other U S defense projects for the Cold War with the then-USSR, laboratory personnel worked on the Distant Early Warning (DEW) Line in the North American Arctic and on its successor, the Ballistic Missile Early Warning System (BMEWS) The radar systems were designed to detect and track any aircraft (DEW) and missiles (BMEWS) that might have been launched against the United States from the Soviet Union

Besides tracking such relatively small targets as missiles soar- ing several hundred kilometers above the earth and several thou- sand kilometers distant, the BMEWS radars had to be able to distinguish the weapons from meteor trails, auroras, and other ionospheric disturbances Already, these electrical atmospheric occurrences had proved capable of crippling military communi- cations and radars

By the spring of 1956, an experimental prototype BMEWS radar had been designed and was under construction at Lincoln Laboratory The radar's location, atop Millstone Hill in West- ford, Mass , was remote from television transmitters and the routes of aircraft, yet close to both MIT in Cambridge and its Lincoln Laboratory The U S Air Force owned and financed the radar, Lincoln Laboratory managed it under an Air Force con- tract through the Air Force Cambridge Research Center, which was adjacent to the lab

What the Millstone Hill radar embodied was a new genera- tion of radars capable of detecting smaller objects farther off than any predecessor It was intended to have a peak pulse trans- mitting power of 2 5 MW at a frequency of 440 MHz thanks to two custom-designed, 3-meter-tall klystrons Klystrons are large vacuum tubes used to generate high-frequency power for radar and other transmitters The Millstone Hill radar began operat- ing in October 1957 Shortly beforehand, the United States had been stunned by the USSR's launch of Sputnik 1, the first ob- ject to be sent into orbit around the earth

One day over lunch ... It was not Sputnik, but the unprecedented power of the

Millstone radar that suggested to a handful of Lincoln Labor- atory electrical engineers that the radar might be capable of a

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laboratory's work on both the DEW (Defense Early Warning) Line and BMEWS (Ballistic Missile Early Warning System) radars, which were developed in the 1950s for the US. Department of Defense for use against Soviet aircraft and missiles.

feat never before achieved bouncing radio waves off Venus, the planet nearest the earth

The idea arose during one of the lunchtime discussions that were a habit of Robert Price and Paul E Green Jr As MIT doc- toral students, and later as Lincoln Laboratory electrical engi- neers, Price and Green worked closely together under Wilbur B Davenport Jr , their laboratory supervisor and dissertation direc- tor They had been applying themselves to different aspects of Nomac, a high-frequency communication system that used pseudonoise sequences, and on Rake, a receiver that solved Nomac multipath propagation problems (Nomac stood for noise modulation and correlation, the system also went by the A m y Signal Corps production name of F9C ) Price and Green's work was vital to maintaining military communications in the face of enemy jamming, and helped to trail-blaze the develop- ment of viable spread-spectrum techniques

During that October lunch, Green and Price wondered if the Millstone radar was powerful and sensitive enough to detect radar signals bounced off Venus The goal would be simply to determine whether it could be done But after jotting some cal- culations on a paper napkin, they concluded the receiver of the Millstone radar was not sensitive enough, even if it was assumed that Venus was perfectly reflective The two engineers were familiar with earlier radar experiments with the moon, but knew the radars used then could not attempt the more distant Venus.

So the idea of bouncing radio waves off Venus went nowhere, that is, until Robert H Kingston, who had a joint MIT and Lincoln Laboratory appointment! joined the discussions a few months later Kingston, trained as an electrical engineer at MIT, had Just built a new type of solid-state microwave amplifying device called a maser (for microwave amplification by stimulated emission of radiation) The maser, the group calculated, would give the Millstone radar receiver just the sensitivity necessary to carry out the Venus experiment

Price and Green still had to devise a way to separate the return echoes from the background noise They knew that, despite the maseis low noise level, they would have to raise the power level of the Venus echoes above that of the noise Their Nomac anti-jamming work had prepared them for this problem

Their solution was to integrate the Venus-return pulses over

IEEE SPECTRUM DECEMBER 1997

time. In theory, the signals buried in the noise should reinforce each other through addition, while the noise should average out by reason of its random nature. A digital computer, as well as more digital data-processing equipment linked to the Millstone radar, could integrate and analyze the Venusian echoes. An ana- log-to-digital converter originally developed for ionospheric research by William B. Smith, another EE graduate of MIT, could digitize the information on each radar echo. That infor- mation could then be recorded simultaneously on magnetic tape (for future analysis) and fed to the Millstone radar's solid-state digital computer.

