The ground network

It was agreed from the beginning that the Vanguard project would compute the orbits for the Deal satellites, as they had already been preparing to do for the Vanguard satellites. After the Deal project was approved in November 1957, tracking data from the JPL Microlock stations were added to the mix. All tracking data were sent to the IBM 704 computer in the Vanguard Computing Center by high-speed wire and radio teletype circuits.

Optical tracking stations An optical tracking system was established as a compo­nent of the U. S. Vanguard program. It drew upon two cooperating components, an acquisition group (known by the name Moonwatch) and a precision tracking group. The acquisition group drew heavily upon the services of amateur astronomers to pro­vide coarse tracking information. The precision tracking component, conceived and overseen by Fred L. Whipple at the Smithsonian Astrophysical Observatory at Cam­bridge, Massachusetts, used high-precision telescopic Baker-Nunn cameras having an unusually large aperture that were developed for the purpose.

Although the camera development was beset by several problems, the network was ready in time to support the Explorer and Vanguard programs. Precision op­tical tracking stations were located at Jupiter, Florida; Organ Pass, New Mexico; Olifansfontein, Union of South Africa; Cadiz, Spain; Mitaka, Japan; Naini Tal, In­dia; Arequipa, Peru; Shiraz, Iran; Curacao, Netherlands West Indies; Villa Dolores, Argentina; and Haleakala, Maui, Hawaii.

In retrospect, the Minitrack and Microlock networks for radio tracking worked well, and the missions probably could have been conducted without the optical tracking net­works. Nevertheless, they provided a layer of protection, using a very basic capability that had the full confidence of the program planners and scientists. Fully integrated into the computational effort at the Vanguard Orbit Computation Center, the optical data were used throughout the early Explorer and Vanguard programs and made a substantial contribution to the high accuracy achieved in tracking those satellites.

Minitrack stations As a part of the presatellite era’s Viking program, the Naval Research Laboratory (NRL) had developed a Single-Axis Phase-Comparison Angle­Tracking Unit. It served as the basis for the development, for Vanguard, of a tracking and telemetry system, known as Minitrack. Two versions of the ground station were developed, a Prime Minitrack Station and a Mark II Minitrack Station.12

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The Minitrack development depended upon the efforts of many NRL individuals, led by John T. Mengel. It included primary contributions by Roger L. Easton, David (Dave) S. Hepler, Victor (Vic) R. Simas, and Martin (Marty) J. Votaw.

All Minitrack stations produced satellite tracking information by the use of pairs of antennas and receivers along both north-south and east-west axes. The outputs of each pair of receivers were summed. When the angle to the satellite was such that its signal arrived at both antennas in phase, the summed output was twice the amplitude arriving at a single antenna. As the satellite moved so that its signal arrived at the two antennas out of phase, they canceled and the sum was zero. Thus, as the satellite made its transit over the station, the combined receiver output for each axis pair was a variable-amplitude signal, with the peaks occurring when the distance from the satellite to the antennas differed by an integral number of wavelengths.

That information was not sufficient to provide unambiguous position information, as the signals were in phase at a number of different angles. In the Prime Minitrack Stations, those ambiguities were removed by using two pairs of antennas having different spacing along each of the two axes.

The Mark II Minitrack Stations, being simpler for implementation by radio am­ateurs and other smaller groups, lacked the multiple pairs of antennas along each axis, and the receivers were much simpler. Their data were used in the Vanguard Orbit Computation Center to complement the data received from the Prime Minitrack Stations.

For reception of the telemetered data, the signals from the pairs of antennas and receivers were combined in a different manner.

The Prime Minitrack Stations also had command transmitters to trigger the play­back of data from the Deal II onboard storage system.

Prime Minitrack Stations were located as shown in the earlier Figure 11.1. Seven stations were located roughly along the seventy-fifth meridian of west longitude and were positioned so that the satellite would pass within range of at least one of them during each orbit. That basic “picket line” consisted of stations located at (from north to south) Blossom Point, Maryland (this station also served as the engineering prototype for development of the system); Fort Stewart, Georgia; Batista Field, Havana, Cuba; Paramo de Cotopaxi, Quito, Ecuador; Pampa de Ancon, Lima, Peru; Salar del Carmen, Antofagasta, Chile; and Peldehune Military Reservation, Santiago, Chile. An additional Prime Minitrack Station at Rio Hata, Republic of Panama, was planned initially, but it was decided that relocating that station at the Navy Electronics Laboratory, San Diego, would meet that need. An additional advantage of the San Diego location was that it was in a better position to receive the signal near the end of the first orbits of newly launched satellites.

