Argus results

Results related to the Argus experiment were released in two phases: an early Top Secret exchange within a small circle of appropriately cleared individuals, followed later by an unclassified public release. The initial discussions were to help determine the effectiveness of the nuclear detonations in injecting electrons into the Earth’s magnetic field. That was, after all, the primary purpose of the Argus exercise. Although a broad assortment of rocket, aircraft, and ground measurements was made, it was the results from Explorer IV that were the most eagerly awaited.

Classified early discussions As mentioned before, there were four fairly high alti­tude nuclear detonations before the first Argus test. The first was Operation Teapot’s high-altitude shot at about eight miles height in April 1955 to investigate atmospheric effects. Obviously, it was too low to figure in the trapped radiation study. Operation Hardtack I, consisting of 35 tests, was conducted between 28 April and 18 August 1958. Although most of the Hardtack I tests were conducted near the surface or un­derwater at Bikini Atoll and Eniwetok Island in the central Pacific Ocean, three were designed especially to investigate effects within the high atmosphere.

The first of those, Yucca on 28 April 1958, was a balloon-lofted detonation at only about 16 miles altitude, again, too low to be useful in looking for Argus-like effects. The other two, launched by Redstone rockets to a much higher altitude from a pad on Johnston Atoll, were Teak on 1 August 1958 (48 miles high) and Orange on 12 August 1958 (27 miles). Those bursts produced effects widely seen on the ground. The Teak event was observed by a group of New Zealanders at the Apia Observatory in Samoa as a flat, horizontal arc of bright violet rays in their western sky. The display lasted about 14 minutes, shrinking and gradually changing in color to red and finally to green. Fourteen days later, they saw similar results from the Orange blast. For that one, they reported that 10 minutes after the initial flash, the sky looked like a dawn on an overcast morning. The New Zealanders quickly connected the observations with the hydrogen bomb explosions above Johnston Atoll, located over 2000 miles to their north.

The Teak flash, being the higher of the two, was clearly seen from Hawaii, some 800 miles to its northeast. Even though the actual burst was below the horizon from

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Hawaii, the flash in the sky was bright enough to be seen, and the fireball rising above the horizon was photographed. The event also produced a magnetic storm that resulted in radio blackouts that persisted for nine hours in Australia and at least two hours in Hawaii. This was a result, primarily, of the introduction of a large amount of fission debris into the ionosphere, which prevented the normal reflection of radio waves back to the Earth.

The Orange shot, being at a somewhat lower altitude, was seen in Hawaii, but it did not have as much effect on communications.

Explorer IV was in orbit at the times of the Teak and Orange blasts. Despite the high yields of those blasts (3.8 megatons), they produced only small increases in the population of trapped particles at the satellite altitudes. Furthermore, since the blasts were low enough that atmospheric absorption played a major role, the effects persisted for only a few days.26

The three Argus blasts were made at much higher altitudes and in the region over the South Atlantic where the asymmetry of the Earth’s magnetic field causes the trapping region to dip to its lowest height.

Very pronounced effects from the blasts were seen by the Explorer IV instruments, as well by instruments on the ground, aircraft, and rockets. Qualitative and quantitative results from interpretation of the satellite data were provided by our Iowa group to the other Argus Project participants as quickly as they became available. It was eventually deduced that about 3 percent of the electrons from the blasts were injected into durably trapped trajectories. The mean lifetime of the artificially produced shells was about three weeks from the first two of the Argus blasts and about a month for the third. The four detectors on the satellite also revealed that the physical nature of the artificially created shells was substantially different from that of the naturally occurring belts, thus dispelling all previous thoughts that the natural belts might have been created by Soviet high-altitude nuclear detonations.

Still under a strict secrecy umbrella, a 10 day workshop on the interpretation of all Argus observations was conducted at the Lawrence Livermore Radiation Laboratory in February 1959. Van Allen and Carl McIlwain attended from Iowa. At that workshop, many of the general principles of geomagnetic trapping were substantially clarified.

