On October 4, 1957, shortly after midnight local time, the treeless steppe near Tyura-Tam in central Kazakhstan lit up as the rocket motors of a converted ICBM pushed its way into the night sky. After 324.5 seconds of flight, a compressed air release mechanism separated a small payload from the rocket booster sending it on an elliptical path around our planet. This was the dawn of the space age. The former Soviet Union had successfully placed the first man-made object into orbit. Sputnik I, as the world came to know the first artificial earth satellite, was not only an important scientific and technical achievement but also an important historical milestone that marked the beginning of human space exploration and shaped many social and political events over the remainder of the 20th century.
Because the role of the worldwide Amateur Radio community in Sputnik’s launch was significant, it is appropriate, on the 50th anniversary of this event, to review this episode in ham history and to explore some of the details of the radio technology on board the first satellite.
Leading Up To Sputnik
In the early 1950s, a group of American and European scientists proposed an international cooperative research program to study the earth’s outer atmosphere. A period during 1957-1958 was designated for this project and was referred to as the International Geophysical Year (IGY). This time span was, in part, selected because it was the predicted peak of solar cycle number 19. As planning for the program developed, it was suggested that the launch of a low earth orbit scientific satellite should be part of the program. Given the political tone of the times, the military and propaganda implications of this proposal were obvious to both American and Soviet authorities. What began as a cooperative scientific project quickly became a matter of international prestige and strategic position. It was, after all, the height of the Cold War.
In the US, the effort to launch a scientific satellite became Project Vanguard directed by the Naval Research Laboratory (NRL). The American design team selected 108 MHz as a beacon frequency for tracking their planned satellite and developed an elaborate tracking system, called Minitrack. The NRL extended an invitation to US Amateur Radio operators to participate in the Minitrack system through Project Moonbeam. In the July 1956 issue of QST, Roger Easton, NRL director, gave a detailed description of this project 1 . Over the following year, five additional articles appeared in QST to further outline the role of the amateur community in the IGY satellite launch 2 , 3 , 4 , 5 , 6 . Several clubs across the US set up elaborate Moonbeam tracking stations, some of which included large ground-mounted antenna arrays. Amateur astronomers were invited to participate through Project Moonwatch. The details of the Minitrack system constitute an interesting history in their own right. 7
Meanwhile, Russian scientists were also working in earnest to put their own satellite in orbit. The Soviet Special Design Bureau No. 1 (OKB-1) was led by the legendary rocket designer, Sergei P. Korolev. His initial plan was to place a complex 3000 lb scientific observatory into orbit with his first attempt using a converted R7 ballistic missile that was originally designed to deliver atomic warheads. However, thrust tests of the R7 launch vehicle were disappointing and with the urging of his deputy M. K. Tikhonravov the original plan was scrapped in favor of a configuration designated PS-1, a Russian abbreviation for “simple satellite.” This design consisted of little more than an aluminum enclosure, and a battery powered transmitter. Korolev and his team also took a far more pragmatic approach to tracking their satellite than did the Americans. They realized that the geography of the USSR spanned 11 time zones many of which were populated by active Amateur Radio operators. It was decided to exploit this resource and construct the satellite radio transmitter around frequencies that amateurs across the Soviet Union could monitor using their existing equipment. As early as June 1957, the Russian language magazine Radio, an official Soviet publication widely read by Russian amateurs, began publishing a series of articles that described the telemetry system of a planned satellite and its intended downlink frequencies on 20 and 40 MHz 8 . [After the launch of Sputnik I, an English translation of this article was published in QST.]
Even earlier articles had given instructions for converting the popular Soviet military surplus A7A and A7B transceivers for 20 MHz operation. 9 Many other preparations were undertaken in the months leading up to October 1957 that formalized the plans for amateurs in the USSR to track Sputnik I. A network of at least 28 radio clubs along latitude 55 was equipped for tracking by the Soviet Academy of Science and the Ministry of Defense. The chairmen of many radio clubs were taken to Moscow to learn satellite tracking techniques. The Institute of Radio Technology flew a duplicate of the Sputnik 20 MHZ transmitter by airplane to allow receiving practice on the ground. In addition, the ban on communicating with the amateurs in the West was lifted. The preparation of the Russian Amateur Radio community for the launch and tracking of Sputnik I has been researched extensively by the British historian Rip Bulkeley 10 . He concluded that, in the months before launch, sufficient information was available that would have allowed the West to be far more informed and prepared for such an event. As it turned out, however, the American scientific and military establishments were quite unprepared for the launch of a Russian spacecraft.
