Communication Satellites (5th Ed.)

Donald Martin, Paul Anderson, Lucy Bartamian

 

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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 operational commercial 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.

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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

Fig 1.1 SCORE communication system

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 hr 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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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).

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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 diam, 166 lb
Echo 2: sphere, 135 ft diam, 547 lb
Not stabilized, no onboard propulsion
Aluminized Mylar surface, maximum reflectivity 98% 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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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.

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Courier

The objective of the Courier program [1–3] was to develop a satellite of higher capacity and longer life than SCORE, which could be used for communication tests and assessments of traffic handling techniques. The concept was similar to SCORE in that the primary operating mode was store-and-dump using onboard tape recorders. A real-time mode was also available. Unlike SCORE, Courier was a self-contained satellite and had both solar cells and rechargeable batteries for power supply. Except for the final amplifiers of the transmitters, the electronics were all solid state. The details of Courier are as follows.

Fig 1.2. Courier satellite.

Satellite
Sphere, 51 in. diam, 500 lb in orbit
Solar cells and NiCd batteries, 60 W

Capacity
Real time: one voice channel
Store-dump: 13.2 Mb/recorder digital, 4 min voice

Transmitter
1700–1800 MHz band
Two transmitters on, two standby
Solid state except output tubes
2 W output per transmitter

Receiver
1800–1900 MHz band
Two receivers on, two standby
All solid state
14 dB noise figure

Antenna
Two slots at antipodal points, used for both transmit and receive
–4 dB gain
Linear polarization

Recorder
Four digital: each 4 min at 55 kbps (13.2 Mb total)
One analog: 4 min capacity, 300–50,000 Hz

Fig. 1.3. Courier communication subsystem

Life
One year

Orbit
525 x 654 nmi, 28 deg inclination (initial values)

Orbital history
Courier 1A: launch vehicle failure
Courier 1B: launched 4 October 1960, operated 17 days
Thor-Able Star launch vehicle

Management
Developed by Army Signal Research and Development Laboratory

The Courier communication subsystem had four receivers, two connected to each antenna. Signals received through the two antennas were summed in a baseband combiner. The satellite could support a single half-duplex voice circuit in the real-time mode. One analog and four digital recorders, each with a 4 min recording capability, were used for the store-and-dump mode. This allowed any ground terminal to use the satellite for transmission of four separate digital (multiplexed teletype) messages, one to each of four other terminals. Upon command, a recorded message (or the received signal in the real-time mode) would modulate two transmitters, one connected to each antenna. The satellite also had two spare transmitters. The two carrier frequencies were separated about 20 MHz. Various signal-combining techniques were used at the ground to make use of these two signals.

The first Courier launch was unsuccessful because of a booster failure. The second, in October 1960, was successful. Communication tests were performed by two ground terminals, located in New Jersey and Puerto Rico. The satellite performed satisfactorily until 17 days after the launch, when communications were stopped by a command system failure.

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1. G. F. Senn and P. W. Siglin, "Courier Satellite Communication System," IRE Transactions on Military Electronics, Vol. MIL-4, No. 4 (October 1960).
2. P. W. Siglin and G. F. Senn, "The Courier Satellite," Communication Satellites, Proceedings of a Symposium Held in London, L. J. Carter, ed. (1962).
3. E. Imboldi and D. Hershberg, "Courier Satellite Communication System," Advances in the Astronautical Sciences, Vol. 8 (1961).

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West Ford

The West Ford concept [1–4] grew out of a 1958 summer study on secure, hard, reliable communications. The following conclusions were reached.

• Use satellites and microwave frequencies for long-distance communications.
• Put all active equipment on the ground for reliability.
• Use a belt of dipoles instead of a single satellite for hardness.

When the concept was defined openly, there was some adverse reaction because of the uncertain effects on optical and radio astronomy. After some time, the project was allowed to proceed under certain restrictions.

West Ford and Echo were the only two passive communication reflectors put into orbit. Echo could rightly be called a satellite, but the West Ford reflector consisted of 480 million copper dipoles. The length was chosen to correspond to a half wavelength of the 8 GHz transmission frequencies used in the program. Other West Ford details are as follows.

Fig 1.4 West Ford dipoles.

Satellite
480 million copper dipoles, each 0.72 in. long, 7 x 10–4 in. diam
88 lb dispenser plus dipoles; dipoles weighed 43 lb

Frequencies
7750, 8350 MHz

Orbit
1970 nmi nominal altitude
Nearly circular, nearly polar
Dispersion: 8 nmi cross-orbit, 16 nmi radially, 1300 ft average distance between dipoles

Orbital history
First: launched 21 October 1961, dispenser did not release dipoles
Second: launched 9 May 1963, fully dispersed August 1963
Atlas-Agena B launch vehicle

Management
Developed by MIT Lincoln Laboratory
The dipoles were dispensed from an orbiting container in May 1963. At first, all were concentrated in one portion of the orbit. During the first few weeks, voice and frequency shift keying (FSK) data up to 20 kbps were transmitted from Camp Parks (Pleasanton, California) to Millstone Hill (Westford, Massachusetts—the source of the project name). Four months later, when the belt was fully extended, the density was much lower, and only 100 bps data were transmitted. Because of this low capacity and the increasing performance of active satellites, no further experiments of this type were attempted. The last transmission of signals was accomplished in 1965, and a combination of measurements and analytic predictions indicated that all the dipoles would reenter the atmosphere before the end of the 1960s.

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1. Special Issue on Project West Ford, Proceedings of the IEEE, Vol. 52, No. 5 (May 1964).
2. I. I. Shapiro, "Last of the West Ford Dipoles," Science, Vol. 154 (16 December 1966).
3. W. W. Ward and F. W. Floyd, "Thirty Years of Research and Development in Space Communications at Lincoln Laboratory," The Lincoln Laboratory Journal, Vol. 2, No. 1 (Spring 1989).
4. W. W. Ward and F. W. Floyd, "Thirty Years of Space Communications Research and Development at Lincoln Laboratory," in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 8.

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Telstar

The Telstar experiment [1–10] 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 to

• look for the unexpected
• demonstrate transmission of various types of information via satellite
• build a large ground antenna and learn how to use it
• gain experience in satellite tracking and orbital predictions
• study Van Allen radiation belt effects
• 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. diam 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.

Fig 1.5. Telstar satellite.

Satellite
Sphere, 34.5 in. diam 170 lb in orbit (Telstar 1), 175 lb in orbit (Telstar 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 (traveling wave tube)
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

Fig 1.6. Telstar communication subsystem.

Telemetry and command
Telemetry: 136.05 MHz, 200 mW transmitter
Command: approximately 123 MHz
Four-element helical antenna

Life
Two-year goal

Orbit
Telstar 1: 514 x 3051 nmi, 45 deg inclination
Telstar 2: 525 x 5830 nmi, 43 deg inclination

Orbital history
Telstar 1: launched 10 July 1962, operated until 23 November 1962, and 4 January to 21 February 1963
Telstar 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 6 months, about 400 transmission sessions were conducted with multichannel telephone, telegraph, facsimile, and television signals. In addition, more than 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 2 years.

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1. Space Communications and Navigation 1958–1964, NASA SP-93 (1966).
2. 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).
3. K. W. Gatland, Telecommunication Satellites, Prentice Hall, New York (1964).
4. I. Welber, "TELSTAR," Astronautics and Aerospace Engineering, Vol. 1, No. 8 (September 1963).
5. I. Welber, "Telstar Satellite System," Paper 2618-62, ARS 17th Annual Meeting and Space Flight Exposition (November 1962).
6. "Project Telstar," Spaceflight, Vol. 4, No. 5 (September 1962).
7. J. Holahan, "Telstar, Toward Long-Term Communications Satellites," Space/Aeronautics, Vol. 37, No. 5 (May 1962).
8. D. R. Glover, "NASA Experimental Communications Satellites," http://sulu.lerc.nasa.gov/dglover/satcom2. html (10 June 1999).
9. D. R. Glover, "NASA Experimental Communications Satellites, 1958–1995," in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 2.
10. M. B. Punnett, "The Building of the Telstar Antennas and Radomes," IEEE Antenna's and Propagation Magazine, Vol. 44, No. 2 (April 2002).

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Relay

The Relay program [1–9] was undertaken by NASA to perform active satellite communications and to measure Van Allen belt radiation and its effect on satellite electronics. Basic objectives were to transmit telephone and television signals across the Atlantic and to transmit telephone signals between North and South America. During the time the satellite was being developed, foreign governments were invited to participate in communications experiments. Primary ground stations were in Maine, England, and France—the same stations that conducted demonstrations with Telstar 1. Other ground stations were in California, New Jersey, Germany, Italy, Brazil, and Japan.

Fig. 1.7. Relay satellite.

The Relay satellite had a more complex communication subsystem than Telstar, with two identical redundant repeaters. Either repeater could be connected to the common antennas by ground command. Each repeater had one 25 MHz channel and two 2 MHz channels. These channels allowed either one-way transmission of wideband (WB) signals or two-way transmission of narrowband (NB) signals. The communication subsystem block diagram is shown; the satellite details follow.

Satellite
Octagonal prism, 35 in. long, 29 in. diam, 53 in. overall length
172 lb in orbit
Solar cells and NiCd batteries, 45 W
Spin-stabilized, 150 rpm

Configuration
Two double-conversion repeaters (one on, one standby), each with one WB and two NB channels

Capacity
WB: 300 one-way voice circuits or one TV channel
NB: 12 two-way telephone circuits (limited by ground equipment, not satellite bandwidth)

Transmitter
4164.7, 4174.7 MHz (NB), 4169.7 MHz (WB)
All solid state except TWT
10 W output

Receiver
1723.3, 1726.7 MHz (NB), 1725 MHz (WB)
All solid state
14 dB noise figure

Antenna
Two biconical horns (one transmit, one receive)
Approximately 0 dB gain normal to spin axis
Circular polarization

Fig. 1.8. Relay communication subsystem

Life
One year

Orbit
Relay 1: 712 x 4012 nmi, 47.5 deg inclination
Relay 2: 1130 x 4000 nmi, 46 deg inclination

Orbital history
Relay 1: launched 13 December 1962, operated until February 1965
Relay 2: launched 21 January 1964, operated until May 1965
Delta launch vehicle

Management
Developed by RCA for NASA Goddard Space Flight Center

Relay 1 was launched in December 1962. Radiation experiment data were obtained on the first day. That same day, difficulties with communications transponder No. 1 that caused excessive power consumption were noticed. The problem could not be fully corrected, and from January 1963 transponder No. 2 was used for almost all the communication experiments. Relay 1 operated until February 1965.

During 1963, several tests and demonstrations were conducted including telephone and television transmissions. Network TV broadcasts were transmitted from the United States to Europe and to Japan. Several times, both television and telephone transmissions were used for international medical consultations. In October 1964, television coverage of the Olympic Games was relayed from Japan to the United States by Syncom 3 and then from the United States to Europe by Relay 1.