But a puzzle remained. Why did the thin shells of trapped electrons produced by the blasts remain so thin over time? The Earth’s actual magnetic field differs from the shape of a dipole field that might be produced by a simple bar magnet. That was initially expected to result in a radial spreading of the thin shells.

Theoretical physicist Theodore (Ted) G. Northrup at the LLNL, at the urging of Edward Teller, had been working on the problem of longitudinal drift of charged particles in the Earth’s magnetic field. He had found an important key, a so-called longitudinal invariant. At the workshop, he described his work at an impromptu

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seminar for Van Allen, McIlwain, and several others. That train of discussion led to several theorems that greatly simplified the problem of particle drift. Among other things, it clarified the question of radial dispersion of the electron shell.27

Following the workshop, McIlwain devised a way of mapping the trapped radiation that greatly simplified the process of working with the data. It reduced the usual three-dimensional coordinate system used to describe the magnetic field to a two­dimensional one. That two-dimensional system became known as McIlwain’s B, L coordinate system, where B (in gauss) represents the magnitude of the magnetic field at any point in space, and L (in Earth radii) is a parameter that is approximately constant along the specific line of force that passes through that point.

The nuclear bursts had, in effect, provided markers on magnetic shells that permit­ted the rigorous testing of Carl’s system. In that manner, Explorer IV provided a firm observational basis for the B, L coordinate system. That system, and variations of it, has been used ever since in the study of magnetic trapping in the neighborhood of celestial bodies.

It should be noted that the possibility of electronic devices being damaged by nuclear detonations well above the atmosphere was later fully validated. Operation Starfish Prime, conducted by the United States on 9 July 1962, included the detonation of a W49 thermonuclear warhead about 250 miles above Johnston Atoll in the Pacific Ocean. The burst produced an equivalent yield of 1.4 megatons of TNT. It resulted in immediate damage to three low-orbit Earth satellites and damage to a number of others over a period of several weeks.

In addition, it produced major ground effects at Hawaii andNew Zealand, including interference with radios and television sets, the fusing of 300 streetlights on Oahu, the setting off of at least 100 burglar alarms, and the failure of a microwave repeating station on Kauai that cut off telephone service with the other Hawaiian islands.

In addition to the three Argus and one Starfish detonations by the United States mentioned so far, the Soviets produced substantial effects somewhat later with three high-altitude detonations as part of their K Project. Shots K-3, K-4, and K-5 were conducted in October and November 1962. Although the blast yields were only about one-fourth that of Starfish, the tests were conducted above a populated land mass, so that the damage was apparently much greater than that caused by Starfish. The electromagnetic pulse from one of them (K-3, Soviet nuclear test number 184 on 22 October) reportedly fused 350 miles of overhead telephone lines with a measured current of 2500 amperes, induced an electrical current surge in a long underground power line that caused a fire in a power plant in the city of Karaganda, and shut down 620 miles of shallow-buried power cables between Astana and Almaty.28

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Declassification Although the Argus Project was highly classified throughout its planning stage and during the first months after the nuclear detonations, that status could not be maintained indefinitely. A number of factors argued for early declassification. First was that the possibility of artificially injecting charged particles into the Earth’s magnetic field had already occurred to others. Second was that many effects of the high-altitude nuclear detonations were observable worldwide. Third was the probability that Soviet receiving stations were receiving the transmissions from Explorer IV and would be able to see effects of the nuclear blasts directly from that source.

A final factor was the fact that Explorer IV had been widely advertised as a component of the U. S. participation in the IGY, arranged to follow up on the radiation belt discovery. A very basic tenet of the IGY program was that all of its data would be released quickly for use by the entire research community. Although an attempt was made to argue that the IGY data policy did not apply to the Argus-related data, that distinction between the unclassified and classified missions was obviously thin and would be widely challenged.

To elaborate on several of those points, the idea of detonating a nuclear bomb in space as an experiment in electron trapping developed in the summer of 1958 com­pletely independently of the Argus Project, in a totally unclassified environment. Two researchers at the University of Minnesota, Edward Ney and Paul Kellogg, upon hearing of the Earth’s newly discovered trapped radiation in May 1958, suggested that a nuclear device might be detonated some 250 miles high near the southern auroral zone to see what effect it would have on the radiation belt. They figured that it might produce an effect in the Earth’s magnetic field that would “jar loose” trapped electrons, resulting in artificially created auroras in the north and south auroral zones. At the same time, they posited that particles produced by the bomb blast might be injected into the natural belt.

