Why things easily leave earths atmosphere but burn up while re-entering the same atmosphere
In: 1
Because it’s way way cheaper to careen into the atmosphere at ludicrous speeds and use air to slow down, than to use rockets
On the way up a rocket spends very little time in the atmosphere. This helps save a bunch of fuel fighting air resistance. To get the speed to enter an orbit it will accelerate sideways to high speeds only after it it gets high enough to be in very thin atmosphere/vacuum. You just don’t get going fast enough while in atmosphere to really need to deal with heat.
If you wanted to get down the same way you would have to spend fuel to decelerate while in vacuum/thin atmosphere, then calmly drop down lower. Basically you would need to double the amount of time the rocket burns. But that means you need to use even more fuel to lift that up there. And more fuel to lift that fuel See the “tyranny of the rocket equation” for more detsils, but as a very rough estimate to double the burn time means your rocket weight increases 10x.
Or you could use the atmosphere to slow down for the price of some heat shielding and a parschute and have a far smaller rocket.
Latest Answers