Mary Roach's "Packing for Mars: The Curious Science of Life in the Void" is the perfect book for anyone who is curious about the ins and outs (literally) of space travel.
We learn:

• How astronauts urinate and defecate in space, and how this process has changed from the early Apollo missions to the space shuttle to the space station.

• How sex in space would work, and if anyone has ever given it a shot.

• How space food is produced and consumed, and why we would not want to have NASA take over our campus dining services.

• What an astronaut really does in the 99% of the time she is not in space, and what NASA (and the Russian and Japanese space agencies) look for in a potential recruit.

• How astronauts train, getting used to the rigors of zero gravity (think Vomit Comet http://en.wikipedia.org/wiki/Vomit_Comet), the boredom, and the need to spend 24 hours a day with your co-workers without ever being able to leave.

• Why Mary Roach thinks manned space exploration should continue, and why spending the $500 billion or so to get to Mars is a good investment.

I'm a big fan of Mary Roach's books. She has covered sex (Bonk), death (Stiff), and ghosts (Spook). The only problem with "Packing for Mars" is that the title is too long.
And in the category of, "oh what a small world we live in", it turns out that Mary Roach grew up in the small town in which I now reside. Mary, you are welcome to stay at the house if you ever want to come and visit.

What are you reading?