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Re: Since We Are Off Topic Somewhat....

At 10:55 AM 2/15/2008, Joe wrote:

>How come,  going up,,  0 to 17K MPh through the atmosphere, all  is
>fine..  BUT
>coming down,,  17K MPh  to 0  unless it has protection  it will  burn up
>in the atmosphere from friction with the air.

I suspect if you look at the launch profile, you'll find that the 
passage up through the atmosphere is relatively slow, and that the 
bulk of the speed increase occurs above where the air density is 
sufficient to cause problems.

Also, maximum acceleration is towards the end of the main engine 
burn, due to simple physics.  As the propellant is expended, the mass 
of the vehicle is less, but the thrust remains roughly constant, 
unless the engines are throttled back to reduce the G forces, as is 
done with the Shuttle to minimise stress on the crew.  This implies 
that much of the speed increase occurs late in the burn, when you're 
high enough to avoid significant friction heating.

73 de VK3JED

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