# Calculating projectile velocity from moving object

I'm working on a top down space shooter and am having trouble with calculating/understanding the physics for projectiles launched from the space ship.

The ships have a velocity vector and a turret with rotation independent from the body of the ship. Currently projectiles are launched based on the turrets rotation by making a normalized vector then multiplying each component by a speed. However, this doesn't work when the ship is moving faster than the speed scalar.

Right now if the ship is going faster than the projectile speed scalar and the turret is aimed in the same direction as the ship's velocity, the projectile goes backwards (away) from the ship. Assuming there is no drag/gravity (very deep space), how should I go about handling projectiles?

The velocity of a projectile fired from a moving vehicle should be vehicleVelocity + projectileVelocity.