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.