Thanks for the responses all. Just one more question. The applicable duty officer missions that you get. Are they personal missions or is it worth moving between sectors to try to get the mission?
It appears in multiple sectors, so yes it's better to move between sectors. If you have not done so already do all the colonization doff chains. The last mission unlocks a repeatable that can give you a purple doff.
So do a loop of the colonization sectors. You'll find BOFF missions and DOFF missions.