As the geostationary orbit reaches saturation, and as carriers begin to look again at satellites in medium and low orbits, such as the proposed Iridium system, the pioneering work of NASA's Jet Propulsion Laboratory (JPL) and AT&T's Bell Telephone Laboratories in acquiring and tracking the first Echo balloon satellite has taken on new meaning and importance. Donald Elder has provided an overall description of the Echo project, which includes the design, construction, testing, and launching of the inflatable balloon, as well as the political impact of the experiment.2 The focus here is on the acquisition and positioning of the ground equipment necessary to undertake the experiment; the conduct of preliminary acquisition, tracking, and communication tests prior to launch; the performance of operations immediately after launch; and the conclusions reached by engineers of the two main participant organizations, Bell Telephone Laboratories in New Jersey and JPL in southern California.3
In an October 1958 internal technical memorandum outlining "A Program of Research Directed Toward Transoceanic Communication by Means of Satellites," Bell Telephone Laboratories engineers John Robinson Pierce and Rudolf Kompfner suggested that a worthwhile preliminary step would be the establishment of "an experimental narrow-band communication link . . . between two points on the American mainland, far enough apart to preclude the possibility of any other signal path." The main objectives of the experiment were to observe atmospheric refractive effects, to study the influence of satellite shape, and to make signal-to-noise and bandwidth measurements from 100-foot-diameter spheres launched into orbit. Pierce and Kompfner believed that the required  ground equipment for the experiment would be two sixty-foot steerable antennas connected to high-power modulators and amplifiers, low-noise receivers, band compressors, servo-tracking apparatus, and computer facilities.4 "[T]o interest some agency that could launch such a [communications] satellite" and "to convince ourselves and others of the value of such a passive satellite experiment," Pierce and Kompfner presented a paper based on their proposal to the National Symposium on Extended Range and Space Communication, held in Washington, D.C., on 6 and 7 October 1958. That paper subsequently was published in March 1959.5 Their proposal, of course, was the genesis of NASA's Project Echo.
Performing the passive satellite communications experiment called for in the Pierce-Kompfner proposal required two antenna stations, one on each coast of the North American continent. Their proposal did not suggest any specific sites for the two stations. Given their belief that the Bell system would play a leading role in the future development of satellite communications, however, they undoubtedly desired that the east coast station be located at one of the Bell Telephone Laboratories facilities, all of which were in New Jersey.
When they wrote their proposal, Pierce and Kompfner already had in mind both a desirable site and an interested partner organization for the required west coast station. At an Air Force-sponsored meeting on communications satellites held at Woods Hole, Massachusetts, on 13-14 July 1958, Pierce had discussed the feasibility of using 100-foot-diameter (about thirty-one-meter-diameter) balloons as part of a "passive satellite relay system." Among the conference attendees was William H. Pickering, the director of JPL, at that time an Army contract facility operated by the California Institute of Technology (Caltech). Following Pierce's talk, Pickering "raised the question of using the currently proposed balloon experiments for some initial work on the possibility of satellite relay systems."6 Pickering was referring to the twelve-foot-diameter (about four-meter-diameter) orbiting balloons conceived by William J. O'Sullivan, Jr., an engineer at the Langley Memorial Aeronautical Laboratory (under NASA, it became the Langley Research Center) in Hampton, Virginia--a facility of the National Advisory Committee for Aeronautics (NACA)--as a means of measuring air resistance in the Earth's upper atmosphere. The U.S. Department of Defense's Advanced Research Projects Agency (ARPA) had approved that balloon project in late March 1958 for launches in late 1958 and in 1959, and JPL was supplying the upper stages for the Juno II launch vehicles.7
 Pierce, who had known Pickering since the mid-1930s when they were fellow graduate students at Caltech, quickly informed his former classmate of the proposal that he had already made to NACA director Hugh Dryden to use a 100-foot-diameter version of O'Sullivan's balloon for a passive communications satellite experiment. Pierce recalled many years later that Pickering agreed at the Air Force conference that such an experiment "would be a profitable one" and "offered his encouragement and support."8 The support that Pickering undoubtedly offered was the use of an eighty-five-foot-diameter (twenty-six-meter-diameter) polar-mounted antenna that JPL had ordered from Blaw Knox in April 1958. JPL installed the so-called Pioneer antenna in July near Goldstone Dry Lake in California's Mojave Desert in support of two ARPA-approved Army lunar probe launches (subsequently named Pioneers 3 and 4) in late 1958 and early 1959.
