TELSTAR, THE WORLD'S 1ST COMMUNICATIONS SATELLITE

Today, The Grandma has been reading about Telstar, the communication satellite that was launched on a day like today in 1962.

Telstar refers to a series of communications satellites. The first two, Telstar 1 and Telstar 2, were experimental and nearly identical. 

Telstar 1 launched atop of a Thor-Delta rocket on July 10, 1962, successfully relayed the first television pictures, telephone calls, and telegraph images through space. It also provided the first live transatlantic television feed. Telstar 2 was launched May 7, 1963. Telstar 1 and 2 -though no longer functional- still orbit the Earth.

Belonging to AT&T, the original Telstar was part of a multi-national agreement among AT&T (USA), Bell Telephone Laboratories (USA), NASA (USA), GPO (United Kingdom) and the direction générale des Télécommunications (France) to develop experimental satellite communications over the Atlantic Ocean. Bell Labs held a contract with NASA, paying the agency for each launch, independent of success.

Six ground stations were built to communicate with Telstar, one each in the US, France, the UK, Canada, West Germany and Italy. The American ground station -built by Bell Labs- was Andover Earth Station, in Andover, Maine. The main British ground station was at Goonhilly Downs, Cornwall.

The BBC, as international coordinator, used this location. The standards 525/405 conversion equipment (filling a large room) was researched and developed by the BBC and located in the BBC Television Centre, London. The French ground station was at Pleumeur-Bodou. The Canadian ground station was at Charleston, Nova Scotia. The German ground station was at Raisting in Bavaria. The Italian ground station (Fucino Space Centre) was at Fucino, near Avezzano, in Abruzzo.

The satellite was built by a team at Bell Telephone Laboratories that included John Robinson Pierce, who created the project; Rudy Kompfner, who invented the traveling-wave tube transponder that the satellite used; and James M. Early, who designed its transistors and solar panels. 

The satellite is roughly spherical, measures 880 mm in length, and weighs about 77 kg. Its dimensions were limited by what would fit on one of NASA's Delta rockets. Telstar was spin-stabilized, and its outer surface was covered with solar cells capable of generating 14 watts of electrical power.

The original Telstar had a single innovative transponder that could relay data, a single television channel, or multiplexed telephone circuits. Since the spacecraft spun, it required an array of antennas around its equator for uninterrupted microwave communication with Earth. An omnidirectional array of small cavity antenna elements around the satellite's equator received 6 GHz microwave signals to relay back to ground stations. The transponder converted the frequency to 4 GHz, amplified the signals in a traveling-wave tube, and retransmitted them omnidirectionally via the adjacent array of larger box-shaped cavities. The prominent helical antenna received telecommands from a ground station.

Launched by NASA aboard a Delta rocket from Cape Canaveral on July 10, 1962, Telstar 1 was the first privately sponsored space launch. A medium-altitude satellite, Telstar was placed into an elliptical orbit completed once every 2 hours and 37 minutes, inclined at an angle of approximately 45 degrees to the equator, with perigee about 952 km from Earth and apogee about 5,933 km from Earth.  This is in contrast to the 1965 Early Bird Intelsat and subsequent satellites that travel in circular geostationary orbits.

Due to its non-geosynchronous orbit, similar to a Molniya orbit, availability of Telstar 1 for transatlantic signals was limited to the 30 minutes in each 2.5-hour orbit when the satellite passed over the Atlantic Ocean. Ground antennas had to track the satellite with a pointing error of less than 0.06 degrees as it moved across the sky at up to 1.5 degrees per second.

Since the transmitters and receivers on Telstar were not powerful, ground antennas had to be 27 m tall. Bell Laboratory engineers designed a large horizontal conical horn antenna with a parabolic reflector at its mouth that re-directed the beam. This particular design had very low sidelobes, and thus made very low receiving system noise temperatures possible. The aperture of the antennas was 330 m2. The antennas were 54 m long and weighed 340,000 kg.

Morimi Iwama and Jan Norton of Bell Laboratories were in charge of designing and building the electrical portions of the azimuth-elevation system that steered the antennas. The antennas were housed in radomes the size of a 14-story office building. Two of these antennas were used, one in Andover, Maine, and the other in France at Pleumeur-Bodou. The GPO antenna at Goonhilly Downs in Great Britain was a conventional 26-meter-diameter paraboloid.

More information: Space Center Houston

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