The First Satellite
The physical structure of Sputnik I was based on two hemispherical aluminum casings, 58 cm in diameter, that bolted together along their circumference over an o-ring seal. This created an air tight enclosure that contained two radio transmitters, three silver-zinc batteries, and a simple temperature and pressure sensing system. Thermal control of the satellite’s interior was a significant concern for Korolev’s team because of the heat generated by the transmitters. A combination of thermal shields and fan-driven ventilation was employed to manage this problem. These shields and the other internal components are visible in an exploded view of the satellite shown in Figure 2. The sealed casing was pressurized to 1.3 atm (19.1 psia) with dry nitrogen gas and a thermocouple-controlled ventilation fan, set to activate at 30 degrees C, circulated the gas around the transmitter unit and through a space between the thermal shield and the craft’s outer casing to allow heat dissipation. Pressurization of the casing served a second purpose in Sputnik’s design. A barometric relay was set to alter the telemetry signal if the internal pressure fell below 0.35 atm. This system was intended to detect meteorite penetration of the casing. The telemetry was also configured to indicate internal temperatures above 50 degrees C or below 0 degrees C.
The radios on board Sputnik are described as D-200 units and were designed by a member of Korolev’s design team named V. I. Lappo. 11 The meaning of the D-200 designation is unclear and our research thus far has failed to produce a schematic of this transmitter, but Tikhonravov, in a presentation before the 24th International Astronautical Congress in 1973, characterized the transmitters as “vacuum valve-type” with a power of 1 watt. 12 Figure 3 shows the transmitter unit mounted adjacent to the antenna connections in the front casing half. One transmitter operated on a frequency of 20.005 MHz (megacycles in 1957) and the other on 40.002 MHz. The choice of these frequencies not only allowed reception by amateurs using existing equipment but also enabled a receiver set at exactly 20 or 40 MHz to produce an audio tone plus or minus the Doppler shift without ever going through zero Hz. This insured that the telemetry was audible throughout an entire pass without additional tuning of the receiver.
The telemetry mode consisted of modulation of the carrier frequency and what might be characterized as a rudimentary form of pulse width modulation. Tikhonravov described the telemetry as “a change in the frequency of the telegraphic signals and the relationship between the duration of the signals and the intervening pauses.” The transmitter was keyed to generate signals 0.2 to 0.6 seconds in length. A commutator system keyed the two transmitters alternately and encoded whether the pressure and temperature limits had been exceeded. The transmitter units were powered by two silver-zinc batteries that made up 61 percent of the craft’s 83.6 kg mass. The location of the batteries and their support frame mounted in the front half of the casing is shown in Figure 4. A third battery provided power to the ventilation fan and the commutator system.
Sputnik’s antennas consisted of four whips attached to the aluminum enclosure through insulators that were spaced symmetrically around the circumference of the spherical casing. These elements extending at a 70 degree angle to each other and gave the satellite its iconic shape. The antenna configuration was a compromise between simplicity, the space constraints of the launch vehicle and function. During launch, the antenna elements were compressed against the side of the rocket at an angle of 45 degrees and were held in place by clips and a conical shroud that protected the satellite. Only part of the antenna was covered by the shroud, leaving a significant portion of the element exposed during its trip to orbit. When the satellite reached orbital altitude and velocity it was separated from the launch vehicle and the elements were freed to assume their 70 degree angle of separation (Figure 5).
