The following table shows the correspondence between the mission type and the points you get for the successful completion of a mission:
Different kinds of military missions are bound to your rank. In the federation you carry unimportant stuff until you get promoted to Sergeant; then the first secret messages may be carried by you. You will get your first military assassination mission as Sgt-Major. After your promotion to Major you will get additional reconnaissance missions and a Colonel may execute bombing missions. The empire handles equivalent ranks the same way. You seem to get no new type of mission when you advance further in rank although there are many rumors that you get new missions to destroy enemy ships at Commodore/Marquis level.
The above does not hold, if you execute missions for more than one side. I made the mistake of working for the empire after I advanced to Colonel and had gotten my first few bombing missions. I advanced to Squire in the empire and went back to the federation. Now I had the problem, that I got no more bombing missions but had to stay with the usual reconnaissance missions. I eventually got bombing missions again, but working for the empire surely stopped my federal career for a while.
The safest way to advance in the federation and the empire at the same time seems to be the famous ``rank swing'': Advance one rank in the federation, work for the empire and advance one rank there, return to the federation and so on until you are Admiral/Prince and ELITE and bored to death.
Your rank is not the only prerequisite you need to get a certain type of mission. You have to own all the possible medals for earlier missions first. You get medals for:
The complete list of medals for the German and the English version of the game looks as follows: