I might have misinterpreted your English a little so forgive me if i have.
You are spawning only 1 particle is this correct?
is the lifetime long enough for this particle to remain on screen?
if its supposed to be an engine trail you will need more than one particle and a velocity for them to follow.
if its an individual rocket you need to allow the particle to last long enough, so its life must be lengthy and also the timeline needs to be long enough.
Have you thought about just creating the rocket itself in unreal and give it a velocity in there, then add trails with niagara?