Reprinted from: Communication Satellites (5th Ed.)
Authored by
Donald Martin, Paul Anderson, Lucy Bartamian
Courtesy of The Aerospace Corporation

Experimental Satellites

Although the performance of communication satellites could be predicted theoretically, until 1962 or 1963 there was considerable doubt concerning whether their actual performance would match the theory. This was one of the basic motivations for the early communication satellite experiments. Two other important factors were the desire to prove the satellite hardware (since space technology in general was still in its infancy) and the need to test operational procedures and ground equipment. Whereas the first few experiments (SCORE, Courier, and Echo) were very brief beginnings, the Telstar, Relay, and Syncom satellites laid definite foundations for the first operational satellites.

Communication satellites have been in commercial operation and military service since 1965 and 1967, respectively. However, there was, and still is, the need for additional experimental satellites. These are used to prove new technologies for later introduction into operational satellites. Some satellites combine experimental objectives with preoperational demonstrations. Discussions of such satellites are included in this chapter if their emphasis is primarily experimental; those directly continued by operational satellites are described in later chapters.

Echo

During the late 1950s and early 1960s, the relative merits of passive and active communication satellites were often discussed. Passive satellites merely reflect incident radiation, whereas active satellites have equipment that receives, processes (may be only amplification and frequency translation, or may include additional operations), and retransmits incident radiation. At the time of Project Echo, the main advantages given for passive satellites were

• Very wide bandwidths
• Multiple-access capability
• No chance for degradations caused by failures of satellite electronics

The disadvantages were

• Lack of signal amplification
• Relatively large orbit perturbations resulting from solar and atmospheric effects (because of the large surface-to-weight ratio)
• Difficulty in maintaining the proper reflector shape

The progress in active satellites soon overshadowed the possible advantages of passive satellites, and interest in passive satellites ceased in the mid-1960s. In the mid-1970s, there was some interest in passive satellites concerning their use in a nuclear-war environment.

Project Echo [1–12] produced two, large, spherical passive satellites that were launched in 1960 and 1964. The details of Echo are as follows.

• Satellite
  • Echo 1: sphere, 100 ft diameter, 166 lb
  • Echo 2: sphere, 135 ft diameter, 547 lb
  • Not stabilized, no onboard propulsion
  • Aluminized Mylar surface, maximum reflectivity 98 percent for frequencies up to 20 GHz
• Frequencies
  • Echo 1: 960 and 2390 MHz
  • Echo 2: 162 MHz
  • Orbit
  • Echo 1: 820 x 911 nmi, 48.6 deg inclination (initial values)
  • Echo 2: 557 x 710 nmi, 85.5 deg inclination (initial values)
• Orbital history
  • Unnumbered: launch vehicle failure 13 May 1960
  • Echo 1: launched 12 August 1960, decayed 25 May 1968
  • Echo 2: launched 25 January 1964, decayed 7 June 1969
  • Delta launch vehicle
• Management
  • Developed by G. T. Schjeldahl Company (balloon), Grumman (dispenser) for NASA (National Aeronautics and Space Administration) Langley Research Center (Echo 1), NASA Goddard Space Flight Center (Echo 2).

Echo 1 was used for picture, data, and voice transmissions between a number of ground terminals in the United States. In addition, some transmissions from the United States were received in England. Numerous modulation methods were tested during the Echo 1 experiments, and valuable experience was gained in the preparation and operation of the terminals, especially in tracking the satellites. In addition to the communications experiments, Echo 1 was used for radar and optical measurements, and its orbital data were used to calculate atmospheric density.

Echo 2 had a slightly different design to provide a stiffer and longer lasting spherical surface. It was used very little for communications, although some one-way transmissions were made from England to the Soviet Union. It was primarily used in scientific investigations similar to those performed with Echo 1.

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Donald H. Martin is a senior engineering specialist in The Aerospace Corporation’s Architectures and Spectrum Management Office. Martin joined the Communications Department in the Engineering Group at Aerospace in 1968 after receiving B.S. and M.S. degrees in engineering from the University of California, Los Angeles. He has been collecting information on satellite communications since 1972, when his manager offered him a choice of assignments: of the three options, he chose to write a description of communication satellites then in orbit. The assignment grew the next year to include a report describing satellites being built, and gradually expanded to the first edition of Communication Satellites in 1986, with the book now in its Fifth Edition.

* * * * * *
1. Space Communications and Navigation 1958–1964, NASA SP-93 (1966).
2. Special Issue on Project Echo, Bell System Technical Journal, Vol. 40, No. 4 (July 1961).
3. Satellite Communications (Military-Civil Roles and Relationships), second report by the Committee on Government Operations, U.S. House of Representatives, House Report No. 178 (17 March 1968).
4. H. S. Black, “Latest Results on Project Echo,” Advances in the Astronautical Sciences, Vol. 8 (1961).
5. J. R. Burke, “Passive Satellite Development and Technology,” Astronautics and Aerospace Engineering, Vol. 1, No. 8 (September 1963).
6. L. Jaffe, “Project Echo Results,” Astronautics, Vol. 6, No. 5 (May 1961).
7. W. C. Nyberg, “Experiments to Determine Communication Capability of the Echo II Satellite,” Publications of Goddard Space Flight Center 1964, Vol. II.
8. D. H. Hamilton Jr. et al., “Transcontinental Satellite Television Transmission,” Proceedings of the IRE (Correspondence section), Vol. 50, No. 6 (June 1962).
9. A. Wilson, “A History of Balloon Satellites,” Journal of the British Interplanetary Society, Vol. 34, No. 1 (January 1981).
10. D. R. Glover, “NASA Experimental Communications Satellites,” http://sulu.lerc.nasa.gov/dglover/satcom2.html (10 June 1999).
11. D. C. Elder, “Something of Value: Echo and the Beginnings of Satellite Communications,” in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 4.
12. C. B. Waff, “Project Echo, Goldstone, and Holmdel: Satellite Communications as Viewed From the Ground Station,” in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 5.