There are many difficult things about sending humans to space, from dealing with health effects on the human body to the risks of launch and landing to keeping astronauts well-fed and supplied. However, one aspect of space travel that isn't obvious is the effect it can have on human psychology. Astronauts must face the risks of space stays, all while being confined in a small space with a small number of other people. They are far from home, from their friends and families, and they can't simply pop home for a vacation.

Studying these psychological effects is particularly important as space agencies plan out longer-term future missions to even more remote places like the Moon and Mars. So, to understand what psychological factors might be involved in such missions and how to help astronauts cope with them, they look for clues here on Earth from those who also live and work in extreme environments.

Some of this research takes place in remote places like Antarctica, where scientists spend time on research and must also cope with risk and isolation. Other times, space agencies run experiments called analog studies where they simulate off-world environments and place volunteers into them to see how they cope. But there's another way that space agencies are researching extreme environments, as there exists a whole range of people who must also face similar factors of confinement and isolation. They study people who live and work on board submarines.