Retcon article
(covers information that was retroactively changed)
An ion chamber was a piece of advanced sensor technology aboard NASA's Mariner 2 and Ranger Block I space probes when they were launched in the mid-20th century.
Schematics of the Mariner 2 and Ranger spacecraft depicting the location of the ion chamber were stored in the USS Enterprise's library computer database. This database was accessed by the Talosians in 2254. (TOS: "The Cage")
The schematics of the Mariner 2 and Ranger spacecraft were from the archives of the National Aeronautics and Space Administration - Jet Propulsion Laboratory.