This is probably a little late but I found an easier solution...
Add physics behavior to the bullet and spaceship behavior to the ship
The bullet's physics should have no friction or dampening or gravity (obviously)
When you spawn the bullet
Apply physics impulse (some small number like 3.5 or something)
Apply physics impulse (ship.Spaceship.VectorX/100,ship.Spaceship.VectorY/100)
It works perfectly and no trig or extra variables needed!