Those discussions took place in the absence of any knowledge by Ed and Paul of the Argus Project. When they first outlined their idea to friends in the Office of Naval Research in Washington, they received an unexpectedly cool reaction. Instead of greeting the suggestion as an interesting prospect for an IGY experiment, the Washington contacts asked that the pair not discuss their idea with anyone. The two drafted a letter to Herbert F. York, by then the chief scientist of the newly formed Advanced Research Projects Agency. They quickly learned that their letter would most likely be classified secret if sent. So they did not send it, but they decided to publish the idea in the British scientific journal Nature. When the Pentagon learned of that, their initial consternation changed to full-blown alarm. Ed and Paul were swayed to hold off on further discussions of their idea for a while. They kept the idea

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quiet until February 1959, when they finally published their idea in modified form in Nature a short time before the Argus Project was officially declassified.

The idea of injecting charged particles into the Earth’s magnetic field by nuclear detonations did, as it turned out, also occur independently to the Soviets. It is unknown when the idea first occurred to them—it might have been either before or after they learned of our discovery of the region of high-intensity radiation. The idea was certainly well established by 8 March 1959, when several Soviet scientists voiced their thoughts on the subject in a newspaper release.29 Their suspicion apparently resulted from their study of the widely reported visual and electromagnetic effects produced by the Teak and Orange nuclear bursts during the previous August. The article appeared well before the Argus Project was declassified.

The Soviets also had ample opportunity to see the results of the Argus tests by receiving the Explorer IV signals at their receiving stations. On one specific occasion, as Explorer IV was transiting one of the Argus-generated shells, it was easily within range of their Tashkent receiving station.

Walter S. Sullivan was a distinguished science reporter for the New York Times for many years. During the IGY, his primary assignment was to report on its activities. From that vantage point, he played a significant role in publicizing the Argus Project and its results.30

About the end of June 1958, Hanson W. Baldwin, military analyst for the Times, somehow learned of the Argus Project. In a private conversation, he told Sullivan of the plans, stating that he had obtained the information in a manner that placed no limit on its use. However, both had misgivings about releasing the information. Sullivan prepared a summary sheet containing many of the key points about the operation, including the location, height, and yield of the blasts. He carried that information to a friend who was centrally involved in the U. S. space program and knew of the Argus plans. That friend was both horrified and amused upon reading the summary. He told Sullivan, “I can’t tell you not to print it, but I can say this: If you do, the operation will never take place.”31

The next day, Sullivan received a call from the security chief in the Pentagon’s Advanced Research Project Agency, who pleaded with him not to publish the infor­mation. Sullivan and Baldwin agreed to hold the story under wraps until after the firing—they dutifully kept that secret for more than eight months.

Sullivan had been led to believe initially that the project would be declassified soon after the blasts occurred. As the months passed, however, and no announcement was forthcoming, he became apprehensive that he might be scooped on a very important story. After all, by then, literally thousands of individuals, including the many ship crew members who participated, were well aware of the tests. He also believed that the scientific brilliance of the experiment might be eclipsed by prolonged secrecy.

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With time, additional hints surfaced. On 28 November 1958, Christofilos presented his calculations on how an electron shield could be placed around the Earth at a meeting of the American Physical Society. To avoid a violation of security, he made no mention of atomic bombs as the source of the electrons but suggested that an electron accelerator in a satellite could provide them.

In a report released on 26 December 1958, Hugh Odishaw, executive director of the U. S. IGY program, called attention to some of the information then appearing in the news that suggested that the Teak and Orange blasts had caused widespread effects in and above the atmosphere.

The following day, Fred Singer presented a paper, “Artificial Modification of the Earth’s Radiation Belt,” at a session of the American Astronautical Society. In that paper, however, Fred made no direct reference to the Argus Project or its results.

