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

Close.  They actually lower the perigee with the OMS deorbit burn, to  
where the perigee is below a dense enough portion of the atmosphere to  
allow a reentry capture, and then turn nose-forward and wait slightly  
less than half an orbit for entry interface.  The moment they start  
encountering appreciable atmospheric drag, they are headed for the  
surface one way or the other and things start happening fairly  
quickly.  But the key is that deorbit burn that puts the perigee right  
where they want it.  There's no additional push other than atmospheric  
drag at entry interface.  :)

(This is related to the reason why propelling something entirely from  
the surface, even firing something from an enormous cannon that  
propels the projectile far above the atmosphere, will never put it  
into orbit -- it will either escape Earth entirely or impact somewhere  
else on the surface.  There has to be some horizontal acceleration at  
apogee for there to be a perigee afterward, which is why GEO sats have  
to carry an apogee kick motor with them to actually put them in GEO, a  
simple PAM boost from LEO won't do it. :)

On Feb 14, 2008, at 10:04 PM, Alan Sieg WB5RMG wrote:

> I don't think orbital decay would be a good descriptor.
> Orbiter does the de-orbit burn about half-a-rev away, then a nose  
> dive.
> The de-orbit burn puts the brakes on big time, then after it turns
> nose forward, a slight push towards the earth brings it on down fast.

"No nation was ever so virtuous as each believes itself, and none was  
ever so wicked as each believes the other." -- Bertrand Russell

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