You just keep looping around until you've assigned a role to each player, so once you hit the last category listed you loop back around until everyone has been assigned one of the three categories of people. There'll only ever be four systems on the ship though, that's where the debates and conflicts in the game are supposed to arise from as everyone argues over what they should control for that round. I should've probably made it more clear but I was rationing words by that point!
Thanks for the feedback though, I'll be sure to make it more clear in the revision released after the jam!