Imagine the air is a wall. On launch, a rocket starts slow, it finds the door-It pushes through the thick air near the ground politely, and by the time it is going truly fast, the wall has thinned out to almost nothing.

There is nothing left to hit.

Reentry is a different business.

The capsule does not look for the door-It hits the wall at seventeen thousand miles an hour.

The air cannot get out of the way-It piles up, a great cushion getting squeezed so hard and fast it glows white-hot like a furnace.

It is not friction that makes the fire.

It is the anger of the air being compressed-It is the wall hitting back.

A rocket leaving-is a polite guest.

A capsule returning is a man thrown through a window at high speed-The window does not like it.