In the 1970s and 1980s people were interested in space, but in a different way to the resurgence of interest that's happened around the most recent space related boom with private companies like SpaceX, ULA, Rocket Lab, etc creating a huge jump in launch capacity. The interest in space themes came up in many movies and music at the time.

I remember in the past people saying things like:

"That kid is a space cadet"

In the 1980s there was a big heroin epidemic in Australia with a lot of junkies using a lot of heroin. This was a phrase I heard a lot back then because of this context. Mind you this was in a time before the medical "establishment" handed out opioids directly to the masses, a different era for sure.

This phrase was a reference to people who weren't aware of their surroundings, or "lost in space", another phrase I hear far less often now.

These days with a lot of people addicted to their smart phones all the time this phrase has fallen out of use. A lot of people are now permanent "space cadets" just looking at their phones while being completely out of touch with their surroundings. There's a lot of technology these days that helps people detach from their surroundings, one prominent example is people who are wearing headphones when walking around.

What was once seen as abnormal behavior has become frighteningly normalized.