Packing for Mars: The Curious Science of Life in the Void by Mary Roach, and can highly recommend it, even if you've never so much as watched a space launch before. I had initially checked this book out for my son (a teen son: the book is a bit PG13-ish because of Roach's totally straightforward approach to everything that could happen on a space ship), but I started flipping through it, and soon had claimed it for myself (despite my utter lack of interest in all things space-related - that's how good she is!). Roach combines a wonderful sense of humor with a deep and abiding interest in everything under the sun - it makes for a wonderful read about all the behind-the-scenes stuff you never even thought about before, but now can't imagine living without knowing.
Mary Roach's other books:
Stiff: The Curious Life of Human Cadavers
Spook: Science Tackles the Afterlife
Bonk: The Curious Coupling of Science and Sex