Do satellites need to have their orbits externally maintained? Is the speed of a satellite self maintained ? Or it needs anything to be done externally ?
Condition : The satellite is in the orbit where it is held in equilibrium by the force of gravity and its centrifugal force.
 A: All that is needed is gravity. There is absolutely no need to invoke the centrifugal force to explain an orbit. This argument doesn't even make sense because when it is used, the satellite is shown as moving.
A nice simple way to look at orbits is via Newton's cannon. Imagine a cannon atop the only mountain on an airless and, except for this one mountain, spherical planet. Fire the cannon and the cannonball will fly a bit before falling to the surface of the planet. Add a bit more gunpowder and the cannon will fly a bit further. Add even more and now the cannonball flies partly around the curved surface of the planet before finally hitting the surface. Eventually you'll have the cannonball flying halfway around the planet before it hits. What happens if you add a bit more gunpowder? The cannonball is now in orbit. It will eventually come all the way around the planet and hit the cannon from behind.
That said, there are lots of things that perturb a satellite's orbit. Satellites in low Earth orbit fly through the Earth's upper atmosphere. This eventually slows the satellite down to the point where it enters the thicker part of the atmosphere and burns up. To counter this, satellites in low Earth orbit occasionally need to boost themselves back up to a higher altitude.
Other perturbations include the non-spherical shape of the Earth, gravitational perturbations from the Moon and the Sun (and Jupiter and Venus and ...), solar radiation pressure, general relativity, and others. While the satellite might still be in orbit, these perturbations tend to move a satellite from the orbit it is supposed to be in to some other orbit. As is the case for satellites in low Earth orbit, other satellites occasionally need to boost themselves to bring themselves back to the desired orbit.
