Category Dreams, Technology, and Scientific Discovery

In late November, Van Allen and I had a series of discussions dealing with the calibration of the GM counters. One of our key experimental goals was to obtain an accurate measurement of the absolute intensity of cosmic rays as a function of orbital position. Good calibrations were crucial to achieving that goal.

Calibration of GM counters was not a new subject. The procedures were well established, not only at Iowa, but also in all laboratories making cosmic ray ob­servations. This topic was discussed in Chapter 1 in connection with Les Mered­ith’s work in helping to establish the cosmic ray balloon program at the Univer­sity of Iowa. His master’s thesis contains an especially detailed discussion of this subject.23

Although the California Institute of Technology enjoyed a rich history of cosmic ray research, the engineers in the satellite program had not shared in that experience. For that reason, and because Van Allen and I were especially concerned about the calibration of the GM counters, I set up the equipment and procedures personally, made many of the runs, and supervised the entire process.

During a 29 November conversation, Van and I discussed the procedures in consid­erable detail. He agreed to send several items that I needed for the purpose, including a laboratory nuclear event counter, the coincidence circuit schematic diagram that I

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had developed there, two actual coincidence circuit assemblies, and several test jigs. He underscored our discussion several days later with a handwritten note that read as follows24:

State University of Iowa Department of Physics Iowa City 12/2/57

Dear George,

1) Rc’d your wire on [cost of] data reduction machinery, etc. I will add to it some for labor, publication, etc. and submit it in the near future.

2) Principal purpose of this note is to remind you of the essential importance of:

(a) Good effective length measurements on Geiger tubes

(b) Absolute efficiency of Geiger tubes for cosmic rays

(c) Counting rate vs. voltage curves (temp. fixed) and counting rate vs. temperature curves (voltage fixed) (preferably for cosmic rays, but since data comes in so slowly that way, at least for radioactive source!)

These tests must be made!

3) If you can send one or two payloads which realistically simulate the Geiger tube’s physical environment we will fly them here for the orientational test (i. e. effect of orientation on Geiger counter rate at balloon altitude). We will supply telemetering transmitter.

Regards,

JAVA

It should be noted that item 3 in that note was never accomplished. Although I carried a spare Explorer I payload back to Iowa City in April, events had overtaken us by that time. We were completely immersed in analyzing the unexpected trapped radiation data, and GM counter orientation information was by then of relatively little importance.

In early December, Van informed me that the laboratory instrument that I had requested was in use elsewhere and not available. That turned out to create a major problem in the light of calibration difficulties that developed later.25

The GM counter calibrations ultimately applied to the Deal I and Deal II instru­ments were extensive. A short list of them includes the following:

• GM counter rate as a function of its applied voltage, typically referred to as the counter’s plateau

• Counter rate variation as a function of counter temperature

• High-voltage regulator tube voltage as a function of temperature (those three calibrations were needed so that we could correct the counting rate for changes in the instrument temperature)

• Counter absolute efficiency for cosmic rays, i. e., the fraction of cosmic rays entering the counter that produce output pulses

• The effective counter length, used for defining its cross-sectional area (those latter two calibrations were needed to compute the absolute cosmic ray intensity)

CHAPTER 8 • GO! JUPITER C, JUNO, AND DEAL I 237

By 11 December, the technicians had assembled the coincidence circuits needed for the later two calibrations, and I made the first absolute efficiency run. Everything appeared to be working properly, so I prepared a set of detailed instructions and turned that operation over to John Collins.26 27

During the following week, I set up and checked the equipment and procedures for determining the counter effective length and turned that operation over to John as well.28 Making those measurements on a number of GM counters continued for several weeks. Reasonable-appearing calibrations were obtained between 28 December and 2 January 1958 for the counters destined for the Deal I payloads.

However, during the second week in January, I observed that the plateau measure­ments that we had begun to make for the Deal II counters were not fully reproducible. It became obvious that spurious counts were being registered during at least some of the runs. That called into question the validity of all the measurements that had been made up to that time, including those for the Deal I counters.

Analysis of the problem required a frustratingly long and tedious effort, in­cluding countless overnight runs. At various times, I attributed the problem to (1) improperly operating laboratory pulse counters, (2) interference from relay contact closures in a nearby crystal oven, (3) contact arcing in a nearby tempera­ture test chamber, (4) possible unstable discrimination of pulse height in the cir­cuit coupling the GM counter to the scalers, (5) unknown background radiation sources in the laboratory, and (6) damage to the GM counters in previous tests. Even after eliminating all of those possibilities, reproducible readings could not be achieved.

The pulse counters being used were standard laboratory instruments, made by Berkeley Instruments. They were designed to determine the frequencies of sinusoidal, square-wave, and other periodic signals, that is, waveforms that repeated in a regular pattern, as opposed to the randomly occurring pulses from our instrument.

On a hunch, on 21 January, I tried the simple expedient of connecting two identical frequency counters in parallel, to see if they would produce identical results. Even though the dial settings were identical on the two counters, their readings were different, and neither one was repeatable. I concluded that the Berkeley counters were too waveform-sensitive and therefore unsuitable for those measurements.

The need for one of the special nuclear pulse counters that I had earlier requested from Van Allen became urgent. I called him with a frantic appeal for one, and he arranged to send it. But it did not arrive for another week.

Meanwhile, I continued with more tests. I improved the coupling between the GM counter and the Berkeley frequency counters. That, too, produced unrepeatable results. I had planned to leave for Cape Canaveral on 26 January for the Deal I launch. But when I finally left the laboratory bench at 2:00 AM that morning in a very discouraged mood, I was compelled to cancel my plane reservations and continue with the calibrations. After a short sleep, I returned to the lab, packed the entire test

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setup in my car, and took it home, where I would be away from all interference sources at JPL. That was no better!

I was getting desperate, as Deal II payload manager Milton (Milt) Brockman was pressing me for the GM counters for the payloads. The following day, the Nuclear Radiation Instruments Model 161 laboratory pulse counter finally arrived from Iowa City. After substituting that instrument, the problem seemed to be solved, and I asked the technicians to proceed with calibration runs for the Deal II counters.

