Zero Gravity Rotation help?

I made a drawing of a spaceship that is basically a main center piece that has arms branching. These arms rotate. I'm wondering if I need continuous propulsion for the arms to rotate, or just a push to get them going. I'm just not sure and I could use some help. I'm thinking that it just needs a push, because in outer space, if you were to fire a gun the bullet would go in a straight line continuously until it was stopped by something like a planet or an asteroid.