Did you make sure they were colliding with each other? If it still doesn't work, try saving and restarting phun. Sometimes the scripting is typed correctly but you need to reload the scene for it to work. I have to do that alot.
It helps if you put a box on top of the spawner and give it the same collision menu as the spawned circles. Then give the box a negative attraction, between -100 and -1000. This allows the rocket to continually accelerate because it it is pushing even more on the spawned circles.