“Seemed to,” because I still had some lingering misgivings. Of course, by then it was far too late to make any further tests or changes on the Deal I instruments, as the payloads were already at Cape Canaveral and the launch was planned for two days hence.

The calibration of the Deal II counters was, from that point on, reasonably straight­forward, and the success with them helped to allay my concerns about the Deal I counters. As it turned out, the calibration of the Deal I flight instrument was shown to be fully valid.

The network of ground stations was the same for Explorer III as it had been for Explorer I. The major difference in operation was that the high-power system was dedicated to telemetering the stored data from the in-orbit data recorder. Since the high-power transmitter had to be turned on from the ground for that purpose, and since only the Minitrack stations possessed command transmitters, high-power system data reception was limited to those stations.

The low-power signal was used in the same manner as for Explorer I, for tracking and for recovering the continuously transmitted data. Although both the Minitrack and Microlock stations had the technical capability for receiving and recording the

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low-power signals, it was decided to depend primarily upon the Microlock stations for collecting those data, thus permitting the Minitrack stations to concentrate on commanding and receiving the high-power data. Although the Minitrack stations used the low-power signal to assist in pointing their antennas, they did not record the low-power data.

The Explorer III operation is summarized as follows10:

• As in the case of Explorer I, there were no problems with the Explorer III primary mechanical structure or with its provisions for controlling its internal temperatures.

• Since the type of whip antenna used in Explorer I had been replaced for Ex­plorer III, there was no recurrence of the antenna abnormalities seen in that satellite.

• The low-power continuously transmitting system operated perfectly from launch on 26 March 1958 until 8 May. During 8 and 9 May, the operation of one of the telemetry channels was erratic, and on 10 May, the radio frequency carrier disappeared. Although the carrier reappeared on 14 May, it was without the subcarrier tones. It disappeared for the last time on 21 May 1958. Thus, operation was normal for six weeks of operation, somewhat shy of its two-month design lifetime. The pattern of that cessation is not completely understood but may have been due to the depletion of batteries.

• Operation of the entire scientific instrument for the high-power system, with its onboard data storage recorder, command receiver, and associated electronics, was also perfect during the time that it was operational. It operated perfectly for 44 days, until 9 May 1958, when responses to interrogations became intermittent. Response to interrogations ceased completely on 12 May but reappeared briefly on 21 May. The final response was received on 24 May. The 44 days of normal operation again fell short of the design lifetime by about two weeks but were long enough to satisfy all of the mission requirements. The behavior pattern for the high-power system around the end of life was also not completely understood. It is partly explainable by the large number of command attempts that were made during the satellite’s early life, since energy from the telemetry system batteries was consumed each time a command was received by the satellite, whether the data were observed on the ground or not.

• The fact that erratic operation of the entirely independent low – and high-power telemetry systems began at about the same time led to speculation that some external event may have been involved. However, no abnormalities in instrument temperature or radiation intensity were observed during the days leading up to 9 May, so such an event was probably not a factor.

CHAPTER 11 • OPERATIONS AND DATA HANDLING

The secretiveness of the Soviets caused them to miss discovering the Earth’s radiation belts. There have been recurring debates about bragging rights to the basic discovery and to the finding that there were two distinct regions of trapped radiation.54 55

Sputnik 1 carried no scientific instruments (other than those for internal temper­ature and pressure engineering measurements), and so, of course, had no way to detect the trapped radiation. On the other hand, Sputnik 2, launched on 3 November

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1957 (well ahead of Explorers I and III), did carry two GM counters that no doubt responded to the intense radiation. That satellite’s orbit, with an apogee height of 1131 miles and orbital inclination of 65.3 degrees, was admirably suited for detecting and studying the radiation.

But the Soviets did not receive data from regions where the higher readings would have been seen. Their data-receiving stations were located within the northern hemi­sphere, mostly within the Soviet Union, where the satellite was at its lowest height— generally below the trapped radiation.56 To compound the situation, the Soviets did not make information available that would have enabled scientists outside the Soviet Union to work with the satellite data.

The Soviets did obtain a single reading of a mildly increased intensity from Sputnik 2. A station in the northern USSR, on 7 November 1957, showed an increased radiation intensity, by about 50 percent. The indication was similar in general character to the measurements of the auroral soft radiation seen by the Iowa group during their 1953, 1954, 1955, and 1957 rockoon expeditions. Those auroral zone high-intensity readings were centered at about 68 degrees geomagnetic latitude, as shown in Figure 2.14, and at altitudes above about 50 miles. The Sputnik 2 anomaly was seen at a geomagnetic latitude of about 55 degrees over the Soviet Union, at a height of about 188 miles.

It was recognized during 1955-1957 that particles producing the soft auroral readings were being at least funneled into the polar regions by the Earth’s magnetic field. In fact, some of the enhanced radiation may have been from electrons captured in durable trajectories in the Earth’s magnetic field. Therefore, it is possible that the soft auroral radiation may have been the first weak manifestation of the presence of the outer radiation belt. We certainly did not arrive at that conclusion at the time, and never took the position that the detection of the soft auroral radiation represented the discovery of the Earth’s trapped radiation.

The single anomalous Sputnik 2 reading later served as the basis for the frequent claim by the Soviets that they discovered the outer radiation belt.

The first known report of that reading was by Academician A. V Topchiyev, chief scientific secretary of the Soviet Academy of Sciences, who reported at its annual meeting beginning on 25 March 1958:

Observations of cosmic rays by the satellite gave evidence of the variations of the intensity of its radiation. These variations evidently are connected with the condition of the interplanetary medium near the Earth. One case of a sharp rise to 50% of the number of particles of cosmic radiation was observed. Excellent agreement of readings of both instruments exclude the possibility of explaining this case as due to errors in the apparatus. At the same time, cosmic ray ground stations did not detect a substantial increase in cosmic ray intensity at this time.

