FOR THE NATIONAL Committee on the IGY and the Academy's satellite panel, the United States government's determination in fall 1957 to accelerate the American launching program had caused simultaneously satisfaction and apprehensiveness. Glad as scientists were to have their cherished project given a priority long denied it, they were uneasy lest haste to "get something up there" result in shortcuts that would lessen the quality of the scientific returns.¹ The intensive work put into tracking the two Sputniks and extrapolating scientific data from them proved the reliability of the Minitrack system, despite the differences in the radio frequency the Russian transmitters employed. It also established the utility of Moonwatch and Moonbeam Operations and within a few weeks netted some useful geodetic information.² But the mandate to hurry up American launchings placed an additional burden on the scientists responsible for other phases of the American program.

In late October 1957 while waiting for official word of what the White House would authorize as a backup for Project Vanguard, the Working Group on Internal Instrumentation discussed the possibilities for the future. Repeating the suggestion that the panel's ad hoc group had tendered to the USNC nine months before,³ Homer Newell opined that the United States should establish an "Astronautical Laboratory" under civilian control to direct a long-range space program. Here was the second mention of the scheme that would become reality a year later with the organization of the National Aeronautics and Space Administration. Meanwhile men at the Academy had to struggle with the problems immediately confronting them. Anticipating DoD consent to the use of the Army's Jupiter-C rocket as a satellite launcher, the panel had to decide which experiments to switch to the Explorer and what redistribution to make of the remainder among Vanguard satellites. With a bigger payload in prospect, there was also the question of whether to sponsor the development of further experiments for installation in IGY birds. And should the panel support ionospheric studies that would require transmitters and receivers operating on longer wavelengths than the 108 mc chosen for Vanguard? At the same time the IGY secretariat must issue reports to other National Committees on orbital data acquired from Sputnik and forward for CSAGI approval Fred Whipple's proposal that the nomenclature of IGY satellites consist of the year, a Greek letter, and, when appropriate, a number indicating the degree of brightness for each in turn-for example, 1957 Alpha for the first Sputnik. The strong probability that Soviet scientists would not release their findings until they had completed a thorough analysis led the panel and USNC, on the other hand, to postpone overtures for an exchange of technical and scientific data with the U.S.S.R.⁴

Formal authorization of two Explorer shots as a backup for Vanguard came in early November. Pickering had pointed out to the satellite panel six months before that the State University of Iowa experiment would lend itself fairly easily to use in the Jupiter-C payload,⁵ but now he warned that the rapid spin rate of the Explorer satellite would jeopardize the performance of George Ludwig's cleverly designed tape recorder and playback mechanism. While the Jet Propulsion Laboratory stood ready to make the necessary adaptations, the time available would be too short to overcome that hazard in an Army satellite if it was to be launched in January. The only way to proceed was to omit the command receiver and the memory device and rely instead upon continuously operating telemetry to relay signals to ground stations. Sacrifice of the storage device would mean the loss of much of the scientific data, since ground receivers could record them only when the satellite was passing over the tracking stations. This circumstance might defeat one of the primary purposes of the experiment, namely the determination of the latitude effect of cosmic radiation. Two factors, however, tipped the balance. Of the packages planned for the first four Vanguard flights, only two were in the last stages of testing at the Naval Research Laboratory, one containing the Lyman-alpha and environmental studies, the other the cosmic ray observations and meteoritic measurements; the former would need more extensive and therefore more time-consuming changes to fit into the Explorer configuration than would the latter. The second inducement was the Army's promise to supply at the earliest possible moment a Jupiter-C vehicle so modified as to accommodate the data storage equipment omitted from the first Explorer. As the Army satellite was to remain attached to the casing of the fourth-stage rocket after burnout, the eighty, by six-inch cylinder-shaped body presumably would be no more difficult to track optically than the twenty-inch spherical Vanguard. So the TPESP voted for the transfer, provided Van Allen and his colleagues concurred. Van Allen was on an icebreaker in the South Pacific. The Navy was unable to communicate with the ship by radio, whereupon someone suggested sending him a Western Union telegram. To everyone's astonished amusement, the wire, relayed via Australia, reached him and he immediately sent back his approval of the switch. Part of the instrumentation for measurements of interplanetary matter was also to go into the first Explorer.⁶

