Start with the assumption that in 1945 humans began living off world due to first contact with alien/other dimensional beings around the development of the nuclear bomb.

These people would likely suffer from significant home sickness. But not just home sickness of wanting to see home again... but even to be understood and welcomed. Traditional novels or movies from earth wouldn't truly satisfy that human connection that the different entertainment mediums offer. Connections from afar with people just like yourself.

Consider you need something to offer that will make them feel connected to people at home, but integrating the sort of things you deal with day in and day out in your completely alien life.

Enter Asimov, Clarke, (and earlier)... feed them advanced information on technology in some roundabout manner, give them some basic circumstances that characters might be found in, and let them loose. You as a fledgeling branch of the US military can bring in a hefty profit from the book and movie sales on earth. But more importantly... you get to show your men serving "afar" things that speak to them, and connect them with people back home. Even if the people at home don't realize it.

In Ender's game people on world were aware of the space program, but not the true scope of it. Look at that book from the vantage point of *actually* being a kid in some secret off world space program where you couldn't talk to your friends or family anymore. Think about how important a book like that would be to your mental well being?

It's what I'd do if I had a secret space/dimensional program that took intense emotional strains on those early participants.

So rather than an APO or an FPO parents would send them packages of books to a SPO?
Sorry, I don't buy it. I suggest you think of young kids being influenced right here on earth to unworldly things, ideas and concepts. The writers you cited, maybe they were the ones influenced for the likes of myself, a young American that cut my wisdom teeth on sci-fi books back when that word was dispicable in the regular world. Very few of you alive today can even handle that concept, it is so far out of your reality.

No, all of the "education" has been done for the folks right here on Terra, subtle way through the proliferation of strange ideas mixed with bits of strange realities that kept surfacing and direct experiences for some of us.