Originally Posted By: mjoekingz28
Can anyone explain this?
What conditions are present when leaving Earth's atmosphere and going into space AND are the conditions equal upon re-entry?
Further, the conditions of the atmosphere are the same (temperature, pressure, etc.) but the conditions for the vehicle are far, far different because of the physics.
To orbit the Earth, you're going about 18,000 miles per hour. A rocket going up gets well out of the atmosphere before exceeding a few thousand miles per hour.
But upon re-entry, it's going close to 18,000 miles per hour and using only friction with the air to slow down, so, the speed in the atmosphere is far higher, meaning that the vehicle heat load is far, far greater than it is when leaving...just look at meteors! Solid lumps of metal, primarily iron, simply burn up when entering the atmosphere.
That's why a thin aluminum skin can survive the launch, but a really heavy, often ablative, heat shield is required for re-entry...