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The sabotaged turbodyne aboard the Celestra (TOS: "Take the Celestra").

A turbodyne is a device related to sublight starship propulsion. The number 4 turbodyne is sabotaged on the Celestra as part of a mutiny attempt, forcing the Celestra to drop out of the fleet until it could be repaired. It usually takes about two centares to repair a turbodyne (Take the Celestra).