At the Dawn of the Space Age

By George W. Swenson, Jr.

In October 1957 the scientific world was finishing preparations for the International Geophysical Year (IGY). The radio-engineering community had under way a number of investigations of the upper atmosphere, the ionosphere in particular, the latter involving mainly bottom-side sounding with ionosondes, long-range high-frequency-propagation tests, and trans-ionospheric-propagation studies, utilizing noise-like radio radiations from cosmic sources. The US Naval Research Laboratory was planning to launch into orbit, sometime during the 18-month IGY, one or more "grapefruit-sized" earth satellites, which were expected to be the first artificial earth satellites in history. A number of volunteer groups, mainly at universities, were planning to track these satellites, and the Navy had designed a network of "Minitrack" interferometers, with which to produce the official orbits and ephemerides. The launch schedules were still very tentative as of the beginning of the IGY, in October 1957, mainly because of developmental difficulties with the launch vehicles. At the 1957 General Assembly of the International Union of Radio Science (URSI), in Boulder, Colorado, the delegation of the USSR announced that they, too, planned to launch a series of satellites during the IGY, with radio-beacon frequencies chosen especially for ionospheric research. Interested parties, including amateur-radio operators, were invited to observe on the published frequencies. At this point in history, the western world was rather skeptical of Soviet propaganda, so little notice was taken of this announcement.

At Illinois, we had ambitions to build a large radio telescope [1,2] for fundamental observations in astronomy. In this connection, we were visited by Dr. Joseph Pawsey, a pioneer in radio astronomy, on the eve of IGY. I had spent some time with him and his colleagues at his laboratory in Sydney, Australia, trying to learn something about radio telescopes. The night before the official starting date, the event was heralded by an intense geomagnetic storm, which produced a splendid display of Aurora Borealis. Pawsey and several Illinois people repaired to a cornfield, outside of town, to admire the sight, and to rejoice that the IGY should have started so spectacularly.

"What satellite?"

A day later, a dinner at the home of Prof. George McVittie, Head of the Astronomy Department, was attended by Pawsey, Prof. Edward Jordan, Head of Electrical Engineering, and Prof. Frederick Seitz, Head of Physics. Well into the meal the phone rang, and the University's public relations officer wanted to know our collective reaction to the "news of the satellite." "What satellite?" "The Soviets have just announced that they've placed a satellite into earth orbit. It's called Sputnik I." That's all he knew, but it produced in the dining room a Pandemonium of excited speculation. A quick call to our contacts at the Naval Research Lab found them in their office at 9:30 pm, as excited as we were. They thought the frequency was 40.002 MHz, but they hadn't heard it yet. Special news broadcasts from many stations repeated various versions of the breaking story.

Several of us raced to the campus, where we found a suitable radio receiver, and set up a dipole antenna on the roof of the Electrical Engineering building. Hopefully, we wated and listened. After perhaps an hour, we heard and tape recorded a faint, beeping signal, whose frequency increased slowly for a while, then slowly decreased as it faded into the noise. The Doppler effect convinced us that it was indeed the satellite.

I rushed to the campus observatory, where an excited group of graduate students and local radio hams was gathering. With their help, a 40 MHz receiver was secured, along with various scraps of television twin-lead, a WWV time-signal receiver, and a couple of old Esterline-Angus chart recorders. We hastily erected, in the back yard of the observatory, an interferometer on a north-south horizontal baseline, comprising two half-wave folded dipoles of twin-lead, 5.45 wavelengths apart, supported by a miscellany of mop and broom handles, two-by-fours, and a stepladder. Then we settled down to wait, with volunteer students manning the instruments.

At 6:00 am, after a sleepless night, the entire Astronomy faculty (all four of us) drove up to Yerkes Observatory, in southern Wisconsin, for the regular meeting of the neighborhood astronomy association. Returning to Urbana that evening, we found, to our surprise and delight, that the students had observed several passes of the satellite, the chart records indicating much complicated variation of signal strength with time. As we were merely recording the amplitude of the signal from the interferometer, there were no Doppler-shift data; however, by careful examination of the charts, we could identify the nulls in the interference pattern of the antenna system. These provided the data for orbital computation. In addition, there were other nulls and peaks in the signal strength, apparently unrelated to the antenna pattern. We concluded that these must be caused by Faraday rotation of the plane of polarization of the wave traversing the magneto-ionic medium, the ionosphere.

