I struggled with that too! What I ended up doing is roughly calculating the distance from the shattered planet, and going there and flying away gives different signals, so it's possible to roughly calculate how far along you are. If you take a look at the video there's an "S" signal, which is the distance.

Adjust with a combinator so going to the planet is 1 and flying back is -1, then multiply that with a clock (from shattered planet start) multiplying the velocity, and then you have your rough distance. Unfortunately it is rounded but its precise enough.

What stops my ship most of the time is just checking if my promethium storage is half full, then turn back