ISS astronauts Scott Kelly and Kjell Lindgren talk about the challenges of a mission to Mars. Scott Kelly, when asked how the psychology of the mission to Mars would differ from a stint on the ISS said "There's no doubt about it, it will differ vastly." Kelly talked about the length of the trip getting to Mars and the fact that after a few days, astronauts on the way to Mars would not be able to see Earth.
Kelly elaborated on one of the things he misses most about not being home: The ability to leave. As amazing at the ISS is, it's not like any of the residents can open a door and take a stroll down to the local pub. Another difference in a mission aboard the ISS and a journey to Mars is the communication. Astronauts going to Mars will not be able to communicate with Earth easily. Check out the video to hear more from Kelly and Lindgren about the differences between an ISS mission and a Mars mission.