Tracking Sputnik

Prof. Ivan King immediately set to work to write an orbital-computation program for the University's home-developed ILLIAC computer. The interference nulls provided sufficient data to determine the elements of an elliptical orbit, which was quickly produced from the first few days' observations. The single north-south interferometer gave data ill-conditioned for determination of certain orbital parameters so, on King's urging, we moved our operation to a radio-direction-finding research site, operated by Prof. Ed Hayden, at a rural site (Monticello Road) with more space for antennas. There, we built interferometers for both 40 and 20 MHz (as we'd learned that the Sputniks transmitted on the lower frequency, too), for both north-south and east-west baselines. The orbital calculations continued with better data, and we were soon able to publish what I believe to be the first public ephemeris [3] for Sputnik I. Later, these and subsequent data of ours were used by Robert Jastrow, in producing NASA's definitive orbit for Sputnik I.

Ed Hayden and I compared our charts of signal amplitude versus time, and conjectured that these data might be used in ionospheric research. The situation appeared pregnant with possibilities. For the first time, a source existed which transmitted through the ionized regions of the atmosphere monochromatic, distinctly-polarized, radio-wavelength radiation of known strength. Exclusive of the variation produced by the known receiving-antenna patterns, there were on the charts the quasi-sinusoidal oscillations caused by the Faraday rotation of the wave as it was detected by a linear antenna. With a pair of orthogonal antennas feeding separate receivers, it was fairly simple to follow the rotation, and this raised the possibility of determining the integrated electron content along the propagation path, provided we could predict the geomagnetic field along the path.

Also on the charts were other signal-strength variations: these looked like random noise, sometimes so strong as to obscure completely the Faraday-rotation variations, and at other times, not discernible at all. We called this noise "scintillation," by analogy with similar effects in both radio and optical astronomy. The effect was seen only when the satellite was to the north of us, or overhead, and sometimes the transition to or from smooth variation was abrupt, occurring within a few seconds. We were reminded of the "spread-F" phenomenon of bottom-side ionosphere sounding, wherein echoes from the F-region are sometimes spread out in height, as if the ionization occurred in vertically elongated patches. Here, then, was a possible means of studying the irregular structure of the ionosphere in great detail.

As we contemplated these things, we continued to record satellite signals and compute orbits, improving our instrumentation as time and energy permitted. All the effort was voluntary, as there was no funding. After about a month, the signals from Sputnik I failed, probably due to battery exhaustion. The Soviets then launched Sputnik II, this time with a live dog, Laika, aboard. We never heard so much as a yelp out of her, but the radios beeped away, giving us more data to examine. Eventually, Sputnik III appeared, the whole series continuing for a span of 30 months.

Benefiting from increased funding

These research opportunities seemed important, possibly a once-in-a-lifetime chance to make such observations. Others thought so, too, apparently. The official USA participation in the IGY was organized by the National Research Council (NRC), with funding by the National Science Foundation (NSF). The excitement (panic, even), engendered by the evidence that the USSR wasn't so backward in technology after all, had caused the NSF to increase the IGY funding, specifically to permit exploitation of the Soviet satellites. Our early results had attracted some notice, and one day I got a call from Washington, inviting a proposal. I thought it would be nice to rent a car from the University motor pool, instead of letting the students drive my 1953 Plymouth to the field station, and we needed more chart paper and ink, the Air Force wanted the receivers we'd borrowed from Chanute Air Force Base, and the National Bureau of Standards wanted their Esterline-Angus recorders we'd held long past the promised date of return. I compiled a wish list totaling $16,000, and sent it to Washington, prompting a return phone call. "Are you serious? You can't do anything significant for such a paltry sum." What did I know? I'd never had a funded research project. A revised budget, including technician salary, part-time student help, travel money, and more and better equipment, brought a grant of $62,000 in an astonishingly short time. This was the first of a long series of such grants, first from NRC and later from NASA, when it was established by Congress in response to the Soviet head start in space research.

It wasn't long, though, before the situation began to feel overwhelming. The data were piling up, the student volunteers were drifting back to their primary duties, and there was pressure to get on with the job of designing and building a large radio telescope for the University. Clearly, more-expert and dedicated professional help was needed for the ionosphere/satellite program, and funding was now adequate. Dr. Kung-Chie Yeh joined us from Stanford University, in the Fall of 1958, and his arrival immediately accelerated the analysis of the satellite data. This was the real beginning of the ionosphere research program, which has continued for 36 years. Prof. Yeh was joined a year later by Prof. Chao-Han Liu, and together they produced a large body of theoretical and observational research, many PhDs, and many engineers expert in radio technology. Both are now retired, and both serve in educational leadership positions in Taiwan.