The antennas are described as matched pairs, one 2.4 meters and the other 2.9 meters in length. The available literature gives no information on the electrical characteristics of the antenna system but it is probably safe to assume that they were some variation of a center-fed dipole with the longer pair radiating the 20 MHz (14 meter) signal and the shorter pair set up for 40 MHz or 7.5 meters. Figure 6 shows technicians attaching two of these elements to their angled connectors during assembly. Based on our assumption about the antenna configuration, we can use modern modeling software to analyze a dipole with of 5.8 meters in total length, angled to 70 degrees at the center where it is fed by a single 20 MHz source.
NEC-Win Plus™ shows that such a “V-dipole” retains most of the classic bi-lobed radiation pattern of a conventional dipole with significant, symmetrical nulls oriented perpendicular to the axis of the “V.” This pattern fits well with the historical data that indicates that nulls in the satellite’s radiated signal were easily detected and used to monitor the spin rate of the craft. 13 Figure 7 shows some of the original recordings that clearly demonstrate spin-fading as the Sputnik I tumbled along its orbit. In contrast to the stable space platforms of today, Sputnik I had no mechanism for spin-stabilization that would maintain its antennas in any particular orientation relative to a receiving station on earth.
Sputnik I was launched on a heading of 035 degrees from Tyura-Tam, on a trajectory that placed the craft into an orbit with an apogee of 939 km (583 miles), a perigee of 215 km (133 miles) and an eccentricity of 0.5201. This orbit was inclined at an angle of 65.1 degrees relative to the earth’s equator and gave the craft an orbital period of 96 min. This orbital configuration is quite different from that of the present-day LEOs (low-Earth-orbit satellites) active in the amateur service, which have a more circular orbit, a higher perigee and a greater inclination.
Using the Sputnik I orbital parameters listed in the National Space Science Data Center Master Catalog, modern software can be used to reconstruct the orbital path graphically. Figure 8 demonstrates such a reconstruction using Nova for Windows. Three consecutive north-south passes over North America are shown and demonstrate that the satellite’s “footprint” covered the majority of the US. Given the political atmosphere of the Cold War, one can easily see why Sputnik’s launch created such concern.
The World Hears Sputnik I
Soon after the earth’s first artificial satellite achieved orbit, the signal from its transmitter was heard by down-range monitoring stations on the Kamchatka peninsula. When Korolev received this report, he discouraged his team from celebrating until the signal was reacquired from the southwest confirming that the craft had completed its first orbit. On what was likely the satellite’s second orbit, the telemetry was picked up by the BBC monitoring station at Tatsfield, England just southeast of London. This facility, which has a fascinating history as a listening post and played an important role in frustrating German efforts to use BBC transmissions to guide bombing raids during WWII, is credited with being the first to hear Sputnik’s signal outside of the USSR. At almost the same time, American military instillations in West Germany heard and recorded the signal.
America was stunned by the successful Russian launch. Across the US, the level of surprise was displayed in banner headlines and the anxious reaction of public officials 14 . All this was made worse by the inability to adequately track Sputnik over the first few days of its flight. Having assumed incorrectly that any satellite launched during the IGY would use the 108 MHz tracking frequency, the American Minitrack system was initially of no value for tracking Sputnik I. Almost immediately after the launch was announced, a call was issued to US amateur operators via WIAW to provide monitoring data that would allow officials to track the satellite while the Minitrack stations were being reconfigured for the HF spectrum. The response of the amateur community was both enthusiastic and productive. Hams across the country provided signal observations that were passed on to scientists and government agencies for analysis of the orbit and clues to the physics of the outer atmosphere. The breadth of these activities is recorded in the December 1957 issue of QST and the involvement brought praise from NRL officials.
Radio Station WWV also played a role in early space flight. There are numerous recollections among ham operators who were active in 1957 that radio station WWV suspended its 20 MHz time signal transmissions during some night-time passes of the satellite in order to avoid interference with the 20.005 MHz telemetry signal. Roy Welch, W0SL (then W5SLL) recalls this to be the case on October 7 when he recorded the Sputnik I signal during a pass over the North America. 15 This recording can be heard at the AMSAT link listed at the end of this article. 16
An exact record of how many times and for how long the WWV may have turned off its 20 MHz broadcast while Sputnik I was in orbit has been difficult to document. According to Michael Lombardi, KB0VOI, a time and frequency metrologist at the National Institute of Standards and Technology and a WWV historian, the log books for WWV operations during 1957 no longer exist making it difficult to verify that the 20 MHz broadcasts were stopped. However, Lombardi notes that during the Sputnik era, the WWV schedule included a silent period during which transmissions were interrupted every hour for approximately four minutes. These periods began about 45 minutes past the hour 17 . Also well-documented is that during many passes, the WWV signal remained on and was recorded in tandem with the Sputnik telemetry beacon. This provided a stable time reference from which the Doppler shift of the satellite’s signal and its orbital parameters could be calculated 18 .
