I am new to this forum.  I tried the best to see if this has been posted before.  If it was, I apologize.

I had created a small fleet with my original survey ship and a merc ship survey ship called the Facade.  I used this fleet to take out heavily defended artefacts.  After each attack I would park the fleet in one of my mining bases to recover from damages from the battle.  I came back to the fleet after they should have finished recovering and found my original survey vessel; but the merc Facade was gone!  Do merc ships have a limited life span?