At present, a detailed study of this occurrence is being made. It is possible that they are caused by a new phenomena [ліс], namely, by generation of cosmic rays of very low energy on the Sun which are strongly absorbed by the Earth’s atmosphere.57

CHAPTER 12 • DISCOVERY OF THE TRAPPED RADIATION 349

A full-page article in the 27 April 1958 issue of Pravda presented a compilation of results of the experiments conducted by Sputniks 1 and 2. It included a brief mention of the 50 percent increase in intensity mentioned above. The new article repeated the earlier assertion that it may have been a burst of radiation from the Sun.58

Our public announcement of the discovery of the high-intensity radiation was made on 1 May 1958. The paper on which the lecture was based, as well as the lecture itself, clearly attributed the high-intensity radiation to particles trapped in the Earth’s magnetic field. It was later universally agreed that Explorers I and III had observed the lower fringe of the inner radiation belt, with satellite orbital inclinations too low to see the outer cusps of the outer radiation belt.

The story of Sputnik 3 must have been especially galling to the Soviet scientists. That was the satellite that they first designed as their ultimate contribution to the IGY. Being very large and complex, its development required a tremendous effort. The Soviet support institutions and officials were slow at first in rising to the design task, and its schedule slipped month by month. It finally lagged so much that the Soviet hierarchy began to fear that the United States would beat them into space.

As early as January 1957, Sergei P. Korolev, the leader of the Soviet Intercontinental Ballistic Missile (ICBM) rocket program, suggested the development of two satellite versions: the full one envisioned by the scientists and a simpler one that came to be known internally as the Simple Satellite. In August 1957, after the R-7 ICBM successfully propelled a dummy H-bomb warhead over 3500 miles to Kamchatka, Korolev argued to the State Commission for the ICBM, and then to the Presidium of the Central Committee of the Communist Party, for the quick launch of the simpler polished sphere. With their nervous acquiescence, he pushed the preparation of that satellite forward in time for the 4 October launch.

The launch of their more complete IGY satellite was delayed still further following the resounding success of Sputnik 1. Soviet Premier Nikita Khrushchev finally realized what a politically hot property he had and instructed Korolev to launch something new in space in time for the next anniversary of their revolution. That goal could not be met with their primary satellite. By setting aside all normal procedures for designing and producing a new object, his team was able to prepare Sputnik 2 with portions of the leftover Sputnik 1 hardware, and with its dog as added cargo, in less than a month. It was launched on 3 November 1957.

After that, things started coming together for the launch of the much-anticipated larger scientific satellite. The first attempt on 27 April 1958, however, failed. The rocket engine quit at about eight miles’ height, and the satellite separated from its launcher and tumbled to the ground.59

A second launch attempt finally placed Sputnik 3 in orbit on 15 May 1958. But there was another problem. During the prelaunch checkout, the onboard tape recorder

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did not appear to be working properly. Two stories exist about the decision to proceed with the launch in spite of that difficulty. The first is that the recorder’s chief designer, Alexei Bogomolov, supremely confident of his creation, suggested that the testing failure was caused by electromagnetic interference from the many radiation sources in the test room and recommended that the countdown continue.60 The second version is that the order to launch came to Korolev directly from Premier Khrushchev, who wanted the satellite launched before the Italian general elections on 25-26 May, in the belief that that display of the superiority of Communism might help the Italian Communist Party in that election.61 It is possible that both factors played a role. In any event, the launch took place, and it was found that the tape recorder had, indeed, failed, thereby denying them access to data from other than the regions surrounding their ground receiving stations.

Sputnik 3 carried a very impressive array of scientific instruments, including detec­tors that were easily capable of showing the presence of the high-intensity radiation. As in the case of Sputnik 2, however, the array of Soviet ground receiving stations did not include significant coverage outside the Soviet Union. The failed onboard tape recorder did not provide data from the regions where most of the indications of the high-intensity radiation would have been seen. Those shortcomings would have been somewhat ameliorated if the Soviets had made the technical information needed to decode the satellite data available to the outside world. But their obsession with making their satellites appear to the world as unaided triumphs of Soviet Communism made it impossible for outside radio amateurs and eager IGY colleagues to provide additional data.

The 15 May launch of Sputnik 3 was followed by a series of reports of satellite performance in the press and scientific literature. For example, Pravda, on 18 May 1958, carried a full two-page article on Sputnik 3. That article, however, was limited to a general description of the program, of the instruments, and of the planned scientific program and included no mention of scientific results.62

A new Soviet reference to anomalous radiation was finally published in Tass in mid-July. It continued to ignore the U. S. announcement in May of the trapped radiation discovery. That Soviet announcement read:

Thanks to the instruments installed in Sputnik III a new phenomenon in science was discov­ered, a special type of corpuscular radiation which up to now had not been observed in the

composition of cosmic rays. Specialists are now engaged in puzzling out this phenomenon.63

The written papers provided by the Soviets for the Symposium on Rockets and Satellites at the Fifth Meeting of the Comite Speciale de l’Annee Geophysique In­ternationale, Moscow, on 30 July to 9 August 1958, made no mention of particle trapping. But Sergei N. Vernov, during a specially arranged evening address, dis­cussed the Sputnik 2 and 3 results beyond the written papers. The best account of

CHAPTER 12 • DISCOVERY OF THE TRAPPED RADIATION

Soviet information actually presented at the symposium is contained in the summary prepared by William Kellogg soon after the symposium. He reported that Vernov’s evening discussion, as it related to charged particle results, dealt primarily with the traditional cosmic rays.64

According to Kellogg, in that evening lecture, Vernov described the anomalous readings as observations of the “electron component of the cosmic rays” and made no mention of particle trapping. Specifically, he reported that Sputnik 3 had seen variable but high intensities of radiation that often exceeded the dynamic ranges of their detectors over the Soviet Union (in the latitude range from 55 degrees to 60 degrees north). He suggested that the increased flux was likely due to bremsstrahlung radiation from electrons interacting in the material of the satellite and detector and outlined two possibilities for their source. The first was that the elec­trons might be accelerated near the Earth by electric fields like those assumed to exist in aurorae. His second suggestion was that the electrons might originate away from the Earth, possibly on the Sun, and that they penetrated through the Earth’s magnetic field because of irregularities in that field. Van Allen later reported “that [Ernest] Ray had attended the Fifth General Assembly of the IGY from July 30-August 9, 1958, and heard papers by Vernov and Alexander Chudakov, the first exchange of Russian and American scientists regarding the radiation belts. They offered no re­port on the outer belt and no graphic rendering of the belts as shown in Van Allen’s reports.”65

