The Atlas-Agena was an American expendable rocket that was in service with NASA in the mid-20th century. This rocket, which consisted of a primary booster (the Atlas) and a secondary booster (the Agena B), was used for launching a probe into space for its journey to Luna or a planetary body, such as Venus or Mars. The rocket saw use in the Mariner and Ranger programs.
There were two black-and-white drawings that were stored in the USS Enterprise library computer. The first depicted a launch sequence for a Ranger space probe, and the second depicted schematics of the rocket and a Mariner space probe. These drawings were later retrieved by the Talosians when they accessed the starship's computers in 2254. (TOS: "The Cage")