The equipment that Price and Green assembled-in their scant spare time between stints on the high-priority defense pro- jects-made novel use of digital signal processing and marked one of the earliest uses of digital tape recorders.

Onward to Venus ingston's maser was installed at Millstone Hill just in time for an inferior conjunction of Venus (the time K when the planet is closest to the earth). But a klystron

failure left only 265 kW of transmitter power available for the experiment. On 10 and 12 February 1958, the radar was point- ed toward the spot Venus would be 2.5 minutes later, some 45 million kilometers away. The radar signals took about 5 min- utes to travel there and back.

Five runs were made over the two days, a run being 4.5 min- utes of transmission and 5 minutes of echo collection. Four of the digital recordings were usable, that is, the tapes had few enough blemishes to be easily edited for use in a given software format, such as Fortran, and fed through the computer. Two of the four good runs, one from each day, showed no evidence of radar returns. The other two had one peak each. "When we saw the peaks," Robert Price recalled in a 1993 interview with the author, "we felt very blessed."

But were the peaks really echoes or just processed noise? Price, during his earlier Fulbright Fellowship studies in Australia, at the University of Sydney's radio astronomy facility, had seen similarly suspect peaks in his search of signals from space for spectra of deuterium (a hydrogen isotope). Those had suggested molecular spectral lines, yet were only random noise.

The round-trip durations of the two pulses seemed to differ by 0.0022 second, which indicated a discrepancy of 600 km. This time, though, Price ignored the time difference between the two peaks, since it represented the approximate width of one radar pulse. "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 differ- ence, and sat one on top of the other."

Their thinking was so wishful because, just as they were pro- cessing their data, Lincoln Laboratory management was coming under pressure to produce good news about the US. space pro- gram. Indeed, the nation was desperate for good news about the Space Race started by the launch of Sputnik only four months earlier. By early 1958, the U.S. space effort had been marked by repeated failures, while the Soviet Union had launched several satellites successfully, including the orbiting of the dog Laika. The pressure for some positive news was well recognized by Price and Green.

Not surprisingly, then, Lincoln Laboratory management was ecstatic when Price and Green revealed their Venus results. To verify the findings, Lincoln Laboratory invited a consultant, Thomas Cold, then in Harvards astronomy department, to look them over. Gold, who had designed radar sets for the British Admiralty during World War 11, gave them his blessing.

By then, nearly a year had elapsed since the experiment had taken place. The delay reflected both the nights-and-weekends nature of the Venus project and the difficulty of processing reels and reels of magnetic data tapes, some of which were in such bad shape that Price had to shake a special magnetic powder on the tapes and try to read the data with a magnifying glass.

Green and Price published their findings in the 20 March 1959 issue of Science, the journal of the American Association for the Advancement of Science, 13 months after their observations had been made. Simultaneously with that publication, the Lincoln Laboratory publicity department gave the Venus radar experiment the full treatment. In addition to a press conference, Green and Price quickly found themselves on national television and on the front page of Tbe New York Times. President Dwight D. Eisenhower even sent Lincoln Laboratory a congratulatory tele- gram, calling the experiment a "notable achievement in our peaceful ventures into outer space."

Thus, with great fanfare, a handful of Lincoln Laboratory engineers, led by Robert Price and Paul Green, pioneered the founding of planetary radar astronomy. What's more, they pio- neered the use of masers in radar astronom: it was not until April 1958-a full two months after the Venus experiment-that radio astronomers tried their own first maser receiver in a joint effort by Columbia University and the Naval Research Laboratory to observe hydrogen spectral lines in the galaxy. Price and Green were working in a classified facility; nobody knew what they were doing until they went public in 1959. From then on, masers would be at the heart of the low-noise microwave amplifiers used in radio astronomy.

Once Price and Green accepted the validity of the two peaks as being echoes from Venus, the next step was to determine the distance the radar waves traveled to Venus. From that figure,

[2] The Millstone Hill radar antenna, 26 meters in diameter, was used on 10 and 12 February 1959 to send 265 kW of power to the planet Venus, in the first (although unsuccessful) attempt to detect radar waves returned from its surface. The receiver used a maser, the device's first ever application outside a laboratory.

