as semi independent ( literally that time - as it sounds like an explorer that is not bound to house boundaries but rather to other ideals ) - the IMG or the zoner warships would do best...
however.... military warships are not out of question. - depending on your point of view.... there is the option that whoever sponsors you also sponsors the ship.
for example - in the TV show Babylon 5... there are several factions exploring - the large semi private ( civilian ) organization ... i think IEC ( something like "Interstellar explorer corporation" ) with tremendous political power. then there is the earth force ( basicly the space navy ) - and there are private exploration teams.
the earthforce uses destroyers and cruisers of military build to explore, cause those ships provide the instruments, the protection and the highly trained crew ( and also - due to the nature of the earth force - are under a strict command chain, in case something is discovered that must not reach the public )
the explorer corporation is a political power - backed up by the senate. they have their own ships that are ... in the show .... a lot more sophisticated when it comes to deep analysis of a phenomenom but other than that - unarmed and rather weak. - but they are backed up by the earthforce... so when in trouble - they can call for military help.
the last ones are the private explorers that use smaller ships and smaller crews. they often depend on the military - but are not part of the command chain - and do not have to justify their results. - but they do not possess any larger ships.
in sirius .... it might easily be possible that an explorer gets a mandate from the military - and so he gets a military crew and a ship. - so it IS possible to be a civilian explorer in a liberty battlecruiser for example. - such a ship would not be part of the liberty navy as such - but would have to deal with everything the navy stands for ( so you re unlikely to operate in rheinland or most omicron space )
having a zoner / IMG warship would put you more into the IEC folder - being part of a civilian cooperate operation that can afford such a ship. with such a ship you d be free to go anywhere - at your own risk. however - both ships are not really very large. ( i don t think a ship like a zoner destroyer uses more than a few dozens crewmembers - and the IMG BC is about in the same mold )
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