It is interesting to note that one of the laboratories engaged in the analysis of the Sputnik I signal would, over the following decades, expand these same techniques to develop the concept of satellite navigation 19 . The WWV broadcast played another important role during the brief life of Sputnik I by providing a means for studying atmospheric ionization. Electrical engineers at the Ohio State University Radio Observatory noted bursts of the WWV 20 MHz signal at times when the station, then located 330 miles away in Beltsville, Maryland, was normally very weak or could not be heard at all at their location in Columbus. Careful analysis of this phenomenon showed that it correlated well with each pass of Sputnik I over North America. Building on what was already known about meteor scatter propagation; they recognized that the WWV signal bursts were due to ionization of the F2 layer by the spacecraft. 20
It is difficult for us in the media-saturated 21st Century to appreciate how completely the launch of Sputnik I captured the world’s attention. The reverberations of this event were felt across the world but nowhere more profoundly than in the US where it resulted in the reordering of national research and educational priorities, the re-examination of military needs, and the establishment of a civilian space agency. It is fitting that Amateur Radio played a role in this chapter of history. The ham radio legacy of experimentation and pushing the boundaries of electronic communication is clearly visible in the Sputnik I story.
It is hoped that this review honors those Amateur Radio operators, of all nations, who were involved in these events either directly or who simply scrambled to catch a bit of telemetry in their headphones. It is further hoped that the current generation of hams will be inspired to build on this legacy and will continue to “advance the radio art.”
Oleg P. Odinets, RA3DNC, lives in the ancient Russian city of Kashira, located on the river Oka just south of Moscow. He is a communications engineer for the Moscow railway. Oleg has been a ham since 1981 and currently holds a 1st category license. He is active in DXing and contesting.
Ralph Didlake, KK5PM, lives in Madison, Mississippi and holds an Amateur Extra class license. First licensed in 1994, he enjoys DX and refurbishing old equipment. He is a vascular surgeon in private practice.
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2 Simas VR. A low-noise preamplifier for satellite tracking. QST. 1956 Dec; 40(12):42.
3 Easton RL. Calibration of the Mark II Minitrack. QST. 1957 Apr; 41(4):42.
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6 Pickering WH. Project Moonbeam, The radio amateur and the IGY satellite. QST. 1957 Nov; 41(11):15.
7 Berkner LV, editor The Minitrack Mark II radio tracking system. In Annals of the International Geophysical Year 384-410 Permagon Press;1958 New York.
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11 Siddiqi A. Sputnik and the Soviet space challenge. Gainsville: University Press of Florida; 2003, p 163
12 Tikhonravov MK. The creation of the first artificial earth satellite: some historical details. JBIS. 1994; 47(5): 191-194.
13 Warwick JW. Decay of Spin in Sputnik I. Planet. Space Sci. 1959; 1:43-49.
14 Dickson P. Sputnik, the shock of the century. New York: Walker & Co.; 2001.
15 Personal communication
17 U.S Department of Commerce, National Bureau of Standards. Standard frequencies and time signals: WWV and WWVH. Letter Circular LC/023; June, 1956.
18 Burt EGC. The computation of orbit parameters from interferometer and Doppler data. Proc Roy Soc. Series A, Mathematical and physical Science,1958 Oct;248(1252) 48-55.
19 Guier WH, Weiffenbach GC. Genesis of satellite navigation. Johns Hopkins APL Technical Digest. 1997;18(2):178-181.
20 Kraus JD. Detection of Sputniks I and II by CW reflection. Proc IRE. 1958;46:611-612.