Science writer Mary Roach seems to be attracted to unusual subjects, as indicated by her previous books on the science about cadavers, the afterlife, and sex. She would seem, in fact, to be in large part attracted to subjects that others would think unpleasant, at least judging from Packing for Mars.
Roach starts out tamely enough by exploring the differences in how astronauts are chosen by the Japanese versus Americans. Then she logically moves into discussions of past research into the psychological effects of space travel and life without gravity.
Eventually, she gets down to the nitty gritty, for example, designing food for space, but also more, shall we say, earthy topics, such as waste disposal, farting in space, sex in zero gravity, and so on. Indeed, the chapter on food dealt largely with shit, which, since that was the subject of the previous chapter, was a bit too much.
Packing for Mars is well written, interesting, and sometimes amusing. It is perfect for people who like little factoids or like to dabble in science. It would not be my choice for reading normally (it was a book club choice), and I confess I got a little tired of descriptions of floating turds, and so on.
whatmeread 
We were just talking about this book at dinner the other night (my mom is a huge fan of science/space books) when I was visiting family. I think she’d really like it.
She probably would, although there is a bit more scatological information in it than may have been strictly necessary. On the other hand, if you’re going into space, that’s probably a major concern.