[douglas]

All of them have to be at a star when you issue the order.

Star Destroyer: Must be at the star. You can move, but you must return to the same star before setting it off.

Nebula Creator: Must be at the star. You can move to another star before setting it off, but it has to be at a star in order to work.

Black Hole Creator: Will work absolutely anywhere. It has to start at a star, but it can move anywhere and it will work no matter where it ends up, provided that the star it started at still exists. That star will be deleted (*not* destroyed in the sense of setting off a star destroyer there) regardless of where the black hole is actually created. If multiple black hole creators start at the same star, only the first one to trigger will work.

Oh, and Starhawk, star destroyers are actually the most expensive in terms of resources. Nebula creators are the cheapest and only require one more step to rebuild the system. Black hole creators only save on organics, but are the most flexible for use and have the most irreversible effect.