A communications satellite can be either passive, in that it simply reflects a signal back to Earth (without amplification or retransmission), or active, so that it acts as a repeater by receiving, amplifying, and retransmitting a signal back to Earth. Early satellites were passive to avoid the complexity of an on-board transmitter that would require the satellite to have a power-generation capability (although they did require a radio beacon transmitter so that an Earth station could track the satellite and align its antennas). Passive satellites were inefficient, however, since only a very small portion, about one billionth of a billionth (~10–18) of the transmitter power could be reflected back to Earth and detected by the receiver. Modern satellites are active so that transponders can repeat the signal, resulting in larger received powers at the Earth station.

The following is a brief description of the early communications satellites leading to Syncom 1, the first satellite intended for geosynchronous orbit

Communications Moon Relay (CMR)

Strictly speaking, not only is the Moon the Earth’s first satellite, but it was also used in the early 1950s by the US Navy as the first communications satellite to reflect teletypewriter messages from Washington DC to the west coast of the USA. The Communications Moon Relay (CMR) [1] was then established between 1960 and 1962 to provide reliable long-distance communication between Washington DC and Hawaii. Although limited by the availability of a line-of-sight path from the two stations to the Moon, the CMR was used operationally to provide multi-channel radio teletype and two-way circuits for voice and facsimile as an alternate route for HF circuits during periods of heavy ionospheric disturbance. Communications were also established to USS Hancock and USS Oxford whilst at sea. The CMR used UHF frequencies (435–445 MHz) with 16 kHz bandwidth, using 100-kW transmitters and 25-m steerable high-gain antennas.

Sputnik

The first man-made satellite, Sputnik 1 [2], was launched by Russia on 4 October 1957. Sputnik was an 84-kg, 58-cm sphere launched into an orbit between 231 km and 942 km. Although not used directly for satellite communications, Sputnik transmitted telemetry information for 21 days on 20.005 MHz and 40.002 MHz [3] until its batteries were exhausted. The spacecraft itself remained in orbit for nearly three months. Atmospheric drag gradually lowered its perigee until it re-entered the atmosphere and burned up on 4 January 1958.

Explorer 1

Shortly after Sputnik, on 31 January 1958, the US Army launched the first US artificial satellite, Explorer 1 [4] Explorer was a 2-m long, 15-cm diameter, 14-kg cylinder (perigee ≈ 360 km, apogee ≈ 2,550 km), which only operated for about four months until May 1958 when its batteries were depleted. Among its instruments was a Geiger–Müller cosmic-ray counter (designed by Van Allen and colleagues), and anomalies in the captured data ultimately led to the discovery of the Earth’s Van Allen radiation belts. Explorer 1 remained in orbit for more than twelve years until gradual orbital decay eventually caused it to re-enter the atmosphere on 31 March 1970.

SCORE

Sputnik and Explorer signaled the beginning of the race for space and significant effort was devoted to the technologies required for the deployment of space-based communications-relay satellites to provide cost-effective alternatives to terrestrial radio and cable systems, particularly submarine cable. On 18 December 1958, the United States launched SCORE (Signal Communicating by Orbiting Relay Experiment) [5] the world’s first artificial communications satellite capable of relaying terrestrial transmissions. SCORE, launched under the newly formed Advanced Research Projects Agency (ARPA), was based on equipment modified by the US Army Signal Corps and launched by the US Air Force Ballistic Missile Division on an Atlas rocket. It was a 68-kg conical satellite placed in an elliptical LEO (between 182 km and 1,048 km), at an orbital inclination 32.3°, with an orbital period of 101 minutes. SCORE was a store-and-forward, or delayed-repeater system: signals from Earth stations were recorded on magnetic tape and later rebroadcast by the satellite during subsequent passes. The satellite could carry a single voice channel or up to seventy 60-words-per-minute teletype channels, with a maximum recorded message length of four minutes. Its most famous transmission was President Dwight D. Eisenhower’s Christmas message of 1958, the first human voice to be broadcast from space.

SCORE’s simple VHF transponder was quickly assembled from modified commercial components by the US Army Signal Corps to include a pager-type FM receiver paired with a VHF FM transmitter and an external power amplifier to ~8 W (uplink 150 MHz, downlink 132 MHz; 108 MHz beacon). Contrary to popular belief, it was not a direct derivative of the WWII SCR-536 ‘Handie-Talkie,’ which was an HF AM set at 3.5–6 MHz.

