Authored by
Donald Martin, Paul Anderson, Lucy Bartamian
Courtesy of The Aerospace Corporation

Chapter 1: 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.

SCORE
The first artificial communication satellite, called Project SCORE (Signal Communication by Orbiting Relay Equipment) [1–5], was launched in December 1958. The primary objective of the project was to demonstrate that an Atlas missile could be put into orbit. The secondary objective was to demonstrate a communications repeater.

The entire communication subsystem was developed in 6 months by modifying commercial equipment. Two redundant sets of equipment were mounted in the nose of the missile. Four antennas were mounted flush with the missile surface, two for transmission, and two for reception. The subsystem was designed to operate for the expected 21-day orbital life of the missile. Because of the short lifetime, batteries alone were the power source; thus, the complexity of solar cells and rechargeable batteries was avoided. The details about SCORE are as follows:

Satellite

• Communications equipment integral with Atlas launch vehicle
• 99 lb equipment
• Silver-zinc batteries, 56 W maximum load

Capacity

• One voice or six teletype channels
• Real-time and store-dump modes

Transmitter

• 132 MHz, 8 W output
• All vacuum tubes

Receiver

• 150 MHz, 10 dB noise figure - All transistors

Antenna

• Four slots (two transmit, two receive)
• –1 dB gain

Recorder

• 4 min capacity, 300–5000 Hz band
• SCORE comm

Life

• Two weeks

Orbit

• 100 x 800 nmi, 32 deg inclination

Orbital history

• Launched 18 December 1958, battery failed 30 December 1958
• Decayed 21 January 1959
• Atlas B launch vehicle

Management

• Developed by ARPA; communications equipment built by Army Signal Research and Development Laboratory, Ft. Monmouth, New Jersey

Each half of the communication subsystem had a tape recorder with a 4 min capacity. Any of the four ground stations in the southern United States could command the satellite into a playback mode to transmit the stored message or into a record mode to receive and store a new message. A real-time mode was also available in which the recorder was bypassed. About 8 hrs of actual operation occurred before the batteries failed. During this time, voice, single-channel teletype, and frequency-multiplexed six-channel teletype signals were transmitted to the satellite, recorded, stored, and later retransmitted. One of the signals handled in this manner was a Christmas message from President Eisenhower. In addition to the stored-mode transmissions, there were several real-time transmissions through the satellite.

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Author Biography
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.

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1. S. P. Brown and G. F. Senn, “Project SCORE,” Proceedings of the IRE, Vol. 48, No. 4 (April 1960).
2. S. P. Brown, “Project SCORE: Signal Communication by Orbiting Relay Equipment,” IRE Transactions of Military Electronics, Vol. MIL-4, No. 2–3 (April–July 1960).
3. M. I. Davis and G. N. Krassner, “SCORE—First Communication Satellite,” Journal of the American Rocket Society, Vol. 4 (May 1959).
4. S. P. Brown, “The ATLAS-SCORE Communication System,” Proceedings of the 3rd National Convention on Military Electronics (June 1959).
5. D. Davis, “The Talking Satellite. A Reminiscence of Project SCORE,” Journal of the British Interplanetary Society, Vol. 52, No. 7–8 (July–August 1999).