Pickering and his colleagues at JPL, unlike their counterparts at Bell Telephone Laboratories, had little interest in the future development of communications satellites, but they foresaw that much of the additional ground-support equipment that JPL would need to conduct the passive satellite communications experiments at Goldstone could be applied subsequently to the tracking of, and communication with, space probes. By early 1958, JPL already was hoping to devote itself to those activities in the post-Sputnik era. In January 1959, JPL proposed to NASA a list of space probes that called for launches of a circumlunar flight in early July 1960 and two flybys of Mars in mid-October 1960. JPL participation in a NASA-sponsored passive satellite communications experiment in particular might enable its engineers to acquire more quickly the transmitter that eventually would be needed for issuing commands to probes to perform mid-course corrections and for determining probe positions more accurately.
The use of the Goldstone antenna in the proposed satellite communications experiment became more feasible during the latter half of 1958 as a result of the following three developments:
At a meeting on 22 January 1959, representatives from NASA headquarters, Bell Telephone Laboratories, and JPL negotiated an agreement that outlined the equipment that the latter two organizations would be responsible for acquiring, installing, and testing prior to the initial launch attempt of the Echo balloon satellite, then tentatively scheduled for September 1959. At that meeting, Bell Telephone Laboratories engineers announced that they planned to erect, at a site known as Crawford Hill in Holmdel, New Jersey, a twenty-foot-by-twenty-foot-aperture (a six-meter-by-six-meter-aperture) horn-reflector antenna. Horn antennas were known for their demonstrated low-noise properties.9  This particular horn antenna was to receive signals from Goldstone, while a sixty-foot-diameter (eighteen-meter-diameter) parabolic antenna purchased from the D.S. Kennedy Company would transmit signals to Goldstone via the Echo balloon. Possibly because of funding uncertainties in early January 1959, JPL indicated that it would both transmit and receive signals through duplexing, using the existing eighty-five-foot-diameter (twenty-six-meter) polar-mounted antenna at Goldstone.10 JPL project funding was uncertain because at that time NASA was operating on funds transferred from the Department of Defense and other agencies and was in the midst of formulating its first budget request for new funds from Congress.
After NASA's budgetary situation began to stabilize in the early months of 1959, however, JPL engineers opted, as did their Bell Telephone Laboratories counterparts, to use separate antennas for receiving and transmitting. For the second (transmitting) antenna, they chose an azimuth-elevation (Az-El), rather than polar, mounting. This choice was not dictated by Echo requirements. Rather it resulted from a desire by JPL engineers Robertson Stevens (chief of the Communication Elements Research Section), William Merrick (in charge of antenna construction), and Walter Victor (chief of the Communications Systems Research Section) to make a comparative study between the two types of mounts, as well as a scale study for larger antennas that the JPL engineers hoped to design and construct in the future for supporting more sophisticated and more distant space probes. Early design studies had indicated that an Az-El-mounted large antenna would cost less and weigh less than a polar-mounted antenna built to the same specifications of maximum frequency, wind-loading design, and tracking rates. JPL engineers also were aware that counterweight problems inherent in the polar-mount configuration probably would make it easier to scale up an Az-El-mounted antenna to a size comparable to the 210-foot-diameter (sixty-four-meter-diameter) Commonwealth Scientific and Industrial Research Organisation (CSIRO) radio telescope then under construction at Parkes, Australia.
Unlike the situation at Holmdel, where the two Bell Telephone Laboratories antennas would be in sight of each other, JPL engineers in 1958 had selected a site at Goldstone for an anticipated transmitter antenna that would be approximately seven miles from the Pioneer antenna and separated from the latter by a range of intervening mountains. The site had been chosen to preclude the possibility of the transmitter generating radio interference that might prevent the reception of weak radio signals from space probes at the receiver antenna.
JPL's prior and continuing involvement in space probe communications and tracking strongly influenced the selection of frequencies for the Echo experiment. JPL and Bell engineers chose 960.05 megahertz for east-to-west transmissions, because the JPL receiver at Goldstone was operating at this frequency in support of the Pioneer lunar program. For the west-to-east transmissions, they selected 2,390 megahertz because "it was the correct frequency band for future satellite and space-probe experiments."11 In fact, the radio frequency used by NASA's Deep Space Network (managed by JPL and comprised initially of antennas at Goldstone; Woomera, Australia; and Hartebeesthoek near Johannesburg, South Africa) changed from 960 to 2,390 megahertz in the mid-1960s.
