Atom accelerator

An atom accelerator was a TARDIS component. In the Eleventh Doctor's TARDIS, it was a spiky ball on the navigation panel that spun while in flight and during take-off. According to the Eleventh Doctor, it steered the TARDIS. Henry Avery compared it to a wheel on his vessel, the Fancy. (TV: The Curse of the Black Spot)

An identical studded ball also appeared in the Torchwood Hub. (TV: Day One, Greeks Bearing Gifts, Random Shoes)

Behind the scenes

 * The studded ball appeared as a component of the Anomaly Locking Mechanism in Primeval, which appropriately functioned by reversing the polarity of temporal anomalies.
 * The studded ball also appeared as a component of the Groinal Exploder in the  episode Entanglement.