Just thinking out loud: given that we know positions of these satellites, is one able to use it for non-gps navigation? Either by using vision - by tracking or by using some electromagnetic specter - listening to satellites...
Sure, if you're able to accurately determine angles between the Earth's tangent at your location and the satellites. That's how you'd navigate using the sun, moon and stars. I suspect those natural celestial bodies are much less of a hassle than man-made satellites.
This contrasts greatly with actual GNSS – the whole point of GPS and the others is that you don't need to determine those angles. The only thing you need to determine is the signal delay (i.e. distance) from a few satellites. That's a lot more convenient.
Not an expert but I imagine the problem with using vision is the problem of angular error propagation. That is the angle-> distance error problem:
linear error≈Rtan(Δθ)≈RΔθ
Here linear error is the error in position, R is the distance from the observer to the target and θ is the angle error. You would need incredibly good optics and resolution to minimise angular error and thus linear error.
Given the large R (Even starlink satellites are far away compared to positional accuracy needed) and probably pretty large angular error, your still talking error of kilometres, though with good optics you may be able to get this down to hundreds of meters. The other problem is knowing the position isn't trivial, since their position drifts relative to predicted and isn't known very precisely.
There is also the problem that as R shrinks, speed increases relative to you.
Not impossible but it's not as easy as dedicated GNSS satellites. The ranging codes in a GNSS signal are what makes it easy to find your distance from the transmitter. Starlink doesn't have that, there are some observables you could use but it's not simple.