During that same meeting, Van Allen described the unclassified findings from Explorer IV and Pioneer 3 that showed that there were two separate radiation belts. At a press conference following the presentation, Van Allen was asked a very pointed question by a Newsweek reporter, who wanted to know if the John­ston Atoll detonations (Teak and Orange) had produced any measurable effect in the Explorer IV data. Van Allen replied that the effect had not only been seen but was “tremendous.”

Sullivan grew increasingly agitated. After that meeting, he talked quietly with other individuals about releasing his story. Finally, on 2 February 1959, he was able to present his arguments to James R. Killian Jr., the special assistant for Science and Technology to President Dwight D. Eisenhower, telling him that he doubted that he could withhold publication of at least a limited account of Argus for much longer.

Killian’s response was that disclosure at that time might imperil the then ongoing Geneva talks on a nuclear weapons test suspension. He feared that the Soviets would be handed the argument that the only untrustworthy participant in the talks was the one that had sneaked off to fire atomic bombs far from its own shores. Sullivan continued to sit on his story.

In late February, a highly classified 10 day meeting was held at the Lawrence Livermore Radiation Laboratory to discuss Argus results, as mentioned earlier. It included an extended discussion of the need to keep the Argus program classified. The arguments were, at times, heated, with the one side saying that the tests were made at great public expense and that the United States should reap its strategic benefits for as long as possible. The counterargument, primarily by the participating scientists, was that they had been party to a magnificent physical experiment, of which their country should be proud.

Sullivan learned in mid-March that some plans for a limited disclosure were being made with at least some Pentagon backing. With that knowledge, and fearing that the

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movement might gather steam and leave the Times sitting in the dust, he escalated his arguments on 16 March to the top officers of his newspaper. He soon received agreement that he could proceed, but not if the White House called and argued that the story would do serious damage to the United States. To Sullivan’s great relief, that call never came.

Public announcements of Argus Results Walter Sullivan’s first account of the Argus Project appeared in the New York Times a few days later (on 19 March 1959) under the banner “U. S. Atom Blasts 300 Miles up Mar Radar, Snag Missile Plan; Called ‘Greatest Experiment.’” His account was released by wire before press time, and many other newspapers carried the news that morning.

One week after the Times story, James C. Hagerty, press secretary to the president, provided a press release that outlined the Argus experiment and its results in con­siderable detail, and he laid out plans for a major public symposium to discuss them further.

That White House press release, prepared jointly by the President’s Science Advi­sory Committee and the National Academy of Science’s IGY Committee, in addition to providing considerable information about the Argus concept and project, provided a broad outline of many of the experimental results:

A fascinating sequence of observations was obtained. The brilliant initial flash of the burst was succeeded by a fainter but persistent auroral luminescence in the atmosphere extending upwards and downwards along the magnetic line of force through the burst point. Almost simultaneously at the point where this line of force returns to the Earth’s atmosphere in the northern hemisphere—the so-called conjugate point—near the Azores Islands, a bright auroral glow appeared in the sky and was observed from aircraft previously stationed there in anticipation of the event, and the complex series of recordings began. For the first time in history measured geophysical phenomena on a world-wide scale were being related to a quantitatively known cause—namely, the injection into the Earth’s magnetic field of a known quantity of electrons of known energies at a known position and at a known time.

The diverse radiation instruments in Explorer IV recorded and reported to ground stations the absolute intensity and position of this shell of high energy electrons on its passes through the shell shortly after the bursts. The satellite continued to lace back and forth through the man-made shell of trapped radiation hour after hour and day after day. The physical shape and position of the shell were accurately plotted out and the decay of intensity was observed. Moreover, the angular distribution of the radiation shell of the Earth’s magnetic field was being plotted out for the first time by experimental means. In their helical excursions within this shell the trapped electrons were traveling vast distances and were following the magnetic field pattern out to altitudes of over 4,000 miles. The rate of decay of electron density as a function of altitude provided new information on the density of the remote upper atmosphere since atmospheric scattering was the dominant mechanism for loss of particles. Moreover, continuing observation of the thickness of the shell served to answer the vital question as to the rate of diffusion of trapped particles transverse to the shell. All of these matters were of essential importance in a thorough understanding of the dynamics of the natural radiation and were not the subject of direct study by means of the “labeled” electrons released from Argus I.

