Humans are not designed for long-distance travel, which makes the roughly55-million-kilometer trip to Mars a real hassle. It’s hard enough keeping a few of us fleshy weaklings alive next door in low Earth orbit. Now think about a trip to Mars. It’s at best several months away, and once you head out, there’s no stopping for groceries. The job of the astronauts during the journey will be simple: eat, drink, and breathe the bare minimum necessary for survival, while trying not to die of boredom or kill any of their fellow travelers. After the first few months, it’s going to be decidedly unpleasant.