SP-4217 Beyond the Ionosphere


Chapter 2
Moon in Their Eyes: Moon Communication Relay at the Naval Research Laboratory, 1951-1962
by David K. van Keuren


[9] On 24 July 1954, James H. Trexler, an engineer in the Radio Countermeasures Branch at the Naval Research Laboratory (NRL), spoke carefully into a microphone at the laboratory's Stump Neck radio antenna facility in Maryland. Two and a half seconds later, his words speeded back to him at Stump Neck, after traveling 500,000 miles via an Earth-Moon circuit.1 For the first time ever, the sound of a human voice had been transmitted beyond the ionosphere and returned to Earth.

Trexler's achievement marked an early watershed in the Department of the Navy's Communication Moon Relay project (also known as "Operation Moon Bounce"). The ultimate goal was to create the longest communications circuit in human history, with the Earth's satellite acting as a passive relay. Military strategists had long considered secure and reliable communications lines to be a tactical necessity. During the 1950s, the heyday of the Cold War, with the U.S. Navy's fleets encircling the globe, secure and reliable communications links were considered critical to national security. Ionospheric storms had recently cut off radio transmissions to the U.S. fleet in the Indian Ocean, thereby demonstrating dramatically the vulnerability of communication lines.2 The objective of the Communication Moon Relay project was to add another high-tech option within the Navy's inventory of secure global communications technologies.

The origins of Communication Moon Relay, however, lie not in postwar communications research and development, but rather within the secure world of electrical intelligence gathering. The project was the spinoff of a deeply classified program centered on the surveillance of Soviet radar technologies, known as PAMOR (Passive Moon Relay).3 The early history of the two programs demonstrates just how close the linkages between classified and unclassified research and development programs often were within the American military laboratories during the Cold War.



Figure 6. Notebook entry of James H. Trexler, dated 28 January 1945, showing calculations for a long-distance communications link between Los Angeles, California, and Washington, D.C., via the Moon. (Courtesy of the Naval Research Laboratory.)

Figure 6. Notebook entry of James H. Trexler, dated 28 January 1945, showing calculations for a long-distance communications link between Los Angeles, California, and Washington, D.C., via the Moon. (Courtesy of the Naval Research Laboratory.)


[11] Naval Radio and Radar Research


Radio communications, particularly high-frequency communications, had long been a topic of interest at NRL. One of the original two laboratory divisions, when it opened in 1923, had been Radio, under the direction of A. Hoyt Taylor. Under Taylor's direction, NRL personnel throughout the 1920s and 1930s explored the application of high-frequency radio to Navy communications. One side effect of these studies was the accidental discovery in 1929, by Leo Young and Lawrence Hyland, of the underlying principle of what later came to be known as radar. Subsequent work by NRL personnel in the 1930s led to the development of operational radar detection sets by the end of the decade.4

Similarly, collaborative work in the 1920s by Taylor and physicist E.O. Hulburt on the propagation of high-frequency radio waves in the upper atmosphere led to the discovery of radio skip distance.5 Consequently, by the beginning of World War II, NRL had evolved into a leading center for research on the application of high-frequency radio to long-distance communications and detection.

World War II brought most laboratory research programs to a temporary halt, as personnel turned their attention to incremental improvements in existing technologies, as well as the testing and evaluation of contractor-produced war materials.6 However, the war did spark research and development in applied programs, including radar countermeasures. A dual-pronged agenda of technical development aimed at simultaneously countering German and Japanese radar, while improving the effectiveness of American equipment, was put into place in early 1942. In 1945, these programs merged into a newly established Countermeasures Branch within the Ship-Shore Radio Division. Branch research and development continued after the war, with a shift in focus toward the electronic capabilities of an increasingly belligerent Soviet Union.