The information presented by Vernov at the symposium was modified and con­siderably expanded in a paper by him and his colleagues that was later widely pub­lished. That paper, appearing well after the Moscow Symposium, contained the first known Soviet mention of charged particle trapping in the Earth’s magnetic field, stating:

Apparently, two types of variations occur. One type of the variation is caused by cosmic rays, and it must therefore respond to changes in the number of primary cosmic rays. The other type of variation does not concern cosmic rays. Apparently, a new type of radiation, and a variation of the intensity of charged particles and photons caused by this radiation were recorded on the satellites with the help of the apparatus constructed for the study of cosmic rays. This variation is caused by the radiation which can be called “earth radia­tion,” i. e., the particles of high energy originating near the earth and rotating around the earth.

A. I. Lebedinskiy and one of us (S. N. Vernov) considered the possibility of storing a large number of secondary particles near the earth. These particles are able to move quasi­periodically from one hemisphere to another. In the first approximation, the motion of the particle in the magnetic field must take place in such a way that the magnetic moment of the particle will be constant. Therefore, a charged particle is “trapped” in the region of a relatively weak magnetic field. These particles are able to perform a large number of oscil­lations and their intensity must be very large. One source of particles is the decay products of neutrons emitted by the earth under the action of cosmic rays. On the other hand, it is possible that particles from corpuscular streams emitted by the sun may also be such a source.66

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Thus, the situation at the end of the Moscow Symposium in early August 1958 was that the U. S. results from Explorer IV substantiated the earlier discovery of trapped radiation by Explorers I and III. The data were, however, still too sparse to infer the existence of two separate radiation zones. The Soviets were still very tentative in their explanation of the anomalous readings that they had received from Sputniks 2 and 3, had not yet attributed them to particle trapping, and had not postulated two separate regions of radiation. That latter conclusion awaited southern hemisphere data from Sputnik 3 and data from the U. S. Explorer IV satellite launched on 26 June 1958 and from the Pioneer 3 space probe launched on 6 December 1958.

Van Allen much later summarized the situation: “In retrospect, I should say that both the Soviets and we independently did have the basis—as of late August—for speculating on the structure of the [outer] radiation zone. But neither group had the perspicacity to do so at the time.”67,68

There is little doubt that, if the Soviets had openly included the world’s scientists and others in their endeavor, useful Sputnik 2 data would have been available from lower latitudes and higher altitudes—most importantly over South America and the South Atlantic Ocean. With that, the new phenomenon might well have become known as the Vernov Radiation Belts instead of the Van Allen Radiation Belts. Even without those data, if the recorder on Sputnik 3 had worked, the outer belt could have become known as the Vernov Outer Radiation Belt.69

Being solar powered, Sputnik 3 provided scientific data for about a year. In the fall of 1958, some data from south of the equator began to become available to the Soviet scientists. The Soviet research vessel Ob reached the southern hemisphere and began providing data in September. Also in September, the Soviets shared their radio code with Australian researchers, who began providing data from the region where the satellite was near its greatest height, and therefore, ideally sited to provide valuable data on the radiation belts.

The point at which it can be claimed that the outer belt was discovered remains a question of interpretation.

The model established at the beginning of the Space Age by the University of Iowa and several other universities clearly set the pattern for vigorous direct participation in space research by the academic community. Before the highly successful first U. S. satellites, some believed that only larger governmental and industrial laboratories would be able to build the scientific instruments. However, our cosmic ray instruments in Explorers I, II, and III provided an early demonstration that universities could handle the task in a very competent manner.

In addition to building those first individual instruments, the expanded university role on the Explorer IV and V project demonstrated that universities could handle entire satellite projects. Satellite S-46 was a more ambitious multi-instrument payload that was designed and largely built there. After that, the first in a series of Iowa-built Injun satellites, launched on 29 June 1961, transmitted useful space radiation data for nearly two years. Injun 2, a launch failure, was followed by fully successful Injun 3 on 13 December 1962, which operated for nearly a year. Injun 4 (Explorer 25) orbited on 21 November 1964, and Injun 5 (Explorer 40) was launched on 8 August 1968. Hawkeye 1 followed seven years later in June 1975.

Injun 5 represented the first fully all-university built and operated satellite. Al­though some data from the earlier Iowa satellites were recorded locally, NASA’s worldwide network carried the primary burden for satellite operation and data recep­tion. For Injun 5, however, the University of Iowa built and operated a major command and data acquisition station atNorth Liberty, several miles north of Iowa City. To make orbit-wide data recovery productive by that single station, Injun 5 (as had Explorer III) employed an onboard tape recorder. From a control center on the campus, the univer­sity students and staff were fully responsible for satellite operation and data recovery.

Iowa’s leadership role in conducting space experiments has continued to the present day. A 2004 tabulation prepared for the celebration of Van Allen’s ninetieth birthday lists 73 instruments that the laboratory had produced up to that time.

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Thus, Iowa, along with the university laboratories at Wisconsin, Chicago, Minnesota, and Stanford, played a major role in establishing the principle that universities could be relied upon to provide space hardware.

Leslie (Les) H. Meredith was born on 23 October 1927 and lived during most of his childhood in Iowa City. He received most of his college degrees from the University of Iowa: his B. A. in 1950, his M. A. in 1952, and his Ph. D. in 1954, all in physics. His timing was fortunate, as he became Van Allen’s first graduate student.