Relay 2 was modified slightly to provide increased reliability and radiation resistance. Relay 2 was launched in January 1964 and was used in a variety of communications tests similar to those done with Relay 1. By July 1964, Relays 1 and 2 had been used for 112 public demonstrations of telephone and television transmission. Relay 2 was used until May 1965.

The Telstar and Relay programs were both considered successful. They demonstrated that the technology at that time could produce a useful, medium-altitude communication satellite. In addition, ground station technology was proven, and routine operation of ground stations was demonstrated. Measurements of communications parameters indicated no significant deviations from theoretically expected values. Finally, it was shown that satellite communication systems could share frequencies with terrestrial microwave systems without mutual interference.

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1. Space Communications and Navigation 1958–1964, NASA SP-93 (1966).
2. K. W. Gatland, Telecommunication Satellites, Prentice Hall, New York (1964).
3. Final Report on the Relay 1 Program, NASA SP-76, Goddard Space Flight Center (1965).
4. L. Jaffe, "The NASA Communications Satellite Program Results and Status," Proceedings of the 15th International Astronautical Congress (1964), Vol. 2: Satellite Systems (1965).
5. S. Metzger and R. H. Pickard, "Relay," Astronautics and Aerospace Engineering, Vol. 1, No. 8 (September 1963).
6. Publications of Goddard Space Flight Center 1963, Vol. II:
7.   a. S. Metzger and R. H. Pickard, "Relay" (See Ref. 5).
8.   b. R. H. Pickard, "Relay 1 Spacecraft Performance."
9.   c. R. Pickard, S. Roth, and J. Kiesling, "Relay, An Experimental Satellite for TV and Multichannel Telephony."
10. "Development of the Relay Communications Satellite," Interavia, Vol. 17 (June 1962).
11. D. R. Glover, "NASA Experimental Communications Satellites," http//sulu.lerc.nasa.gov/dglover/satcom2. html (10 June 1999).
12. D. R. Glover, "NASA Experimental Communications Satellites, 1958–1995," in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 2.

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Syncom 1 to 3

Fig. 1.9. Syncom satellite.

In the early 1960s, both medium and synchronous altitude communication satellites were of interest to planners. NASA conducted experiments at both altitudes using the Relay and Syncom satellites. The Syncom program [1–12] had three major objectives:

• to place a satellite in synchronous orbit
• to demonstrate on-orbit stationkeeping
• to make engineering measurements on a synchronous altitude communication link

The Syncom satellite had a short cylindrical body that was spun about its axis to provide stabilization in orbit. The antennas were mounted beyond one end of the body and were collinear with the satellite axis. All the satellite equipment was contained within the body. This design formed the basis for several later synchronous altitude satellites. The communication subsystem had two receivers and two transmitters for redundancy; either receiver could be operated with either transmitter. The channelization was similar to Relay, with two 500 kHz channels for NB two-way communications and one 5 MHz channel for one-way WB transmissions. (These capabilities could not be used simultaneously.) The satellite details are as follows.

Satellite
Cylinder, 28 in. diam, 15 in. height
78 lb in orbit
Solar cells and NiCd batteries, 28 W initially, 19 W minimum after 1 year
Spin-stabilized
Solid rocket motor for apogee maneuver, cold gas propulsion for on-orbit use

Configuration
Syncom 1, 2: two 500 kHz bandwidth double-conversion repeaters or one 5 MHz bandwidth double conversion repeater
Syncom 3: one 5 MHz bandwidth and one switchable (50 kHz or 10 MHz) bandwidth double-conversion repeater (some references say 13 MHz instead of 10 MHz)

Fig. 1.10. Syncom satellite details.

Capacity
Several two-way voice circuits or one TV channel

Transmitter
1815 MHz
Two TWTs (one on, one standby)
2 W output

Receiver
7363 MHz
10 dB noise figure

Antenna
Transmit: three-element collinear slotted array, 6 dB gain, 23 x 360 deg beam
Receive: slotted dipole, 2 dB gain

Fig. 1.11. Syncom communication subsystem.

Telemetry and command
Telemetry: 136 MHz, via four monopole antennas
Beacon: 1820 MHz
Command: 148 MHz, via four monopole antennas

Orbit
Syncom 1, 2: synchronous altitude, approximately 32 deg inclination
Syncom 3: synchronous equatorial

Orbital history
Syncom 1: launched 13 February 1963, all communications failed during orbital insertion
Syncom 2: launched 26 July 1963, operated through 1966, final turn off April 1969
Syncom 3: launched 19 August 1964, operated through 1966, final turn off April 1969
Delta launch vehicle

Management
Developed by Hughes Aircraft Company for NASA Goddard Space Flight Center

Syncom 1 was launched in February 1963. The intended orbit was at synchronous altitude with a 33 deg inclination. The satellite operated properly during the ascent, but all communication was lost when the apogee motor fired to inject the satellite into its final orbit. The cause of the failure was the rupturing of a tank of nitrogen that was part of the on-orbit control subsystem. Syncom 2 was successfully launched in July 1963. Like Syncom 1, it was not intended to achieve a stationary synchronous orbit because of the extra propellant weight and control complexity required to attain 0 deg inclination. NASA conducted a number of tests using this satellite, including voice, teletype, and facsimile. During its first year, in addition to engineering tests, 110 public demonstrations were conducted. Their purpose was to acquaint the public with communication satellites and to gain a broader-based, subjective appraisal of system performance.

Syncom 3 was launched in August 1964. By this time, launch vehicle technology had progressed to the point where a true synchronous equatorial (inclination <1 deg) orbit was possible. The only major change in the communication equipment was a channel, with greater bandwidth than Syncom 2, to be used for television transmissions.

The Department of Defense (DOD) also conducted a number of tests using Syncom 2 and 3. During 1965 and 1966, both were used extensively. Five ground stations and one shipborne terminal were in regular system use. Also, tests with aircraft terminals were conducted using the very high frequency (VHF) command and telemetry links. By February 1966, the Syncom 2 and 3 repeaters had a cumulative operational time of 27,000 hr. DOD use of Syncom diminished when the Initial Defense Communication Satellite Program (IDCSP) satellites became operational.

While the Syncom satellites were being developed and tested, an Advanced Syncom study was also being conducted. The Advanced Syncom program was sometimes called Syncom II, which, in some references, is difficult to distinguish from the second satellite of the original Syncom program (Syncom 2 in this report). The conceptual satellite was larger than Syncom, generated more prime power, had higher antenna gain, and had repeaters of two different designs. This program grew beyond an advanced communications experiment and became the Applications Technology Satellite (ATS) program.

* * * * * *

1. Space Communications and Navigation 1958–1964, NASA SP-93 (1966).
2. L. Jaffe, "The NASA Communications Satellite Program Results and Status," Proceedings of the 15th International Astronautical Congress (1964), Vol. 2: Satellite Systems (1965).
3. C. G. Murphy, "The Hughes Aircraft Company's Syncom Satellite Program," Paper 2619-62, ARS 17th Annual Meeting and Space Flight Exposition (November 1962).
4. R. M. Bentley and A. T. Owens, "Syncom Satellite Program," Journal of Spacecraft, Vol. 1, No. 4 (July–August 1964).
5. P. E. Norsell, "Syncom," Astronautics and Aerospace Engineering, Vol. 1, No. 8 (September 1963).
6. W. H. Edwards and J. S. Smith, "Experience of the Defense Communications Agency in Operating Pilot Satellite Communications," Paper 66-268, AIAA Communications Satellite System Conference (May 1966). Reprinted in Communication Satellite Systems Technology, Progress in Astronautics and Aeronautics, Vol. 19, R. B. Marsten, ed. (1966).
7. F. P. Alder, "Syncom," Proceedings of the 14th International Astronautical Congress (1963), Vol. 2: Satellite and Spacecraft (1965).
8. C. G. Murphy, "A Syncom Satellite Program," Paper 63-264, AIAA Summer Meeting (June 1963).
9. D. D. Williams, "Synchronous Satellite Communication Systems," Advances in Communication Systems, Vol. 2, A. V. Balakrishnan, ed. (1966).
10. D. R. Glover, "NASA Experimental Communications Satellites," http://sulu.lerc.nasa.gov/dglover/satcom2. html (9 June 1999).
11. D. R. Glover, "NASA Experimental Communications Satellites, 1958–1995," in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 2.
12. Syncom, HSC 98035/500/7-98, Communications and Customer Relations, Hughes Space and Communications Company (July 1998), available at http://www.boeing.com/defense-space/space/bss/factsheets/376/syncom/syncom. (25 October 2004).

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Lincoln Experimental Satellites

The Massachusetts Institute of Technology (MIT) Lincoln Laboratory had been active for a long time in various aspects of military communications before the space age. With the early developments of space technology, Lincoln Laboratory began investigations of applications to military communications. The outcome of some of these investigations was the Lincoln Experimental Satellites (LES) series.

LES-1 to -7

Early work in ionospheric and tropospheric scatter communications at Lincoln Laboratory evolved into the West Ford orbital scatter program. At the conclusion of that program in 1963, Laboratory efforts were directed toward active communication satellite techniques [1–8]. The large West Ford ground stations were to be used in the new programs. In addition, smaller mobile terminals were to be developed. The basic goals of the program included demonstration of

Fig. 1.12. LES-1 satellite.

• high-efficiency, all solid-state transmitters
• electronically despun antennas
• communications with small mobile terminals
• techniques for stationkeeping and attitude control

Experimental techniques were developed with a view toward eventual application in synchronous altitude military communication satellites.

LES-1 and -2 were essentially identical. They had small polyhedral bodies and were spin-stabilized. The primary experiment was an all solid-state X-band repeater and an eight-horn electronically switched antenna. The other experiments were in attitude sensing and control. The transmitter source was a crystal oscillator and multiplier chain that was used for upconversion of the signal from intermediate frequency (IF). The X-band power was 200 mW.

The eight horns were mounted so as to provide omnidirectional coverage. Sensors were used to determine the direction of the Earth and the satellite spin rate. Onboard logic then controlled switches to use the antenna most closely pointed toward the center of the Earth. Other details of LES-1 and -2 are as follows.

Satellite
26-sided polyhedron, approximately 24 in. in each dimension
82 lb in orbit
Solar cells, 25 W beginning of life, no batteries
Spin-stabilized with magnetic torquing, 180 rpm

Configuration
20 MHz bandwidth triple-conversion repeater

Fig. 1.13. LES-4 satellite.

