Would this work for you?:
Tap any key to toggle motion.
You can add extra belts by duplicating the spawner object.
Set the variables on the spawner object to alter the belt's properties:
no = belt number - this will be assigned to the asteroids in that belt and is used to set the asteroid's frame no
eOriginX & Y = the origin points for the ellipse that the asteroids in that belt follow
spawnNo = the number of asteroids in the belt, determined by spawnMin/Max
speed = the speed of the asteroids around the origin
sizeMin/Max = limits of asteroid size
eAngleOffset = angle of the ellipse
angleMin/Max = limits for initial spawning of asteroids
bandWidth = band within which asteroids will spawn, added to ellipse width/height
eWidth/eHeight = ellipse size. Set these values equal for a circle
I cribbed heavily off this thread, so shout out and big ups to R0J0hound and cincipon: