Definition & Meaning of "space cadet"

What is the origin of the idiom "space cadet" and when to use it?

The origin of the idiom "space cadet" can be traced back to the mid-20th century, specifically the 1950s. It emerged during the space race era when interest in space exploration was on the rise. The phrase often carries a playful or lighthearted tone, but it can also carry a slight negative connotation, implying a lack of seriousness or engagement.