As noted previously, the principal objective of Project Echo was to demonstrate the feasibility of long-range communications using a reflecting sphere as a passive satellite. To accomplish this objective, JPL and Bell engineers had to develop systems that could not only perform the communications experiment itself, but also rapidly acquire the fast-moving satellite soon after it rose above the western horizon and track it during subsequent periods of visibility. Indeed, in the view of JPL engineers, the acquisition and tracking of Echo would be more challenging than the communications aspect of the project. Once the acquisition and tracking problems were solved, according to JPL's Walter Victor and Robertson Stevens, "the communications problem would be no more difficult than a laboratory experiment with comparable signal and noise powers." Not surprisingly, therefore, most of the new equipment procured by JPL for the project was used for acquisition and tracking.12 By comparison, the acquisition and tracking of later geostationary satellites were in certain ways less daunting, because these essentially remained stationary in the sky.
At its Goldstone facility, JPL engineers developed for the Echo experiment two methods of acquisition: "slaving" the antennas to a precalculated pointing program using digital techniques and local optical sighting. They also developed three methods of tracking:  digital slave, optical, and automatic radar. When the digital-slave method (for both acquisition and tracking) was required, the NASA Minitrack network of stations generated and transmitted primary tracking data to a general-purpose digital computer at NASA's Goddard Space Flight Center in Beltsville, Maryland. This computer then issued antenna-pointing commands via teletype to Goldstone. Because of the two different types of antennas at Goldstone, JPL engineers developed a digital encoding and computing system that converted antenna-pointing data from one antenna site and coordinate system to the other.
The principal optical antenna-positioning method used a television camera and lens subsystem located on the structures of both antennas, along with the regular boresight telescope and boresight camera. The images provided by this system were displayed on a control console directly in front of the servo operator's position at each antenna site. This subsystem was not suitable for the initial acquisition of the satellite, however, because of its very narrow field of view (about 0.5 degree). Therefore, JPL engineers provided broad field-of-view acquisition telescopes at each site.
Because of a blind spot in the coverage of the polar-mounted receiver antenna, Goldstone personnel used a third optical means to acquire the satellite during its first orbit. On its first orbital pass, the satellite was expected to approach Goldstone from the northwest, but the mounting of this antenna (which had been set to track and communicate with space probes having declinations varying from about thirty degrees north to about thirty degrees south) prevented it from being pointed to the horizon in this direction. As a result, the antenna would be unable to monitor the satellite for the first eight minutes of the first pass. However, positional data on the first orbital pass were considered critical for initial orbit determination, so Goldstone personnel used a stand-alone Contraves phototheodolite to provide time-tagged Az-El data during the initial part of this pass. The main limitation of all three optical methods was, of course, that the satellite had to be visible. Thus, satellite observation had to occur at night, in clear weather, and when the Sun illuminated the satellite.
The third method of tracking the satellite developed by JPL engineers was a continuous-wave radar subsystem. Once either the digital-slave or one of the optical methods acquired the satellite, this subsystem tracked the satellite automatically. Control signals generated from a simultaneous lobing antenna feed and receiver positioned the polar-mounted receiver antenna, to which the Az-El-mounted transmitter antenna was slaved via the coordinate-converter computer and related equipment.
Bell Telephone Laboratories engineers employed similar tracking methods at their Holmdel station. The antennas were usually slaved to the tracking information provided by the drive tape from Goddard. Differences between the predicted and true positions were compensated by manual corrections obtained from either optics, radar, or (when a west-to-east transmission was being made) the strength of the received signal. Alternatively, the antennas could be slaved to the positional readouts of an optical tracker operated manually to track the satellite.
The optical telescope (borrowed by Bell engineers from a surplus M-33 fire-control radar system) consisted of a large trailer carrying a periscope-type optical train leading down to convenient operator positions inside the trailer. A ten-kilowatt transmitter (used for both communication and the radar system and purchased from ITT) was installed on the sixty-foot-diameter (eighteen-meter-diameter) antenna. The radar signals reflected off the satellite were received by a separate eighteen-foot-diameter (about five-meter-diameter) antenna located about a mile and a half away from Crawford Hill so as to increase the separation between the transmitted signals and the radar receiver.