Transmitter
7750 MHz (continuous-wave beacon at 7740 MHz)
All solid state
200 mW output, 115 mW at antenna

Receiver
8350 MHz
16 dB noise figure
G/T: –37 dB/K, maximum

Antenna
Eight horns, electronically switched (only one used at a time)
Approximately 3 dB gain

Telemetry
Telemetry: 237.00 MHz, 0.8 W transmitter

Life
Two years

Orbit
1500 x 8000 nmi, 32 deg inclination

Orbital history
LES-1: launched 11 February 1965, launch vehicle failure left satellite in 1500 x 1500 nmi orbit and tumbling
LES-2: launched 6 May 1965, operated until September 1966, final turn off May 1967
Titan IIIA launch vehicle

Management
Developed by MIT Lincoln Laboratory
Operated by MIT Lincoln Laboratory

LES-1 was launched in February 1965. A launch vehicle failure left the satellite in the wrong orbit. The results of limited tests conducted indicated that the repeater and the switched antennas were operating properly. The satellite then entered a tumbling mode that ended its usefulness. LES-2 was launched in May 1965 and operated as planned until it was turned off in September 1966.

LES-3 was not a communication satellite; its purpose was to transmit an ultrahigh frequency (UHF) signal for propagation measurements. LES-3 is described in a later chapter. The LES-4 satellite was similar to LES-1 and -2. The interior structure was the same, but the solar array was mounted on a cylindrical shell rather than on a polyhedral shell, the cylindrical array being more efficient for the synchronous equatorial orbit of LES-4. The satellite details are as follows.

Satellite
10-sided cylinder, 31 in. diam, 25 in. height
116 lb in orbit
Solar cells, 36 W initial minimum, no batteries
Spin-stabilized with magnetic torquing, 11 rpm

Configuration
20 MHz bandwidth triple-conversion repeater

Transmitter
7750 MHz (continuous-wave beacon at 7740 MHz)
All solid state
230 mW at antenna, 3 dBW EIRP

Receiver
8350 MHz
9 dB noise figure
G/T: –29 dB/K, maximum

Antenna
Transmit: eight horns electronically switched, 10 dB peak gain, circularly polarized, each horn covered about 26 x 45 deg of a 26 x 360 deg toroid
Receive: biconical horn, 26 x 360 deg, circularly polarized

Fig. 1.14. LES-1, -2, and -4 communication subsystem.

Telemetry
237.00 MHz

Life
Three years

Orbit
Intended: synchronous equatorial
Actual: 105 x 18,200 nmi, 26 deg inclination

Orbital history
Launched 21 December 1965. Launch vehicle failure resulted in wrong orbit and orientation; decayed 1 August 1977.
Titan IIIC launch vehicle

Management
Developed by MIT Lincoln Laboratory
Operated by MIT Lincoln Laboratory

The LES-4 repeater design was nearly the same as the LES-2 design, but improved components significantly lowered the receiver noise figure and increased the transmitter power. The LES-4 transmitting antenna comprised eight horns uniformly spaced in a plane normal to the satellite spin axis. Sun and Earth sensors and logic circuits controlled the switches to despin the antenna electronically. The difference in the antenna design from LES-2 was possible because LES-4 was intended for use in a synchronous equatorial orbit, where coverage could be limited to 26 deg in the north-south plane.

LES-3 and -4 were launched in December 1965. As the result of a launch vehicle malfunction, the satellites were placed in an elliptical synchronous transfer orbit. Originally, the orientation of LES-4 was such that only enough power was available for operation of the telemetry system. Five days after launch, the spin axis orientation had changed enough so that power was available for the operation of all the satellite systems. From that time, the LES-4 repeater and antenna operated as expected.

The LES-5 and -6 satellites had cylindrical shapes with equipment mounted on a platform near the center of the cylinder and normal to its axis. Both had multiple-element antennas mounted around the cylindrical surface. In addition to their communications equipment, the satellites carried solar cell degradation and radio frequency interference (RFI) experiments. LES-6 also had a prototype autonomous stationkeeping subsystem. The details of LES-5 are as follows.

Fig. 1.15. LES-5 satellite.	Fig. 1.16. LES-6 satellite.

Satellite
Cylinder, 48 in. diam, 64 in. height
230 lb in orbit, beginning of life
Solar cells, 136 W initial maximum, no batteries
Spin-stabilized with magnetic torquing, approximately 10 rpm

Configuration
Single 100 or 300 kHz bandwidth double-conversion repeater

Transmitter
228.2 MHz, beacon at 228.43 MHz
Solid state
35 W output, 16.3 dBW EIRP beginning of life nominal in satellite's equatorial plane

Receiver
255.1 MHz
3.6 dB noise figure
G/T: –26 dB/K nominal in satellite's equatorial plane

Antenna
Eight dipoles parallel to satellite axis, 2.5 dB gain circularly polarized (electronic despin logic tested on satellite, but not used with antennas)

Fig. 1.17. LES-5 communication subystem.

Telemetry
236.75 MHz

Life
Five years

Orbit
18,000 x 18,180 nmi (30 deg drift per day), 7 deg initial inclination

Orbital history
Launched 1 July 1967, operated until May 1971
Titan IIIC launch vehicle

Management
Developed by MIT Lincoln Laboratory
Operated by MIT Lincoln Laboratory

The details of LES-6 are as follows.

Satellite
Cylinder, 48 in. diam, 66 in. height
398 lb in orbit, beginning of life
Solar cells, 220 W initial maximum, limited battery capacity
Spin-stabilized with magnetic torquing, approximately 8 rpm
Cold gas propulsion for on-orbit use

Configuration
Single 100 or 500 kHz bandwidth double-conversion repeater

Transmitter
249.1 MHz (500 kHz mode), 248.94 MHz (100 kHz mode), beacon at 254.14 MHz
Solid-state amplifiers
Variable output power, 120 W initial nominal (see text)
EIRP: 29.5 dBW at beginning of life, 21 dBW after 5 years

Receiver
302.7 MHz (500 kHz mode), 302.54 MHz (100 kHz mode)
3.6 dB noise figure

Antenna
Sixteen sets of dipoles and cavity-backed slots arranged in eight collinear pairs, circularly polarized
Electronically despun, 9.5 dB gain, 34 deg (north-south) x 54 deg (equatorial plane) beamwidth

Fig. 1.18. LES-6 communication subsytem.

Telemetry
236.755 MHz

Orbit
Synchronous altitude, 3 deg initial inclination

Orbital history
Launched 26 September 1968, operated until turned off in March 1976, still operable in 1978, 1983, and 1988 tests
Titan IIIC launch vehicle

Management
Developed by MIT Lincoln Laboratory
Operated by MIT Lincoln Laboratory

LES-5 and -6 had all solid-state communications equipment that operated in the military UHF band. (This is called UHF, although the standard designation is VHF up to 300 MHz and UHF above that.) The LES-5 communication subsystem had a final amplifier of conventional design and had very good efficiency—68-percent direct current (dc) to radio frequency (RF). The LES-6 amplifier was an experimental design in that it was directly connected to the solar-array power bus without any intervening power converters. In this design, all power not required by other satellite systems was directly available to the transmitter, and the transmitter power varied with the available prime power. It was claimed that this design provided an extra 3 dB of transmitted power initially and 0.5 dB extra at the end of satellite life. In-orbit measurements indicated that transmitter power was in the range of 100 to 130 W. LES-5 did not have a despun antenna, but it was used to test some logic that was used in LES-6. The despun circuitry in LES-6 was based on LES-2 and -4 experience and used similar techniques involving Earth and sun sensors.

LES-5 was launched in July 1967 with three IDCSP satellites and was placed into a subsynchronous orbit similar to theirs. Both Lincoln Laboratory and the military services conducted a number of tests with LES-5. Aircraft, shipborne, and fixed and mobile ground terminals were all involved in the tests, which were considered very successful. LES-5 operated until May 1971.

LES-6 was launched in September 1968 and was used in tests similar to those conducted with LES-5. The satellite operated satisfactorily. The communication subsystem continued in active use, although by 1975 the effective radiated power (EIRP) had decreased 8 dB from its initial value. It was turned off early in 1976 to avoid any frequency conflict with the Marisat launched in February 1976.

The LES-7 satellite was intended to have an all-solid-state, 100 MHz bandwidth, single-conversion, X-band repeater and a multibeam antenna. Although the program was canceled before the satellite was built, a prototype antenna was built and tested. This antenna was a waveguide lens-type with a cluster of 19 feed horns and was capable of generating beam sizes as small as 3 deg and as large as Earth coverage.

* * * * * *

1. H. Sherman et al., "The Lincoln Experimental Satellite Program (LES-1, -2, -3, -4)," Journal of Spacecraft and Rockets, Vol. 4, No. 11 (November 1967).
2. H. Sherman et al., "The Lincoln Experimental Satellite Program (LES-1, -2, -3, -4)," Paper 66-271, AIAA Communications Satellite Systems Conference (May 1966).
3. D. MacLellan, H. MacDonald, and P. Waldron, "Lincoln Experimental Satellites 5 and 6," Paper 70-494, AIAA 3rd Communications Satellite Systems Conference (April 1970). Reprinted in Communications Satellites for the 70s: Systems, Progress in Astronautics and Aeronautics, Vol. 26, N. E. Feldman and C. M. Kelly, eds. (1971).
4. R. Berg, R. Chick, and D. Snider, "LES-7 Transponder," Paper 70-511, AIAA 3rd Communications Satellite Systems Conference (April 1970).
5. A. R. Dion, "Variable-Coverage Communications Antenna for LES-7," Paper 70-423, AIAA 3rd Communications Satellite Systems Conference (April 1970).
6. A. R. Dion and L. J. Ricardi, "A Variable-Coverage Satellite Antenna System," Proceedings of the IEEE, Vol. 59, No. 2 (February 1971).
7. W. W. Ward and F. W. Floyd, "Thirty Years of Research and Development in Space Communications at Lincoln Laboratory," The Lincoln Laboratory Journal, Vol. 2, No. 1 (Spring 1989).
8. W. W. Ward and F. W. Floyd, "Thirty Years of Space Communications Research and Development at Lincoln Laboratory," in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 8.

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LES-8 and -9

LES-8 and -9 [1–8] were the latest in a series of experimental military communication satellites developed by the MIT Lincoln Laboratory. They were operating with a variety of fixed and mobile terminals with the use of both UHF and K-band (36–38 GHz) for uplinks and downlinks. A K-band crosslink between LES-8 and LES-9 was a significant part of the program. The communications electronics were all solid state. Two K-band receivers and transmitters were on each satellite, one used with a horn antenna and the other with an 18-in. parabolic reflector. The paraboloid worked with a steerable flat plate and a five-horn feed to provide a narrowbeam tracking antenna. This antenna was normally used for crosslink communications but was also used for uplink/downlink traffic. The satellites acquired the crosslink with initial pointing uncertainties greater than ±1 deg and maintained tracking to better than 0.1 deg at typical signal levels. The horn antenna was fixed and used only for uplinks and downlinks. The K-band transmitters used parallel Impatt diode amplifiers to produce an output power of 0.5 W. The crosslink bit rate was either 10 or 100 kbps, using phase shift keying (PSK) modulation. The K-band uplinks used both eight-tone FSK and differential quadriphase shift keying (DQPSK); the K-band downlinks used DPSK. All UHF transmissions used eight-tone FSK. For transmissions involving UHF links, which were primarily for relatively simple mobile terminals, the basic data rate was 75 bps. The K-band links handled selected information rates up to 19,200 bps, which was adequate for computer data or digitized voice. Except for an optional UHF frequency translation mode with a bandwidth of 500 kHz, all received uplinks were translated to intermediate frequencies and then demodulated. All signal routing was controlled by switches set by commands from the ground. The basic routings are shown in Fig. 1.20.

