Strewth!!
How did you guys ever graduate from Starfleet academy?
Space is empty. A vaccuum. There's nothing there. It is a void. Zilch. Nothing. Devoid of matter. Lacking substance. Vacant, Unfilled. Bare. Blank. Unoccupied. It is bleedin.....space.
Therefore there is no friction. No drag. Nothing to conduct sound or vibration. Nothing to absorb energy.
If it is producing thrust it will accelerate. If it isn't it will continue in a straight line until it is influenced by an external force. (see above)