After the installation of the new equipment, JPL and Bell Telephone Laboratories engineers began a testing program of the equipment and personnel at Goldstone and Holmdel prior to the launch of the first Echo balloon. The testing program consisted of a series of exercises that simulated as nearly as possible an actual Echo mission.13 The most striking of these exercises was a series of seventeen so-called "Moon Bounce" communications experiments that began 23 November 1959 and continued until 7 August 1960, just five days before the launch of Echo. These experiments involved using the Moon as a passive reflector (in the manner of the Echo balloon) between the Holmdel and Goldstone stations. Such tests were useful because the combination of the Moon's ability to reflect energy to the receiving antenna (known as its radar cross section) and its distance from the Earth provided a transmitter-to-receiver path loss (that is, the amount of radio signal power lost between the transmitter and receiver) nearly equal to that expected for the Echo satellite.14
As for acquisition and tracking problems, however, the Moon was too easy a target compared to Echo because of its highly predictable orbit, good visibility, and relatively slow motion across the sky. Therefore, Goldstone and Holmdel personnel participated in two types of tests with a "dark" satellite in a relatively high-altitude, stable orbit--namely, the TIROS 1 polar-orbiting meteorological satellite launched 1 April 1960. In one type of test, JPL engineers used basic TIROS tracking data generated by the Minitrack network to position the Goldstone antennas; then they tested the accuracy of the ephemeris by attempting to obtain a radar echo from the satellite. Another type of test involved bouncing continuous-wave radio signals off the satellite. The satellite's polar orbit made these tests more difficult, because it was visible over the Goldstone and Holmdel antennas for a period of only a few minutes. As a result, station operators had to rely on Minitrack-generated orbital data to position their antennas.15
 Other tests conducted at Goldstone addressed the difficulty of tracking targets optically. Some tests involved tracking stars optically to check the absolute and relative alignment of the two antennas and to measure the sensitivity of the television cameras mounted on them. Other tests used a helicopter with an optical target light and a 2,388-megahertz radio beacon to exercise the optical equipment and to train antenna operators in the acquisition and tracking of visible satellite targets.
After conducting a series of five suborbital ballistic ("Shotput") tests of the balloon payload in late 1959 and early 1960, NASA ignored superstition and made its first attempt to launch the Echo satellite into orbit on Friday, 13 May 1960. The day indeed turned out to be unlucky for the Echo project. The attitude control jets on the second stage of the Thor-Delta rocket failed to fire during a coast period after the main engine of that stage burned out. Incapable of maintaining the proper angle for orbital insertion, the final stage and payload ultimately plunged into the Atlantic Ocean.
A second launch attempt on 12 August 1960 succeeded in placing Echo 1 into the desired 1,000-mile-attitude orbit. On the first orbital pass, the phototheodolite at Goldstone optically spotted the satellite at 4:31 a.m. (Pacific Daylight Time) as it came over the northwest horizon. Three minutes later, the receiver antenna began collecting signals from the satellite's radio beacons. The radar acquired the balloon at 4:37 a.m. and tracked it automatically over the next 15 minutes until it disappeared below the southeast horizon. In the meantime, beginning at 4:36 a.m., the transmitter antenna began sending a 2,390-megahertz radio signal toward the satellite.
At Holmdel, the acquisition of the Echo target was more difficult. Station operators lacked optical visibility, and their efforts were hampered by the use of a radar that was "still unproven." Bell engineers therefore used a drive tape supplied by the Goddard Space Flight Center prior to the launch. It was based on one of the nominal trajectories and adjusted approximately to the actual launch time. This method allowed the horn antenna to begin receiving Goldstone's reflected signal at 4:41 a.m. (Pacific Daylight Time). One minute later, engineers at Goldstone used the transmitter antenna to begin sending a prerecorded message from President Eisenhower, and the Holmdel antenna clearly received it after its reflection off the balloon.