During parts of 1953 and 1954, Les went to Princeton University to work with Van Allen on the Matterhorn nuclear fusion project.6 Upon receiving his Ph. D. in 1954, he began his postgraduate career at the Naval Research Laboratory (NRL) in Washington, D. C., serving

CHAPTER 1 • SETTING THE STAGE AT THE UNIVERSITY OF IOWA 9

as head of the Rocket Sonde Branch and Meteor and Aurora Section. After the National Aeronautics and Space Administration was signed into law in October 1958, Les became one of the cadre of scientists transferred from the NRL to form what became the Goddard Space Flight Center in Greenbelt, Maryland. Serving for 12 years as chief of its Space Science Division, he provided outstanding leadership in the buildup of Goddard’s research staff and program. By mid-1970 he took over as deputy director of the Space and Earth Sciences Directorate, and after October 1972, he served for nearly three years as Goddard’s assistant director.

During subsequent years, Les moved through a progression of upper-level management positions, culminating in a short tour as the Goddard Center’s acting director. After his retirement as a federal government employee, he worked for nine years with the 13-agency U. S. Global Change Research Program.

In 2003, he and his wife, Marilyn, moved to their retirement home at North Myrtle Beach in North Carolina. Marilyn died in 2008, but Les has continued to reside there.

Les’ early balloons were launched from a football practice field on the east bank of the Iowa River from 16 June 1951 (beginning only five months after Van Allen’s arrival) through 26 January 1952. His scientific objective was to measure the incoming cosmic ray intensity as a function of altitude with a directional telescope using thin-walled Geiger-Muller (GM) counters. A concomitant purpose was to help the department gain initial experience with counters and coincidence circuits, telemetering techniques, and balloon flying.

That first Iowa balloon apparatus employed an array of three in-line, thin-walled, cylindrical, Victoreen-type 1B85 GM counters, with a coincidence circuit to form a directional telescope. An event from the center counter was counted, but only when the top and bottom counters were triggered at essentially the same time. Thus, only particles traveling vertically through all three counters were registered. The output of that telescope, along with an altitude measurement, was sent to ground by a frequency-modulated (FM/FM) telemetering system adapted from a design originally developed by Thomas Coor at Princeton University.7 Height-measuring barometers and transmitters taken from surplus weather radiosondes were included. Meredith’s circuits employed 13 miniature acorn vacuum tubes, each measuring about one-half inch in diameter and one and one-half inches in length.

His apparatus, with batteries, was assembled in a frame constructed of one-half inch, lightweight angle stock riveted together to form a boxlike structure measuring 15 by 15 by 30 inches. The gondola was completely covered with celluloid and partly covered with white paper to control the temperature of the instrument during its several-hour flight.

A number of inexpensive Darex type-J weather balloons of about six foot diameter were used to loft the instruments. Multiple small balloons were used rather than a single larger one. Not only were the smaller ones less expensive, but their use also freed the flights from the tight constraints of the Federal Aviation Administration— the larger balloons would have presented a potential hazard to aviation, whereas the smaller ones would not endanger the aircraft. The number of balloons was chosen so

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that their net free lift was about twice the total weight of the gondola and its rigging. For a payload weight of 27 pounds, a typical arrangement included nine balloons, each with 6 pounds lift.

Some of Les’ recollections about these earliest developments are entertaining and revealing.8 He stated, “The system test… was to take [the instrument] to the first high hill that you came to on the highway going south along the river, I think it was about five miles out of town, and then turn it on. The signal strength and counter operation were then checked at the receiving station, which was located in the attic of the physics building.” He continued, “Each balloon was of… some kind of rubber that had to be boiled just prior to launch to be flexible.” Recalling the field operation: “At launch, with the balloons at an angle because of any breeze, I and a helper ran with the payload until the balloons were high enough so the gondola wouldn’t swing down and hit the ground.”9

Out of Meredith’s seven flights in that series, the first two, flown on 16 June and 6 July 1951, produced somewhat noisy but usable data. Flight 3 failed to produce any usable data. Flights 4, 5, and 6 were flown with simple test equipment instead of with the more valuable instruments in order to work out some of the remaining technical details. The seventh and last flight in the series, launched 26 January 1952, produced good data throughout most of the flight. Preparation for the launch of the final flight is shown in Figure 1.1.

The three productive flights in this series served as the basis for Meredith’s master’s thesis, in which he established a new value for cosmic ray vertical intensity at that latitude for particles above an energy threshold that was lower than had previously been measured.10

he program of the International Geophysical Year—1957-1958 (IGY) provided a unique opportunity for cosmic ray research in general, and for us at Iowa City. As an active leader in the overall planning, James Van Allen had helped to shape both the general and specific character of the IGY program. In that role, he provided a great service to the research community.

In our Physics Department, Van Allen set the stage for the next few years of research. Acting to take advantage of the tremendous opportunity, he met in early 1956 with his graduate students to discuss possibilities for projects that they might undertake for their thesis work. By Carl McIlwain and Larry Cahill’s recollections, the list of possible projects that he placed on the table in that session included six cosmic ray, two auroral soft radiation, and two magnetic field studies.12 He envisioned that they could use a variety of balloons, ground-launched rockets, rockoons, and satellites. Those suggestions were in addition to the cosmic ray satellite experiment which he had proposed, and on which I had already begun work.

Following that session, decisions were made quickly, and specific proposals for IGY projects were submitted to Washington and funded. The work was undertaken with great enthusiasm and energy by the department’s graduate students, faculty, and staff.

Ground-launched rockets

The Iowa IGY research program, as it evolved, included experiments employing a mix of ground-launched rocket, balloon, rockoon, and satellite instruments. Carl McIlwain initiated the rocket program with an ambitious plan to probe the northern auroral zone.

