Isn't there one more after Skullheart? I forgot what it is called.
Today, I picked up a book from my school library called "The High Frontier: Human Colonies in Space", which is the book that inspired the UC space colonies. I'm only like 4 chapters, but it is pretty fascinating. It's fun seeing what ended up being right (particularly in regards to population projections and economic concerns), and what has been wrong (O'Neill projected that its possible to have a colony up by the mid 1990s). That said, he pretty much said that there was a myriad of political and economic issues that would delay it.
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"Don't freeze up girl, you're looking quite a sight." - Adam Ant.
"Baby, can you dig your man? He's a righteous man." - Larry Underwood