Space Cadet

Greetings, Space Cadet! Which usage of the term are you here to explore?
 * Space Cadet (novel), the Young Adult novel by Robert A. Heinlein
 * Eager Young Space Cadet, a character much like the lead characters from Heinlein's novel
 * Cloudcuckoolander, somebody who doesn't match the characters from the novel but is often derisively described as a "space cadet"