Escape velocity is a bit of a fictional construct. Essentially it works like this:
- Consider the earth to be a body in a universe of it's own.
- To increase height, you need to give a body more potential energy.
- To do this, you must initially give it kinetic energy (move it upwards)
- The faster you push it, the higher it'll go.
Escape velocity is the speed at which, in an otherwise empty universe, the object would theoretically reach zero speed, at an infinite distance from the earth. But it ignores certain things:-
- We don't fire spacecraft out of a gun and give them all their speed in one go, we apply continuous thrust, so they never need to see escape velocity near the surface.
- If you want to, say, fly to Mars in any sensible time then escape velocity may be much too slow and you actually want to go much faster.
In practice, there are all sorts of other factors that apply to spaceflight. For example, between any two bodies in space (say the Earth and Moon) there are points in space called the "Lagrange points" where the two gravities balance out, so an object placed there, with no speed, will in theory stay put forever, a tiny nudge either way and it'll eventually hit (or orbit) the earth or moon.
An orbit is a different thing. To put a spacecraft into orbit, you need to give it:
(a) enough potential energy that it'll get that high
(b) enough additional kinetic energy that it's speed when it gets there gives it a centrifugal force equal to the pull of gravity at that height.
In practice, a lower orbit needs less energy than a higher orbit, because the potential energy is the biggest player. So if a spacecraft wants to orbit higher, it pushes itself forward faster, and if it wants to go lower, pushes itself backwards / slower (not unlike an aeroplane).
In all of this you can use the spin of the earth. If you launch at or near the equator, you can use the energy from the spin to give you "free" kinetic energy, hence most space-launch sites are near the equator.
At a certain height, around 35,000,000 metres, the speed you need to stay at constant height, takes you around the earth once per day (23 hours and 56 minutes to be exact). This means that you stay over one spot on the equator, since the speed matches the spin of the earth. This is where the biggest communications satellites are, and is either called "geostationary orbit" or "Clarke orbit", named after Arthur C Clarke, the British scientist and writer who first suggested putting satellites there (in a paper in "practical mechanics" magazine in 1949).
Arthur C Clarke also wrote a novel "Fountains of Paradise" which is all about building a "space elevator", essentially the very long ladder that was talked about. He is always very careful to get his science right, and to explain it clearly - I'd recommend reading it.
G