Although SCORE’s batteries failed after 12 days and the spacecraft re-entered Earth’s atmosphere after only 34 days, the mission was an experimental success. It demonstrated the feasibility of satellite relay communications and validated the Atlas B rocket as a space launch vehicle.

Echo

On 12 August 1960, NASA, Bell Telephone Laboratories and the Jet Propulsion Laboratory launched a passive reflector, Echo 1 [6] on a ThorDM-19 Delta rocket into a ~47.2° inclined LEO between ~966 km and ~2,157 km. Echo 1 (officially Echo 1A) was a 30-m plastic balloon (with a mass of 61.2 kg) with an aluminum coating. The balloon had 82 panels that were folded before launch and inflated in orbit.

Echo was used principally for FM voice, facsimile and data transmission. The first transmission was a recorded message from President Eisenhower sent from the NASA station at Goldstone, California to Bell Laboratories at Holmdel, New Jersey, followed by the first two-way telephone conversation via space. Echo was also used on 19 August 1960 to test picture transmission. Although a passive reflector, Echo contained two tracking beacons transmitting with a power of 10 mW at a frequency of 107.9 MHz.

Echo was simple and reliable but was severely limited by being a passive reflector of microwave frequencies between ~0.96 GHz and 2.39 GHz—despite the sphere having a reflectivity of 98%, Earth stations required extremely high-power transmitters of approximately 10 kW, with large 18-m antennas. Even with these high powers, usable receive powers were only possible because the reflector operated at a low height. At that height, however, the orbital periods were very small (118.3 minutes) so that the satellite was only accessible to ground stations for a brief time. Ground stations used FM receivers with phase-lock loops, and low-noise maser amplifiers.

Echo 1 wrinkled and shrank with age, becoming unusable by late 1962, but remained in orbit from until it re-entered the atmosphere on 24 May 1968—about 7.75 years of orbital life. There was no active de-orbit system; the satellite gradually decayed due to atmospheric drag, solar radiation pressure effects, and perturbations in its orbit until it burned up upon re-entry.

A follow-on satellite, Echo 2, launched on 25 January 1964 into near-polar orbit of ~81.5° inclination between ~1,030 km and ~1,315 km, was larger and constructed with a thicker skin to improve durability. In addition to the microwave frequencies used for Echo 1, Echo 2 conducted VHF experiments at ~162 MHz. Like Echo 1, Echo 2 decayed naturally until atmospheric drag and orbital perturbations caused it to re-enter and burn up in Earth’s atmosphere on 7 June 1969—after about 5.5 years in orbit.

Courier

On 4 October 1960, the US Department of Defense launched Courier 1B [7] aboard a Thor–Able rocket (Courier 1A had failed at launch on 18 August 1960). Courier was placed into an elliptical LEO between 396 km and 1,212 km, with a period of 107 minutes and an inclination of 28.3°. Courier had a launch mass of 102 kg, had a 4-W UHF analog FM transmitter and five magnetic tape recorders to provide store-and-forward (delayed-repeater) transmission of voice, data, and facsimile messages. The satellite operated on uplink frequency of 1.8–1.9 GHz and a downlink frequency of 1.7–1.8 GHz, was powered for the first time by solar cells providing ~55 W, which were also used to trickle-charge Ni-Cd batteries to provide power during eclipse periods. Despite its promise, Courier’s mission lasted only 17 days before a malfunction in its command system prevented further operation. Nevertheless, it demonstrated the feasibility of solar-powered, active communications satellites and laid the groundwork for later operational systems. Courier 1B remained in orbit for more than a decade before decaying naturally and re-entering Earth’s atmosphere on 17 August 1967, nearly seven years after launch.

Telstar

On 10 July 1962, AT&T launched Telstar 1 [8] which was the first satellite to provide real-time repeated transmission of voice, TV, and data. The 88-cm sphere has a mass of 77 kg and was powered by 3,600 solar cells. Telstar was launched on Douglas Thor-Delta (Delta A) launch vehicle into an elliptical orbit between 952 km and 5,933 km with 44.8º inclination and an orbital period of 157.8 minutes. Telstar contained 2,528 semiconductor devices and only one travelling wave tube amplifier (TWTA)—the first to be carried on a satellite—providing a gain of 40 dB (10,000 times amplification). Andover, Maine and Holmdel, New Jersey had two large horn antennas—transmit/receive at Andover and receive only at Holmdel. For the first time, a satellite used FM analog signals: relay TV, telephone, and telegraph images. Due to its non-geosynchronous orbit, availability of Telstar 1 for transatlantic signals was limited to the 30 minutes in each 157.8-minute orbit when the satellite passed over the Atlantic Ocean.