Incorrect data points on the drive tape, however, caused the horn antenna to slew away from the actual satellite track during this first pass. Although angular offsets were quickly implemented to compensate for these errors, the reception of the Goldstone signal was split into three separate periods lasting from one to three minutes. Bell Project Echo engineer William Jakes candidly acknowledged that "had the launching not been virtually perfect, there would have been no reception at all on the first pass because of the severe acquisition problem" at Holmdel.16
In summarizing JPL's participation in project Echo, Stevens and Victor concluded that acquisition and tracking of the balloon with sufficient accuracy (0.1 degree) to make communication possible was "the most difficult task." By far the most reliable method, they pointed out, was optical acquisition and tracking. The desired accuracy was easily obtained by this method "as long as [the servo operators] were not fatigued." Slaving the  antennas digitally by means of a perforated teletype tape resulted in an average difference between the slave command and the measured Goldstone angles of between 0.1 and 0.15 degree "as long as the orbital parameters were updated daily." Atmospheric drag on the balloon, which neither remained constant over time nor varied in a predictable manner, caused the largest uncertainty in predicting the orbit.17
Victor and Jakes noted that the Echo project, through a large amount of organizational coordination, had accomplished the "unprecedented feat of simultaneously slaving narrow beam antennas located a continent apart to a computer so that a relatively fast-moving satellite could be accurately tracked." They concluded, however, that the procedure "probably does not represent the most efficient use of a large scale, general purpose computer or the personnel involved."18 JPL's Stevens and Victor also felt that the reliability of this method needed to be improved before it could be considered operationally feasible. They reported that radar tracking of the balloon had been accurate to 0.03 degree for the receiving antenna and about 0.1 degree for the transmitting antenna at Goldstone.19
Looking to the future, Stevens and Victor suggested that "standard television might be relayed on a reasonably practical basis via passive satellites" if 1,000-foot-diameter balloons could be launched instead and if transmitter power and antenna gain could be boosted. While these improvements were "technically feasible," the JPL engineers warned that they were not necessarily "economically feasible or desirable"; other satellite techniques might prove more suitable for the transmission of wide-band video signals. On the other hand, Stevens and Victor judged, passive satellites "may be a good solution for narrower bandwidth data-transmission systems."20
1. Most of the research for this paper was conducted as part of the author's work from 1989 to 1992 as Deep Space Network contract historian at the Jet Propulsion Laboratory (JPL) in Pasadena, CA.
2. See Donald C. Elder, "Something of Value: Echo I and the Beginnings of Satellite Communications," chapter 4 in this publication; Donald C. Elder, Out From Behind the Eight-Ball: A History of Project Echo, AAS History Series, Vol. 16 (San Diego: American Astronautical Society, 1995).
3. The overall roles played by JPL and Bell Telephone Laboratories in Project Echo are summarized in Walter K. Victor and Robertson Stevens, "The Role of the Jet Propulsion Laboratory in Project Echo," IRE Transactions on Space Electronics and Telemetry SET-7 (March 1961): 20-28; William C. Jakes, Jr., "Participation of Bell Telephone Laboratories in Project Echo and Experimental Results," The Bell System Technical Journal 40 (July 1961): 975-1028; William C. Jakes, Jr., and Walter K. Victor, "Tracking Echo I at Bell Telephone Laboratories and the Jet Propulsion Laboratory," in H.C. van de Hulst, C. de Jager, and A.F. Moore, eds., Space Research II, Proceedings of the Second International Space Science Symposium, Florence, April 10-14 1961 (Amsterdam: North-Holland Publishing Company, 1963), pp. 206-14. JPL reported its involvement in Project Echo more fully in a series of progress reports appearing in issues (nos. 6 and 37-1 to 37-6) of its bimonthly Space Programs Summary series covering the period from 15 September 1959 to 15 November 1960, as well as in its final report on the project, Robertson Stevens and Walter K. Victor, eds., The Goldstone Station Communications and Tracking System for Project Echo, JPL Technical Report No. 32-59 (Pasadena, CA: JPL, 1 December 1960).
4. John Robinson Pierce and Rudolf Kompfner, "A Program of Research Directed Toward Transoceanic Communication by Means of Satellites," manuscript, Technical Memorandum MM-58-135-24, 22 September 1958, p. 20, Vol. KK, Filecase No. 20564, AT&T Archives, Warren, NJ. The author is grateful to Sheldon Hochheiser, AT&T archivist, for assistance in locating this paper and granting permission to quote from it.
5. John Robinson Pierce and Rudolf Kompfner, "Transoceanic Communication by Means of Satellites," Proceedings of the IRE 47 (March 1959): 372-380.
6. William H. Pickering, "Notes on Satellite Conference, July 13-14, 1958," 22 July 1958, doc. no. 15, microfilm roll 33-4, JPL Archives, Pasadena, CA.