LES-8 and -9 were practically identical. Most of the electronic subsystems were contained in the satellite body, which is 46 in. long and about 44 in. across. The two radioisotope thermoelectric generators (RTGs) were mounted one upon the other on the back end of the satellite body. These RTGs provide all the electrical power used by the satellite; no solar cells were used. The UHF antenna was also attached to the back end of the satellite body. The K-band antennas and some electronics, plus Earth sensors, were mounted on the front end. The overall length of the satellite was about 10 ft. The satellite was three-axis-stabilized by a gimballed momentum wheel and 10 gas thrusters. The satellite details were as follows.

FIg. 1.19. LES-9 satellite.

Satellite
Approximately 10 ft long
LES-9, 948 lb in orbit, beginning of life
LES-8, similar to LES 9
Two RTGs, 152 W each initially, 130 W each after 5 years (design goal was 145/125 W)
Three-axis stabilization using a gimballed momentum wheel, ±0.1 deg about pitch and roll axes, ±0.6 deg about yaw axis
Cold gas propulsion for on-orbit use

Transmitter
UHF: 240–400 MHz band, 32 W or 8 W output, EIRP 25 dBW (high power mode) or 18 dBW (low power mode)
K-band: 36 to 38 GHz band; 0.5 W output, 21 dBW EIRP (horn); 0.5 W output, 39 dBW EIRP (dish)

Receiver
UHF: 240–400 MHz band, system noise temperature approximately 1000 K, G/T –20 dB/K
K-band: 36–38 GHz band, system noise temperature 1400 K, G/T
≥–8 dB/K (horn), ≥10 dB/K (dish)

Antenna
UHF: three crossed dipoles on a ground plane, 35 deg beamwidth, approximately 8 dB gain (edge of Earth)
K-band: horn, 10 deg beamwidth, 24 dB gain (on axis); dish, 18 in. paraboloid, 1.15 deg beamwidth, 42.6 dB gain (on axis), steerable ±10 deg in elevation and 104 deg in azimuth by gimballed flat plate

Fig. 1.20. LES-8 and LES-9 communication subsystem.

Telemetry and command
Telemetry: 2240 MHz and 236.75 MHz (LES-8), 2250 MHz and 249.36 MHz (LES-9); alternate via K-band communications downlink or crosslink
Command: in 240–300 MHz band; alternate via UHF communications uplink or K-band communications uplink or crosslink

Orbit
Synchronous, 25 deg inclination, 40°W and 110°W longitude, later collocated near 106°W longitude

Orbital history
Launched 14 March 1976
Titan IIIC launch vehicle
In use (1989)

Management
Developed by MIT Lincoln Laboratory
Operated by MIT Lincoln Laboratory

LES-8 and -9 were launched together on a Titan IIIC booster on 14 March 1976. The first tests showed that all important communications parameter values were in good agreement with the prelaunch measurements. Since then, the satellites were exercised in a variety of modes, both for detailed performance measurements and for functionally oriented demonstrations to prove the operability of the various links. These tests involved ground and mobile terminals developed by Lincoln Laboratory, the Air Force, and the Navy. The test results were all satisfactory and showed that the LES-8 and 9 communications features operationally useful. The satellites were still in good condition and being used in 1989.

* * * * * *

1. A. R. Dion, "Satellite Crosslink K-Band Antenna," NEREM 72 Record.
2. F. W. Sarles Jr., "The Lincoln Experimental Satellites LES-8 and -9," Paper 21-1, EASCON '77 Conference Record (September 1977).
3. L. J. Collins, "LES-8/9 Communications System Test Results," Paper 78-599, AIAA 7th Communications Satellite Systems Conference (April 1978).
4. F. J. Solman, "The K-Band Systems of the Lincoln Experimental Satellites LES-8 and LES-9," Paper 78-562, AIAA 7th Communications Satellite Systems Conference (April 1978). Revised version in Journal of Spacecraft and Rockets, Vol. 16, No. 3 (May–June 1979).
5. D. M. Snider and D. B. Coomber, "Satellite-to-Satellite Data Transfer and Control," Paper 78-596, AIAA 7th Communications Satellite Systems Conference (April 1978).
6. W. W. Ward, D. M. Snider, and R. F. Bauer, "A Review of Seven Years of Orbital Service by the LES-8/9 EHF Intersatellite Links," Paper E1.1, International Conference on Communications: ICC '83 (June 1983).
7. W. W. Ward and F. W. Floyd, "Thirty Years of Research and Development in Space Communications at Lincoln Laboratory," The Lincoln Laboratory Journal, Vol. 2, No. 1 (Spring 1989).
8. W. W. Ward and F. W. Floyd, "Thirty Years of Space Communications Research and Development at Lincoln Laboratory," in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 8.

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Applications Technology Satellites

The ATS program evolved from the Advanced Syncom study. The ATS series continued some of the communications experiments planned for Advanced Syncom and also included meteorological, attitude control and stationkeeping, and space environment experiments. ATS 1 through 5 (called ATS B, A, C, D, and E before launch) constituted the first generation of the program; the second generation was the single ATS 6 (ATS F before launch) satellite.

Fig. 1.21. ATS 1 satellite.

ATS 1 to 5

The first objectives of the ATS program were to

• investigate and flight test technology common to a number of satellite applications
• investigate and flight test technology for the geosynchronous orbit
• conduct a gravity gradient experiment
• conduct flight test experiments for a number of types of satellite applications on each individual spacecraft

ATS 1 to 5 [1–9] had some basic similarities, which are summarized in Table 1.1.. The main distinction between the designs of these satellites was that two used spin stabilization and three used gravity-gradient stabilization. Table 1.1 delineates the communications experiments in each satellite; block diagrams of the equipment associated with each experiment are shown graphically.

The C-band communications experiment was the only experiment common to all five satellites. The transmit and receive frequencies were in the satellite communication bands used by the Intelsat satellites. Three modes of operation were possible in each of the two repeaters, which could operate simultaneously. The frequency translation mode was used for WB data relay between two ground stations. In this mode, only one carrier was present, and the signal could occupy the entire 25 MHz repeater bandwidth. Several frequency division multiplexed, single-sideband modulated signals were received in the multiple access mode, and the composite signal was used to phase modulate the transmitter in the satellite. All the ground stations received the transmitted signal and selected the channels of interest from the recovered baseband, which contained all the channels in use. In this way, a number of ground stations could be connected simultaneously. The WB data mode was used for transmission of information generated by onboard meteorological cameras. Various types of antennas were used on ATS 1 to 5 with the C-band communications experiment. Details of the experiment are as follows.

Fig. 1.22. ATS 4 satellite.

Configuration
Two 25 MHz bandwidth repeaters

Capacity
1200 one-way voice circuits or one color TV channel

Transmitter
4120 and 4179 MHz
Two TWTs per repeater, used singly or together
4 W output per TWT, except 12 W at 4179 MHz on ATS 3
EIRP: ATS 1: 19.5, 22.0 dBW (1, 2 TWTs); ATS 3: 22.0, 25.0 dBW (1, 2 4W TWTs), 26.5 dBW (1 12 W TWT); ATS 5: 22.5, 25.0 dBW (1, 2 TWTs)

Receiver
6212 and 6301 MHz
Tunnel diode preamplifiers
6.2 dB noise figure

Antenna
ATS 1: Transmit: phased array, 16 sets of four collinear dipoles, 14 dB gain, 17 deg (north-south) x 21 deg (equatorial plane) beamwidth. Receive: six-element collinear array, 6 dB gain
ATS 2: Horn, 10.5 dB gain
ATS 3: Mechanically despun cylindrical reflector with linear feed on cylinder (and spin) axis, 18 dB gain, 17 deg beamwidth
ATS 4, 5: Receive: planar array, four slots in each of four waveguide sections, 16.3 dB gain, 23 deg beamwidth; transmit: similar array, 16.7 dB gain
The VHF experiment, which was on ATS 1 and 3, had the primary objective of evaluating communications between ground stations and aircraft. Other objectives were (1) to demonstrate the collection of meteorological data from remote terminals, (2) to communicate with ships, and (3) to evaluate the feasibility of a VHF navigation satellite. The VHF equipment on the two satellites was similar. The antenna was an eight-element, but with a common IF amplifier.
It was possible to operate only four transmitters to conserve prime power, or to equalize the phase shifters to generate a toroidal antenna pattern. On ATS 3 only, it was possible to receive a VHF signal and transmit it with the C-band transmitter. Details of the experiment are as follows.

Fig. 1.23. ATS 1 satellite details.

Configuration
100 kHz bandwidth double-conversion repeater

Transmitter
135.6 MHz
ATS 1: 5 W per element, 40 W total, 22.5 dBW EIRP
ATS 3: 6.25 W per element, 50 W total, 25.2 dBW EIRP

Receiver
149.2 MHz
ATS 1: 4.5 dB noise figure
ATS 3: 4.0 dB noise figure

Antenna
Eight-element (dipoles) phased array
ATS 1: 9 dB gain
ATS 3: 10 dB gain
The millimeter-wave experiment on ATS 5 was designed to measure atmospheric effects on propagation. No repeater was included in the satellite. Rather, on both uplinks and downlinks, a carrier was phase-modulated by a sine wave. The modulation index was selected to equalize power at the carrier and the first two sideband frequencies. Measurements were made at two frequencies, one for the uplink and the other for the downlink. These measurements provided data on absorption, refraction, and fading characteristics. The use of the modulated sidebands provided data on the coherence properties of the atmosphere. Details of the experiment are as follows.

Transmitter
15.3 GHz
Solid state
200 mW output

Receiver
31.65 GHz
15 dB noise figure

Antenna
Two horns (one each for transmit and receive)
20 deg beamwidth, 19 dB gain
Modulation (uplinks and downlinks)
Phase modulation, 1.43 modulation index to provide approximately equal power in carrier and first sidebands
Modulation frequency: none, 100 kHz, 1 MHz, 10 MHz, or 50 MHz
The L-band (1550/1650 MHz) equipment on ATS 5 had a design similar to the C-band (4 and 6 GHz) communications equipment on all five ATS satellites. Its purpose was to investigate navigation and traffic control communications for aircraft. For these functions it may have been more suitable than VHF, where the available bandwidth is limited and propagation variations limit navigation accuracy. The L-band equipment could be operated as a repeater in the frequency translation mode. In the multiple access mode, as many as 10 single-sideband modulated signals were received at L-band and combined into a composite signal that frequency modulated either the L-band or the C-band transmitter. An alternative frequency translation mode used the C-band receiver and the L-band transmitter. The transmitter could also be modulated by data from onboard experiments.

