wrote:

I think I understand why objects heat up when going through the
atmosphere and therefore why re-entry vehicles need heat shielding. My
question is why we don't need heat shielding when launching. Aren't we
going through the same atmosphere?

BigKhat

Most of the accelleration that occurs with the shuttle is after it's
left the thickest part of the atmosphere, they keep the throttle
down until they've cleared that. Once above the atmosphere the shuttle
goes mostly horizontal and accelerates to orbital velocity. When
re-entering the shuttle has full speed as it hits atmosphere and
it has to scrub off speed using the atmosphere. If you had unlimited
fuel you could fire the engines and mostly stop the shuttle in orbit,
then let it drop pretty much straight down with no atmospheric friction
heating at all.

JazzMan
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