I don't know if I have ever seen this in a game, but what about this?
Have the program be able print out a list of planets--particularly unowned or foreign--particularly
with sector numbers.
Right now I spend time writing down names of planets to colonize with my own sector numbers:
1,1 is the bottom left; 1,2 is on the bottom row one to right, etc.
In the end game, I do the same for enemy planets I need to invade.