The video starts with TV coverage of the arms reduction talks between USA, Europe and USSR. TV coverage was possible using satellite links as follows:

Outside Broadcast unit at event sends pictures and commentary via a dish aerial on their van to a satellite, where the signal is amplified and beamed back to the studios (ground station). Here the broadcast is then sent out via land lines / conventional TV transmitters.

Mostly, satellites carry TV pictures, phone calls, telexes, faxes, videoconferencing, maritime service information and weather information.

The Technology is not all that new!

In 1901, Marconi made the first transatlantic radio broadcast. He used relatively long waves from 15cm to 15km. This is because long waves follow the curvature of the Earth better than short waves. (Works well over sea but not so well over land).

The upper part (high f, short wavelength) of the spectrum was left to amateurs. They found that radio waves with frequencies in the range from 3MHz - 30MHz gave good transmission over long distances! This worked because the waves were being reflected off the IONOSPHERE. The Ionosphere is a layer of electrically charged particles which reflect radio waves.

The Ionosphere is unreliable - it can be affected by solar wind activity. We need a more reliable reflector!

The solution is to build our own - satellites! The science fiction author Arthur Clarke envisaged three satellites in GEOSTATIONARY orbits above the Earth. These would allow all the world to be covered by satellite. GEOSTATIONARY means that the satellite appears to hover above the same part of the Earth - it turns in its orbit at the same (angular) rate as the Earth.

The speed that a satellite orbits at depends on how close to the Earth it orbits. If it orbits nearer to the Earth it orbits faster (going from horizon to horizon in as little as 20 mins).

The first satellite used for communications was TELSTAR. It orbited low and was visible only for 20mins at a time. It was in a polar orbit (so it went over the North and South Poles and back again). It was used mainly for Geological, Agricultural and Educational purposes.

EUOSAT is also in polar orbit and is used for educational purposes. It orbits every 90 mins with a radius of 600km. It too is only visible for 20 mins at a time.

A geostationary orbit needs a much higher orbit than this. The maths on the video shows that it needs to orbit at about 42000km (36000km above Earth's surface). So, much more powerful rockets are needed to reach geostationary orbits.

'Early Bird' was one of the first to be so positioned. It was the first in the INTELSAT series. It carried 240 phone lines. INTELSAT 5 carried 15000 phone lines and 2 TV channels. INTELSAT 6 carried 44000 phone lines and 3TV circuits.

The main elements of a satellite are

Solar cells - give power for the satellite (2.2kW in INTELSAT 6)

Rotating lower part - for stability

Upper part - always points toward the Earth (aerials are kept here)

Signals used in high frequency range 4 - 12 GHz (microwaves). Can pass straight through the Ionosphere. Can carry more information. Need smaller aerials.

Transmitting aerial sends on 4 GHz, receiver on 6 GHz. (Use of different frequencies means that signals don't interfere)

The dishes are parabola shaped (this helps to send parallel beam signals and to collect signals over a wider area).