Eli5: why can spacecrafts not be slowed down enough to red-enter the atmosphere without burning up?
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If a spacecraft is in orbit, it has a very high tangential velocity relative to Earth. If it didn’t, gravity would pull it in instead of it being flung around. And this is exactly what happens should a spacecraft start slowing down. And as soon as you slow down enough to hit the outer layer of the atmosphere, air resistance starts to slow you even more, causing you to be pulled in more, causing you to descend to more thicker atmosphere and slow down even more. This process is carefully planned out for re-entry but inevitably involves crashing through the air at high enough speeds for air compression to cause significant heat.
You can have a craft that briefly enters space at non-orbital speeds and have it re-enter with a lot lower velocity. The highest skydive was performed from an altitude close to what many would consider space. But in these cases, you aren’t coming from orbit.
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