I understand it has something to do with satellites, but not exactly how.
Orbital Coverage is the area that you can launch satellites in. Anything outside of that area means you can't affect that area with them. You can see what your Orbital Coverage area is by clicking the Orbital Layer button (the one that looks like a satellite).
For example, if you're trying to clear miasma, you can use Miasma Repulsors to do so. But since that's a satellite, you only have limited range around your cities to use them, which puts a finite limit of how much area you can clear of miasma with them.
You can expand your Orbital Coverage with some buildings and wonders, and a specific tile improvement your workers can build called Arrays.