Fig. 1.24. ATS 1 to 5 communication subsystems.

Configuration
25 MHz bandwidth repeater

Transmitter
1550 MHz center frequency
Two TWTs used singly or together
12 W per TWT, 22.4 dBW EIRP (one TWT), 25.4 dBW EIRP (two TWTs)

Receiver
1651 MHz center frequency
8 dB noise figure

Antenna
17.2 dB gain

Of the five ATS launches, three satellites were successfully placed in orbit. ATS 2 and 4 did not achieve the desired orbit because of launch vehicle malfunctions, and few experimental data were obtained. The ATS 2 C-band repeaters operated 12 and 626 hr, and the ATS 4 repeaters operated only 9 and 30 hr. ATS 4 was in orbit only 2 months. ATS 2 was in orbit over 2 years but was deactivated after 6 months.

The experiments on both ATS 1 and ATS 3 were used extensively after the satellites were in orbit. Through March 1971, the four microwave communication repeaters on these satellites had accumulated about 35,000 hr of use. Tests were run in all modes, and numerous spacecraft parameters were measured. Various tests were run to determine the values of system noise, delay, frequency response, and intermodulation. In general, system performance was satisfactory according to commercial standards. The C-band communications equipment was also used a number of times for international television broadcasts of public interest.

Engineering performance measurements were also performed on the VHF equipment. System performance was evaluated for ground-satellite-aircraft links using equipment installed on several commercial aircraft. The U.S. Coast Guard performed tests using several shipborne terminals. In general, the results with both aircraft and ships were fair to good communications, and the quality of the satellite link was usually as good as, or better than, alternative communication links. The VHF equipment was also used for experiments in clock synchronization, navigation, and meteorological data collection and dissemination. Results were varied, often limited by available equipment or satellite design, but the experiments did provide a database and recommendations for future work. Since April 1971, the VHF repeater of ATS 1 was used regularly about 20 hr a week as a single channel international communication system called Project PEACESAT (Pan Pacific Education and Communication Experiments by Satellite). PEACESAT provided cultural and emergency communications to about 20 nations (mostly small island nations) of the Pacific basin. ATS 3 also provided communication services in the Pacific basin. Both ATS 1 and ATS 3 degraded in performance, but both continued in use for more than six times their 3-year design lives. In 1985, ATS 1 failed to respond to commands; therefore, it could no longer be kept at the correct location to serve all the Pacific basin users, even though its electronics remained usable. ATS 3 was still functioning properly into 1986.

ATS 5 was successfully placed into synchronous orbit. The satellite was to be spinning upon orbital injection and then despun, at which time the gravity-gradient stabilization would begin. During orbital injection, however, the satellite developed a spin about an axis normal to the intended spin axis. In this orientation, the satellite could not be despun. Because of the spinning condition, the satellite antennas pointed toward Earth only a small portion of each revolution. Hence, the communication experiments were operated with limited success in a pulsed type of operation synchronized with the periods of correct antenna orientation.

* * * * * *

1. Technical Data Report for the Applications Technology Satellite Program, Goddard Space Flight Center (3 March 1967; revised periodically until 20 April 1971), 6 volumes.
2. R. H. Pickard, "The Applications Technology Satellite," Proceedings of the 16th International Astronautical Congress (1965), Vol. 4: Meteorological and Communication Satellites (1966).
3. Spaceflight, Vol. 27, No. 7–8 (July/August 1985), p. 295.
4. Satellite Communications (January 1982), p. 22; (November 1985), p. 45.
5. NASA Semiannual Reports to Congress, Vols. 16 (July–December 1966), 21 (January–June 1969).
6. R. J. McCeney, "Applications Technology Satellite Program," Acta Astronautica, Vol. 5, No. 3–4 (March– April 1978).
7. "Space Systems Summaries," Astronautics and Aeronautics, Vol. 13, No. 2 (February 1975).
8. D. R. Glover, "NASA Experimental Communications Satellites," http://sulu.lerc.nasa.gov/dglover/satcom2. html (15 June 1999).
9. D. R. Glover, "NASA Experimental Communications Satellites, 1958–1995," in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch. 6.

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ATS 6

The ATS 6 satellite [1–28] was the second generation of the NASA Applications Technology Satellite program. Prior to launch, the satellite was designated ATS F. The program had included a second, very similar satellite called ATS G, but it was canceled for budgetary reasons. ATS 1 to 5, launched in 1966 through 1969, constituted the first generation. Eight of the experiments on ATS 6 were for communications and propagation studies that covered a frequency range from 860 MHz to 30 GHz.

ATS 6 consisted of a 30 ft diam parabolic antenna, an Earth-viewing module located at the focus of the parabola, two solar arrays, and the interconnecting structures. The antenna and the solar arrays were deployed after the satellite was in orbit. All the communications experiments were located in a section of the Earth-viewing module. Feed horns for the large parabola were mounted on top of the module and other antennas on the bottom. General satellite characteristics are as follows.

Fig. 1.25. ATS 6 satellite.

Satellite
30 ft diam parabolic reflector, 6.5 ft diam hub section with copper-coated Dacron mesh supported by 48 aluminum ribs
Earth-viewing module at antenna focus with experiment sections and support subsystems, 54 x 54 x 65 in.
Two solar arrays (deployed in space), each half a cylinder, 54 in. radius, 94 in. long
Maximum height, 27 ft, 6 in., maximum span, 51 ft, 8 in.
Initial orbital weight 2970 lb

Power
Solar cells and NiCd batteries
645 W initial maximum
415 W minimum after 5 years

Stabilization
Three-axis-stabilized with inertia wheels, 0.1 deg pointing accuracy
Pointing to any location on Earth
Tracking of low-altitude satellite over ±11 deg from local vertical

Telemetry and command
Telemetry: 136.23, 137.11 MHz via two dipole antennas or main reflector; alternate path through C-band transmitter and horn antenna
Command: 148.26, 154.2 MHz via two dipole antennas or main reflector; alternate path through C-band receiver and horn antenna

Life
Two years (required), 5 years (goal)

Orbit
Synchronous equatorial; 94°W longitude until June 1975, 35°E longitude from July 1975 to July 1976, 140°W longitude until July 1979; moved out of synchronous orbit late 1979 or early 1980

Orbital history
Launched 30 May 1974
Titan IIIC launch vehicle
In use until turned off (July 1979)

Management
Developed by Fairchild for NASA

ATS 6 was launched in May 1974. It was originally positioned at 94°W longitude, where it was used with U.S. ground stations for 1 year. During June 1975, it was moved to 35°E longitude for the instructional television experiment broadcasts to India. At the same time, the NASA millimeter-wave experiment was used in conjunction with several European ground terminals. After the 1-year Indian experiment, in the fall of 1976, the satellite was slowly returned to the Western Hemisphere. During the transfer period, demonstrations of the social benefits possible with such a satellite were made in 27 countries. ATS 6 was then located at 140°W longitude and used in several experimental programs. It was turned off in the summer of 1979.

The position location and aircraft communication experiment (PLACE) was an extension of similar experiments conducted at ATS 1, 3, and 5. Like ATS 5, ATS 6 used frequencies near 1550 and 1650 MHz (L-band) for transmissions to and from aircraft. Both voice and digital data transmissions and a four-tone ranging system for aircraft position determination were part of the experimental program. The system was configured to permit multiple access voice from 100 aircraft in 10 kHz channels. At first, three ground terminals were used to simulate aircraft, with later experiments involving actual aircraft. The ranging signal operation had a transmission to all aircraft, with a coded data channel to designate one aircraft at a time to return the signal. All frequencies were coherently related to the ground station transmitter frequency so that range rate as well as range could be determined. Experiments included multiple aircraft tracking, determination of capacity limitations (ground equipment simulated most of the aircraft), determination of multipath effects, and evaluation of ground and aircraft terminals. Details of the experiment are as follows.

Configuration
Two-way link through ATS 6 between a ground terminal and aircraft for both voice and ranging functions

Transmitter (ATS 6 to aircraft link)
1550 MHz
40 W output, 40.3 or 51.0 dBW EIRP

Receiver (aircraft to ATS 6 link)
1650 MHz
G/T: –4.4 or –5.5 dB/K

Antenna
30 ft parabola, 28–29 dB gain with 0.8 x 7.5 deg fan beam, 38.5 dB gain with 1.5 deg pencil beam, circular polarization

Transmitter (ATS 6 to ground link)
One of 3750, 3950, or 4150 MHz
12 W output, 28 dBW EIRP on axis

Receiver (ground to ATS 6 link)
One of 5950, 6150, or 6350 MHz
G/T: –17 dB/K peak

Antenna
Horn, 16.3 to 16.5 dB gain, 13 x 20 deg beamwidth, linear polarization
The satellite instructional television experiment (SITE, or sometimes ITV) was a cooperative effort by NASA and the government of India. The basic objectives were to demonstrate the use of satellite television broadcasting for instructional purposes and to evaluate the various techniques and equipment. The television programs were prepared by the Indian government and transmitted at 6 GHz to ATS 6 from one of three ground stations in India. The satellite retransmitted the signals at 860 MHz. The 860 MHz signal was directly received in 2000 villages by community television receivers with simple 10 ft parabolic antennas. The signal was also received by regular television stations and rebroadcast to about 3000 villages in the standard VHF television band. The television signal had two audio channels with different dialects. (Operational systems may have as many as 14 audio channels to cover the major dialects and languages used in India.) The 1 year of SITE operation provided experience for development of a national television broadcast satellite system being planned by India. Details of the experiment are as follows.

Configuration
40 MHz bandwidth double-conversion repeater

Transmitter
860 MHz (3750 MHz used occasionally to monitor signals)
80 W output, 51.0 dBW EIRP peak

Receiver
5950 MHz
G/T: –17 dB/K peak

Antenna
Transmit: 30 ft parabola, 33 dB peak gain, 2.8 deg beamwidth, circular polarization
Receive: horn, 16.3 dB peak gain, 13 x 20 deg field of view, linear polarization (30 ft parabola might be used for receiving instead of horn, 48.4 dB peak gain, 0.4 deg beamwidth, +13.7 dB/K G/T)

Fig. 1.26. ATS 6 communication subsystems.

The TRUST experiment (television relay using small terminals) was similar to SITE and used the same equipment in ATS 6. SITE was used in a year-long instructional program with evaluations of that program, whereas the main objectives of TRUST were hardware oriented. System performance was compared with design values, and ionospheric effects on system performance were measured. Considerable emphasis was placed on the small 860 MHz receiver. A program goal was to develop a terminal that would cost less than $200 in large-volume production. The experiment details are the same as given for SITE.

