Communication Satellites (4th Ed.)
Donald Martin
Chapter 1: Experimental Satellites (cont.)
Telstar
The Telstar experiment [1–9] grew out of the Bell Systems' interest in overseas communication. Bell Telephone Laboratories was a major participant in communication experiments using Echo 1. The positive results of those experiments strengthened the interest in satellite communications generated by earlier analytical papers. Therefore, American Telephone and Telegraph Company (AT&T) decided to build an experimental active communication satellite. The objectives of the Telstar program were:
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Telstar Satellite |
- To look for the unexpected
- To demonstrate transmission of various types of information via satellite
- To build a large ground antenna and learn how to use it
- To gain experience in satellite tracking and orbital predictions
- To study Van Allen radiation belt effects
- To face the design problems required for a spaceborne repeater
An active satellite was decided on, because the required balloon size for television bandwidths was much beyond the state of the art. The choice of the Delta launch vehicle provided basic design constraints such as size, weight, and orbit. In accordance with the fifth objective, the satellite contained a number of sensors to make radiation measurements. The third objective was accomplished by the construction and use of a ground station at Andover, Maine.
Two Telstar satellites were produced. The satellites were 34.5-in.-diameter spheres with solar cells covering most of the outer surface. The solar array output alone could not support operation of the communication subsystem, so batteries were used to supply the peak power requirements. The batteries were recharged during the periods when the satellite was not in view of the ground terminals and the communication subsystem was turned off. This subsystem had a single channel with a 50-MHz bandwidth. The program details are as follows:
Satellite
Sphere, 34.5-in. diam
170 lb in orbit (1), 175 lb in orbit (2)
Solar cells and NiCd batteries, 15 W
Spin-stabilized, 200 rpm
Configuration
One 50-MHz bandwidth double-conversion repeater
Capacity
600 one-way voice circuits or one TV channel
60 two-way voice circuits (tests limited to 12 circuits by ground equipment)
Transmitter
4170 MHz
All solid state except TWT
TWT operated linear at 3.3 W (saturated power: 4.5 W)
Receiver
6390 MHz
All solid state
12.5-dB noise figure
Antenna
Transmit: 48 small ports equally spaced around satellite waist
Receive: 72 small ports
Uniform pattern around waist and ±30 deg from waist plane
Circular polarization
Telstar Communication Subsystem |
Telemetry and command
Telemetry: 136.05 MHz, 200-mW transmitter
Command: approximately 123 MHz
Four-element helical antenna
Design life
Two-year goal
Orbit
1: 514 X 3051 nmi, 45-deg inclination
2: 525 X 5830 nmi, 43-deg inclination
Orbital history
1: launched 10 July 1962, operated until 23 November 1962, and 4 January to 21 February 1963
2: launched 7 May 1963, operated until May 1965
Delta launch vehicle
Management
Developed by Bell Telephone Laboratories for AT&T
Telstar 1 was launched in June 1962. In the following six months, about 400 transmission sessions were conducted with multichannel telephone, telegraph, facsimile, and television signals. In addition, over 250 technical tests and measurements had been performed. Stations in the United States, Britain, and France participated in these activities. In November 1962, the command subsystem on the satellite failed. The cause was later established as degradation of transistors due to Van Allen belt radiation. Various operations effected a recovery that allowed the satellite to be used for another month and a half early in 1963, after which the command subsystem failed again.
Telstar 2 was nearly identical to Telstar 1. The only significant design change was the use of radiation-resistant transistors in the command decoders. The Telstar 2 satellite orbit had a higher apogee than Telstar 1, which increased the time in view of the ground stations and decreased the time in the Van Allen belts. Telstar 2 was launched in May 1963 and operated successfully for two years.
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- Space Communications and Navigation 1958–1964, NASA SP-93 (1966).
- Special Telstar Issue, Bell Systems Technical Journal, Vol. 42, No. 4 (July 1963). Reprinted as Telstar I, NASA SP-32, Vols. 1–3 (July 1963) and Vol. 4 (including Telstar II supplement) (December 1965).
- K. W. Gatland, Telecommunication Satellites, Prentice Hall, New York (1964).
- I. Welber, "TELSTAR," Astronautics and Aerospace Engineering, Vol. 1, No. 8 (September 1963).
- I. Welber, "Telstar Satellite System," Paper 2618-62, ARS 17th Annual Meeting and Space Flight Exposition (November 1962).
- "Project Telstar," Spaceflight, Vol. 4, No. 5 (September 1962).
- J. Holahan, "Telstar, Toward Long-Term Communications Satellites," Space/Aeronautics, Vol. 37, No. 5 (May 1962).
- D. R. Glover, NASA Experimental Communications Satellites , (10 June 1999).
- D. R. Glover, "NASA Experimental Communications Satellites, 1958–1995," chapter 6 in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997).
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