QUESTION:
How do you keep the engine at the right temperature as the shuttle 
moves up through the atmosphere and the rapidly changing tempeatures?

ANSWER from Jay C. Buckey on Janury 11, 1998
Although the temperature outside the Shuttle does change quite a bit 
as you go through the atmosphere, it is a really small change compared
to the the temperature extremes within the engines. The fuel for the 
main engines is liquid oxygen and liquid hydrogen. The are pumped into
the engine at a temperature of apprioximately -300 degrees F. In the 
engine, these two  liquids are introduced to each other in the 
combustion chamber, where they meet, explode and produce the hot 
steam coming out of the main engine exhaust. The temperature in the 
combustion chamber is +6000 degrees F. One problem for rocket engine 
designers is to find materials that can stand the high and low 
temperatures within the engine.