One program of particular interest to the Countermeasures Branch was the interception of what was referred to as "anomalous propagation."7 The study of random, anomalous signals from around the world had been of interest to Radio Division researchers as far back as the mid-1920s.8 Interest in this phenomenon heightened during World War II, as increasingly powerful and sensitive Navy radar receivers picked up stray radio signals from Europe and Japan. After the war, under Trexler's direction, several German Wuerzburg antennas were shipped to Washington and scavenged for parts. Wuerzburg antenna arrays were subsequently erected at NRL's Blue Plains field station in 1947 for a program aimed at developing intercept direction-finding equipment for anomalous signals originating in Europe and the Soviet Union.9

[12] Consequently, with this history of research in the long-range propagation of radio waves, the Army Signal Corps's detection of radar waves bounced off the Moon in March 1946 did not come as a surprise to NRL researchers.10 Indeed, there is evidence that laboratory researchers had unsuccessfully attempted to retrieve echoes from the Moon as early as 1928.11 Efforts ceased during World War II and did not resume until 1948. Nevertheless, it appears that the Signal Corps program did attract the attention of Dr. Donald Menzel of the Harvard College Observatory. In 1946, Menzel, a commander with the U.S. Naval Reserve during World War II, as well as a member and the chair of the radio propagation committee of the Joint and Combined Chiefs of Staff, proposed to the Department of the Navy that it use Moon-reflected radio signals for secure communications.12

The response to Menzel's suggestion within the Department of the Navy is unclear. There does not seem to be a copy of the Menzel proposal or a Navy Department response within departmental records. A Navy program for using the Moon for active communications, as suggested by Menzel and pioneered by the Army, was not immediately forthcoming. However, the idea of using the Moon for communications and radar intercept purposes came under active consideration within two years. The moving force in this case was NRL engineer James Trexler.


James Trexler and Electronic Surveillance


Trexler had studied electrical engineering at Southern Methodist University (SMU), where his father taught in the Political Science Department. He had demonstrated little interest in traditional academic subjects, to his family's disappointment. However, he did prove himself to be an excellent, hands-on electrical engineer and amateur radio technician, thereby able to support himself during his undergraduate days.

In 1942, he came to NRL as a junior radio engineer, following in the footsteps of a former SMU engineering professor, Dr. Samuel Lutz, and simultaneously avoiding imminent induction into the U.S. Army. At NRL, Trexler was assigned to the Measurement and Direction-Finding Unit, where he spent much of the war working with various forms of high-frequency direction-finding units, before being assigned to the new electronic countermeasures group in 1945.13

While at SMU, Trexler had experimented with the reflection of high-frequency radio waves off meteor ionization trails as part of a study on the impact of atmospheric ionization on radio propagation. He continued in the mid-1940s to follow the work of investigators probing the upper atmosphere and near space with high-frequency radio transmissions. A paper by D.D. Grieg, S. Metzger, and R. Waer of ITT's Federal Telecommunication Laboratories in New York City, published in May 1948, proved to be particularly intriguing.14 Trexler noted in his scientific notebook on 24 June 1948 that in Grieg, Metzger, and Waer's paper:


[13] [I]t was pointed out that there is a possibility that the Moon has an ionosphere. If this is true then there is a possibility that certain radio frequencies will be reflected from the Moon's ionosphere with considerably higher efficiency than from the rugged surface of the Moon. The possibility of this being true was suggested by the recent experiments in Australia reported by [Grote] Reber at the Radio Astronomy meeting recently. In these tests standard transmitting and receiving equipments were used in a pulse system whereby the identity of the reflected signal was determined by coding. Delays of the correct magnitude were noticed. If there is any possibility of this mode of transmitting being useful to RCM [Radio Counter Measures] it should be given some very careful thought.15


Trexler pondered how a test might be set up to explore this possibility and what sort of equipment might be required. "The method of test could consist of using a beamed antenna having a sharp East-West pattern and a broad North-South shape," he wrote in his scientific notebook. "The intensity of the signal would be noted continuously and an attempt would be made to correlate it with the position of the Moon."16 He computed antenna size to determine how many antenna elements were needed to achieve a 0.5-degree beam width. Using 270-degree spacing, Trexler determined it would take "about 150 elements" to obtain such a beam width with constant phase and amplitude across the aperture. Such an instrument would be expensive to build, but worth the expense, he noted.

His laboratory notebook indicates that Trexler continued his calculations throughout the week of 24 June 1948. By 29 June, Trexler had come to the following conclusion:


From the RCM [Radio Counter Measures] point of view this system hold[s] promise as a communication and radar intercept device for signals that cannot be studied at close range where normal propagation is possible. It might be well to point out that many radars are very close to the theoretical possibility of contacting the Moon (the MEW [Ballistic Missile Early Warning System, BMEWS] for example) and hence the practicability of building a system capable of intercepting these systems by reflections from the Moon is not beyond the realm of possibility. . . . The strictest security should be maintained as to the existence of such intercept devices since the enemy could with little difficulty restrict the operations of these sets so as to avoid Moon contact. One immediate application of the system would be the detection and analysis of the Russian Radar signals that have been monitored at 500 MC [megahertz] near Alaska.17


Trexler's efforts over the following two years were directed toward demonstrating that such a Moon-intercept program was technically viable.