BUTRICA - IN C O N J U N C T I O N WITH VENUS 33

14 Gathered around a table is the historic MlT Lincoln Laboratory team that attempted to bounce radar signals off Venus in 1959. From the right, they are: Paul E. Green Jr. and Robert Price, the exper- iment's originators; Thomas J. Goblick Jr., role uncertain: Gordon H. Pettengill, who would replace Green as leader in 1960; computer pro-

they calculated a value for the astronomical unit-a fundamental astronomical yardstick defined as the average distance between the earth and the sun-to be 149 467 000 km see "The leap to the sun," p 361

Meanwhile, out West ... n a September 1959 experiment conducted during the fol- lowing Venus conjunction, radio astronomers at England's Jodrell Bank observatory under Sir Bernard Lovell confirmed

the Lincoln Laboratory results using patchwork radar equipment built around a 408-MHz SO-kW klystron

During that conjunction, however, Price and Green were unable to corroborate their own results This second time around, they clearly had no echoes What made the t 959 results all the more vexing was that the Millstone Hill radar had bene- fited from several technological improvements-higher peak transmitting power of 500 kW [almost twice the 1958 level of 265 kW), a more stable microwave amplifier, and greater signal detectability Moreover, the 1959 experiment involved not just five runs, but almost 200, only one of which displayed a peak far enough above the noise level to be statistically significant When subjected to detailed analysis, though, the peak turned out to be only noise

The inability of the Lincoln Laboratory researchers to cor- roborate their own results in spite of improved equipment led another set of electrical engineers to suspect that both the 1958 Lincoln Laboratory and the 1959 Jodrell Bank results were erro- neous Eberhardt Rechtin, Robertson Stevens, and Walter K Victor, of the Jet Propulsion Laboratory in Pasadena, Calif, determined to obtain the first unambiguous radar echoes from the Venusian surface during the March 1961 conjunction

The Jet Propulsion Laboratory UPL)had begun modestly in 1 936 as the Cuggenheim Aeronautical Laboratory! California Institute of Technology (Galcit), it was headed by Hungarian- born professor Theodore von K6rmLn and had financing from New York City philanthropist Harry Guggenheim But in 1940, after the U S entry into World War 11, Galcit turned into a vital rocket research, development, and testing facility with under-

34

grammers Roland Silver and William B. Smith; and Leon G. Kraft Jr., an operator of the transmitter. Not pictured is Robert Kingston Jr., who built the maser used in this first experiment in planetary radar astronomy. On the blackboard is a block diagram of the Venus radar instrumentation.

writing from the Army Air Corps-which became the Army Air Force and ultimately the U S Air Force

In 1944, a contract with the Army Air Force and the Calif ornia Institute of Technology (Caltech) transformed Galcit into a large, permanent military R&D laboratory renamed the Jet Propulsion Laboratory Its major responsibilities were research, development, and testing of military missile technology, includ- ing the first tactical U S nuclear missiles-the Corporal and the Sergeant-for the Army When the U S National Aeronautics and Space Administration was created in 1958, JPL became a NASA facility

The laboratory's involvement in electronics arose out of the need for missile guidance and tracking systems William Pickering, a Caltech professor of electrical engineering, became its director in 1954, retaining the position until 1976 More interested in electronics than in propulsion, Pickering stimulated the growth of electronics R&D at the laboratory His agenda included the creation of what is now named the Deep Space Network (DSN), the worldwide, civilian network for tracking satellites, lunar missions, and interplanetary spacecraft That net- work, originally called the Deep Space Instrumentation Facility (DSIF), was the home of planetary radar experimentation at JPL In fact, all three of the laboratory's 1961 Venus radar experiment leaders-Rechtin, Stevens, and Victor-were engineers who had been instrumental in the tracking network's design

JPL sited the networks antennas in the Mojave Desert, about 160 km from its headquarters, on the Fort Irwin firing range near Goldstone Dry Lake, where Galcit earlier had tested Army rock- ets The two antennas used f 1961 Venus experiment had been built for military com ation studies of the Army's Pioneer probes to the moon, launched in Echo balloon, launched in 1960

Project Echo was an early test of the fe satellite communications It began in 1955 independently at AT&T CO and at NASA? predecessor, the National Advisory Committee for Aeronautics, before evolving in January 1 959 into a joint undertaking of NASA, JPL, and Bell Telephone Laboratories Basically, Echo was a 30-meter balloon of alu-

IEEE SPECTRUM DECEMBER 1997

minized Mylar launched into low earth-orbit to test the practi- cality of satellite communications.