Sputnik I transmitted for exactly one month. During that time many of the ionospheric phenomena mentioned above were observed, piquing the curiosity of many observers throughout the world. Immediately after transmissions ceased, Sputnik II was launched. It proved not to be so useful to us, but shortly thereafter Sputnik III appeared. It transmitted for nearly two years on 20 MHz, providing opportunity to observe seasonal effects and to accumulate statistically significant numbers of observations. These satellites were in high-inclination orbits, covering the entire band of latitudes from plus to minus 65 degrees. This was useful, as it gave good geographical coverage. Sputnik III was in a rather eccentric orbit, so that at times it passed over us above the region of maximum ionization, and at times below. This permitted an approximate determination of the height at which the scintillation-producing irregularities existed. The American satellites, which were launched soon after the first Soviet ones, were in lower-inclination orbits and transmitted at higher frequencies, in the VHF range, so were less suitable for ionosphere investigations. The first exception was Transit 4A, a Navy-navigation satellite launched in June, 1961, which transmitted on 54 MHz in a 67 degree orbit. Prior to that, efforts were made by NASA to provide suitable satellites for ionospheric research; unfortunately, all failed to achieve orbit. So, when it became clear to us from the data that Sputnik III would decay from orbit with no replacement in sight, we thought that extraordinary measures were called for. We were especially anxious to continue our studies of the nighttime scintillation, observed during the earliest days of Sputnik I, and to delineate the boundaries of the regions where it occurred.

Nora-Alice in the night . . .

We learned from Dr. Jules Aarons, of the Air Force's geophysics research organization, that there was a chance to include a scientific payload on one or more of the Discoverer series of satellites, which were being developed for some classified military purposes. These were in near-polar orbit (approximately 80 degrees inclination), so they covered essentially all the earth. There would be no extra money; we'd have to scrape any necessary funds from our yearly NASA grant. The Lockheed company, the Air Force's contractor for the program, would supply us with a box in which to install our beacon transmitter, and would specify other constraints, such as environmental-test specifications, etc. The package would have to be completely self sufficient in power: the Air Force would supply only a trigger signal to initiate operation, after the carrier rocket achieved orbit. The instrument package would remain on the last-stage rocket, which could serve as a counterpoise for the furlable antenna of the beacon. No, they couldn't supply the dimensions or a drawing of the rocket: that was classified information. We'd have to guess at that.

On our project staff was William W. Cochran, an electronics engineer who had been responsible for building and operating our field stations for a couple of years. He'd demonstrated exceptional skill with transistor circuits. Bill and I decided we could build a couple of satellite payloads, and we started to experiment with circuits and various kinds of batteries. We were concerned by our lack of knowledge of the rocket configuration. How were we to predict the right antenna-matching parameters without it? One day I stopped in at the office of our department head, Ed Jordan, and saw a small plastic model of the last-stage rocket on his desk, left by some Lockheed recruiter. I borrowed it. Of course, it had no dimensions. However, I happened to see in the Proceedings of the IRE a recruiting advertisement by Lockheed, which had a picture of the rocket. Standing next to it was a man, whom I recognized as a former student. A phone call to him determined his height, somewhat to his puzzlement, I'm sure. We had our dimensions.

We were allowed ten pounds total-payload weight, including antenna and batteries and enclosure. We wanted to transmit on 20 MHz, the same frequency as the Sputniks, so we needed a long antenna, on the order of 3.75 meters, to get the best possible efficiency. It had to be confined to the Lockheed-supplied box during launch, and to erect itself upon signal after orbital injection. The Air Force suggested a design for a pin-puller, an explosively activated latch which could release a spool, upon which the antenna could be rolled during the launch phase. The antenna itself was a steel tape, with a lengthwise crimp to give it some stiffness. We just walked down to the neighborhood hardware store and bought a carpenter's tape measure. (When an Air Force engineer asked why our antenna had inch marks, I told him it was to measure the mean-free path in the ionosphere.)

 

About six pounds of mercury cells supplied enough energy to power the transmitter for one month. The transmitter had two stages, was crystal-controlled, and contained five transistors. Its output was 100 milliwatts.

In order to design the antenna-matching circuit, we needed to measure the antenna impedance when it was on the rocket, or on a reasonable facsimile thereof. We built a frill-scale "rocket" of wire mesh, on the roof of the Electrical Engineering building, and tied the tape measure to a bamboo pole to hold it erect. In orbit, with zero gravity, we trusted, the natural stiffness of the steel tape would hold the antenna in the right position. Environmental testing was performed, as a courtesy, by the Magnavox corporation, in their Urbana, Illinois, plant, just across town. We had no difficulty with vibration, acceleration, or thermal specifications.