In late 1948 and early 1949, NRL constructed two large long-wire antennas designed for the high-angle observation of the Moon at its Blue Plains field facility.18 The antennas were designed to carry out observations in bands where Soviet radar signals were known to exist. By August 1949, regularly scheduled observations of the Moon were under way, operating under the code name "Joe," with the intent of intercepting Soviet radar signals. In January 1950, the Navy consulted Group Captain Dunsford, the Royal Air Force's electronic warfare coordinator with the U.S. Navy; he helped NRL researchers hone their search with improved Soviet target parameters.

[14] Although information on this early period of the program is sketchy, it seems that the results were sufficiently promising to allow Trexler and his immediate supervisor, Howard Lorenzen, to request approval from NRL's commanding officer, Captain Frederick Furth, for extended tests with more powerful radars.19 By June 1950, the Chief of Naval Operations coordinator for electronic countermeasures had been briefed and had issued an official military requirement for Moon-intercept intelligence. The Chief of Naval Research, Rear Admiral T.A. Solberg, subsequently provided $100,000 for an experimental program, which included money for a new radar.20 The effort, now an official Navy intelligence program, was renamed project PAMOR (Passive Moon Relay).


Communication Moon Relay


A site was chosen for the new antenna at Stump Neck, Maryland, on the annex grounds of the Navy's Indian Head Propellant Plant. Construction began in late December 1950 and was completed by the following September.21 The design chosen for the Stump Neck antenna was a parabola having an elliptical opening 220 by 263 feet (sixty-seven by eighty meters). Earth-moving equipment scooped a hole out of the ground and paved it with asphalt; then a galvanized iron grid with three-inch-by-three-inch (7.5-centimeter-by-7.5-centimeter) openings was attached to provide a reflecting surface good for wavelengths of one meter or more. A cable-supported boom housed the focal point feed structure, which could then be steered in celestial coordinates of right ascension and declination by adjusting the cable length. The antenna was oriented so as to maximize observations of the "Sino-Soviet Block," although only a few hours per month of observation time were available.22

The first short-pulse radar contact with the Moon was made on 21 October 1951. The 750-watt transmitter sent ten-microsecond, 198-megahertz pulses.23 The results surprised even Trexler. The fidelity of the received echo proved to be unexpectedly high. It had been assumed that the echo from a short pulse would have a fast rise, but a short fall. Theories predicted that energy would be returned from the entire illuminated sphere; however, the majority of the energy from the reflected pulse was received during the first 100 microseconds, meaning that half the power in the echo had to come from a circle on the Moon only 210 miles (338 kilometers) in diameter, or almost exactly one-tenth the diameter of the Moon.24 The consequence was a much more coherent signal than originally expected. An immediate aftermath of the early test results was that Navy officials placed a higher priority and security status on the project.25 The intelligence potential of passive Moon reflection was greater than originally surmised. A second consequence was the inauguration of the Communication Moon Relay project.

[15] The high fidelity of the reflected transmissions presented Trexler and his coworkers with an unexpected spinoff of their project. The quality of the received signal was potentially good enough to be manipulated for communications purposes. As B.E. Trotter and A.B. Youmans, Trexler's coworkers in the Countermeasures Branch, reported later, the results of the 1951 trials demonstrated that "the fidelity of this circuit was higher than suggested" and "implied that the circuit would be usable in modern communication systems."26 Experiments using continuous wave, modulated continuous wave, and audio-frequency-modulated signals followed.

Lunar communications signal and equipment testing continued over the next three years. On 15 June 1954, Trexler summarized the status of the work done with the Stump Neck and earlier NRL radio telescopes in a memorandum to Louis Gebhard, the NRL Radio Division's superintendent. "From the experience gained over several years of work," he noted, "it appears that the fidelity of the Moon circuit is much better than predicted resulting in the possible use of many types of circuits such as high-speed teletype, facsimile and voice." The potential uses for such a telescope included functions associated with radar intercept, jamming, communications, navigation, satellite search, and ionospheric and atmospheric research. Under "Communications," Trexler proposed using the Moon as a passive reflector to "broadcast to half the world at any one time" at very high frequencies (VHF), as well as for two-way communications between the United States and ships, submarines, or large aircraft.27 Early work had already advanced in this direction.

