Re: Site information why elevation..

Dale Ireland (
Thu, 10 Jun 1999 08:27:24 -0700

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
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
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
>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
>precision, which makes elevation relevant.