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Throughout the testing period the planned series of firings of high altitude sounding rockets was carried out with full success and with valuable results in the lower fringes of the trapping region.

Explorer IV continued to observe the artificially injected electrons from the Argus tests, making some 250 transits of the shell, until exhaustion of its batteries in latter September, though by that time the intensity had become barely observable above the background of natural radiation at the altitudes covered by the orbit of this satellite.

It appears likely, however, that the deep space probe Pioneer III detected a small residuum of the Argus effect at very high altitudes on December 6, 1958. But the effect appears to have become unobservable before the flight of Pioneer IV on March 3, 1959.

The site of the Argus tests was such as to place the artificially injected radiation shell in a region where the intensity of the natural radiation had a relative minimum. If the bursts had been produced at either higher or lower latitudes, the effects would have been much more difficult to detect, plot and follow reliably for long times after the blasts.

The immense body of observations has been under study and interpretation by a large number of persons for about seven months. Only now are satisfactory accounts becoming available from the participating scientists.32

The press release concluded with an announcement of the arrangements by the National Academy of Sciences for the presentation of Argus results in a special unclassified symposium at its annual meeting planned for 27-29 April 1959.

At Iowa City, while I focused primarily on preparing instruments for the next satel­lites, Van Allen and McIlwain were concentrating on writing up our Explorer IV results for the National Academy’s meeting. Our first unclassified report was soon ready.33 It began with a discussion of the background of the Argus Project, the role of Explorer IV, and the relationship between its orbit and the Argus electron shells. Figure 13.5 portrays the geometry, as shown in that paper. There would have been four intersections of each satellite orbit with the Argus shells, except for details of the geometry and data recovery. In the sample shown here, there were three full transits at positions B, C, and D. The intersection at position A did not provide a full transit because the Argus shell was at the same height as the satellite’s height (161 miles or 258 kilometers). There were other cases in which the Argus shell lay well below the satellite height at its time of closest approach. In other cases, the intersection occurred where there were no ground stations to receive the data. The actual numbers of useful full penetrations of the electron shells were 37, 39, and 88 for Argus I, II, and III, respectively.

Data from a sample receiving station transit are shown in Figure 13.6. Note that the vertical axis is logarithmic, so the counting rate covers a huge range during the time of this pass. Proceeding from the left of the chart (at 6:00 AM), the satellite was descending from the intense inner natural radiation belt and moving northward. As it moved through about 22 degrees north latitude (at about 6:08, as indicated in the figure), the Argus shell produced the sharp spikes in counting rates from the

FIGURE 13.6 A plot of data from the two GM counters on Explorer IV, taken about 3.5 hours after the Argus I burst on 27 August 1958. (Courtesy of the University Archives, Papers of James A. Van Allen, Department of Special Collections, University of Iowa Libraries.)

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two counters. By about 6:10, the satellite had passed north of the Argus shell and was in the slot between the two natural radiation belts for a few minutes, and then passed through the lower fringes of the outer natural belt to produce the broad peak seen between about 6:13 and 6:23. Comparable results were seen in all four satellite detectors for all three of the Argus bursts.

The special symposium in late April 1959 titled “Scientific Effects of Artificially Introduced Radiations at High Altitudes” addressed the full range of results from the grand experiment. Christofilos outlined its concepts, including an extended discussion of the theory of trapping. Additional theoretical information was provided by Jasper A. Welch Jr. and William A. Whitaker of the Air Force Special Weapons Center at Kirtland Air Force Base, New Mexico. Sounding Rocket results were provided by a group of authors led by Lew Allen of the Air Force Special Weapons Center. Optical and electromagnetic observations were described by Philip Newman of the Air Force Cambridge Research Center and Allen M. Peterson of the Stanford Research Institute.