Telstar was a simple repeater that received signals at 6.390 GHz, amplified them, and retransmitted them at 4.170 GHz. These C-band frequencies were chosen because of the ready availability of existing terrestrial microwave radio-relay equipment in that band. The satellite’s solar cells generated 14 W, and the power amplifier used a specially developed 50-MHz bandwidth, 2-W broadband TWTA allowing the first color TV signals to be relayed across the Atlantic. The telemetry link operated at 136 MHz.

After five orbits of Earth—tracked by stations in South Africa, South America and Australia—the first live telephone call was between Vice-President Lyndon Johnson in Washington and Frederick R. Kappel, Chairman of the Board of AT&T in Andover. To support Telstar, six ground stations were constructed in the US, France, the UK, Canada, West Germany, and Italy.

Telstar’s significance extended far beyond engineering. For the first time, live TV pictures crossed the Atlantic, allowing audiences in Europe and North America to share events in real time. The initial broadcasts on 11 July 1962 included the US flag at Andover, a baseball game between the Philadelphia Phillies and the Chicago Cubs, and a press conference by US President John F. Kennedy. The following day, the BBC and Eurovision sent images from Europe to the US, including footage of Big Ben and the Eiffel Tower. On 11 July 1962, the first live TV signals were exchanged. On 23 July, full-scale program exchanges took place, reaching more than 200 million viewers in North America and Europe, an unprecedented, shared experience that vividly demonstrated the potential of global satellite communications.

Telstar also captured the public imagination. Its name quickly became synonymous with the dawning “space age,” and it inspired popular culture. Most famously, the British band The Tornados released the instrumental single “Telstar” in August 1962, which topped charts in both the UK and the US. The song’s futuristic electronic sound, created with a Clavioline keyboard, reflected the sense of wonder surrounding satellite communications. To this day, Telstar remains one of the few satellites to have left such a lasting imprint on both technology and popular culture.

Although Telstar 1 was expected to operate until 1964, its electronics were soon damaged by radiation in the Van Allen belts. The problem was worsened by high-altitude nuclear tests, notably the US “Starfish Prime” explosion on 9 July 1962, which greatly increased radiation levels. Telstar 1 ceased continuous operation by 21 February 1963. A more radiation-resistant Telstar 2 was launched on 7 May 1963 into orbit at 1,322 km perigee, 7,439 km apogee, at an inclination of 47.7°, with a period of 225 minutes. Telstar 2 was used for telephone, TV, facsimile, and data transmission until its VHF system was switched off on 16 May 1965. Neither satellite was actively de-orbited. Both remain in their high orbits today as space debris.

It should be noted that later satellites carrying the Telstar name, beginning in the 1980s, were more advanced commercial geostationary spacecraft that shared only the name with Telstar 1 and 2.

Relay

Relay 1 [9] was an early 78-kg spin-stabilized satellite communications system launched by NASA on a Thor-Delta B rocket on 13 December 1962 into an elliptical orbit between 1,300 km and 7,500 km with 47.5° inclination and an orbital period of 185 minutes. Relay was designed as a one-way experimental repeater to demonstrate wideband, multi-channel analog FM voice communication using a 14-MHz bandwidth transponder. It carried two redundant repeaters, operating with an uplink at 1.725 GHz and a downlink at 4.170 GHz, delivering approximately 10 W of RF output power from a traveling-wave tube amplifier. Electrical power was provided by 8,740 solar cells charging six Ni-Cd storage batteries. In addition to its communications payload, Relay 1 supported radiation experiments intended to map the Van Allen belts.

Relay 1 became the first satellite to broadcast TV across the Pacific Ocean, from the US to Japan. Its first planned broadcast, a pre-recorded address from President John F. Kennedy to the Japanese people on 22 November 1963, was overtaken by the breaking news of Kennedy’s assassination. In August 1964, Relay 1 was again used in a landmark demonstration, carrying coverage of the Tokyo Olympic Games from the US across the Atlantic to Europe, after Syncom 3 relayed the signal from Japan to the US. This marked the first use of multi-satellite intercontinental television relays.

Despite early difficulties—including susceptibility to spurious commands and regulator leakage attributed to radiation damage from the Starfish Prime nuclear test in July 1962—Relay 1 functioned successfully until 10 February 1965. With no propulsion or de-orbit capability, it remains in orbit.

