Packing for Mars
This book can get a bit crude at times and the voice actor took a chapter or so to get accustomed to. Once you get past these two negatives, there's a lot of great information about the development of manned spaceflight technologies, and the physiological questions associated with putting a human body in space.
Think about that ... before Yuri Gagarin, we didn't know if human bodies would even function in zero g! We sit here in the early 2000's with the benefit of hindsight, knowing spaceflight is possible, but in the early days there were thousands of unanswered questions. Mary Roach draws the parallel between our ignorance of low earth orbit in the 1940's, to interplanetary travel today. This was a very enjoyable book once you get past the sometimes unnecessary crudeness.