Living in space is even more challenging than it seems. Microgravity affects your body in weird ways, the high-risk environment can create high-stress situations, and you don’t have the comforts of your daily life on Earth: no showers, no fresh food, no fresh air, and no loved ones to go back to at the end of your work day.

Astronauts usually endure all that for six months on the International Space Station (ISS). But a trip to Mars will last two to three years. How will humans fare that long in space? And what will be the psychological challenges that astronauts face on their way to the Red Planet, the furthest away any human being has ever been from home?

How will humans fare that long in space?

The Verge asked Scott Kelly, the former NASA astronaut who spent 340 days on the ISS — the longest any American has lived in space. His one-year mission is a stepping stone to future missions to Mars. Kelly told us how his year in space changed him and how he’s gotten a better appreciation for the environment.

Despite the physical and psychological challenges, Kelly said he’d volunteer for a mission to the Red Planet — with one caveat: he has to have a return ticket to Earth. "Having spent a year on the space station," he says, "I can’t imagine spending the rest of my life in an environment like that, where you can’t go out and get fresh air."