89

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Mcllwain’s Fort Churchill flights At the time of the graduate student meeting, Carl was completing the work for his master’s degree. He received that in June 1956, with a thesis based upon the data from his Loki rockoon flights during the summer 1955 Davis Strait expedition.3

Van Allen’s suggestion that Carl might take advantage of the IGY program to fly some Nike-Cajun rockets at Fort Churchill, Canada, caught his attention, and he began thinking about various possibilities. He was captivated by the possibility that those rockets might be able to directly detect the particles that created the aurora, and thus shed light on the particle composition and energy spectra. It was known at the time, based on the alignment of the visible auroral features with the Earth’s magnetic field, that the auroral light was due to charged particles entering the Earth’s atmosphere. It was also known that at least some of those particles were protons in the 100 keV energy range, based on the presence of Doppler-shifted H„ and Hg spectral lines. The earlier direct detection of the soft auroral radiation by State University of Iowa (SUI) rockoons, however, indicated the presence of electrons, and Carl was eager to follow up on that new information.

To emphasize once again the trust placed by Van Allen in his graduate students, he assigned projects to them and then gave them tremendous freedom in seeing them through to completion. In this case, he designated Carl as the SUI chief scientist, and Carl bore full responsibility for preparing the instruments and conducting the field operation.

Carl’s first major technical challenge was to devise detectors that could detect and measure the very soft radiation that was capable of penetrating only very small amounts of material. Developing those instruments occupied much of 1957. He was joined in that work by Donald (Don) Enemark, a second-year electrical engineering student, and Donald (Don) Stilwell, an undergraduate physics student. They developed and built instruments capable of detecting the low-energy electrons in time for two Nike-Cajun flights that were scheduled for late summer 1957. Carl is shown working on one of his instruments in Figure 4.1.

Carl’s apparatus included three charged-particle detectors, a photometer, and a magnetometer. The first particle detector employed a thin thallium-doped cesium iodide (CsI [Tl]) scintillator crystal mounted on the face of a photomultiplier tube. Apertures, plus a 400 gauss permanent magnet, prevented electrons with less than 1 MeV energy from reaching the scintillator. The light sensitivity of the scintilla­tor crystal was reduced by a coating of 40 microgram per square centimeter alu­minum that was evaporated on its surface. Although the detector was sensitive to both protons and heavier ions, such as alpha particles, it was referred to as the proton detector.

The second particle detector was designed to characterize electrons. It, too, used a CsI (Tl) scintillator on the face of a photomultiplier tube. This one was annular in shape, with a thick plastic baffle filling the center opening. A ring aperture was located ahead of the detector, and an electromagnet between the aperture and scintil­lator focused electrons having specific energy ranges onto the scintillator. The pulses produced in the photomultiplier tube were integrated, and the resulting current was passed through a nonlinear network to produce a current that was roughly propor­tional to the logarithm of the electron energy flux over the range from 10-2 to 10+2 ergs per second per square centimeter per steradian. The magnet current was se­quenced through seven steps to make the detector sensitive to electrons in various energy ranges. The highest magnet current focused electrons with energies in the neighborhood of 100 keV The crystal on that second detector, too, was covered by a thin coat of aluminum to reduce its light sensitivity. That coating set the lower energy sensitivity of the detector at about 3 keV

A Geiger-Muller (GM) counter was included in the particle detector complement. It was surrounded by a one-sixteenth inch thick lead shield, except for a slit located

OPENING SPACE RESEARCH

next to a thin aluminum window in the side of the instrument package. It was sensitive to directly impinging electrons having energies in the range of 1 to 5 MeV In addition, it served as a low-efficiency detector for lower energy electrons through the process of converting electrons to X-ray photons (bremsstrahlung) in the atmosphere and the mass of the instrument. That arrangement provided a way to relate the new measurements to those made earlier with GM counters on the rockoon flights.

Carl included a photometer to measure the total directional intensity of visible auroral light. And a flux-gate magnetometer assisted in determining the pointing direction of the detectors during flight. Finally, a narrowly focused photometer was used on the ground during the flight to measure the auroral intensity straight above the launch site. In addition to being used to interpret the data, its output was used to help determine the best times to fire the rockets.

Carl’s two inaugural flights ran into difficulties. In the first firing (rocket number II 6.22F on 27 August 1957),4 the Nike first stage had not quite completed its burn when the two stages separated, and the Nike nudged the Cajun enough to break off the instrumented nose cone. Carl later reported that he found the payload in the muskeg the next day, and some of the electronics were still operable. His second flight (rocket II 6.23F on 30 August 1957 to a height of 70 miles) was somewhat more successful. The payload reached an aurora, but the Cajun, by chance, was pointing the instruments downward during the critical portion of the flight. Thus, he was not able to observe the incoming auroral particles.

Early the next year, Carl was ready with four more instruments of the same design. When he arrived at Fort Churchill, he found Les Meredith, who was by then working at the Naval Research Laboratory (NRL), with Leo Davis, also from NRL, already there with low-energy detectors that they had developed for flight on Aerobee-Hi rockets. They had made a successful flight (rocket NN 3.03F on 20 January 1958 to a height of 112 miles) by the time that Carl arrived and triumphantly announced that they had “already found what causes the aurora—low energy electrons, and that Carl might as well go home.”5

Believing that there was still new information to be gained, Carl proceeded, never­theless, with the checkout of his instruments (Figure 4.2). He made four flights during a 13-day period in February (II 6.24F on 13 February 1958 to 80 miles, II 6.25F on 16 February 1958 to 75 miles, II 6.26F at 05:34 UT on 22 February 1958 to 80 miles,6 and II 6.27F at 05:48 UT on 25 February 1958 to 80 miles). Fortuitously, a large solar flare occurred during the night of 11 February, a few days before his launches. It was quickly followed by a severe magnetic storm at the Earth, marked by decreases in the cosmic ray and neutron monitor intensities. That night was also marked by a bright red aurora that was observed over a large range of latitudes and longitudes. The following two weeks were characterized by moderate magnetic activity and frequent

occurrences of high-latitude visible auroras. The weather conditions at Fort Churchill were good throughout most of that period, permitting excellent observations.

Carl’s first three flights were technically successful, but data were obtained from only relatively dim and quiescent auroras. The flight on 22 February, for example, produced excellent data on the flux and energy spectra of protons and electrons but was not located in a very active region.

