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Why have different types of orbit?

Unless a satellite is always in the same place from your point of view, it would be impossible to point a satellite dish in the right direction and receive a continuous signal. Without the 'geosynchronous' satellites, we could never have satellite television!

Geosynchronous or geostationary satellites are positioned far enough away from the earth that it takes then a whole day to complete one orbit. They are 36,000 km above the Earth. This means their orbit radius is:


In 24 hours they travel the complete circumference of their orbit =

So geostationary satellites travel over 250 million metres per day just to keep up with the Earth.

To do this their speed must be:

So their speed = 3,080 m/s or 3.1 km/s

Compare this with the speed you are travelling due to the spin of the Earth.

Polar orbiting satellites orbit from North to South while the Earth spins beneath them. This way they can see the whole Earth, slice by slice, over a day. From our point of view the satellite will pass over head travelling North to South in the morning but will pass South to North later in the day. It takes quite a bit of imagination to see how this works!

Polar satellites are only about 700 km above the Earth. This gives them a total orbit radius of 7,000 km approx.

Their circumference of orbit is

If they travel at 7.5 km/s, time taken = distance / speed = 44,000 / 7.5

So the time taken for one orbit = 5,900 seconds = 97 minutes.

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