Did you try picking up a physics book? It can explain just about everything you are asking and wondering. It is challenging but it's rewarding. There is far more evidence that the earth is sphere (technically an ellipsoid), however only small portion of the population understand it. This is not because there is some sort of secret rather because only those in the higher end of the IQ bell curve are capable of understanding. Ask every physics student or professor if they think the earth is flat. They will all disagree, regardless of the region. There are some that will but in proportion to the rest they would insignificant. If you are willing to go thorough the nightmare classes to understand the universe it is really beautiful how everything works.

The reason why the shuttle does not enter the earth atmosphere is because it has two kinds of acceleration not just gravitational. One pulls it in and the other moves it the x y plane. Since the earth is a sphere you end simply orbiting the planet. If the earth was somehow flat it would hit the plane and not go around it. That and the flat earth would collapse on its self.