The health/education experiment (formerly the educational television experiment) was used to test satellite distribution of educational and medical programs. The educational programs were primarily for children, and the medical programs covered both professional education and consultation and general health care. The receiving terminals for the experiment were in areas where present television services are limited because of either geographical (Rocky Mountain states, Alaska) or social (Appalachia) factors. Two separate television channels could have been transmitted by ATS 6 using separate antenna beams (produced by two feed horns and the 30 ft reflector). Since a 1 deg beamwidth was used, transmission to the various geographic areas occurred at different times. The transmissions from ATS 6 were at 2570 and 2670 MHz (S-band). Some of the receiving terminals were equipped to provide an S-band return link through ATS 6. Details of the experiment are as follows.

Configuration
Forward link: two 30 to 40 MHz bandwidth repeaters for two FM-TV carriers with sound subcarriers plus separate telephone carriers
Return link: for telephone carriers

Transmitter
2570 and 2670 MHz (also C-band for monitoring)
15 W output, 53.0 dBW peak EIRP

Receiver
5950 MHz
G/T: –17 dB/K peak

Antenna
Transmit: 30 ft parabola, 41.5 dB peak gain, 1 deg beamwidth, circular polarization
Receive: horn, 16.3 dB peak gain, 13 x 20 deg field of view, linear polarization (30 ft parabola might be used for receiving instead of horn, 48.4 dB peak gain, 0.4 deg bandwidth, 13.7 dB/K G/T)

In the tracking and data relay satellite experiment, ATS 6 was used to relay commands and tracking signals to, and data and tracking signals from, GEOS-3 and Nimbus 6. The returned data were compared with data received from the spacecraft at a standard ground terminal. The orbit was computed from the range and range rate data obtained through ATS 6 and the uncertainty of the orbit determination compared with theoretical predictions. ATS 6 used S-band for communications with the spacecraft and C-band for communications with the ground. An array of feed horns under the 30 ft reflector was switched to allow the antenna beam to track the spacecraft along its orbit. The same equipment was also used to provide a communications relay between the ground and an Apollo spacecraft during the Apollo-Soyuz Test Project. Details of the experiment are as follows.

Configuration
Two 12 or 40 MHz bandwidth channels
Two-way link through ATS 6 between ground and a low-altitude satellite

Transmitter (ATS 6 to satellite link)
2063 MHz
20 W output, 48.0 dBW EIRP minimum

Receiver (satellite to ATS 6 link)
2253 MHz
G/T: 7.0 dB/K minimum

Antenna
30 ft parabola, 36.4 dB gain minimum, 13.2 deg overall field of view using switched feeds, circular polarization

Transmitter (ATS 6 to ground link)
3753 MHz primary (alternates 3953 or 4153 MHz)
12 W output, 28.0 dBW EIRP peak

Receiver (ground to ATS 6 link)
5938 MHz primary (alternates 6138 or 6338 MHz)
G/T: –17 dB/K peak

Antenna
Horn: 16.5 dB transmit gain (peak), 16.3 dB receive, 13 x 20 deg field of view, linear polarization
The frequencies from 5925 to 6425 MHz are shared by terrestrial and satellite communication services. The RFI experiment was used to determine the extent of interference between these two services. When the RFI experiment was operating, the entire 500 MHz bandwidth of interest was received by ATS 6 and retransmitted to a ground station. Data processing at the ground station was used to determine the power levels and geographic and frequency distribution of the terrestrial sources of noise. The minimum detectable noise source EIRP was 10 dBW, and the frequency resolution was 10 kHz. A portable ground station was used as a tracking beacon for ATS 6 and as a system calibration source. Details of the experiment follow.

Receiver
5925 to 6425 MHz
G/T: +17.0 dB/K (30 ft parabola) or –17.0 dB/K (horn) peak, minimum detectable ground source is 10 dBW EIRP

Antenna
30 ft parabola, 48.4 dB gain peak, 0.4 deg beamwidth, circular or linear polarization
Horn, 16.3 dB gain peak, 13 x 20 deg beamwidth, linear polarization
ATS 6 had two millimeter-wave experiments. The NASA experiment used a C-band uplink and 20 and 30 GHz downlinks, whereas the Communications Satellite (Comsat) Corporation experiment used 13 and 18 GHz uplinks and a C-band downlink. In the NASA experiment, the 20 and 30 GHz downlinks could have been unmodulated, modulated by an onboard tone generator, or modulated by a communication signal received on the C-band uplink. The continuous-wave propagation tests had sufficient power to accommodate fades as deep as 60 dB, whereas the communication mode was used with digital data rates up to 40 Mbps. A 4 GHz downlink was used with the millimeter-wave downlinks for comparisons. The objectives of the experiment were to measure the characteristics of the millimeter-wave links and to compare directly measured propagation effects with indirect measurements such as radiometric sky temperature, radar backscatter, and meteorological conditions. Details of the experiment follow.

Configuration
Propagation modes: continuous-wave or multitone downlinks
Communications mode: 40 MHz bandwidth repeater

Transmitter (propagation modes)
20.0 and 30.0 GHz
Continuous wave: 2 W output, 30 dBW peak EIRP
Multitone (nine tones): 0.06 W output/tone, 15 dBW peak EIRP/tone

Transmitter (communications mode)
20.15 and 30.15 GHz and one of 3750, 3950, or 4150 MHz
20.15 GHz: 2 W output, 40 dBW peak EIRP
30.15 GHz: 2 W output, 42 dBW peak EIRP
C-band: 12 W output, 28 dBW peak EIRP

Receiver (communications mode only)
One of 5950, 6150, or 6350 MHz
G/T: 13.7 dB/K (30 ft parabola), –17 dB/K (horn)

Antenna
Propagation mode: horn, 27 dB peak gain, 5 x 7 deg beamwidth, linear polarization
Communication mode:
20.15 GHz: 1.5 ft parabola, 37 dB gain, 2.4 deg beamwidth
30.15 GHz: 1.5 ft parabola, 39 dB gain, 1.6 deg beamwidth
C-band transmit: horn, 16.5 dB gain, 13 x 20 deg beamwidth
C-band receive: horn, 16.3 dB gain, 13 x 20 deg beamwidth or 30 ft parabola, 48.4 dB gain, 0.4 deg beamwidth
In the Comsat Corporation millimeter-wave experiment, 39 unmodulated uplinks were received by ATS 6 and retransmitted to a ground station on a C-band downlink. Fifteen stations scattered throughout the eastern part of the United States (>100 miles separation) each transmitted 13 and 18 GHz uplinks. Nine additional stations transmitting 18 GHz uplinks were placed in groups of three near (<25 miles separation) three dual-frequency stations. The experiment operated on a nearly continuous basis for about 1 year. The results are useful for determining the required weather margins for future communication links using frequencies near 13 or 18 GHz. Data from the three groups of stations, with smaller separations, were used to determine attenuation correlation and, hence, the uplink improvement possible with space diversity. Details of the experiment are as follows.

Fig. 1.27. Feed structure for the ATS 6 30-ft reflector.

Configuration
Thirty-nine unmodulated uplink carriers received and retransmitted to a control ground terminal in a 30 MHz bandwidth

Transmitter
4150 MHz
0.2 to 1.3 mW output per carrier
–13 to –21 dBW EIRP per carrier

Receiver
Fifteen carriers near 13.19 GHz and 24 near 17.79 GHz
10 dB noise figure

Antenna
Transmit: horn, 17 dB gain
Receive: 1 ft parabola, 26/28 dB peak gain (13/18 GHz), 4 x 8 deg beamwidth, linear polarization

The communications equipment on ATS 6 included four receivers (C-, S-, L-band, and 13/18 GHz), three IF amplifiers, and five transmitters (C-, S-, L-band, 860 MHz, and 20 and 30 GHz). The 13/18 GHz uplink was downconverted to C-band, amplified, and routed to the C-band transmitter. The other uplinks were amplified and filtered before downconversion to the 150 MHz intermediate frequency. Any receiver (except 13/18 GHz) could have been connected to any one of the three identical IF amplifiers, which could have provided either 12 or 40 MHz bandwidths. The IF outputs could have been connected to any of the transmitters. The transmitters included upconverters, driver amplifiers, and power amplifiers; most of these elements were redundant. The C-band and 20 GHz transmitters used TWTs, whereas the lower-frequency transmitters were all transistorized. The primary communication antenna was the 30 ft parabola. In addition, the satellite had a C-band horn and two small parabolas and a horn for the millimeter-wave experiments. The feed structure for the large reflector included 36 elements to provide efficient performance for the various frequencies and beam patterns used in the communications experiments. The arrangement of the feed elements on the top surface of the Earth-viewing module is shown.