Those results were tantalizing, but not really what Carl was looking for. He de­cided to make a special effort to place his last rocket into a more active aurora and played the waiting game during the next several nights. His account of that launch read:

So, just visualize the scientists who were waiting around for me to get my last rocket off so they could fire theirs, and the impatience of the range safety people. Even though a graduate student, I still had control of when to launch. I told them, “Things are still not quite right.”

We waited at T minus 5 minutes night after night, and they said, “Come on, there is some aurora up there. Fire the thing,” but I insisted on waiting, and was very lucky. Upon seeing an auroral breakup just to the south of Churchill, I finally decided it was the time to finish the countdown.7

That launch (II 6.27F) finally took place in the early morning of 25 February 1958, and the Cajun reached observing altitude just as the aurora appeared over­head. The instrument remained pointed upward during the time of peak interest and

OPENING SPACE RESEARCH

produced the first-ever direct measurements of particles producing a bright auroral display.8

Enormous fluxes of low-energy electrons were detected, but they had an energy spectrum substantially different than had been seen earlier by both Les Meredith and Carl in the more quiescent auroras. Whereas the earlier measurements had revealed a broadly spread spectrum, the spectrum from this flight showed a strong peak at about 6 keV Carl concluded that the electrons had fallen through an electric potential that must have had a component aligned parallel to the magnetic field lines. That finding was highly controversial, as most of the theoreticians were quite convinced that it was impossible to have an electric field aligned parallel with magnetic field lines in a plasma. So he was hesitant about putting that conclusion into print, but did so somewhat later. Although still not universally accepted, the strong preponderance of belief today is that parallel electric fields do, in fact, exist and that they serve as a prime driver for the auroral particles.

I have tremendous admiration for Carl and his work. Following his arrival at Iowa, he very rapidly gained a deep understanding of physical processes when photons and charged particles move through space and interact with matter. The accomplished musician had become a virtuoso physicist!

The CSAGI Conference wrapped up its work on Saturday morning following the momentous announcement of the preceding evening. The closing session in the U. S.

CHAPTER 6 • SPUTNIK! 171

National Academy of Sciences’ Great Hall was marked by a mood of great excite­ment. But at the same time, it seemed anticlimactic and bittersweet. Of course, formal congratulations were offered to the Soviet delegates by Plenary Session chairman Lloyd Berkner. Soviet delegate head Anatoly Blagonravov took to the floor with understandable pride to speak at length about their Sputnik. On the blackboard, he sketched their new satellite, with its four antennas ranging from 5 to 10 feet in length. The main body was highly polished to make it more visible to observers on the ground. The total satellite weight of 184 pounds included 70 pounds of batteries that were expected to keep it transmitting for two to three weeks. He pointed out that this was not an instrumented satellite of the type called for by the IGY program, but rather, a test vehicle designed to demonstrate the effectiveness of the launching system. He indicated that its temperature measurements would determine, roughly, the effective­ness of the measures taken to control the internal satellite temperature. In addition, any later rise in temperature would signify that the sphere had been penetrated by a meteoric particle, allowing the escape of the nitrogen gas that circulated internally and served as a kind of air-conditioning system. The use of two frequencies at 20 and 40 MHz, he pointed out, was in general accord with the article published four months earlier in Radio magazine.19 The use of the dual frequencies was cited by Blagonravov as an advantage over the single frequency of 108 MHz being used by the United States, in that derivations of electron density in the ionosphere could be deduced from the signals.

It was obvious that many of the first Soviet satellite’s features were designed to maximize its political impact. Putting it up without scientific instruments was a shortcut to enable its launch ahead of the Vanguard satellites. The use of the highly polished surface ensured that it would be easily visible to the world’s population. The transmitter signals of 20 and 40 MHz, at a 1 watt power level, were easily received by the international community of radio amateurs and helped to make its reality more obvious throughout the world.

In Blagonravov’s remarks that morning, he conveyed an attitude that rankled U. S. attendees. He needled us for talking so much about our satellites before having one in orbit. That sentiment had actually been expressed quite explicitly a day earlier, when one of the Soviet delegates had told an American counterpart, “We will not cackle until we have laid our egg.” Although there was some justification for the Soviets’ more secretive approach (as we were later to discover to our chagrin in connection with a series of failed Vanguard launch attempts), Blagonravov seems to have entirely missed the point. The rest of the planners felt that much of the advance discussion was useful in (1) providing information that would help others who wished to cooperate in the tracking or other operational aspects of the program and (2) enhancing the scientific payoff. As Newell pointed out later, “in view of the fruitlessness of CSAGI’s efforts to elicit any such accommodation from the Soviets, either at Barcelona in 1956 or

172 OPENING SPACE RESEARCH

at the meetings in Washington, the remarks of their Russian colleague were doubly frustrating.”20

In spite of those negative aspects, admiration for the Soviet achievement was genuine and universal, and all at the session were able to applaud when Blagonravov ended his comments with his expression of hope that

this first step… would serve as an inspiration to scientists throughout the world to accelerate their efforts to explore and solve the mysteries and phenomena of nature remaining to be explored.21

Following Blagonravov’s remarks, John P. Hagen of the Naval Research Labora­tory reported that the U. S. Minitrack observing network had detected the transit of the satellite on its third or fourth orbit and that a regular tracking program was being established.22 Some stations of the Minitrack system, designed to operate at 108 MHz, were being hastily modified to operate at the Soviet frequency of 40 MHz as well.

He played a recorded tape of the telemetered signal, at which point Blagonravov’s normal reserve vanished, and he declared with obvious excitement, “That is its voice!”

Wrapping up the conference, working group members hurried to put their resolutions in order for the official reports. The resolutions were adopted in the Plenary Session, and the eventful conference was gradually brought to a conclusion.

