NavList:

Forgot this in my last reply. Peter M, you wrote of visual observations of GPS satellites:
"The downside is that all of these are dim, visual magnitude at best around 12. But with a modest telescope they could certainly be imaged against the background star field, and then it's just triangulation. GPS satellite shots are really just lunars, but 20 times better."

Yes. Just to clarify, getting a position fix by lunars (something I introduced to NavList about four years ago) is equivalent to getting a fix by artificial satellites, and that's one of the ways that I introduce the concept. And as you note the required angular accuracy for a fix with a given positional accuracy is inversely proportional to distance. So a fix by GPS satellites is twenty times better than a fix by lunar distances (position fix --not the historical "GMT by lunars"), and a fix by LEO satellites is again some twenty times better than that. It is possible to get an exceptionally accurate fix by visual observation of low altitude satellites. If a satellite passes 250 miles overhead, a shift in its angular position of one minute of arc (easily attainable with a camera) corresponds to a position line accuracy of +/-400 feet, if I've done my math right.

-FER

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