24. The Longest Mission Was 342 Days
The One-Year Mission was a scientific research project aboard the International Space Station. The goal was to understand the health effects of long-term spaceflight for future exploration of the solar system.
What makes the mission even more interesting is the N.A.S.A Twin Study conducted on astronaut Scott Kelly and his brother Mark Kelly (also an astronaut, but who stayed on earth during the study).
Sever longlasting changes were found including changes in DNA and cognition.