This all presumes the elements and predictions have that kind of accuracy. I understand there is a lot of "extrapolation" in the various orbital calculation algorithms, in the elements, etc, etc. I am wondering what is considered the "standard deviation" of the predicted positions in meters or degrees, or however it may be measured. I mean do your common week old elements for a LEO satellite calculated with SGP4 give you a positional accuracy around 100 meters, or 1 meter, or 1000 meters?? That may determine if knowing your elevation is even relevant. My experience with the shuttle and MIR is that when you use the "latest" elements for both objects (but dated just one day apart) when they are actually docked, give positions up to 5 km apart. That's .3 degrees at 1000km, and makes elevation correction irrelevant. Dale Ireland Astronomy Page http://www.drdale.com Comets, Satellites, Eclipses, Photography, Fabrications -----Original Message----- From: Ted Molczan >I'll add my $0.02 to the discussion: > >A skilled visual observer can measure satellite positions to a precision >approaching 0.01 deg. At a range of 500 km, that is 87 metres. For that >precision to be useful, the observer's position must be known to the same >precision, which makes elevation relevant.