Thank you both for your help. I've got my missile working just the way I want it to. I'm glad to hear part of my problem is a bug because I was beginning to go crazy trying to figure out what was wrong. Hope it'll be fixed soon.
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!