Hi Peter Cone,

 > I think I have it - assuming the satellite 
 > illuminates the whole side of the earth facing it 
 > - I.E., the satellite's beam is *not* focussed to 
 > a smaller cone.

Sounds plausible.  So we are still searching the 
crux of the problem and the thread has become xfb
and unrelated to coding.  Let's move it to
xfb@....

I'm posting a satelite-navigation question there 
right now.

Cheers,

Laurent S