> When mirroring a site in particular, 
> <http://antwrp.gsfc.nasa.gov/apod/archivepix.html>), 
> if a secondary link should later becomes extinct, does 
> HTTrack remove the link and associated files from my 
local 
> hard drive?
Yes
>  If yes, how do I prevent that?  I would like to 
> preserve whatever was once there or update whatever has 
> changed but never delete locally what was once captured.

Options / Build / "Do not purge old files" option