A follow-on spacecraft, Relay 2, was launched on 21 January 1964 aboard another Thor–Delta B. Although physically similar in overall configuration, Relay 2 had a substantially higher launch mass of 184 kg, reflecting a more capable and robust second-generation design. The additional mass supported improved power generation and storage, enhanced telemetry, command, and tracking subsystems, and a more reliable and longer-lived communications payload, incorporating lessons learned from Relay 1’s radiation-related anomalies. Relay 2 was inserted into an orbit with an apogee of approximately 7,600 km, a perigee of about 1,870 km, and an inclination of ~46.4°.

NASA officially ceased operations with Relay 2 on 26 September 1965, when the Mojave ground station—the only one capable of communicating with it—was repurposed. However, one of its transponders continued operating until 20 November 1966, albeit with delays coming online, and the other persisted until 9 June 1967, when it stopped working properly. Like its predecessor, Relay 2 was never actively de-orbited and remains in orbit today as debris.

Project West Ford

In 1963, the US Air Force conducted Project West Ford (originally Project Needles) [10], an experiment to create an artificial orbiting communications medium. Nearly 500 million hair-thin copper dipoles, each 1.78 cm long and 25.4 µm thick, were released into a circular orbit at ~3,700 km altitude, producing a belt with an average density of about five dipoles per cubic kilometer. Designed to resonate at 8.35 GHz, the dipoles acted as passive scatterers. Tests demonstrated data rates up to 20 kbps using frequency shift keying (FSK), sufficient for intelligible digitized speech between Camp Parks, California and Westford, Massachusetts. As the belt dispersed, the data rates dropped to 100 bps.

The project drew strong objections from radio astronomers, concerned that the artificial belt would permanently interfere with celestial observations. To mitigate these concerns, the dipoles were designed to disperse and eventually decay. By early 1966, most of the belt had disappeared. However, clumping caused some fragments to remain in orbit much longer than anticipated, and dozens of West Ford debris clusters continue to be tracked more than sixty years after the experiment. The West Ford experiment was never repeated, but it demonstrated that point-to-point communications via an artificial scattering medium could be highly survivable.

Syncom

On 14 February 1963, NASA and the US Department of Defense launched Syncom 1 [11], the first satellite intended for geosynchronous orbit and the first to employ range and range-rate tracking. Although Syncom 1 was lost during injection into synchronous orbit, Syncom 2 and Syncom 3 were launched successfully on 26 July 1963 and 19 August 1964, respectively. Syncom 2 became the world’s first operational geosynchronous communications satellite, while Syncom 3 became the first geostationary communications satellite.

The Syncom series were cylindrical, spin-stabilized satellites with a mass of 39 kg. Syncom 2 achieved a 24-hour orbit but with a 33.1° inclination, making it a geosynchronous orbit but not stationary over a single longitude. Syncom 3 was placed in near-GEO at 180°E with only 1° inclination, effectively appearing fixed in the sky. Each carried two transponders: one supporting two 500-kHz narrowband channels, the other a single 5-MHz wideband channel. The transmitters produced 2.3 W of RF power and operated with uplinks at 1.78–1.85 GHz and downlinks at 2.2–2.3 GHz, supporting full-duplex transmission using both FM and phase shift keying (PSK).

Syncom 2 enabled the first voice call via a geosynchronous satellite, when US President John F. Kennedy spoke with Nigerian Prime Minister Abubakar Tafawa Balewa on 23 August 1963. It also carried telephone, teletype, and facsimile traffic between Africa, Europe, and the US. Syncom 3 achieved greater fame when it was used to broadcast live coverage of the 1964 Tokyo Olympic Games —the first global TV broadcast relayed from space.

Following completion of NASA’s experimental program, both satellites were transferred to the US Department of Defense on 1 January 1965. Both satellites continued to be used for military communications thereafter. Syncom 3, for example, supported US communications in Vietnam. Both satellites remained operational until they were deactivated in 1969.

edVirtus Satellite Communications Courses

You may be interested in the edVirtus satellite communications courses:

• One-day Satellite Communications—Overview.

• Three-day Satellite Communications—Intermediate.

• Five-day Satellite Communications—Advanced.

Related edVirtus Courses

You may be interested in the related edVirtus courses:

• Fundamentals of Communications Systems.

• Introduction to Radio Frequency Propagation.