7. The launch attempts of the twelve-foot-diameter balloons were made on 22 October 1958 and 14 August 1959, but both ended in failure. See Elder, Out From Behind the Eight-Ball, pp. 45, 65.
8. John Robinson Pierce, The Beginnings of Satellite Communication (San Francisco: San Francisco Press, 1968), pp. 11-12.
9. A description of this antenna is given by A.B. Crawford, D.C. Hogg, and L.E. Hunt, "A Horn-Reflector Antenna for Space Communication," The Bell System Technical Journal 40 (1961): 1095-1116. The authors noted that this type of antenna had originated at Bell Telephone Laboratories in the early 1940s. The antenna employed in the Echo experiment later gained fame as the instrument used by Arno Penzias and Robert Wilson in 1965 to discover the cosmic microwave background radiation.
10. The agreement reached at the 22 January 1959 meeting is outlined in Rudolf Kompfner, "A Proposed Plan for a Joint JPL-BTL Experiment in Communication by Means of a Passive Satellite," 9 February 1959, attached to Rudolf Kompfner to Leonard Jaffe (chief of the Communications Satellite Program in NASA's Office of Advanced Technology), 10 February 1959 (copy to Pickering), "Satellite Tracking 1959" section, microfilm roll 614-93, JPL Archives.
11. Victor and Stevens, "The Role of the Jet Propulsion Laboratory," p. 22.
13. Regarding the overall philosophy behind these tests, see the section "Systems Tests for Project Echo" in Stevens and Victor, eds., The Goldstone System, pp. 48-52; Jakes, "Participation of Bell Telephone Laboratories," pp. 980-82.
14. For detailed descriptions of the "Moon Bounce" tests, see "Moon Bounce Experiments," in JPL, Space Programs Summary No. 37-1 for the period 15 November 1959 to 15 January 1960, 1 February 1960, pp. 40-41; "Project Echo," in JPL, Space Programs Summary No. 37-2 for the period 15 January 1960 to 15 March 1960, 1 April 1960, pp. 44-45; "Project Echo," in JPL, Research Summary No. 36-2 for the period 1 February 1960 to 1 April 1960, vol. I, pt. 1, 15 April 1960, pp. 1-3; "Moon-Bounce Experiments," in JPL, Space Programs Summary No. 37-3 for the period 15 March 1960 to 15 May 1960, 1 June 1960, p. 39; Jakes, "Participation of Bell Telephone Laboratories," p. 981. Press coverage of the first publicized "Moon Bounce" communication on 3 August 1960 is in Marvin Miles, "Attempt to Bounce Voice Off Moon Scheduled Today; Two-Way Phone Talk Scheduled," Los Angeles Times, 3 August 1960; "JPL Sets First Long Distance 2-Way Phone Call Via Moon," Pasadena Independent, 3 August 1960; "Moon Used to Relay Phone Calls," Los Angeles Mirror, 3 August 1960; Marvin Miles, "East and West Coasts Converse in Phone Call Bounced Off Moon," Los Angeles Times, 4 August 1960; "JPL Call Via Moon Success," Pasadena Independent, 4 August 1960; Bill Sumner, "No Hamming in Historical Phone Call" and "Something Wroughten in Space" ("Daily Report" column), Pasadena Independent, 5 and 8 August 1960, all in JPL News Clips, 3 August 1960, JPL Archives.
15. For detailed descriptions of these tests, see "Dark Satellite Tracking Experiment," in JPL, Space Programs Summary No. 37-3 for the period 15 March 1960 to 15 May 1960, 1 June 1960, pp. 38-39; "Project Echo," in JPL, Space Programs Summary No. 37-4 for the period 15 May 1960 to 15 July 1960, 1 August 1960, pp. 43-45; Richard van Osten, "Goldstone Uses Now-silent Tiros I for Bouncing Signals," Missiles and Rockets, 15 August 1960, cited in JPL News Clips, 15 August 1960, JPL Archives.
16. For the most detailed description of the Shotput tests and the launches of 13 May and 12 August, see Elder, Out From Behind the Eight-Ball, pp. 68-70, 79-80, 84-85, 88-97, 103-09.
17. Stevens and Victor, eds., The Goldstone System, p. 55.
18. Jakes and Victor, "Tracking Echo I," p. 214.
19. Stevens and Victor, eds., The Goldstone System, p. 55.
20. Victor and Stevens, "The Role of the Jet Propulsion Laboratory," p. 28.