* * * * * *

1. P. J. McCeney, "Application Technology Satellite Program," Acta Astronautica, Vol. 5, No. 3–4 (March– April 1978).
2. "Space Systems Summaries," Astronautics and Aeronautics, Vol. 13, No. 2 (February 1975).
3. J. P. Corrigan, "The Next Steps in Satellite Communications," Astronautics and Aeronautics, Vol. 9, No. 9 (September 1971).
4. A. B. Sabelhaus, "Applications Technology Satellites F and G Communications Subsystem," Proceedings of the IEEE, Vol. 59, No. 2 (February 1971).
5. W. N. Redisch and R. L. Hall, "ATS 6 Spacecraft Design/Performance," EASCON '74 Conference Record (October 1974).
6. W. A. Johnston, "ATS-6 Experimental Communications Satellite: A Report on Early Orbital Results," National Telecommunications Conference: NTC '74 (December 1974).
7. W. N. Redisch, "ATS-6 Description," International Conference on Communications: ICC '75 (June 1975); also, EASCON '75 Convention Record (September 1975).
8. Special Issue on ATS 6, IEEE Transactions on Aerospace and Electronic Systems, Vol. 11, No. 6 (November 1975):
9.   a. E. A. Wolff, "ATS-6—Introduction."
10.   b. R. B. Marsten, "ATS-6—Significance."
11.   c. W. N. Redisch, "ATS-6—Description and Performance."
12.   d. J. P. Corrigan, "ATS-6—Experiment Summary."
13.   e. J. L. Boor, "ATS-6—Technical Aspects of the Health/Education Telecommunications Experiment."
14.   f. J. E. Miller, "ATS-6—Satellite Instructional Television Experiment."
15.   g. J. E. Miller, "ATS-6—Television Relay Using Small Terminals Experiment."
16.   h. P. E. Schmid, B. J. Trudell, and F. O. Vonbun, "ATS-6—Satellite to Satellite Tracking and Data Relay Experiments."
17.   i. V. F. Henry, "ATS-6—Radio Frequency Interference Measurement Experiment."
18.   j. L. J. Ippolito, "ATS-6—Millimeter Wave Propagation and Communications Experiments at 20 and 30 GHz."
19.   k. G. Hyde, "ATS-6—Preliminary Results from the 13/18 GHz COMSAT Propagation Experiment."
20. M. Howard, "ATS-6: The First Twelve Months," Spaceflight, Vol. 17, No. 11 (November 1975).
21. A. A. Whalen and W. A. Johnson, Jr., "ATS-6—A Satellite for Human Needs," Paper 75-900, AIAA Conference on Communication Satellites for Health/Education Applications (July 1975).
22. The ATS-F and -G Data Book, Goddard Space Flight Center (October 1971; revised September 1972).
23. "The Community Satellite" (in three parts), Spaceflight, Vol. 16, Nos. 9–11 (September, October, and November 1974).
24. "The ATS-6 Satellite," Telecommunication Journal, Vol. 41, No. 10 (October 1974).
25. L. H. Westerlund, "ATS-F Comsat Millimeter Wave Propagation Experiment," Comsat Technical Review, Vol. 3, No. 2 (Fall 1973).
26. A. L. Berman, "The ATS-F Comsat Propagation Experiment Transponder," Comsat Technical Review, Vol. 3, No. 2 (Fall 1973).
27. J. L. Levatich and J. L. King, "ATS-F Comsat Millimeter Wave Propagation Experiment," Paper 8A, National Telecommunications Conference: NTC '72 (December 1972).
28. J. L. King and G. Hyde, "The Comsat 13 and 18 GHz Propagation Experiment," International Conference on Communications: ICC '75 (June 1975).
29. L. J. Ippolito, "The GSFC 20 and 30 GHz Millimeter Wave Propagation Experiment," International Conference on Communications: ICC '75 (June 1975); also, EASCON '75 Convention Record (September 1975).
30. V. F. Henry and G. Schaefer, "System Design of the ATS-F RFI Measurement Experiment," Paper 38D, National Telecommunications Conference: NTC '72 (December 1972).
31. J. G. Potter and J. M. Janky, "The ATS-F Health-Education Technology Communications System," International Conference on Communications: ICC '73 (June l973).
32. A. A. Whalen, "Health Education Telecommunications Experiment," International Conference on Communications: ICC '75 (June 1975).
33. J. R. Burke, "Experimental Systems in Applications Technology Satellite F and G," Paper 72-578, AIAA 4th Communications Satellite Systems Conference (April 1972).
34. W. A. Johnson, "ATS-6 Experimental Communications Satellite Report on Early Orbital Results," Journal of Spacecraft and Rockets, Vol. 13, No. 2 (February 1976).
35. E. V. Chitnis and J. E. Miller, "Social Implications of Satellite Instructional Television Experiment," International Conference on Communications: ICC '76 (June 1976).
36. D. L. Brown and Y. P. G. Guerin, "Aeronautical and Maritime Communications Experiments with the ATS-6 Satellite," ESA Bulletin, No. 5 (May 1976).
37. F. O. Vonbun, P. D. Argentiero, and P. E. Schmid, "Orbit Determination Accuracies Using Satellite-to-Satellite Tracking," IEEE Transactions on Aerospace and Electronic Systems, Vol. 14, No. 6 (November 1978).
38. D. R. Glover, "NASA Experimental Communications Satellites," http://sulu.lerc.nasa.gov/dglover/satcom2. html
39. D. R. Glover, "NASA Experimental Communications Satellites, 1958—1995," in Beyond the Ionosphere: Fifty years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D. C. (1997), ch. 6.

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Communications Technology Satellite

The Communications Technology Satellite (CTS), formerly called Cooperative Applications Satellite C (CAS-C), was a joint effort of the Canadian Department of Communications and NASA [1–22]. The main purpose of CTS was to demonstrate advanced spacecraft techniques that were applicable to higher-power transmissions in the 12 to 14 GHz band, including a high-power transmitter, a lightweight extendable solar array with an initial output above 1 kW, and a three-axis stabilization system to maintain accurate antenna pointing. Canada developed the satellite. NASA provided the primary experiment, which was a 200 W output, 50-percent efficient 12 GHz TWTA (traveling wave tube amplifier). NASA also had the responsibility for launching the satellite. The European Space Research Organization (ESRO), now known as ESA (European Space Agency), participated in the CTS program by supplying one of the TWTAs, a parametric amplifier, and some other items.

The satellite body was roughly a cylinder 6 ft in height and diameter, which was injected into a synchronous equatorial orbit in a spinning condition. Solar cells on the satellite body supplied power during this time. After it was despun, two 51 x 244 in. solar panels were deployed from opposite sides of the body. The solar panels rotated about their long axis to track the sun continually. The antennas were mounted on gimbals on the front (Earth-viewing) end of the body and required no deployment. Satellite details are as follows.

Fig. 1.28. Communications Technology Satellite.

Satellite
Body 72 in. diam, 74 in. height with two solar arrays 51 in. wide and 20 ft, 4 in. long; total satellite span 52 ft, 9 in.
738 lb in orbit, beginning of life
Sun-tracking solar array and NiCd batteries, 1360 W initially, approximately 930 W minimum during last year (1979)
Three-axis stabilization using a variable-speed momentum wheel, ±0.1 deg about pitch (north-south) and roll (velocity vector) axes, ±1.1 deg about yaw (radial) axis
Solid rocket motor for apogee maneuver, hydrazine thrusters for on-orbit use

Configuration
Two 85 MHz bandwidth single-conversion repeaters

Transmitter
11.843–11.928 GHz and 12.038 to 12.123 GHz
Normal configuration 20 W TWTA on low band and 200 W TWTA on high band, alternately both bands share the 20 W TWTA (at reduced capability)

Receiver
14.010–14.095 GHz and 14.205 to 14.290 GHz
Two preamplifier chains (one on, one standby)

Noise temperature:
Approximately 2000 K with tunnel diode preamplifier or approximately 1350 K with parametric amplifier
G/T: 6.4 dB/K on-axis with parametric amplifier

Antenna
Two 28 in. diam antennas, 36.2 dB gain on axis for transmit and receive, 2.5 deg beamwidth, steerable over ±7.25 deg linear polarization

Fig. 1.29. CTS communication subsystem.

Telemetry and command
Telemetry: 2277.5 MHz, 2 W transmitter
Beacon: 11.7 GHz, 200 mW transmitter
Command: 2097.2 MHz

Life
Two years

Orbit
Synchronous equatorial, 116°W longitude, (142°W last half of 1979) ±0.2°E-W stationkeeping, inclination ≤0.8 deg through mid-1979

Orbital history
Launched 17 January 1976
Delta 2914 launch vehicle
In use until turned off (November 1979)

Management
Developed by Canadian Department of Communications

The communication equipment included 20 and 200 W TWTAs. Two 85 MHz channels were available. Normally, one of the redundant 20 W TWTAs was the power amplifier for one channel as well as the low-level driver for the 200 W TWTA on the second channel. In a backup mode, the 200 W TWTA was bypassed, and the output of the 20 W TWTA was divided between the two channels. Some characteristics of the 200 W TWTA, as demonstrated during the first 6 months in orbit, were

• construction: coupled cavity, multistage depressed collector, conduction cooling
• RF output at saturation: 200 W continuous-wave minimum over the operating band, 240 W peak, 30 dB gain, 3 dB bandwidth ≥85 MHz
• center frequency: 12.080 GHz
• efficiency: 45% at 224 W output (including power supply)

The CTS had redundant receivers, one with a tunnel diode preamplifier and the other with a parametric amplifier. Both receiver chains were single conversion and had a tunnel diode amplifier (TDA) following the mixer. The receivers fed redundant field effect transistor amplifiers that provided the input signals for the TWTAs. The satellite had two narrowbeam antennas, one directed toward a control terminal and the other toward remote terminals. The two channels were used for two-way communications. The high-power TWTA was used for transmission to the remote terminals that used relatively small antennas.

Canada, NASA, and other U.S. Government agencies started conducting communication experiments with the CTS following its launch on 19 January 1976. Canada had its control terminal at Ottawa and remote terminals in the north. The capability of the CTS allowed the remote terminals to be relatively small, as indicated by the characteristics given in Table 1.2. The CTS could support several simultaneous links with these terminals. For example, the 8 ft terminal noted in Table 1.2 could receive a television signal transmitted with only a quarter of the total CTS power. In May 1976, the CTS was renamed Hermes in Canada. By mid-1978, 32 experimental programs had been completed or were in progress and seven more were planned. These experiments were in the fields of propagation, communications engineering, television broadcasting, education, medicine, government, and community affairs. Results were positive and encouraged further work. The operational viability of many of these projects was studied further using the 12 and 14 GHz channels on Anik B. In July 1979, CTS was moved to support satellite communications testing in Australia. CTS was used until November 1979, at which time it was turned off.

* * * * * *

1. C. Franklin and E. Davison, "A High Power Communications Technology Satellite for the 12 and 14 GHz Bands," Paper 72-580, AIAA 4th Communications Satellite Systems Conference (April 1972). Reprinted in Communications Satellite Systems, Progress in Astronautics and Aeronautics, Vol. 32, P. L. Bargellini, ed. (1974).
2. V. O'Donovan, "Design of a 14/12 GHz Transponder for the Communications Technology Satellite," Paper 72-734, CASI/AIAA Meeting: Space—1972 Assessment (July 1972).
3. P. L. Donoughe, "United States Societal Experiments via the Communications Technology Satellite," International Conference on Communications: ICC '76 (June 1976).
4. L. J. Ippolito, "Characterization of the CTS 12 and 14 GHz Communication Links—Preliminary Measurements and Evaluation," International Conference on Communications: ICC '76 (June 1976).
5. L. D. Braun and M. V. O'Donovan, "Characteristics of a Communications Satellite Transponder," Microwave Journal, Vol. 17, No. 12 (December 1974).
6. J. Day, "CTS Communications Experiments," Paper 35B, National Telecommunications Conference: NTC '72 (December 1972).
7. D. L. Wright and J. W. B. Day, "The Communications Technology Satellite and the Associated Ground Terminals for Experiments," Paper 75-904, AIAA Conference on Communications Satellites for Health/ Education Applications (July 1975).
8. E. F. Miller, J. L. Fiala, and I. G. Hansen, "Performance Characteristics of the 12 GHz, 200 Watt Transmitter Experiment Package for CTS," EASCON '75 Convention Record (September 1975).
9. G. H. Booth, "The Canadian/U.S. High Power Communications Technology Satellite," Satellite Systems for Mobile Communications and Surveillance, IEE Conference Publication No. 95 (March 1973).
10. J. Kaiser, "Experiments in Satellite Communications with Small Earth Terminals," Paper 80-0535, AIAA 8th Communications Satellite Systems Conference (April 1980).
11. H. R. Raine, "The Communications Technology Satellite Flight Performance," Acta Astronautica, Vol. 5, No. 5–6 (May–June 1978).
12. Journal of the British Interplanetary Society, Vol. 29, No. 9 (September 1976), p. 608.
13. R. E. Alexovich, "On-Orbit Performance of the 12 GHz, 200 Watt Transmitter Experiment Package for CTS," Paper 1.3, International Conference on Communications: ICC '78 (June 1978)
14. N. G. Davies, J. W. B. Day, and M. V. Patriarche, "The Transition from CTS/Hermes Communications Experiments to Anik-B Pilot Projects," EASCON '78 Conference Record (September 1978).
15. A. Casey-Stahmer, "From Satellite Experiments to Operational Applications: Canadian Experiences and Plans," Acta Astronautica, Vol. 8, No. 1 (January 1981).
16. N. G. Davies et al., "CTS/Hermes—Experiments to Explore the Applications of Advanced 14/12 GHz Communications Satellites," Proceedings of the XXIXth International Astronautical Congress (October 1978).
17. C. A. Siocos, "Broadcasting-Satellite Signal Reception Experiment in Canada Using the High-Power Satellite Hermes," International Broadcasting Convention, IEE Conference Publication No. 166 (September 1978).
18. H. R. Raine and J. S. Matsushita, "Hermes Satellite (CTS): Performance and Operations Summary," Paper 80-0578, AIAA 8th Communications Satellite Systems Conference (April 1980).
19. J. W. B. Day, N. G. Davies, and R. J. Douville, "The Applications of Lower Power Satellites for Direct Television Broadcasting," Acta Astronautica, Vol. 7, No. 12 (December 1980).
20. D. R. Glover, "NASA Experimental Communications Satellites," http://sulu.lerc.nasa.gov/dglover/satcom2.html (10 June 1999).
21. 21 B. C. Blevis, "The Pursuit of Equality: The Role of the Ionosphere and Satellite Communications in Canadian Development," in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997), ch 14.
22. "Hermes, Communications Technology Satellite (CTS)," Online Journal of Space Communication, No. 4, http://satjournal.tcom.ohiou.edu/Issue4/historal_hermes.html (25 October 2004).