• RF Radiation Safety Officer (RFRSO) – Level 2

• RF Radiation Safety Officer (RFRSO) – Level 1

Notes

[1] Van Keuren, D. K., “Moon in Their Eyes: Moon Communication Relay at the Naval Research Laboratory, 1951–1962,” in Beyond the Ionosphere: Fifty Years of Satellite Communication, NASA SP-4217, A.J. Butrica, (ed.), Washington, DC: NASA, 1997, pp. 9-18.
The Applied Research Lab / The Pennsylvania University / U.S. Navy, From the Sea to the Stars: A Chronicle of the U.S. Navy’s Space and Space-Related Activities, 1944–2009, Washington, DC: Naval History & Heritage Command, 2010.
American Physical Society, “July 24, 1954: Operation Moon Bounce,” APS News, July 2012.

[2] Staff of the Jodrell Bank Experimental Station, “Radar Observations of the First Russian Earth Satellite and Carrier Rocket,” Nature, vol. 180, 9 Nov 1957, pp. 941–942.
Staff of the Jodrell Bank Experimental Station, “Orbit of the Artificial Earth Satellite,” Nature, vol. 180, 19 Oct 1957, p. 784.
Staff of the Jodrell Bank Experimental Station, “The Artificial Earth Satellite: Observations at Jodrell Bank,” Nature, vol. 180, 2 Nov 1957, p. 890.

[3] Brown, R. R., P. E. Green, Jr., B. Howland, R. M. Lerner, R. Manasse, and G. Pettengill, “Radio Observations of the Russian Earth Satellite,” Proceedings of the IRE, vol. 45, Nov 1957, pp. 1552–1553.
Peterson, A. H., and Staff, “Radio and Radar Tracking of the Russian Earth Satellite,” Proceedings of the IRE, vol. 45, Nov 1957, pp. 1553–1555.

[4] National Aeronautics and Space Administration, The Explorer I Mission: Report on the United States’ First Earth Satellite, NASA Special Publication SP-12, 1958.

[5] Pierce, J. R., “The Orbital Radio Relay Experiment (SCORE),” Bell Telephone System Technical Publications Notebook, AT&T, 1959.
NASA, “The SCORE Mission,” in NASA Historical Data Book, Vol. II: Programs and Projects, 1958–1968, NASA SP-4012, Washington, DC, 1988, pp. 39–42.
U.S. Army Signal Research and Development Laboratory, Signal Communication by Orbiting Relay Equipment (SCORE): Mission Summary, Fort Monmouth, NJ, 1959.
Fitzpatrick, E. J., “SCORE—The First Active Communications Satellite,” IEEE Transactions on Aerospace and Electronic Systems, vol. AES-6, no. 3, May 1970, pp. 445–451.

[6] Pierce, J. R., “The Project Echo Satellite,” Bell System Technical Journal, vol. 40, no. 4, Jul. 1961, pp. 1041–1051.
NASA, Project Echo—Technical Report 1: Description and Performance, NASA TR R-5, Washington, DC, 1961.
NASA, Echo I Spacecraft and Passive Communications Experiments, NASA SP-32, Washington, DC: NASA, 1962.

[7] Cummings, L.H., “Courier Satellite Communications System,” Advances in the Astronautical Sciences, vol. 8, 1961.
Siglin, P. W., and G. F. Senn, “The Courier Satellite” in Communications Satellites (Proceedings of a Symposium, London, 12 May 1961), L. J. Carter (ed), London: Academic Press, 1962.
NASA Historical Data Book, Vol. II (Programs and Projects, 1958–1968), Washington, DC: NASA, 1988.

[8] Solomon, L., Telstar: Communications Breakthrough by Satellite, New York: McGraw-Hill Book Company, 1962.
Taylor, A. S., “Telstar—Communications Satellite,” Bell System Technical Journal, vol. 42, no. 4, July 1963, pp. 1061–1120.
Glover, D. R., “NASA Experimental Satellites, 1958-1995,” in Beyond the Ionosphere: Fifty Years of Satellite Communication, NASA SP-4217, A.J. Butrica, (ed.), Washington, DC: NASA, 1997, pp. 51-64.

[9] Glover, D. R., “NASA Experimental Satellites, 1958-1995,” in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, Ed., NASA SP-4217, 1997, pp. 51-64.

[10] Special Issue on Project West Ford, Proceedings of the IEEE, vol. 52, no. 5, May 1964.

[11] Glover, D. R., “NASA Experimental Satellites, 1958-1995,” in Beyond the Ionosphere: Fifty Years of Satellite Communication, NASA SP-4217, A.J. Butrica, (ed.), Washington, DC: NASA, 1997, pp. 51-64.