The 196 1 Venus experiment by JPL had originated a year ear- lier, in August 1960, as the Goldstone facility made ready to take part in Project Echo. The then assistant chief of communi- cations system research, under Walt Victor, was Solomon Golomb, and he asked his employee, Richard Coldstein, to design a space experiment-specifically, one that would feed the friendly personal rivalry between Eb Rechtin and Albert R. Hibbs, respectively program director for the DSlF tracking net- work and chief of the space science division. Goldstein, a Caltech EE graduate student, suggested the Venus radar experi- ment. Victor and Stevens, who was communications elements research section chief, became the project managers.

To bounce radar off Venus, JPL had to modify the Echo equipment. Venus was a much farther target than Echo. Besides, the two objects were radically different as radar tar- gets. Venus had a smaller angular diameter, and its radar reflec- tivity was much lower. Echo was known to be a smooth bal- loon, while Venus had an unknown surface roughness and an atmosphere whose effect on radar waves was unknown. Also unknown was the dielectric constant of the planet's surface, which was known for Echo. Victor and Stevens, moreover, wanted to avoid the Lincoln Laboratory approach: long- term integration and after-the-fact data reduction and analysis. Instead, JPL wanted to detect radar echoes from Venus in real time.

As tor the antennas, JPIls were unlike those at Lincoln Laboratory. First, two JPL antennas operated concurrently: one transmittcd while the other received. This bistatic mode, as it is called, had advantages over the monostatic mode of the Millstone radar, which alternated between sending and receiving. In effect, while monostatic radars have to stop transmitting half the time in order to receive, bistatic radars can operate continuously, gathering twice the data in a given time period.

What's more, the Goldstone radars operated at a high- er frequency (2388 MHz versus 440 M H z ) , which increased their signal sensitivity. It also sent a continuous wave, instead of the discrete pulses of the Lincoln Laboratory radar.

Not conlent with those advantages, JPL boosted the radars' transmitting power and receiver sensitivity. A nom- inal average power output of 13 kW was coaxed out of the transmitter's IO-kW klystron. More boldly, two EEs at the laboratory-Charles T. Stelzried and Takoshi Sato-made the maser receiver sensitive enough to sense echoes from another planet, while keeping it rugged enough to with- stand thc rain, dust, and snow of Coldstone's desert cli- mate, not forgetting temperatures that ranged from -1 1 to +39 "C. The radar's resulting overall average system noise temperature was about one-third that of the Millstone Hill radar in 1958 (64 K versus 170 K). As Victor and Stevens proclaimed in a JPL publication, 'This is believed to be the most sensitive operational receiving system in the world.''

'No echo, no thesis' oldstein's involvement in the JPL Venus radar experiment presented him with t h e unique opportunity of using it for his EE thesis topic at

Caltech. But his advisor, Hardy Martel, thought the task impossible. After all, the inability of Lincoln Laboratory

million kilometers in about 6-1/2 minutes. During the 68 sec- onds of electronic signal integration time, one of the seven sty- luses on Goldstein's spectrum recorder 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 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 repeated imme- diately 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.

Six days later, Eb Rechtin telexed Paul Green that JPL had been obtaining real-time radar signals from Venus since 10 March. The following day, Green and Bob Price telexed back: "HEARTIEST CONGRATULATIONS ON YOUR SUCCESS WITH THE FICKLE LADY."

The results obtained ultimately by Lincoln Laboratory dur- ing that same 1961 inferior conjunction, and using Millstone Hill's full 2.5 MW of power, agreed with those obtained by JPL. That agreement led the Lincoln Laboratory group to recalculate its earlier results. In The Astronomicdl Journal of May 1962, Green and Price wrote:

to detect Venus was pretty common knowledge. Under Goldstein's persuasiveness, Martel finally agreed, but with the firm admonition: "No echo, no thesis."

On 10 March 1961, a month before the inferior con- junction, the Goldstone radars were pointed at Venus to begin collecting data. They at once got echoes from the planet. The first signals completed the round-trip of 1 1 3

BUTRICA - IN CONJUNCTION WITH VENUS

[4] Robert Price [left] discusses with Paul Green Jr. the Venus observations taken at the Millstone Hill Radar Observatory. In the background are the IBM computers used to record the radar data on reels of magnetic tape, such as the one held by Price in his left hand; Green is sitting on the corner of a punched- card reader. All four Lincoln Laboratory photographs in this article are from the original publicity packet prepared for the release of the Venus radar results.