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Sirio

The Italian industrial research satellite (Sirio) [1–12] was developed for use in propagation and communication experiments at 11.6 and 17.4 GHz. These frequencies were selected prior to the 1971 World Administrative Radio Conference and, therefore, did not exactly coincide with the satellite communication frequency bands defined at the conference. A large part of the Italian aerospace industry participated in construction of the satellite under direction of the Italian National Research Council (CNR). Three ground stations in Italy plus stations in other European countries participated in the Sirio experiments.

The satellite had a cylindrical, spin-stabilized body with a despun antenna on one end. All the equipment was mounted on an internal platform. The payload was primarily for support of the three primary experiments: propagation, NB communications, and WB communications. Secondary experiments were for measurements of the natural environment at synchronous altitude.

Fig. 1.30. Sirio satellite.

In the propagation experiment, the 17.4 GHz uplink was amplitude-modulated at 386 MHz to produce two sidetones 772 MHz apart. In the satellite, they were converted to about 386 MHz with a separation of 20 kHz, and a calibrated reference signal was inserted between them. This combined signal was further converted to 266 MHz and used to amplitude-modulate the 11.6 GHz downlink carrier. The downlink carrier amplitude was controlled to provide a reference level. This combination of uplinks and downlinks allowed all measurements to be performed on the ground. The measurements made were absolute attenuation at 11.6 and 17.4 GHz, and relative attenuation and phase delay over frequency intervals of 772 MHz and 532 MHz. In addition, multiple ground receivers were used to measure space diversity improvement. Space diversity on the uplink was achieved by having two sidetones transmitted from different locations.

In the NB communication mode, as many as 12 biphase modulated carriers were transmitted to the satellite by frequency division multiplexing. The data rate on each carrier was 70 kbps, and the satellite bandwidth was 2.5 MHz. In the satellite, the combined signal was amplified at IF and then used to modulate the downlink carrier. The WB communication mode was similar, except that the satellite bandwidth was 35 MHz. The uplink transmission was a single television channel or high-rate digital data.

The satellite was operated in any one of the three modes. The satellite equipment was common for all the modes except for portions of the IF section. The transmitter output power was 10 W from either of two TWTAs. The equipment details are as follows.

Satellite
Cylinder, 56 in. diam, 34 in. height (78 in. overall)
480 lb in orbit, beginning of life
Solar cells, 135 W beginning of life, 100 W minimum after 2 years
Spin-stabilized, 90 rpm
Solid rocket motor for apogee maneuver, hydrazine thrusters for on-orbit use

Configuration
Communication experiment: 2.5 MHz bandwidth repeater with as many as twelve 70 kbps carriers, or 35 MHz bandwidth repeater with one TV channel
Propagation experiment: 40 kHz bandwidth repeater

Transmitter
11.597 GHz
10 W output TWTA (one on, one standby)
EIRP: propagation mode, 16 dBW; NB communication, 24 dBW; WB communication, 26 dBW; all at edge of coverage (all 5 dB higher in central 1 deg of beam)

Fig. 1.31. Sirio communication subsystem.

Receiver
17.395 GHz
G/T: –16 dB/K (–10 dB/K over central 3 x 5 deg of beam)

Antenna
Fixed feed horn with mechanically despun reflector, >22.5/23.5 dB gain on axis (11.6/17.4 GHz), 6 x 10 deg beamwidth (6 deg is north-south beamwidth), beam center 6.5 deg above equatorial plane, steerable 3.5°W to 4.5°E of satellite nadir, circular polarization

Telemetry and command
Telemetry: 136.14 MHz, 6.5 W transmitter
Command: 148.26 MHz
Four quarter wave monopole antennas

Life
Two years

Orbit
Synchronous equatorial, 15°W longitude, later moved to 12°E longitude; moved to 65°E in early 1983; drifting in 1990s

Orbital history
Launched 25 August 1977, in use until 1985
Delta 2313 launch vehicle

Fig. 1.32. RF spectra in the Sirio satellite.

Management
Developed by Italian aerospace industry for CNR (Consiglio Nazionale della Richerche)

The Sirio experiment was defined in 1968 and was originally scheduled to be launched in 1972. A number of delays occurred as the result of technical, political, and financial reasons. The satellite was launched 25 August 1977 and used in a variety of experiments. In 1983, it was moved to a position over the Indian Ocean for cooperative Chinese-Italian experiments, which lasted until October 1984. Sirio was turned off in 1985.

The Sirio 2 satellite was an ESA program. The satellite was primarily constructed with hardware left over from the basic Sirio program, but the payloads were different. Sirio 2 had an S-band transponder for distribution of meteorological data between ground sites, and a detector and retroreflector for a laser clock synchronization experiment.

The Sirio 2 program started in 1978. The satellite was launched together with a Marecs satellite on an Ariane launch vehicle in September 1982. A failure in the Ariane third stage resulted in the loss of both satellites.

* * * * * *

1. F. Carassa, "The Italian Satellite Sirio," Paper 70-501, AIAA 3rd Communications Satellite Systems Conference (April 1970). Reprinted in Communication Satellites for the '70s: Systems, Progress in Astronautics and Aeronautics, Vol. 26, N. E. Feldman and C. M. Kelly, eds. (1971).
2. P. Fanti and S. Tirro, "The Italian Sirio Experiments: Satellite and Ground Equipment," Paper 70-502, AIAA 3rd Communications Satellite Systems Conference (April 1970). Reprinted in Communication Satellites for the '70s: Systems, Progress in Astronautics and Aeronautics, Vol. 26, N. E. Feldman and C. M. Kelly, eds. (1971).
3. Aviation Week & Space Technology (23 August 1971), p. 92.
4. "Space Programmes Around the World: 2. Italy," Interavia, Vol. 26 (June 1971).
5. "The World of Aerospace," Interavia, Vol. 29 (January 1974).
6. G. Perrotta, "The Italian Sirio 12–18 GHz Experiment: The Forerunner of 20–30 GHz Preoperational Satellites," Paper 78-631, AIAA 7th Communications Satellite Systems Conference (April 1978).
7. F. Carassa, "The Sirio Programme," Acta Astronautica, Vol. 5, No. 5–6 (May–June 1978).
8. Special Issue on the Sirio Programme, Alta Frequenza, Vol. 47, No. 4 (April 1978) (English Issue No. 2). Partial contents:
9.   a. F. Carassa, "The Sirio Programme and Its Propagation and Communication Experiment."
10.   b. A. Canciani, "System and Subsystem Design Criteria of the Sirio Satellite."
11.   c. G. Perrotta, "The SHF Experiment Onboard Equipment."
12.   d. S. Tirro, "The System Design of the SHF Experiment."
13. F. Carassa et al., "The Sirio SHF Experiment and its First Results," Astronautics for Peace and Human Progress, Proceedings of the XXIXth International Astronautical Congress (October 1978).
14. E. Saggese, "In Orbit Performance of the SIRIO SHF Experiment," Alta Frequenza, Vol. 48, No. 6 (June 1979).
15. P. Ramat, "Propagation Measurements in Circular Polarization on a Satellite-Earth Path Through SIRIO Experimental Satellite," Alta Frequenza, Vol. 48, No. 6 (June 1979).
16. P. Berlin, "The Sirio-2 Programme," ESA Bulletin, No. 19 (August 1979).

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Japanese Satellites

Japan built and launched several low-altitude satellites in the early 1970s, but its first communications and broadcasting satellites were built in the United States and launched by NASA. These are described in chapter 8. At the same time, Japan was developing smaller synchronous orbit satellites and a launch vehicle for them. The launch vehicle was the N rocket, which was based on the 1970 design of the U.S. Thor-Delta. An improved version, the N-2, was based on the mid-1970s Delta. The first synchronous orbit mission for this launch vehicle was the Engineering Test Satellite-II (ETS-II), described in chapter 9. The successor to ETS-II was the Experimental Communication Satellite (JECS), which was also launched by the N rocket. Japan continued the development and test of satellite bus and payload technologies and the demonstration of improved launch vehicles with a series of Engineering Test Satellites (ETS), also known by the name Kiku. This section describes the Engineering Test Satellites that have or had a communications or broadcasting payload. Three closely related satellites not numbered in the ETS series are also described: the Communications and Broadcasting Engineering Test Satellite (COMETS), the Optical Intersatellite (or Inter-orbit) Communications Engineering Test Satellite (OICETS), and the Wideband InterNetworking Engineering Test and Demonstration Satellite (WINDS).

Japanese Experimental Communication Satellite

The objectives of the Japanese Experimental Communication Satellite (JECS) program [1–4] were to develop techniques for launch and on-orbit control of synchronous satellites, to make propagation measurements, and to conduct communications experiments. The satellites were launched on the Japanese N rocket. JECS was based on the Skynet I design, because the Skynet was sized to the Delta launch vehicle from which the N rocket was developed; both satellites were built by the same manufacturer. Like Skynet, JECS was spin-stabilized with a mechanically despun antenna. The solar array was moun