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How the satellites are launched - escape velocity

For a spacecraft to leave the Earth it must have enough energy to overcome the pull of the Earth. Imagine throwing a ball upwards. The faster it leaves your hand the further upwards it will travel before gravity slows it to a halt and accelerates it back down. If you could throw it fast enough it would go far enough that gravity could not drag it back. On Earth you would have to throw it at around

The theory of this is that the rocket has to have enough kinetic energy to overcome the potential energy of the Earth's gravitational field.

Gravitational potential is worked out as V = GM/R, where R is the distance from the Earth.

On the Earth's surface the gravitational potential is:

At the radius of a geostationary satellite's orbit the gravitational potential is:

(The negative is because attractive forces require energy to be put in to the system to overcome the attraction and move them apart. The 'expending' of energy is shown as negative. Repulsive forces such as two positive electrical charges would be shown as having a positive potential as the system provides the energy to move them apart)

To get a satellite into geostationary orbit you need to give it:


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