The hub contains the bridge [main control room for Space Kid Island], main communications tower, the large dock/airlock for the S.S. Starflame, and the super-atomic reactor which powers the space station [operating by the same advanced principles which govern the Starflame‘s super-atomic engine].
Also shown are two of the six elevators which connect the wings to the bridge. The hub is the only section of Space Kid Island which does not have artificial gravity generation [with the exception of the bridge]. This allows the elevator pods to be easily moved through the shafts magnetically!
For more info about utilities, shielding, and gravity, see here.