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In addition to that basic picket line, Prime Minitrack Stations were positioned at Coolidge Field, Antigua, British West Indies (primarily for downrange reception immediately following launch), and at Woomera, Australia (to provide some very limited coverage in the eastern hemisphere).

Special Minitrack stations with wider antenna beams were established on May – gauana and Grand Turk islands in the British West Indies to assist in tracking the Vanguard first-stage rockets.

A Minitrack station was established by the National Telecommunications Research Center near Johannesburg, South Africa. The primary motivation for that station was to obtain tracking information following injection of Vanguard satellites. It provided valuable tracking information for the Explorer I and III satellites but was not called upon for telemetry data recovery.

Microlock stations As mentioned earlier, JPL had developed a high-performance tracking and telemetry system as a part of their work in testing the Corporal and Sergeant missiles at the White Sands Missile Range in the early 1950s. It operated at very low signal levels (thus, over very long distances), in spite of Doppler shifting of the frequencies of signals received from rapidly moving rockets. That Microlock system was the product of a very energetic and dedicated team under the leadership of JPL’s Eberhardt (Eb) Rechtin. His team included Richard Jaffe, Robertson (Bob) C. Stevens, and Walter (Walt) Victor.13

The Microlock system was sufficiently mature by 1954 that it was introduced into the JPL and Army Ballistic Missile Agency (ABMA) collaborative planning for project Orbiter. Following the end of all officially sanctioned Orbiter planning, the Microlock system remained an integral part of the behind-the-scenes planning for a satellite by ABMA and JPL.

The Microlock receiver was designed with an extremely narrow (10 hertz) radio frequency bandwidth. It employed a phase-locked-loop technique to track the arriving signal’s frequency. For tracking the motion of the satellites, multiple receivers and antennas used the interferometer principle in a manner similar to that described above for the Minitrack system.

A Microlock station was set up at PAFB, Florida, for checking the payloads at Cape Canaveral and for receiving data during their launches. Additional stations were located in Pasadena, California (the developmental station at the JPL home location); Temple City, California (by an amateur radio club, as discussed below); Earthquake Valley, California (at an exceptionally radiation-quiet location); and at Ibadan, Nigeria, and Singapore (for improved global coverage). The locations of the Microlock stations are also indicated in the map of Figure 11.1.

Conventional stations Some early satellite receiving stations were designed in a more conventional manner. The most notable of those was a station established

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and operated by the Radio Research Laboratories at Kokubunji, Tokyo. Although not equipped to provide tracking data, it contributed valuable eastern hemisphere telemetry data throughout the Explorer I and III operating lifetimes.

Radio amateurs Both satellite-launching nations made major efforts to enlist sup­port by the amateur radio community. In the United States, the primary medium for communicating with the amateurs was the American Radio Relay League, through its publication QST. The Soviets used their amateur radio magazine Radio for a similar purpose.

The first to appear in the United States was a pair of articles in the July 1956 issue of QST that dealt with the U. S. Vanguard program’s Minitrack system.14 They were followed over the next two years by a string of articles dealing with equipment and techniques for receiving the signals from the Vanguard satellites.

After the Microlock system entered the picture, radio amateurs were encouraged to receive its signals, as well. The San Gabriel Amateur Radio Club in Temple City, California, went so far as to build and operate a substantial station. The club’s activity was strongly supported by JPL under Henry Richter’s (W6VZA) leadership. The club obtained equipment loans and donations from a variety of sources and facilities and support from the Los Angeles Sheriff’s Department. Members of the club built much of the specialized equipment under the direction of Robert Legg (W6QYY), Lamont Shinn (W6PFR), Jack Pattison (W6POP), and Howard G. Wheeler (W6GRW). Being tightly integrated into the Primary Microlock communications network by JPL, that station provided valuable tracking and telemetered data from the early Explorer satellites. The club documented its work in a handbook that was made available to all interested radio amateurs.15

A Mark II Minitrack tracking and receiving station was established by 12 amateur radio members of the Sohio Moonbeam Group, in Cleveland, Ohio. Other radio amateurs also provided data during the early Explorer flights. Their primary value was in helping to establish the initial orbit parameters.

