I enjoyed this book very much when I read it in the late 70s. I'd been devouring a lot of science fiction, having moved from the space operas of E.E. "Doc" Smith to the "harder" SF of Isaac Asimov and, particularly, Larry Niven, and was now wanting learn more about the facts behind the stories.What I remember most about reading this book, however, is not the contents, but an incident that happened while I was reading it. I was waiting one winter evening at a bus stop when some passing yobs, presumably astounded at seeing somebody with a book outside of school, demanded to know what I was reading. I told them the title of the book and one of them made a vulgar comment about vaginas. Do I remember the comment because I enjoyed the book, or do I remember the book because of the comment?On reflection, I think I remember the incident because I thought I was going to get beaten up for just for reading a book. I wasn't, though.