Not tested.
Firstly do you need to use physics just to rotate your ship - cant you just rotate (sprite) towards mouse position ?
If physics is the way to go I suggest you look at dampening the sprites rotational angle (physics angular dampening ?)
Using anglelerp(ships angle,required angle,0.5)*multiplier to give your required torque towards angle(self.x,self.y,mouse.x,mouse.y) might help ?