35

”In view of the generally excellent agreement among the vari- ous observations made at several wavelengths in 1961, it seems likely that the results reported from observations of the 1958 inferior conjunction are in error.”

In other words, JPL was unquestionably the first to detect radar waves unambiguously reflected off Venus.

How far is it? The key question addressed by these electrical engineers-

who were now on their way to becoming planetary radar astronomers-was the size of the astronomical unit. To deter- mine more precisely the distance between the earth and Venus, JPL ran ranging experiments from 1 8 April through 5 May 196 1.

In the July 1961 issue of Science, Victor and Stevens announced a preliminary value for the astronomical unit of 149 599 000 km with an accuracy of 1500 km. The figure was more than 100 000 km larger than the false radar value of 149 467 000 km determined by Lincoln Laboratory in 1958 and confirmed by Jodrell Bank in 1959. Values obtained from preliminary anal- yses of the radar data gathered at Lincoln Laboratory in 196 1, however, agreed closely with those of JPL.

When Lincoln Laboratory undertook its March 1961 Venus radar experiment, Gordon Pettengill took over the leadership role of Bob Price (he and Green were by then researching the detec- tion of seismic waves so as to monitor nuclear testing by Cold War opponents). Pettengill had studied physics at MIT before completing his doctoral dissertation under Nobel prize winner Emilio Segrk at the University of California at Berkeley. At Lincoln Laboratory, Pettengill had an office at the Millstone Hill

radar site, where he studied ways of detecting ballistic missiles as part of the radar group to which Price and Green belonged.

During the March 1961 Venus experiment, the Millstone radar had run at its peak transmitting power of 2.5 MW, making it a far more capable instrument. But the upgraded radar still lacked the low-noise receiver and high-power transmitter of the JPL bistatic radar. Pettengill and his colleagues began aiming the radar a t Venus on 6 March 1961-four days earlier than Goldstein’s JPL test-but detected no echoes until 24 March.

Preliminary analysis in May 1961 yielded a Lincoln Labora- tory value for the astronomical unit of 149 597 700 km i 1500 km. That agreed closely with JPLs preliminary value of 149 599 000 km. Jodrell Bank investigators also found a value for the astronomical unit in 1961 that agreed with the JPL value, name- ly, 149 600 000 r5000 km, close to both preliminary values but with a far greater possible error of measurement.

Quest for the astronomical unit ndependently of these Venus radar measurements, the International Astronomical Union (IAU) was beginning a re- evaluation of the astronomical unit. Their study was part of

an international effort to reform the system of astronomical con- stants used to compute the future positions of the planets, or planetary ephemerides.

The contemporary system of ephemerides rested on observa- tions made in the 19th century and on values of astronomical constants adopted at international conferences held in Paris in 1896 and 19 i 1 . On 2 1 August 196 I , shortly after the Jet Pro- pulsion and Lincoln laboratories announced their first calcula-

36 IEEE SPECTRUM DECEMBER 1957

151 The Pioneer antenna at the Jet Propulsion Laboratory’s Deep Space Instrumentation Facility (DSIF) received the first radar signals to be successfully bounced back to earth from the surface of Venus. The antenna was built in 1958 near the Goldstone dry lake in the Mojave

tions of the astronomical unit, the IAU executive committee decided to organize a symposium on the system of astronomical constants, now 50 years old.

The symposium’s organizing committee rallied astronomers from within Europe (Britain, France, Portugal, and West Germany) and without (South Africa, the Soviet Union, and the United States). They met at the Paris Observatory from 27 through 31 May 1963. By then, Lincoln Laboratory and JPL had further refined the accuracy of their calculations of the astronomical unit, to 149 597 850 i400 km and 149 598 600 +250 km, respectively. The inaugural address at the symposium was given by astronomer Walter Fricke, professor of astronomy at the Astronomisches Rechen-Institut, Heidelberg, Germany,

[61 Standing in the Goldstone antenna’s control room [above], where in November 1959 they helped carry out tests in preparation for the Project Echo balloon program, are [from right] Robertson Stevens, Walter K. Victor, and an unidentified Jet Propulsion Laboratory (JPL) employee. Stevens and Victor were two of the three project man- agers of the laboratory‘s 1961 Venus radar experiment and also two of the three principal designers of the Goldstone antenna and the Deep Space Network.

desert in California so that the lab could track and receive telemetry from Pioneer military rockets. Later it became part of the Deep Space Network for communicating wi th interplanetary spacecraft. The 26-meter-diameter antenna could only receive; it had no transmitter.

and in it he lauded the accuracy and general agreement of the radar measurements.