The press version of the transfer caused some heart-burning at the Naval Research Laboratory, for when Robert Baumann, who had done much of the work on the engineering layout of the instrument package, handed the pot over to William Pickering of JPL, the newspaper story gave no hint that the Vanguard team had spent months in working out reliable temperature controls, in testing the scientific instrumentation, and in producing the ingeniously miniaturized package. The caption of the accompanying photograph labeled the pot in Pickering's hands: "The 20-pound satellite the Army hopes to launch."⁷ So far from realizing that Vanguard had contributed anything at all to the later success of Explorer, much of the American public thereafter assumed that the Army, notably Wernher von Braun with a minor assist from JPL, had prepared the Explorer payload from start to finish and in less than eleven weeks. Inasmuch as George Ludwig and Jet Propulsion Laboratory engineers undertook the redesign and the testing, the assumption was unjust to them also.

The panel meanwhile had little choice about reshuffling the packages to fly in the Vanguard satellites. In keeping with earlier plans, the gauges for environmental studies and the ionization chamber for the Lyman-alpha experiment should have the first priority. At Newell's suggestion. however. with Herbert Friedman's endorsement, the panel approved preparation of a solar x-ray experiment as an alternative to the Lyman-alpha, since the substitution would necessitate only minor changes in the ionization chamber and could easily constitute package I a; in fact, extreme solar activity at the time of launching might make I a more valuable than package I. The cloudcover experiment was to go into package II: the magnetometer and the NACA inflatable sphere, provided they were ready in time, were to be the next flown. Suomi's radiation balance equipment was to make up package IV. If, before the expiration of the IGY, additional launchings were to provide space for other projects, one or more of those on the backup lists-Singer's, JPL's, or the heavy nuclei experiment under development by Martin A. Pomerantz of the Bartol Foundation and Groetzinger of RIAS-would be the logical choice. Just as the panel was unwilling to recommend cutting short the tests of the scientific instruments to be flown, so, with four of the eighteen months of the IGY already gone, members saw the impracticality of looking for new, still undeveloped, onboard experiments. They stood by that decision even after Sputnik II carrying the dog Laika on her week-long journey evoked questions about expanding the American program to include experiments in the life sciences. Although a biologist at the National Institutes of Health had already submitted a proposal to study the effects of radiation on yeast cells in the vacuum of space, and although the Vanguard scientific group thought the package would fit into the 6.4- inch satellite, the panel concluded that that experiment, like other more complex new schemes, would have to await a post-IGY program.³

Nevertheless, as the Soviet satellites with their 20-and 40-mc radio transmissions opened up a unique opportunity for radio propagation studies and ionospheric research, the TPESP believed it could not ignore that promising field of investigation. Accordingly it set up a Working Group on Satellite Ionospheric Measurements under the chairmanship of Alan Shapley of the Bureau of Standards to recommend particular projects. Most of the studies would not require changes in the instrumentation within the satellites and would rely on the use of ground receivers attuned to the longer wavelengths of Russian radio transmissions. Although the panel envisaged the possibility of later putting into American satellites 20- and 40-mc transmitters in addition to the far more accurate 108-mc-an eventuality that materialized in October 1959 in the last IGY bird put into orbit-the bulk of the work would concentrate on the data to be acquired from Sputniks. The ionospheric studies were thus ancillary to, rather than an intrinsic part of, the American satellite program. Still, in early 1958 the panel endorsed eight ionospheric projects and undertook to obtain grants to support them. Added to other expenses unforeseen earlier, the cost increased the demands on the IGY budget.⁹

Money indeed posed a problem to the United States National Committee at every turn in the months following the appearance of Sputnik I. Within the first three weeks, Newell told the panel that the costs of tracking and analyzing the telemetry signals from Sputnik were outrunning Vanguard's financial resources, while Whipple estimated that Moonwatch would have to have at least $50.000 more a year, and as much as $200,000 might be necessary to expedite delivery of the Baker-Nunn cameras. The IGY committee must also find money to cover the expense of completing the engineering and testing of instrumentation for backup experiments. Changing over the cosmic ray apparatus to fit Jupiter C would alone cost about $161,200, considerably more than the $106,375 allotted to construction of the original. There was also the matter of solar cells. Although the Explorer would have to depend on conventional batteries inasmuch as redesign of the circuitry in its payload would delay an early flight, the panel was gratified to learn that the six-inch grapefruit to be launched by the first complete Vanguard test vehicle was to carry six solar cells. The wisdom of providing for solar power in future American satellites seemed self-evident, despite the additional cost consequent upon the longer period of time during which radio tracking stations and data reduction centers would have to operate.¹⁰ New expenses meanwhile were growing out of the necessity of mailing out from the Academy thousands of pieces of literature and individual letters in answer to inquiries from people all over the country; good public relations forbade ignoring either the school child's or the influential citizen's request for information.

