Yeah, it was powered by the SA fodders. Took some time to get the cannon 100% going because of the vast quantity of chakra required. At the end of the day, they didn't fire it at the moon because there were comrades (Shikamaru, Naruto, etc...) up there fighting Toneri and trying to solve everything themselves. Ay was going to do it but the other Gokages told him to give them more time and put trust in them. They fired it at the meteorites (fragments of the moon that was falling) instead which posed a threat to the people on Earth.