Van Allen presented our paper with its huge body of satellite data. He provided a preamble and a short outline of the instruments and observations, and then presented arguments for the conclusion that the observed thin electron shells were, in fact, created by the Argus bursts, and that the natural belts were not the result of previous high-altitude nuclear detonations. Those key arguments were as follows:

(a) The observed energy spectrum and the nature of the radiation [in the shells] were found to be in essential agreement with those expected for the decay electrons from fission fragments.

(b) A peak with similar characteristics was found at every observed intersection of the orbit of the satellite with the appropriate magnetic shell, irrespective of latitude and longitude.

(c) The geometric thickness of the shell was similar to that of pretest estimates.

(d) The observed intensity of trapped electrons was in order-of-magnitude agreement with pretest estimates.

(e) The temporal decay of trapped intensity resembled pretest estimates.34

Our paper concluded with an extended discussion of the thickness of the Argus shells, their positions in space, their angular distributions, trapped lifetimes, injection efficiencies, and the distribution of the electron turning points.

After the examination of data from Pioneer 3 (launched earlier on 6 December 1958), the two-belt structure of the intense radiation zone was fully understood. That discovery had been published in Nature in February.35 The figure in that paper clearly

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INNER ZONE {NATURAL]

В ARGUS SHELL

C OUTER ZONE (NATURAL)

FIGURE 13.7 Copy of a figure presented at the April 1959 Symposium on Argus results. The re­lationship between the Earth, inner radiation zone, Argus shells, and outer radiation zones is shown to approximate scale. (Courtesy of the University Archives, Papers of James A. Van Allen, Department of Special Collections, University of Iowa Libraries.)

showed the two-belt structure and was adapted for our Argus paper by adding the location of the Argus shell, as shown in Figure 13.7.36

As was mentioned earlier, following our original announcement of the discovery of the radiation belts in May 1958, some on both sides of the cold war thought that the radiation might be residue from nuclear weapons testing already conducted above the atmosphere. The Americans thought the Soviets might have been responsible for them, and the Soviets suspected the Americans. Although the earliest satellites were able to map the extent of the belts, they provided only crude information about the particle composition and were not capable of demonstrating persuasively that the radiation was not man-made. It was not until the data were received from Explorer IV that the more qualitative and quantitative information permitted us to discriminate unambiguously between residue from nuclear detonations and the naturally occurring radiation.

Van Allen attended the Cosmic Ray Conference arranged by the International Union of Pure and Applied Physics in Moscow in July 1959. Although the Argus results had been declassified and presented orally in the United States before then, there had still been no published results available for the Soviet scientists to study. So at least some of the attending Soviets still believed that the radiation belts might have been man-made and that the United States was trying to conceal that information from them.37

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Everyone was edgy during those cold war years. A federal official, most likely an agent from the U. S. Central Intelligence Agency, visited Van Allen before his departure for that meeting, asking that he prepare a “trip report” upon his return covering 11 areas of interest. They wanted information on recent cosmic ray work, names of the institutions and individuals involved, individuals behaving secretively or evasively, copies of all materials distributed at the conference, and other subjects. It was only natural for Van Allen to assume that he would be similarly observed by Soviet agents during his stay in Moscow.

While at the Moscow conference, Van Allen outlined the Explorer IV and Argus findings essentially as he had presented them in his lecture at the U. S. National Academy’s symposium more than two months earlier. The Soviets were very interested in that information, and Academician Leonid Sedov gave him a spontaneous invitation to give a more detailed technical seminar at the USSR Academy of Sciences that evening. Van Allen was apprehensive about the invitation. It was not unknown in those days for visitors to the USSR to disappear. Van invited fellow U. S. conference attendees John A. Simpson of the University of Chicago and George W. Clark of MIT to accompany him, figuring that “if all three of us disappeared, someone would certainly investigate.”

At the Academy, Van Allen spoke, showed our slides, and engaged in lengthy discussions with his Soviet cosmic ray counterparts. It was only after their careful ex­amination of the Explorer IV and Pioneer 3 data that the Soviets were fully convinced that the natural radiation belts and the artificially generated shells were two markedly different phenomena.