The Theoretical Propulsion log was the log of the Theoretical Propulsion Group's work in developing the propulsion systems of Galaxy-class starships. It was retained in the engineering section computer for reference by the chief engineer and his or her team. Geordi La Forge once referred to it when he was unable to explain why the USS Enterprise-D had no forward momentum, despite the apparent lack of impediment.

He was surprised to discover that the log had both spoken and visual output. Opting to have its entries read to him, La Forge heard Leah Brahms' voice for the first time. (TNG: "Booby Trap")

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