The Soviets, too, were eager to include radio amateurs in their program. After all, one of the primary reasons for their choice of 20 MHz and 40 MHz as transmitting frequencies for Sputnik 1 was to allow the worldwide community of radio amateurs to receive its signals. That could be done without modifying the receivers possessed by a majority of amateur radio operators. An article in the USSR publication Radio in June 1957 provided technical details about the motion of their planned satellite in its orbit, the propagation of its signal, and arrangements for receiving it. That article was largely unknown in the West until after the Sputnik 1 launch.16 After that occurred, a translation was provided to the International Geophysical Year (IGY) technical panel on ionospheric physics, and a condensed version of that translation appeared

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in QST in November 1957.17 The primary emphasis in that article was on the use of amateur radio observations for orbit determination—telemetry reception instructions were notably absent. For the next several months, QST carried a number of articles dealing in one way or another with Sputnik 1 signal reception.18

As another interesting historical note, during one of our telephone conversations on 27 November 1957, Van Allen mentioned his interest in adding a capability to transmit continuously from the U. S. satellites at a lower frequency to extend the coverage to a wider network of ground receiving sites, including radio amateurs.

The signals at the IGY-approved satellite-transmitting frequencies of 108.00 and 108.03 MHz would propagate only in straight lines. That band had been chosen for just that reason, so that the satellite orbital path could be measured to the desired precision. The straight-line propagation was not important for transmitting the telemetry data, however, and, in fact, limited the area over which reception would be possible. Van Allen knew from his personal experience in receiving the Sputnik 1 signal during his South Pacific expedition that transmission at a frequency of 20 MHz would expand coverage because the signal path would be bent by the ionosphere. He reasoned that it should be possible to meet more of the cosmic ray experiment’s wide-area coverage requirement if a 20 MHz transmitter were added. He stated that unspecialized receiving equipment should permit the reception of the 20 MHz signal for periods of about 25 minutes on each pass, and that it should be possible to receive sequences of at least five consecutive passes.19

The idea was alluring enough that he elevated that question two days later in a letter to the two working groups of the Technical Panel on the Earth Satellite Program (TPESP). That letter advocated continuous 20 MHz satellite data transmission at a level of about 0.1 watt. His letter expressed a set of personal observations, including his belief that a single well-located receiving station could provide telemetry recovery for about one-fourth of the time, that the change would lend itself to added telemetry recovery by radio amateurs and others, and that continuous transmission at that frequency might eliminate the need for onboard data storage in future missions in the interest of simplifying the onboard instruments.

His recommendation was seconded nine days later by Vern Suomi at the University of Wisconsin, who stated that such a transmitter would permit substantial simplifica­tion of the Vanguard instrument he was developing to measure the Earth’s radiation balance.20

Van also discussed this point with Pickering, who once informed me that his working group had discussed transmitting at the 20 MHz frequency from the Deal satellites at an earlier meeting of the TPESP but had decided against it “for political reasons.”

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Nevertheless, by the time of Van Allen’s letter, it was too late to make the change in any of the Deal satellites. His recommendation was implemented later in the Explorer 7 satellite, as related in Chapter 13. As the space program evolved after that, however, the demands for higher data rates from Earth orbit required the higher transmitting frequencies. The specially designed satellite receiving stations became an established feature of space operations, and the possibilities for radio amateur participation dimin­ished. To my knowledge, no other U. S. satellites were designed to transmit at 20 MHz, not even the Oscar satellites that were built by the amateur radio enthusiasts some years later.

Major problems in preparing the ground networks Preparing the network of Mini­track and Microlock stations for the Deal satellites was not without its share of prob­lems. Building the completely new Minitrack system by NRL was a major project in its own right and encountered the typical problems of such endeavors.

The Microlock effort at JPL encountered a major snag at the outset. The Department of Defense (DoD) was initially reluctant to provide the needed financial support. In fact, soon after approval of the Deal program, it issued a directive that limited the Microlock network to the station at Cape Canaveral, Florida (essential for launch support), and the engineering development station in Pasadena. Upon learning of that directive in the early afternoon of Wednesday, 27 November, I immediately called Van Allen. He was, at that moment, preparing for concurrent meetings of the IGY Rocket and Satellite Research Panel and its TPESP to be held on 6 December. He asked me to inform Pickering of that meeting and to tell him that Caltech’s Lee Dubridge would be attending it. He suggested that the two of them might be able to address the problem there.

Pickering immediately set up a conference call that included Henry Richter, Al Hibbs, C. I. Cummings, K. W. Linnes, and me.21 He informed us that, al­though IGY officials had not expressed any opposition to the addition of Microlock (even though it represented a major change in several years of Vanguard planning), they were not willing to openly contest the DoD directive. During that conversa­tion, we identified five possible options for providing the Microlock coverage that we felt we needed: (1) get the DoD position reversed in some way, (2) get ad­ditional coverage without major DoD financial support as a shoestring operation, (3) get the IGY program to help fund it, (4) get IGY participants in India or Japan to set up stations, or (5) see if the University of Iowa could help in some way.

