Non-RAH YA Sci-Fi?

[jeriendhal]

Here's a query: Can anyone point me in the direction of some good 1940's-50's science fiction juvenile novels that weren't written by Robert Heinlein? I know there were many, but for the life of me I'm blanking on any titles or authors beyond Isaac Asimov's "Lucky Starr" books (which aren't exactly what I'm looking for, since the protagonist in them is an adult.)

Just trying to get some further inspiration for GURPS Solar Space, so I can re-start it and perhaps submit for consideration to e23.