On top of all these demands, in the opinion of the Academy's IGY Committee, larger sums should go into final interpretation of the scientific findings after reduction of the raw data. John A. Simpson, professor of physics at the University of Chicago, called this last phase all-important, as it concerned "the truly scientific aspects of the work." Foreign scientists, Simpson contended, could exploit the data assembled by American experimenters unless generous grants enabled the latter to spend time on "the fundamentals of research growing out of the IGY program.… Many new scientific discoveries await the full analyses of these data."¹¹ The United States must not neglect the final harvest. Hence, whereas the TPESP concluded that a $2.2 million supplementary appropriation would suffice, the National Committee believed $3.2 million necessary. Alan Waterman, however, remembered the assurances he had given Congress in 1956 that the universities would meet most of the costs of interpreting and publishing scientific results; the Science Foundation submitted a request for $2.2 million in January 1958. On 31 March the President signed the bill appropriating an additional $2 million for the IGY, and somewhat later the USNC itself pared $294,334 from the amount allotted to the expanded and accelerated program. By then the United States had three satellites orbiting the earth.¹²

Rejoicing over the triumphant flight of Explorer I on 31 January 1958, the much less touted orbiting of Vanguard I forty-five days later, and Explorer III's performance on 26 March calmed public furor over the American program without noticeably lessening popular interest in what would come next. If much of the public was primarily eager to read of or see on TV further American exploits, and if Moonwatchers and Moonbeamers waited impatiently for chances to exercise their tracking skills on new satellites, scientists were above all anxious to learn what the accumulating data relayed to earth added up to. By 3 April, when the Academy's panel met to assess accomplishments to date and consider future plans, few precise data were on hand. Those from the cosmic ray apparatus in Explorer I, 1958 Alpha, were confusing and, because it had not carried a storage device as originally planned for Vanguard, about eighty-five percent of the signals were lost, not received at ground stations. Most of the information obtainable from the scantily instrumented six-inch Vanguard, 1958 Beta 2, had to derive from analysis of its orbit and was still incomplete. Explorer II had failed to orbit. Although the instruments in Explorer III were working fairly well and its tape recorder and storage mechanism were enabling Minitrack and microlock stations by interrogation to receive about eighty percent of the telemetered signals, the results were as puzzling as and largely duplicated those from 1958 Alpha. Tentative reports on Dubin's experiment were interesting but still inconclusive. Meaningful interpretations of what the American satellites were revealing would have to await more intensive study.¹³

Dubin, however, was able to present at the Second Astronautics Conference in April a paper entitled "Cosmic Debris of Interplanetary Space" in which he discussed his initial findings. The signals recording the quantity, spatial distribution, and size of interplanetary matter colliding with Explorer I and Explorer III were easier to understand than those coming from the cosmic ray apparatus. The gauges for micrometeoritic measurements indicated fairly clearly that the average influx of particles of as much as ten microns in diameter was not more than one per thousand per square meter per second, while the influx of particles with diameters of four to nine microns was about ten times greater. Readings from twelve days of operation of the equipment in Explorer I showed very much higher rates of impact during about eight hours of every twenty-four than occurred during the remaining sixteen hours. The experimenters' hypothesis ran that "meteor showers" accounted for the difference, an explanation substantiated by ionospheric observations made at several ground stations, notably at White Sands, New Mexico. Extrapolation then permitted estimates that the earth may have a daily accretion of up to l0 million kilograms of cosmic dust. Later studies would confirm this thesis.¹⁴

