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

11 January 2009


Why do rockets go up without resistance into the stratosphere and yet come back with resistance and have heat shields and stuff like that? Meteors experience the same thing so why does that happen?


Dave - Basically, does a burn up on the way down but not the way up? 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 and the air's fairly thick. They get faster up in much thinner air so there's less heating. On the way down they're going really fast and they're still going fast through the thin air. 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.

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