Mars One plans on sending astronauts to our neighboring planet in 2023, sans return ticket. Even if the mission doesn’t crash, the astronauts might–psychologically. From “Voyage of No Return,” by Peter Guest at the Ascender:

“After all that technical effort, the flaws in the project could not be in the technology or the financing. The biggest risk to Martian colonization could well be the astronauts themselves. If successful, they would face unprecedented levels of isolation and disconnection from the world, which in turn could lead to depression and severe psychological stress. While it might feel to would-be astronauts like [Timothy] Gatenby that seeing the Earth from above might keep them going for the long journey ahead—in fact the scientific literature, such that there is, suggests that gaining a perspective of Earth is one of the principal positive psychological benefits experienced by astronauts—the downsides are dangerous.

Researchers Michel Nicolas, Gro Mjeldheim Sandal, Karine Weiss and Anna Yusupova, from universities in France, Norway and Russia, studied the Mars500, a 105-day Mars simulation, and noted that over the course of the ‘journey’, participants demonstrated ‘significant’ deterioration in their emotional wellbeing.

A 2010 paper by Nick Kanas, professor of psychiatry of the University of California, noted that astronauts in long orbital missions show some signs of psychological distress, including depression, which could stem from a sense of dislocation and isolation. Candidates are intensely screened for psychiatric conditions and for their emotional resilience, as Mars One candidates would be, but even so, problems are manifest. In his study, Kanas notes, for example, the emergence of psychosomatic reactions—physical symptoms that are thought to have psychological roots.

‘For example, an on-orbit cosmonaut wrote in his diary that he experienced tooth pain following some anxious dreams he had of a tooth infection and his concern that nothing could be done about such an infection should it occur in space,’ Kanas writes.'”