Why dont satellites need a continuous supply of fuel?

Answer 1

An orbit, for the most part, does not require any work to maintain. A satellite

orbiting earth is essentially in freefall and is continuously pull toward Earth.

However, it is moving "sideways" so fast that it continously misses. Some fuel is

needed to make occasional adjustments to the orbit, but not to maintain the

orbit overall.

Notice that the moon doesn't need any fuel to stay in orbit round the Earth,

just as the Earth doesn't need any rocket engines or rubber bands to stay

in orbit around the sun.

Answer 2

They are circling the earth outside the atmosphere. There is no air friction in outer space, so they are not slowed down by anything. Satellites get their velocity needed to stay on their intended orbit when they are launched, and without friction, they have no need for fuel to keep it.

Satellites do, however, need some kind of energy supply (be it solar panels or nuclear batteries) to power their electronics.

Answer 3

When an artificial satellite is going around the earth, the force it is subjected to is mg where m is the mass of the satellite. This force is towards the center of the Earth. At every point in the orbit, the displacement of the satellite is exactly perpedicular to this direction of the force. If we remember that the work done is ForceXdisplacement(in the direction of the force), then this product is Zero because the force is perpendicular to the displacement all the time. So there is no work done on the satellite and it will continue to revolve. If the orbit is with in the atmosphere then the air drag will reduce the velocity of the satellite and it will gradually lose height and fall down and mostly get burnt in the dense lower atmosphere.

Incidentally, this holds good even for the natural satellites like the planets or the moon.