Why things easily leave earths atmosphere but burn up while re-entering the same atmosphere
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Being in orbit is a lot less about being *up* than it is about being *fast*. The reason rockets go up first and then roll to start going fast is so that they can get above the thickest parts of the atmosphere where drag would slow the rocket down. If there were no atmosphere, it would be more efficient to go closer to a tangent to the surface – more sideways. But with the atmosphere, it’s more efficient to burn fuel and get over the air.
Conversely, coming out of orbit is less about going down than it is going slow. How you slow down doesn’t matter – once you slow down you will fall. You could use fuel and thrust in reverse to slow down, but you would have to carry that fuel up in the first place. Instead, just use a tiny bit of fuel and slow down *just* enough to touch some air and the drag from the air will slow you down.
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