Apparently the space shuttle disaster occurred just after re-entering the Earth’s atmosphere. I’m curious to know - is exiting the Earth’s atmosphere as hazardous as entering? If not, why?
Depends what you mean.
Exiting the atmosphere per se isn’t dangerous (in an airtight ship). However, ascent clearly is, because the propulsion required to get you out of the atmosphere means tons of explosive fuel.
The reason entering the Earth’s atmosphere is dangerous is because of atmosphere - stuff - hitting your ship as you go several thousand miles per hour. And if you were in orbit, you necessarily go several thousand miles per hour.
No, and the reason is speed. When the shuttle re-enters, it has essentially fallen a hundred miles or so, and is moving at its maximum speed, about 17,000 mph. It heats up because it hits the air like a meteor.
On launch, when the shuttle is exiting the atmosphere at an altitude of 80 miles up, it is much slower. It does heat up, but not as much on re-entry. The shuttle really gains most of its speed in the last three minutes before it reaches orbit. By then, it is above the atmosphere, in the vacuum of space.
To echo what others are saying compression is what really heats the shuttle when it enters the atmosphere. So from a launch the speed is slow and the atmosphere thick, when its going fats the atmosphere is mainly gone. When entering the shuttle is moving fast and the atmosphere is thickening leading to the problems of heating.