You can't use the dbMoveObject command easily for this kind of movement.
Basically, you would have a vector for current velocity. Add to this a vector for acceleration due to the engines (which would normally be in a forward motion, ie related to your current angles), then add the vectors for acceleration due to gravity for all planets & the local star. That becomes your new velocity. The final step is to add your velocity vector to your current positional vector.
It's not scientifically accurate, but more than good enough for a game.