Pickering also sent identical letters to Professor Masasi Miyadi at the Tokyo Astro­nomical Observatory and to A. P. Mitra, secretary of the Indian National Committee for IGY.22 Those letters outlined the need for global telemetry coverage and en­couraged them to construct stations suitable for recovering the Deal telemetry. The

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Japanese did follow through in time to provide valued support by establishing a station near Tokyo, as mentioned earlier.

The next morning, I informed Van Allen that Pickering would be in New York on 5 December to argue the Microlock issue.23 Van offered his help in presenting the scientific basis for increased Microlock coverage and prepared charts to help clarify the issue.

Ultimately, by a combination of continuing vigorous actions and some good luck, a robust network of Microlock ground stations was operational by the time of the Deal I launch.

A second major ground station crisis occurred relatively late in the game. Through a telephone conversation with Roger Easton at NRL on Wednesday, 19 February, just two weeks before the planned launch of Deal II (Explorer II), I learned that the interrogating transmitters were not ready at the NRL Minitrack ground stations, except for the station at Blossom Point, Maryland. The others lacked antenna-matching networks, and about half of them still needed work on the transmitter control panels. That threatened the success of our experiment, as without them we would have been unable to read the data from the onboard tape recorder for most of the orbits. I immediately called Van Allen, who, in turn, called Bill Pickering at JPL and John Hagen, the Vanguard project director at NRL.

Apparently, in the rush of switching our Iowa experiment from the Vanguard program to the Jupiter C program, although we thought the requirement for Vanguard command support was fully understood, no explicit written request for such support had been filed. That omission was immediately rectified by a letter from Pickering to Vanguard’s John Mengel. The text of that letter read:

This is to state that a requirement exists for the operation of interrogation transmitters for the University of Iowa satellite experiment. This payload contains a tape recorder used in connection with the ground interrogation system for the recording and transmission of the complete cosmic ray counts each orbit. It is essential that as many of the Minitrack fence stations as is possible be prepared to interrogate the satellite communications system. The time is very short in which this must be set up. For this reason, details will be worked out in a meeting between us on February 21. If a sufficient portion of the Minitrack system cannot be made available in time, our firing date will have to be delayed in order that a meaningful experiment will result.24

Henry Richter and I made a hasty departure for Washington on Thursday afternoon to be there for a meeting with John Mengel, Roger Easton, and Marty Votaw the next morning. Mengel’s and my independent reports summarized the results. Agreements were reached to retune the Minitrack receivers to the Deal II frequencies and to ready the Minitrack command transmitters for the mission. We received assurance that the Blossom Point, Maryland, station was in operation, and that the Fort Stewart, Georgia; Havana, Cuba; Antigua, British West Indies; Lima, Peru; Antofagasta, Chile; and San

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Diego, California, stations would be ready in time. As parts for the Quito, Ecuador, station had been lost in transit, and the Santiago, Chile, station was dealing with various cable problems, their readiness was in some question.25 26

In reality, it took a heroic effort on the part of the Vanguard engineers and station personnel to complete the arrangements during the short time remaining. Installation and checkout of the command transmitters for the South American stations were performed by Fred Friel of NRL and C. Cunningham of the Lima Station, with Friel hand carrying the necessary parts and instructions. The full array of Minitrack interrogating stations was completed only about a week before the Deal II launch. That seemed then, and even more so now, a miracle. The NRL engineers and operators certainly extended themselves magnificently to achieve that goal.

That January meeting also provided an opportunity to address other details in preparation for the Deal II launch. They included backup procedures for pointing the antennas in case the satellite’s low-power transmitter should fail prematurely, procedures for recording and forwarding ancillary information about interrogation times and performance, and the handling of the ground-recorded telemetry tapes. Henry and I also made a brief stop at the IGY Office in downtown Washington, and we visited the Vanguard Computing Center at 615 Pennsylvania Avenue, Northwest to learn whether all necessary preparations had been made for orbit computation and initial data processing. Henry returned to Los Angeles that evening.

The next morning I had some slack time before leaving Washington for Florida. That gave me an opportunity for some Washington tourism, including walking down the stairs in the Washington Monument. That evening, I flew to Orlando and made my way to Cocoa Beach. On Monday, 24 February, I joined the JPL engineers at Cape Canaveral to help in preparing the satellite instruments for flight.