Telstar - Description

Description

Belonging to AT&T, the original Telstar was part of a multi-national agreement between AT&T (US), Bell Telephone Laboratories (US), NASA (US), GPO (UK) and the National PTT (France) to develop experimental satellite communications over the Atlantic Ocean. Bell Labs held a contract with NASA, reimbursing the agency three million pounds for each launch, independent of success. The US ground station was Andover Earth Station in Andover, Maine, built by Bell Labs. The main British ground station was at Goonhilly Downs in southwestern England. This was used by the BBC, the international coordinator. 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 (48°47′10″N 3°31′26″W / 48.78611°N 3.52389°W / 48.78611; -3.52389) in north-western France.

The satellite was built by a team at Bell Telephone Laboratories, including John Robinson Pierce, who created the project; Rudy Kompfner, who invented the traveling wave tube transponder used in the satellite; and James M. Early, who designed its transistors and solar panels. The satellite is roughly spherical, measures 34.5 inches (876.30 mm) in length, and weighs about 170 pounds (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 to generate electrical power. The power produced was 14 watts (0.019 hp).

The original Telstar had one innovative transponder to relay data, which was a television channel or multiplexed telephone circuits. An omnidirectional array of small antenna elements around the satellite's "equator" received 6 GHz microwave signals to be relayed. 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 was for 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 in 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 kilometres (592 mi) from Earth and apogee about 5,933 kilometres (3,687 mi) from Earth This is in contrast to most of today's communications satellites, which are placed in circular geostationary orbits.

Due to its non-geosynchronous orbit, Telstar's availability for transatlantic signals was limited to the 20 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 transmitting and receiving radio systems on board Telstar were not powerful, the ground antennas had to be huge. Morimi Iwama and Jan Norton of Bell Laboratories were in charge of designing and building the electrical portions of the system that steered the antennas. The aperture of the antennas was 3,600 square feet (330 m2). The antennas were 177 feet (54 m) long and weighed 380 short tons (340,000 kg). The antennas were housed in radomes the size of a 14-story office building.