Van Allen and his associates, on the other hand, were excited and baffled by the data coming in from the 1958 Alpha and Gamma satellites. At altitudes below 1,000 kilometers, the readings obtained from the Geiger counters were consistent with known theories of cosmic ray activities, but above 1,000 to 1,200 kilometers very high counting rates occurred and then at periods fell abruptly to essentially zero At a special session of the American Physical Society at the Academy on 1 May Van Allen gave a paper in which he described the enigma. The cause, he noted, might be malfunctioning equipment, but that explanation seemed invalid because the instrumentation in Explorer I differed from that in Explorer III; the latter carried a tape recorder. Possibly the satellites passed through regions to which few cosmic rays could reach, but Van Allen thought that "extremely unlikely." The only remaining explanation, and the one Van Allen concluded must be correct, was that the Geiger counter tubes encountered such intense radiation during the high-altitude portions of the orbits that the detectors had to operate above the overload level, greater than 35,000 counts per second. Analysis indicated the existence of radiation consisting in part of energetic particles, presumably protons and electrons, in geomagnetically trapped orbits. Further exploration of this phenomenon would greatly help scientists to understand it fully.¹⁵

Explorer IV, launched in late July at a fifty-degree inclination to the equator in order to establish a different orbit, consequently carried one Geiger counter shielded with lead and one unshielded counter capable of handling 1,500 times the radiation intensity that had saturated the detectors in the first two Explorers; it also contained two scintillation counters, one to measure approximately the total energy and the other to count the incident corpuscular radiation. As the data came in, a plotting of the counting rates with reference to the earth's magnetic fields revealed clearly and unambiguously a radiation zone related to the lines of force of the geomagnetic field. Since the Advanced Research Projects Agency in the Department of Defense and the Atomic Energy Commission conducted in August a rocket test which produced a small high-altitude nuclear explosion, scientists had the additional benefit of data showing the effects of artificially introduced radiation of a known quantity and energy spectrum. By means of these observations and extrapolation, the State University of Iowa team mapped out the contours of the radiation zone and concluded that its structure must be more complex than they had suspected earlier. Deep space Pioneer probes launched by powerful rockets during the autumn of 1958 then enabled the experimenters to chart with some certainty what came to be known as the Van Allen radiation belts. This, the most significant scientific discovery achieved during the IGY, gave the United States a "first" in space exploration that wiped out most of the sting of having been second to the U.S.S.R. in putting a satellite into orbit.¹⁶ Although American experts early realized that the first Sputniks might well have detected the existence of this phenomenon, had the Russians launched them at a higher angle of elevation to the earth, the American feat was none the less gratifying to the National Academy and the American public.

Each of the first three successful Explorer satellites had a short operating life, respectively under four months, less than three months, and just over ten weeks. From the six-inch Vanguard I, on the contrary, signals continued to come through clearly month after month despite the 2,460-mile apogee of the orbit; indeed receivers on the earth would be able to pick up the "beeps" for the next seven years. But because the grapefruit carried no instrumentation except the transmitters and two thermistors on its shell, the scientific information it could furnish at first looked meager-at least compared to the cosmic ray data deriving from the Explorer-and initially it appeared to be far less useful than that transmitted from the sophisticated Russian Sputnik III, 1958 Delta-even though signals from the latter were extremely difficult for American receivers to intercept.¹⁷ Nevertheless, the little 1958 Beta proved more valuable than most people expected.

From study of the orbit, scientists at the Naval Research Laboratory and the Smithsonian Astrophysical Observatory were able to report some interesting discoveries: the earth is not a globe somewhat flattened at the poles, but is pear-shaped; the gravitational fields of the moon and the sun modify the orbit of earth satellites; the radiation pressure of light from the sun affects the movement of a satellite in its orbital path, and magnetic drag damps the rotational motion of metallic satellites. The repeated passages of the small artificial body enabled experts as time went on to determine the dimensions of the earth's equatorial and polar diameters, to demonstrate variations in atmospheric density with the rotation of the sun, and to show that the density of the upper atmosphere is far greater than formerly supposed. In 1961 when Vanguard I had been in orbit for three years, Hagen pointed out that if its life endured through the full solar cycle of eleven years, accurate estimates would be possible of the effect of atmospheric density upon drag and the satellite's length of life.¹⁸ Although the mercury cell batteries ceased to function in June 1958, the solar cells continued to supply enough power to transmit signals to the Minitrack stations until 1965; thereafter optical tracking still permitted observation of orbital decay.¹⁹ The probabilities are that the tiny object will remain in orbit for another 240 years.