By the end of 1954, Stump Neck was nearing the end of its usefulness to the PAMOR project. A much larger antenna was needed to actually collect the weak Soviet radar signals. As noted in his 15 June 1954 memorandum, Trexler felt that "to utilize many of the possibilities of Moon relay an antenna having a 600-foot [183-meter] diameter would be required at VHF. For many applications, this diameter does not change fast with frequency since it is the absolute area that is important in receiving."28 This marked the beginning of an extensive lobbying and development effort for a 600-foot radio antenna at Sugar Grove, West Virginia. It also marked the effective separation of PAMOR from what became the Communication Moon Relay project.

An advantage of the communications project was that simple antennas could be used at the receiving end. This advantage was particularly enhanced by the use of a 10-kilowatt klystron amplifier covering the ultrahigh frequency (UHF) band.29 With the Stump Neck parabola serving as the transmitter, the receiver used an array of antennas, the basic element of which was a standard Model SK-2 radar antenna.30 Early testing included both teletype and voice transmission, with Trexler's voice, as mentioned previously, being the first to make the round-trip lunar circuit.

After preliminary tests between the Stump Neck site and Washington, D.C., the first transcontinental test was set for the week of 20 November 1955. The receivers were established at the Navy Electronics Laboratory in San Diego, California, and after orientation of the field equipment, the Communication Moon Relay circuit began operating at [16] 301 megahertz on 27 November. Because of the low declination of the Moon, initial performance was weak. Further adjustment of the equipment allowed a successful teletype message to be sent and received at 11:51 p.m., Pacific Standard Time, on 29 November. Dr. Robert Morris Page, the associate director of research at NRL, as well as one of the American inventors of radar, signaled Dr. Franz Kurie, the technical director of the Navy Electronics Laboratory, to "lift up your eyes and behold a new horizon." NRL conducted further experiments during December 1955 and early January 1956 to understand and to counter the signal fading that had been observed during the November tests.32

Beginning on 21 January 1956, the experimental baseline was extended to Hawaii, where an array of eight SK-2 receivers was set up at Wahiawa, Oahu. Teletype signals were sent at 300 megahertz from a ten-kilowatt transmitter. On 23 January, the system received its U.S. Navy christening when Admiral Arleigh Burke, Chief of Naval Operations, signaled a message of congratulations to Admiral Felix B. Stump, Commander-in-Chief of the Pacific Fleet.33

The reaction of the Department of the Navy to the experimental system was quick. Assistant Secretary of Defense for Research and Development Donald A. Quarles, who witnessed the tests, became a strong supporter and provided special Department of Defense funds to cover development costs. Also, Admiral Burke directed the Bureau of Ships to develop a demonstration model of a reliable, long-range communications system using the new technique. By May 1956, a Department of the Navy contract had been issued to the Developmental Engineering Corporation of Washington, D.C., for system development.34 The costs for total development (including construction) were approximately $5.5 million.35 An indication of the popularity of the Communication Moon Relay system may be found in the National Academy of Science's Advisory Committee on Undersea Warfare, which recommended in December 1956 that future American submarines use Moon-reflection path signaling for ship-to-shore communications.36

As the Communication Moon Relay system went into its production phase, the Communications Section of the NRL's Radar Division, which had inherited the project from the Radio Countermeasures Branch, began emphasizing improvements in receiver and transmitter design, including more powerful transmitters and transmission at higher frequencies. By mid-1957, lunar echo experiments were being conducted in the UHF band at 290 megahertz.

The experimental system produced by the Developmental Engineering Corporation for the Bureau of Ships quickly led to the development of a fully operational satellite communications system between Washington, D.C., and Hawaii. The system, functional by 1959, was inaugurated publicly in January 1960.37 As part of the inaugural ceremonies, pictures of the aircraft carrier U.S.S. Hancock were beamed from Honolulu to Washington via the Communication Moon Relay system. The transmitted facsimile featured thousands of Hancock officers and seamen spelling out "Moon Relay" to a worldwide audience.



