Retcon article
(covers information that was retroactively changed)

A lunar capsule was a piece of advanced sensor 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 lunar capsule 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.
The lunar capsule contained a seismometer, a device for measuring motion in a ground. A Ranger Block II space probe would launch this capsule to the surface of Luna. The shock wave caused by the impact would be measured by this seismometer. Knowledge gained from this event would help scientists on Earth to chart the interior of the moon.
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