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The Solar System

Artificial Satellites - Geostationary Orbit and Gravity.

A satellite needs to be in an orbit with a radius of about 42,000 km
from the Earth's centre to be geostationary. This means
that the satellite is about 35,000 km above the Earth's surface.

We have seen from the planets that the orbital speed
depends on the force of gravity felt by the planet
at its particular distance from the Sun.
The further away it is from the Sun, the weaker
the force of gravity and the slower the orbital speed.

Gravity is not inversely proportional to distance.
This means that doubling the distance does not halve the gravity.
Gravity is actually proportional to 1 ÷ (distance)2.
Doubling the distance reduces the gravity to 1 ÷ 22
= ¼.

For a satellite to orbit the Earth exactly once in 24 hrs
it must be at exactly the right height above the Earth.
This means that all geostationary satellites are at the same height.
There is enough space for about 400 geostationary satellites.
If they are too close together,
their signals start to interfere with each other.

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