Facsimile picture of the U.S.S. Hancock with ship officers and crew spelling out <<Moon Relay.>>

Figure 7. Facsimile picture of the U.S.S. Hancock with ship officers and crew spelling out "Moon Relay." This picture was transmitted via the Moon from Honolulu, Hawaii, to Washington, D.C., on 28 January 1960. (Courtesy of the Naval Research Laboratory)


The completed system used eighty-four-foot-diameter (twenty-eight-meter-diameter) steerable parabolic antennas and 100-kilowatt transmitters installed at Annapolis, Maryland, and Opana, Oahu, with receivers at Cheltenham, Maryland, and Wahiawa, Oahu. The system operated at frequencies around 400 megahertz, it could accommodate up to sixteen teleprinter channels operating at the rate of sixty words per minute, and it was capable of processing teletype and photographic facsimiles.38

During the next two years, the Communication Moon Relay system expanded to include ship-to-shore communications. A sixteen-foot (five-meter) steerable parabolic antenna and receiving equipment installed on the U.S.S. Oxford in 1961 permitted one-way shore-to-ship lunar satellite communications for the first time.39 The addition of a one-kilowatt transmitter to the Oxford in 1962 permitted two-way communications, as the ship sailed in South American waters. These successful trial experiments with the U.S.S. Oxford led to the establishment of the Navy's worldwide artificial satellite communications system later in the decade.


[18] Conclusion


The Communication Moon Relay system was the unexpected outgrowth of research and development in electronics intelligence--an allied but distinct field. The perceived need by the U.S. Navy and the American military as a whole to constantly assess Soviet technical capabilities rationalized and facilitated the diversion of funds and talent to fields that otherwise might not have been developed at such a comparatively early date. The construction of large-scale antenna facilities at Stump Neck, as well as the provision of technical support functions, such as the then-cutting-edge computational capabilities of the NAREC computer, provided the technical and scientific background that made the Communication Moon Relay system possible. Indeed, it was not only the Communication Moon Relay project that benefited, but also Navy radio astronomers who had access to the facilities during those substantial time periods when the Moon's position did not permit the use of the facilities for intelligence gathering.

If anything, the history of the Communication Moon Relay project demonstrates the complex and often hidden history of early space communications. It clearly illustrates, moreover, that during the Cold War, even the most basic research, such as radar studies of the lunar surface, often had a national security component. As the declassification of documents from this era progresses, the intricate and interwoven history of national security needs, science, and technological development should become clearer.



1. A reference to the l954 voice transmission is found in the James H. Trexler biographical file, NRL Historian's Reference Collection, Naval Research Laboratory, Washington, DC. The first transmission on 24 July, because of security concerns, consisted only of the repetition of vowel sounds. The broadcast of actual words followed on 22 August. James H. Trexler, private communication, 15 October 1995.

2. Discussed in James H. Trexler, interview with David K. Allison, 30 October 1980, Historian's Office, Naval Research Laboratory, Washington, DC.

3. This discussion of PAMOR is based on previously classified documents within the NRL record collection now in storage at the Federal Records Center, Suitland, MD. Important documents are James H. Trexler, comp., "A Chronological History of U.S. Naval Radio Research Station (NRRS), from 1946 to 14 April 1962, prepared 22 July 1962"; anonymous, "Unique Aspects of the Elint [electrical intelligence] Collection Potential of the U.S. Naval Radio Research Station, Sugar Grove, West Virginia, January 1962." This reference is to edited versions in the files of the Historian's Office, NRL. Additional key documents include "Communications by Satellite Relay," March 1959, NRL Historian's Files; James H. Trexler, "Proposed URSI Paper for May 1955: Lunar Radio Circuits," collection of Countermeasures Branch memoranda dating to 1954, NRL records, Federal Records Center, Suitland, MD.

4. David K. Allison, New Eye for The Navy: The Origin of Radar at the Naval Research Laboratory (Washington, DC: Naval Research Laboratory, 1981); David K. van Keuren, "The Military Context of Early American Radar, 1930-1940," in Oskar Blumtritt, Hartmut Petzold, and William Aspray, eds., Tracking The History of Radar (Piscataway, NJ: Institute of Electrical and Electronics Engineers, 1994).

5. Allison, New Eye for the Navy, pp. 56-57; Bruce William Hevly, "Basic Research Within a Military Context: The Naval Research Laboratory and the Foundations of Extreme Ultraviolet and X-Ray Astronomy, 1923-1960," Ph.D. diss., Johns Hopkins University, 1987, pp. 11-53.