With the highest apogee attained by any IGY satellite, Vanguard I achieved "a highly useful orbit," as the IGY summary report noted. Unlike the cylinder-shaped Explorer satellites, its spherical configuration saved it from tumbling and from developing propeller-like motions which hampered or prevented precision tracking. "The accelerations of 1958 Beta 2 correlate very well with occurrence of solar flares and the radio emission from the sun, and also show the 27-day solar revolution. This correlation, discovered by Luigi G. Jacchia, an eminent mathematician at the Smithsonian Astrophysical Observatory, is interpreted as arising from the heating of the atmosphere by solar radiation, causing the atmosphere to expand, thus increasing the density at high altitudes. Jacchia also discovered a bulging of the atmosphere, apparently from radiation heating, wherein the 600-km density level rises to about 950 km. The bulge follows the sub-solar point by approximately two hours." While 1958 Beta 2 was not the only American satellite to lend itself to calculation of a precise orbit, it furnished the material for a score of learned papers which like that of Jacchia, presented to the world new scientific knowledge.²⁰

Hagen declared with justifiable pride that Vanguard I also contributed "firsts in the space program" by proving the effectiveness of solar cells as a source of power and by revealing "the peculiar and operationally annoying after-burning of solid propellant rockets." And, thanks to calibration of the crystal-controlled radio-frequency oscillator as a function of temperature, the tiny bird equipped only with two transmitters and two thermistors supplemented the data that came from the Sputniks and Explorer I and III about the extreme of heat and cold encountered under various conditions in a satellite or space vehicle.²¹

While the Academy's Technical Panel, Army and JPL scientists, and the Vanguard team were appraising the results of the launchings undertaken during the first half of 1958, the administrative arrangements under which the satellite program operated underwent change. In February, the Department of Defense transferred the direction of its share from the Assistant Secretary for Research and Engineering to the Advanced Research Projects Agency, and in April, when the bill to create the new civilian space agency came before Congress, the National Academy, in turn, prepared to adopt a somewhat different regime for pursuing research in space. During the preceding December, members of the TPESP had drafted a report to the National Committee recommending a long-term plan, calling first for experiments adapted to vehicles already under development, progressing step by step to "planetary and interplanetary investigations," and culminating in "manned space flight." The USNC executive committee had approved the proposals in January, and the 11 April 1958 issue of Science published them. Two months later, President Bronk's appointment of a Space Science Board, with Lloyd Berkner as chairman, to take charge of future planning, relieved the panel of one of its major responsibilities. The Working Group on Tracking and Computation and the WGII had already held their last meetings. The panel, after its session on 17 July, saw its own usefulness diminishing to the vanishing point, not only because passage of the National Aeronautics and Space Act on 29 July meant that NASA would soon set up its own scientific advisory staff, but also because impending changes in IGY management were likely sharply to reduce panel activities in channeling information to CSAGI.

At the CSAGI meeting in Moscow in August, the international committee announced that the IGY would run till 1960, but after 1958 in somewhat different guise: its official name would become the International Geophysical Cooperation and a body known as the Comité Internationale Geophysique, or CIG, would direct the program. CSAGI would go out of existence at the end of June 1959. Although CIG would devote to some fields of IGY interest less intensive effort than had prevailed during 1957-1958, clearly the satellite program would not suffer, for in October 1958, the International Council of Scientific Unions established a new international Committee on Space Research (COSPAR) to deal with fundamental research in the celestial regions. Since the attempted launchings of two Explorers and one Vanguard satellite had failed during the late summer and fall, the extension of the IGY was especially gratifying to Americans.²²

When NASA took over direction of Project Vanguard and the lunar probes in October 1958, the new agency absorbed most of NRL's Vanguard team and, through a Space Science Section at NASA headquarters, assumed most of the duties of the TPESP's working groups. As the Academy's Space Science Board handled other responsibilities formerly resting upon the panel, the TPESP met only once more, in July 1959, to make a last appraisal of the program. The Army Ballistic Missile Agency meanwhile remained in charge of Explorer development in Huntsville, at JPL, and at the Cape. At the beginning of the International Geophysical Cooperation in January 1959, Project Vanguard, still located physically at NRL, had four vehicles available for satellite flights; ABMA and the Jet Propulsion Laboratory were working to ready the powerful Juno II rocket for launching a 100-pound satellite.²³

