The first results to emerge from a simulated Mars mission have revealed some of the crew experienced depression, and troubles with sleep patterns.
The would-be astronauts spent more than 500 days in a capsule meant to replicate some of the conditions of long-terms space travel, such as subjecting the men to recirculated air and dehydrated food for over a year.
The findings, from Russia's Mars-500 project, suggest not all current astronauts will be suited to interplanetary travel.
Al Jazeera's Emma Hayward reports from Moscow.
Source: Al Jazeera