SATELLITES GOONHILLY HAS WORKED WITH



Telstar



Produced by Bell Laboratories, TELSTAR 1 & 2 were two of the first Communications Satellites in a Low Earth Orbit (LEO) and with a single transponder provided the means of exploring the experimental trans-Atlantic tests between America and Europe. Four Earth Stations in Europe, Goonhilly (UK), Pleumeur Boudou (France), Fucino (Italy), and Raisting (Germany) connected to Andover in Maine (USA) and Mill Village (Canada).


These Satellites were both spheres around 3 ft (90cm) diameter. Although now inactive, are still orbiting the Earth. Visit the www.heavens-above.com website Satellite database to see when they are in your sky.



Relay



RELAY 1 & 2 joined the TELSTAR satellites in Low Earth Orbits to continue transmission experiments across the Atlantic.



These Satellites, although now inactive, are still orbiting the Earth. Visit the www.heavens-above.com website Satellite database to see when they are in your sky.



OUT TO GEOSTATIONARY ORBIT



As the original experiments proved, it was possible to bridge the main Oceans using the orbiting satellites, but it became apparent that communication times were limited by times where only one Earth Station is seeing the satellites. Work directed to a concept which was postulated by Arthur C. Clarke in an article in the technical periodical "Wireless World" in 1945, whereby total coverage of the populated world for communications purposes could be made using just three satellites spaced equally around the world at the Equator at a distance of approximately 22,000 miles (36,000Km) above sea level with an orbital velocity of 6,900 mph (11.000 Kph).







NASA , in the meantime, had implemented a programme to explore geostationary experiments and three Syncom satellites were built for them by the Hughes Space & Communications company. The tests were all made over the Pacific Ocean, so Goonhilly was not involved. Syncom 1 failed to achieve orbit, but the others achieved synchronous orbit. Syncom 2 was used to test voice, teletype and fax capabilities, whilst Syncom 3, with a wideband channel fitted proved TV capability.



Earlybird (HS303 / Intelsat I)



The first commercial geostationary satellite placed over the Atlantic Ocean was at 28*W. It was made by the Hughes Space & Communications company (model HS303) and was given the name of "Earlybird". INTELSAT renamed it Intelsat I Flight 1 to follow the final reference system for all its satellites.


Launched in April 1965, it was retired in January 1969, but due to a failure of a later Intelsat it was re-activated in June to cover the Apollo 11 Moon landing flight until August 1969.



Intelsat II



The second generation geostationary communications satellites consisted of a series of four satellites based on the same design of Earlybird. The Flight 1 satellite motor malfunctioned leaving it only part way to its orbit. The other three achieved position successfully.


Each satellite had two transponders capable of carrying 240 telephone channels, but the second transponder provided a "Contingency" service in case the first failed. It was, however, used for Occasional TV traffic if not needed for telephony.





DEVELOPMENTS IN GEOSTATIONARY SATELLITES



Intelsat III



This generation of satellites, built by TRW Ltd., attempted to resolve a number of problems. The omni-directional antennas of the HS303 model of satellite meant only a small amount of the transmit power was being used, so a more directed beam was fitted to route the full power towards the Earth. Uneven solar heating on the satellite body was also causing problems, so a slow spin was adopted to even out the temperatures. This meant that the directional horn had to be reverse spun to keep the antenna pointed at the Earth. A new challenge was the need for the de-spin bearings to function in space. Of the 8 satellites launched 6 failed for various reasons listed on the Wikipedia web-site.


These satellites had two Transponders which could accommodate 1500 voice circuits or 4 TV channels.



Intelsat IV



This generation of satellites made by Hughes Space, building on the discoveries of the previous satellites, were much larger compared to the earlier generations. The body diameter was 8ft (2.5m) and the overall height was 17ft (~5m). The configuration of the electronics included 12 C-band Transponders with high power amplification connected to a de-spun antenna array, made up from two large global receive dishes, two smaller global transmit horns, and two steerable spot beam transmit horns which also used the parabolic dishes to direct the beams accurately to points on the Earth. Each of the 12 C-band transponders could handle 500 communications circuits making a total capacity of 6,000 mixed-traffic circuits.


Eight of these satellites were launched, but Flight 6 failed to separate cleanly from the booster rocket so was lost. The remaining Satellites were very reliable and exceeded their design lives, the last one finally being retired 1987.


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Intelsat IVa



The IVa's, continuing to be built by Hughes Space, were an upgrade on the IV's, with different electronics and antenna arrays. presumably because of improvements in the electronics. The new platform remained the same size body, being just under 8ft (2.3m) diameter, but with the new extended antenna system now had a height overall ~23ft (7m).


Transponder count on this version had increased to 20, with 4 providing wide beam coverage for land mass areas.The remaining 16 transponders worked as small spot beams which could be directed to specific areas. The total capacity of this new version was 10,000 circuits.


This design incorporated beam separation by having more directional antennas which could point to east and west land masses. This meant that frequencies could be re-used for each route.


Six of this generation were launched, but 30 seconds into Flight 5, a fire started in the engine compartment which necessitated destroying the out of control rocket. The remaining five satellites performed well and exceeded their planned operational life.




INTELSAT CHANGES OF DESIGN.



As more countries joined the Satcomms service satellites were needed with increasing capacity, and problems with some of the previous developments needed rectifying. A new style of satellite was needed, particularly as terrestrial developments were going towards digital transmission systems, and the available microwave C-band capacity was becoming fully used. Exploration of a higher Ku-band had been undertaken, so the following Generations were equipped with transponders for both bands, Also, new communications techniques had to be accommodated so here are the new versions developed.



Intelsat V



This generation was constructed by Ford Aerospace to a new format where power was generated by flat solar panels spanning nearly 16 metres which could track the Sun through orbits. The main cubic style body was three axis stabilised using momentum wheels, and housed 21 C-band and 4 Ku-band transponders which could handle 15,000 voice circuits and two TV channels. The first launch of this generation was in 1980, with 9 launched, one of which failed to reach orbit.


A further 5 enhanced satellites classed as Intelsat VA F-10 to F-15 were launched from 1985.These had enhanced capacity with 26 C-band and 6 Ku-band transponders the extra being used to provide Inmarsat maritime services. The F-14 suffered a launch failure.




Intelsat VI



Yet another design was manifest with the Intelsat VI's, again contracted and produced by Hughs Space. Five were built and followed their previous designs of cylindrical slow spinning bodies with a de-spun antenna platform on the top. A concentric cylinder of solar panels slid down the 3.6 m (~12 ft) diameter body at deployment revealing more panels on the body and increasing the power available for the satellite. The antenna dishes and components were also deployed when in orbit, making a final height of 11.7 m (38.5 ft). These satellites were equipped with 38 C-band and 10 Ku-band transponders, and using digital modulation techniques could handle 120,000 communications circuits and 3 TV channels.



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