Why do rockets not 'burn up' on the way up?

Dave Ansell answered this question...

Dave - The amount of heat you're generating is all to do with how fast you're going and how thick the atmosphere is. The thicker the atmosphere, and the faster you're going, the more heat you generate. 

Although space rockets can go several times the speed of sound, they do get some heating on the way up. It's not that much because they're going fairly slowly while they're near the ground where the air's fairly thick. But they get faster up in the much thinner air, but there the thinner air means the heating effect is weaker. 

On the way down, they're going really fast. As the air gets thicker, they've still got lots of energy.

Chris - The escape velocity's 13-14,000 miles an hour or something ridiculous, isn't it? They have to have a way of dissipating heat?

Dave - They can't dissipate all that energy in the upper atmosphere. They have to dissipate it lower down, which is why they get hot...