In the final closing, the U. S. National Academy of Science president Detlev Bronk congratulated the conference on its achievements, and added his congratulations to the USSR IGY National Committee with respect to the launching of the first satellite. He stated:

All scientists are fellow explorers on the frontiers of knowledge, who rejoice and ben­efit in the discoveries and achievements of their colleagues. And so we of the United States rejoice in yesterday’s great achievement of our Russian colleagues and applaud their success.23

CSAGI president Sydney Chapman made the final statement for this first CSAGI Conference on Rockets and Satellites. He hinted at what others were saying privately:

The launching of the Sputnik without advance warning had taken tracking systems in the West unaware, and hence had reduced the amount of scientific observations that could be made. In congratulating the Russians on their “magnificent achievement,” Chap­man noted in his gentle, British way, that news of the launching had been “indirectly received.”24

Despite all of our attempts to put on a good face following the Soviet triumph, we Americans felt a palpable sense of betrayal.

CHAPTER 6 • SPUTNIK!

A corona discharge problem was described in Chapter 5 in connection with the development of the Vanguard prototype instrument much earlier at Iowa City. It reared its head again during the Deal I payload assembly in mid-December, when I discovered that the high-voltage power supplies had not been checked in a vacuum chamber.29 The JPL engineers stated that it was “no problem,” as the power supplies were “safe for direct shorting.” I knew from my testing at Iowa that electrical transients from arcing in a partial vacuum would destroy the supply. I had to prove my point by a series of overnight tests. They showed, first, that there was a problem, and second, that the encapsulation technique that I had worked out at Iowa solved the problem. After making that change, there were no further corona discharge incidents for the rest of the program, and the instruments operated in orbit without incident.

That episode was the most contentious one that I encountered during my stay at JPL. Without appropriate tests and an effective solution, there can be little doubt that our cosmic ray instruments would have failed soon after liftoff.

The first recordings of the Explorer III low-power telemetered data were obtained near the end of the first orbit by the JPL, Earthquake Valley, and Temple City Microlock stations, beginning at about 19:38 UT on 26 March. The next pass (pass 2) provided useful data at about 21:40 UT from Temple City. Pass 3 was received at Temple City at about 00:37 UT on 27 March, and Patrick Air Force Base (PAFB) received it a short time later. For the next five orbits, the satellite passed out of range south of the Microlock stations, and low-power telemetered data were not obtained. But when the orbit passes reappeared over the United States, Temple City immediately recorded a long 15 minute pass beginning at about 12:25 UT, and PAFB received the signal a short time later. And so it continued, with the Microlock stations receiving useful low-power data during essentially every orbit that carried the satellite over their locations.

A complete tabulation of the low-power continuously transmitted data similar to that for Explorer I was never assembled. Although the low-power data were used at JPL for engineering assessment, at Cambridge for the micrometeorite data, and for cursory examinations of the cosmic ray data, the primary focus of the data analysis efforts in our laboratory quickly turned to the tape recorder dumps telemetered by the high-power system.

The high-power system was completely new with Deal II. The satellite transmitter was turned on by ground command, and it remained on only long enough to transmit the data that had been stored on the onboard recorder since its previous readout. Typically, for a dump of the data from a full orbit of recording, the transmitter was turned on, the tape readout began after about two seconds, and it lasted for about six seconds. The transmitter was turned off by the onboard programmer immediately after completion of the readout to conserve battery power.

The first attempts to recover the onboard-recorded data from Explorer III were disappointing, as described earlier. It was not until I arrived in Huntsville the day after the launch that I was able to get an encouraging summary of the first 11 passes from Jack Mengel in Washington. There were at least hints of proper operation of the complete system during passes 2, 4, 6, 7, 10, and 13.11 It was only shortly after that, a full day after launch, that anything approaching the expected performance was achieved. On pass 14, Quito, Ecuador made the first completely successful single­command interrogation that resulted in the successful recording of data that had been accumulated over a full satellite orbit. That result was achieved increasingly as the stations became more proficient.

During the 44 day period of normal operation of the onboard storage and readout system, the satellite completed 523 orbits, and recorder interrogations were attempted

on 504 of them. Of those, 408, or 81 percent, resulted in useful data. The success rate was only about 23 percent on the first day but climbed steadily throughout the operating lifetime. By the third day of operation, the average daily success rate reached about 80 percent, and by the end of the operating lifetime, the rate was consistently averaging more than that figure. The interrogation success rate for the entire operational period is shown graphically in Figure 11.2.

There were several reasons for the disappointing initial performance. In the first place, this was the first use of the ground station command transmitters, and it took some time for the operators to resolve equipment issues and to fine-tune the procedures. Adding to the problem was the fact that the high-power system used a completely different and more complex operational mode than had been used for both the low – and high-power systems on Explorer I, and for the low-power system on Explorer III. After the interrogation command was transmitted, the responding data flow began after only two seconds. Thus, all equipment had to be pretuned, and the ground tape recorder had to be running before the command was sent. It took time for the operators to become proficient in this new and somewhat complex operation.

A second problem aggravated the data acquisition problem. It took time for the Vanguard Computing Center to accumulate enough tracking data to produce orbital predictions accurate enough to prealign the antennas. Since the entire high-power operation had to take place in a matter of seconds, there was no time to realign the

antenna if it had not been properly preset. By the end of the first day, the orbital prediction accuracy improved, thus contributing to the improved data recovery.

A very interesting account of the radiation belt discovery from the Russian point of view was published in History and Technology in 2000. The paper’s abstract reads:

The most important scientific discovery of the early space era—the 1958 discovery of the radiation belts of the Earth—was made in the context of Cold War rivalry between the USSR and the USA. The paper uses previously unavailable archival records to reconstruct the relative contributions of American and Soviet researchers and their interations [sic: iterations or interactions?] during the process of discovery. The former discovered what is now known

CHAPTER 12 • DISCOVERY OF THE TRAPPED RADIATION

as the inner radiation belt, while the latter observed the outer radiation belt and gradually came to realize the existence of two distinctively different zones of radiation. The uses of science for the purposes of Cold War political propaganda affected the behavior of scientists and led to the misrepresentation of the events in mass media.70

Although I believe that that paper is largely historically accurate, there are some differences in detail and interpretation between its account and the one presented here. Most of those differences appear to relate to the authors’ understandings of the timing and venues of various information releases.