When Vanguard II, SLV-4, put 1959 Alpha into orbit on 17 February, it flew the cloud-cover experiment. The sensor system worked well, indicating in considerable detail the variations of the reflected earth radiation received by the satellite, but the data proved difficult to reduce because the satellite developed a large precession that caused it to move erratically, shifting its attitude relative to the earth.²⁴ Although the experimenters were therefore unable to make a complete mapping of the earth's cloud cover, the experience gained from the flight helped in designing and carrying out later meteorological experiments. Three unsuccessful American launching attempts, two Vanguard and one Explorer, followed before Vanguard III, 1959 Eta, began its orbit on 18 September.²⁵ As this was the last of the seven launch vehicles built under Navy aegis for the IGY, and as NASA decided not to commission more, Project Vanguard came to an official end shortly after this flight.²⁶

Equipped with the Allegany Ballistic Laboratory's third-stage rocket with a fiberglass casing and nosecone, Vanguard III rose with a fifty-six pound payload, a weight made possible by the lightness of the fiberglass and by leaving the casing attached to the satellite during orbital flight instead of using a separation device. The twenty-inch sphere had a lower sector made of polished aluminum and an upper of fiberglass with a twenty-six-inch fiberglass tube projecting from it to support a magnetometer; it accommodated also the instruments for the solar x-ray and the Lyman-alpha experiments and the gauges for environmental study. The Lyman-alpha and solar x-ray experiments produced nothing useful because electrons in the Van Allen radiation belt swamped the ionization chambers with particles whose energies exceeded 150 keV. A seventy-day monitoring of temperature recorded changes ranging from about 40°C to -2°C; the average was about 20°C. No meteoritic penetration of the shell occurred, inasmuch as pressure readings remained constant. The impact rate of interplanetary matter, on the other hand, was highly variable, during one brief interval running as high as 1,900 an hour; a preliminary analysis put the influx of cosmic dust impinging upon the earth at about 10,000 tons a day.²⁷

Of the more than 4,200 magnetometer signals received during 1959 Eta's eighty-four day flight, 2,872 were designated as a "prime data" set on the basis of quality and freedom from possible coded time errors. This set permitted charting the magnetic field with greater accuracy than ground measurements provided. The proton magnetometer, moreover, acted as a receiver for "whistler" signals in the 0.4- to l0-kc range and for a few "risers." The whistlers, very low frequency signals, came from dispersed lightning-produced ionospherits; the risers, according to some interpretations, were radiation from trapped particles. These observations enabled analysts to estimate electron densities above the F-peak of the ionosphere, to check theories of whistler propagation, and to study the conditions that allowed propagation of very low frequency signals from the troposphere to the satellite in the whistler mode. Since six periods of magnetic disturbance occurred during the operating life of 1959 Eta, measurements of the effects were attempted, but with generally inconclusive results. Greater disturbance was observable, however, at the northern and southern limits of the inner part of the outer Van Allen radiation belt than at magnetic latitudes greater than 25°.²⁸

The finale of the IGY-IGC satellite program came with the launching of Explorer VII on 13 October 1959. A first Explorer VII had failed in July; eighteen months after the inception of the plan, the so-named "heavier payload" satellite with seventy pounds of instruments for six experiments was at last in orbit. Enormous effort had gone into design of the multiple package. As early as April 1958 representatives from the Army Ballistic Missile Agency had met with NRL experts in order, in Roger Easton's phrase, "to permit ABMA to learn as much about satellites as possible in the least possible time." As the heavily laden bird was to accommodate a 20-mc transmitter as well as two 108-mc transmitters, the layout had posed "a stiff problem" in arranging the telemetering equipment and the complex scientific instrumentation. The Academy's panel, deviating from its earlier decision to sponsor no new experiments for IGY-IGC flights, had requested the inclusion of instruments designed by Hermann LaGow of NRL to detect, by means of cadmium-sulphide photosensitive cells, micrometeoroid erosion and penetration. So the second Explorer VII²⁹ carried the NRL solar x-ray, Lyman-alpha, and micrometeor detection instruments, an elaboration of Van Allen's and Ludwig's earlier cosmic radiation apparatus, the equipment for Pomerantz's and Groetzinger's heavy nuclei experiment, and, sixth, Suomi's sensors for measurement of the earth's radiation balance which, after the failure of the Vanguard SLV-6 launching in June, were redesigned to fit into the Explorer package.³⁰