As the Air Force was to abandon the rocket after activating our transmitter, we'd be on our own for tracking data, so we reactivated our interferometers and our orbit-computation programs. Our aim was to map the geographical incidence of scintillation, and we solicited cooperation from other observers to whom we would supply orbital data. Researchers in Australia, New Zealand, Wales, and California responded, and we had, in addition, our own stations at Urbana and at Baker Lake, in the Northwest Territories of Canada.

The payload needed a name, of course. We decided on "Nora-Alice" after the heroine of Walt Kelly's ode to the IGY, as recited by Pogo:

0, roar a roar for Nora, 
Nora-Alice in the night, 
For she has seen Aurora Borealis burning bright.
etc...

A sidelight on the satellite

Nora-Alice 1 performed well, producing strong signals at all stations, from its 100 mW transmitter, for exactly one month. So did Nora-Alice 2, which transmitted for three months, starting a month later. The second payload had two frequencies, 20 and 40 MHz, and some more-sophisticated features. Good data were obtained from all participants, and were duly reported [4]. Meantime, observations of other satellites resulted in studies of the total-electron content of the atmosphere as it depended upon geography, diurnal and seasonal effects, and solar activity [5].

As a coda to the story of Nora-Alice, we might claim a successful space experiment, with two satellite payloads managed, designed, and constructed by a half-dozen people, some of them students working part time, at a cost of a few thousand dollars. The success of this project prompted the Air Force to ask for four more payloads, transmitting relatively high power, on 10 and 20 MHz. These were built, as a private venture, by the writer and his colleague, Kwang-Shi Yang, using the same low-cost methods. All performed well.

There's a sidelight to this story. Bill Cochran, while he was designing satellite transmitters and receivers, was also moonlighting for wildlife biologists of the Illinois Natural History Survey. They had the idea that small radio transmitters, attached to rabbits, might allow them to track the animals into their burrows, and establish their activity patterns. It worked. Success led to a suggestion from an ornithologist that perhaps birds could be tracked in flight. A mallard duck was sent over from the research station on the Illinois River. At our Urbana satellite-monitoring station, a tiny transistor oscillator was strapped around the bird's breast, by a metal band, which also doubled as the oscillator tank circuit and antenna. The duck was disoriented from a week's captivity, and sat calmly on the workbench while its signal was tuned in on the receiver. As it breathed quietly, the metal band periodically distorted and pulled the frequency, causing a varying beat note from the receiver. An audio-frequency discriminator was available, so the frequency variations could be recorded on a strip chart. When the bird was released into the air, its breathing was recorded on the chart, and in addition, a higher-frequency modulation representing its wing beats. The biologists informed us that we'd made the first measurements of the relation between the wing beats and the breathing of a flying bird, thus answering a long-standing question.

Bill Cochran followed these successes with a long career in radio-telemetry applications in wildlife research. After leaving our program, he developed wildlife radio tracking to a high degree of effectiveness, founding the company that pioneered the business, AVM Instruments, Inc. Most of the equipment one sees on television programs on wildlife research can be recognized as his designs. He recently retired as Senior Scientist from the Illinois Natural History Survey.

References

1. G. W. Swenson, Jr., and Y. T. Lo, "The University of Illinois radio telescope,"IRE Transactions on Antennas and Propagation, AP-9, January, 1961, pp. 10-16.

2. G. W. Swenson, Jr., "Reminiscences: The Illinois 400-foot radio telescope,"IEEE Antennas and Propagation Society Newsletter, 28, No. 6, December, 1986, pp. 12-16.

3. I. R. King, G. C. McVittie, G. W. Swenson, Jr., and S. P. Wyatt, Jr., "Further observations of the first satellite," Nature, No. 4593, November 9, 1957, p. 943.

4. K. C. Yeh and G. W. Swenson, Jr., "F-region irregularities studied by scintillation of signals from satellites," Radio Science, 68-D, August, 1964, pp. 881-894.

5. K. C. Yeh and G. W. Swenson, Jr., "Ionospheric electron content and its variations deduced from satellite observations," J. Geophys. Research, 66,April, 1961, pp. 1061-1067.

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Copyright (c) 1994 Institute of Electrical and Electronics Engineers. Reprinted from the IEEE Antennas and Propagation Magazine,>vol. 36, no. 2, pp.32-35, April 1994.
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