Retcon article(covers information that was retroactively changed)
A mid-course motor was a piece of advanced propulsion technology aboard NASA's Ranger 5 space probe when it was launched in the mid-20th century.
A schematic of the Ranger 5 spacecraft depicting the location of the mid-course motor was stored in the USS Enterprise's library computer database. This database was accessed by the Talosians in 2254. (TOS: "The Cage")
A schematic of the Ranger 5 spacecraft was from the archives of the National Aeronautics and Space Administration - Jet Propulsion Laboratory.