He and other participants also weighed a mcthod for deter- mining the astronomical unit devised by Eugene Rabe, an astronomer from the Cincinnati Observatory, in Ohio. Rabe‘s method, using data from visual observations of the asteroid Eros made between 1926 and 1945, attempted to take into account the gravitational effects of the earth, Mars, Mercury, and Venus on the orbit of Eros. His value for the astronomical unit was 149 530 000 * lo 000 km.

An attempt to reconcile the results obtained by radar and by Eugene Rabe was made by Brian G. Marsden, an astronomer at the Yale University Observatory who later specialized in aster- oids, meteors, and comets. He concluded by favoring the radar measurements because they yielded a smaller error of measure- ment. Rabe argued, however, that the radar observations were inconsistent with the observed orbit of Eros, as well as with gravitational theory.

Nonetheless, the increasing accuracy of the radar results was compelling. The IAU general assembly, meeting in Hamburg in 1964, was asked to vote on a list of revised astronomical con-

Network, as well as the third project leader of JPL‘s 1961 Venus radar experiment. He is shown here in the control room of the Goldstone antenna, which was used in November 1959 for tests in preparation for the Echo balloon program.

BUTRICA - IN CONJUNCTION WITH VENUS 37

stants, including the astronomical unit. Again, the Lincoln Laboratory and JPL radar astronomers presented their results, which now gave values of 149 598 000 and 149 598 500 km, respectively, for the astronomical unit, with errors of measure- ment in each case of only * 100 km, the smallest yet.

Although the radar values were inconsistent with each other by a few hundred kilometers, the inconsistencies did not trouble astronomers, as the accuracy offered by radar was beyond their needs Indeed, the value they adopted a t the 1964 general assembly meeting in Hamburg-1 49 600 000 km-differed from the radar values on which it was based by 2000 km. Once adopted, the new value had to be incorporated into the various national almanacs and ephemerides.

Other major discoveries he new value for the astronomical constant came at an opportune moment in history. NASA was starting to explore the solar system, and an accurate knowledge of

planetary distances was crucial to steering spacecraft successfu- ly to their targets. The first fruits of planetary radar astronomy thus benefited not only astronomers and those using almanacs and ephemerides, but also the U.S. and Soviet programs of space exploration.

As for the early ambiguity of the results, the Millstone Hill radar was operating at the limits of its ability to detect echoes. The equipment had been designed to improve BMEWS and defense technologies for detecting small targets in the earths atmosphere, not planetary targets in space at the limit of radar detectability. The engineers at Millstone Hill were pushing the envelope (as would now be said) of what the equipment could

do. In such a context, sometimes a bad call is made. The same planetary radar astronomers who bounced signals off Venus later determined the planet's period of rotation, and discovered that it was retrograde-that is, opposite to that of most other plan- ets. They also bounced radar signals off Mercury and correctly calculated that it rounded the sun in 59 days, gainsaying the long-standing belief in 88 days.

These findings, all achieved between 1961 and 1965, forged the new scientific specialization of planetary radar astronomy. Every one of these pioneering astronomical discoveries was made by electrical engineers.

Finally, in view of current budgetary cutbacks, what must not be overlooked is the fact that these early Venus radar experi- ments belonged io no official laboratory program-nor was any other special laboratory funding involved. This astronomical research by EEs using laboratory equipment flowed from the funding largesse of the early years of the Cold War.

The media blitz initiated by Lincoln Laboratory revealed the pressures put on U.S. research laboratories and researchers to serve the political ends of the Cold War, namely, to demonstrate that the Soviet Union was not the only country capable of space achievements. Of equal importance, the early radar astronomy experiments mirrored the high degree of freedom that reigned ai Lincoln Laboratory and other military research facilities to follow "blue sky" ideas. Such was the environment that facilitat- ed the determination of the astronomical unit-and the found- ing of planetary radar astronomy-by electrical engineers at Lincoln Laboratory and JPL +

Spectrum contributing editor: Trudy E. Bell

38 IEEE SPECTRUM DECEMBER 1997