The results obtained from several of the experiments were disappointing. Again Friedman's ion chambers were flooded by radiation electrons. This time, however, by plotting the latitude, longitude, and altitude of the points at which the saturation occurred, it was possible to identify trapped radiation as the cause and to plan an experiment to be flown in an orbit that would not enter the radiation belts. Carried out in June 1960, that scheme successfully recorded ultraviolet and solar x-ray radiation from a solar flare during its onset and development. In the micrometeoroid detection experiment in Explorer VII, 1959 Iota, one of the three Cds cells was damaged and desensitized during the launching; another, designed primarily for calibration of the sunlight penetrating it, was relatively insensitive; and the signals received from the third cell were of a character that precluded reducing the data to satisfactory form. For a time, defeat also threatened the acquisition of usable readings of the flux of heavy primary cosmic ray nuclei, for the ion chamber encountered interference from the solar radiation experiment, and the circuitry associated with one channel early underwent a change in mode of operation. Although the consequent rather fragmentary data were hard to translate, study of recordings made over a six-month period around the world in the northern hemisphere eventually permitted plottings of the integral energy spectrum and of changes in its shape.³¹

The additional information collected about the Van Allen radiation belts, on the other hand, quickly supplemented that assembled from earlier satellites. Signals recorded a number of solar-terrestrial-coupled events-the arrival of solar protons following their acceleration in a solar flare. for example, and a polar cap display marked by increased ionospheric absorption inside the auroral zone. From observations made during a severe geomagnetic storm on 29 November 1959 an hypothesis evolved that, when solar plasma encounters the earth's magnetosphere, a distortion of the magnetic field occurs in fashion that causes particles normally trapped in the outer radiation belt to be "dumped" out of the belt so as to interact with the atmosphere at altitudes below the mirror points and to spread to lower latitudes. The direct correlation shown by Explorer VII between occurrences in the radiation belts and auroral activity in the high atmosphere supported the "dumping" theory. The delineation of zones of geomagnetically trapped, high-energy particles, to be sure, left many unknowns, but it widened knowledge of the "population identity" and energy spectrum of the trapped particles. And it gave clues to the mechanism of trapping, helped explain the behavior of the belts during solar and interplanetary disturbances, and clarified the relationships between terrestrial manifestations of solar disturbances and activity in the belts.³²

The measurements of the earth's radiation balance were also significant. albeit less complete than Suomi hoped for. Even so, with as many as 432,000 separate measurements made in a single month, the accumulation gave meteorologists more than they could work through in the next seven years. As Explorer VII carried no storage unit, data reduction was difficult. Scientists first undertook analysis of the earth's radiation losses, leaving till later the computation of the gains from the sun in the earth's heat budget; the findings on gains were only beginning to emerge at the end of 1965. As redesigned for Explorer VII, the essential instrumentation for this experiment consisted of glass-coated bead thermistors making contact with the sensors, two spheres. and four hemispherical bolometers, that is, electrical devices that register minute quantities of radiant heat. The spheres, one black-coated and one fitted with a shade to protect it from direct sunlight, were mounted on the spin axis of the satellite. The four bolometers were placed in the satellite's equatorial plane close to, but thermally insulated from, a mirror so coated as to have high resistance in the ultraviolet. One hemisphere, coated white, was more sensitive to terrestrial than to solar radiation; two black-coated hemispheres responded about equally to solar and terrestrial radiation, while the fourth, coated with gold, responded chiefly to solar.

Although the lack of a data storage unit prevented a synoptic mapping of fields of radiation outgoing from the earth, study of the measurements indicated that patterns of a large-scale outward flux of radiation exist and are related to large-scale features of the weather; cloud cover and circulation patterns control the earth's loss of radiation; and within the atmosphere a pronounced vertical divergence of net long-wave radiation occurs. Further study permitted meteorologists in the course of time to estimate the heating and cooling of the atmosphere and to make a beginning on gauging the role of differential cooling in supplying atmospheric energy.³³

At the official termination of the IGC on 31 December 1959, some three weeks after Explorer VII had ceased to relay signals to the earth, reduction of the telemetered data had not progressed far; meaningful interpretations of all the findings would take years. Indeed, in 1967 experimenters would still be examining the results of IGY-IGC satellite flights. But by 1960 the richness of the scientific harvest from the satellite program was already manifest to the scientific world. "Space science," a little ruefully defined by an academician as "any scientific inquiry that NASA will pay for," had come into its own.

(GRAPHICS MISSING: An ad hoc committee met at the Boulder Laboratories of the National Bureau of Standards, Boulder, Colorado, on 16 December 1959 to discuss continued operation of the U.S. World Data Centers.)