6. Alfred T. Drury, "War History of The Naval Research Laboratory," 1946, unpublished history in the series, "U.S. Naval Administrative Histories of World War II," deposited in the Department of the Navy's library.

7. Trexler interview, 30 October 1980.

8. See Allison, New Eye for the Navy, passim; Hevly, "Basic Research Within a Military Context," passim.

9. Trexler interview, 30 October 1980.

10. John H. DeWitt, Jr., and E. King Stodola, "Detection of Radio Signals Reflected from the Moon," Proceedings of the IRE 37 (1949): 229-42; Jack Mofenson, "Radar Echoes from the Moon," Electronics 19 (1946): 92-98; Herbert Kauffman, "A DX Record: To the Moon and Back," QST 30 (1946): 65-68; James Trexler, "Lunar Radio Echoes," Proceedings of the IRE (January 1958): 286-92.

11. See correspondence between Kenneth B. Warner and A. Hoyt Taylor, 31 January-7 February 1946, NRL Historian's Files, NRL, Washington, DC; Trexler interview, 30 October 1980.

12. See Trexler, "A Chronological History"; Trexler interview, 30 October 1980.

13. Trexler interview, 30 October 1980.

14. D.D. Grieg, S. Metzger, and R. Waer, "Considerations of Moon-Relay Communication," Proceedings of the IRE 36 (May 1948): 652-63.

15. James H. Trexler, Laboratory Notebook No. N-124, 14 June-15 July 1948, p. 61, NRL records, Federal Records Center.

16. Ibid., p. 65.

17. Ibid., pp. 70-71.

18. Trexler, "A Chronological History."

19. Ibid.

20. James H. Trexler, Laboratory Notebook No. N-411, 12 June-13 October 1950, p. 47, NRL records, Federal Records Center.

21. Trexler, "A Chronological History"; anonymous, "Unique Aspects"; Trexler, "Lunar Radio Echoes"; B.E. Trotter and A.B. Youmans, "Communication Moon Relay (CMR)," 21 June 1957, declassified NRL Secret Report; Trexler, "Proposed URSI Paper for May 1955."

22. Anonymous, "Unique Aspects."

23. Trexler, "A Chronological History"; Trexler, "Lunar Radio Echoes."

24. Trotter and Youmans, "Communication Moon Relay (CMR)," p. 1; Trexler, "Lunar Radio Echoes," p. 290.

25. Trexler, "Chronological History."

26. Trotter and Youmans, "Communication Moon Relay (CMR)," p. 1.

27. James Trexler to NRL Code 5400, Memorandum, 15 June 1954, in James H. Trexler, Laboratory Notebook No. N-756, 14 April-20 September 1954, p. 91, NRL records, Federal Records Center. Quoted text is from facsimile in NRL Historian's files.

28. Ibid.

29. Louis A. Gebhard, Evolution of Naval Radio-Electronics and Contributions of the Naval Research Laboratory (Washington, DC: NRL, 1979), p. 115.

30. Trotter and Youmans, "Communication Moon Relay (CMR)," p. 3.

31. Ibid., pp. 7-10.

32. Eventually, frequency diversity operations and the use of circular polarization were recommended. Ibid., p. 10.

33. Ibid., p. 16.

34. "U.S. Navy Communications Moon Relay (CMR) System," Naval Research Reviews (March 1960): 17-20.

35. Department of the Navy press release, 26 January 1960, in NRL document file labeled "CMR--thru 1960," NRL records, Federal Records Center.

36. National Academy of Sciences-National Research Council, Advisory Committee on Undersea Warfare, Project Nobska, The Implications of Advanced Design on Undersea Warfare, Final Report, Volume 1: Assumptions, Conclusions, and Recommendations (Washington, DC: National Academy of Sciences, 1 December 1956), pp. 16-19.

37. Gebhard, Evolution of Naval Radio-Electronics, pp. 115-16.

38. Ibid., pp. 117-18.

39. Ibid., pp. 121-22; L.H. Feher, V.W. Graham, W.E. Leavitt, and M.L. Musselman, "Satellite Communication Research--Communications by Moon Relay (CMR)," Report of NRL Progress (Washington, DC: NRL, May 1962), pp. 36-37; "Moon Used to Transmit Shore-to-Ship Radio Messages," Naval Research Reviews, February 1962, pp. 21-22.