Moon, Mars trips will pose physical, mental health risks Houston Chronicle

As the Earth fades into the rearview mirror, the astronauts who set out on the missions that NASA proposes to the moon and Mars will face new challenges to stay mentally and physically fit.
Confinement on spacecraft and isolation from friends and family create psychological stress. Bones weaken without gravity and there is solar and cosmic radiation exposure.
“The risks to human health on long-duration missions beyond Earth orbit, if not solved, represent the greatest challenge to human exploration of deep space,” concludes Safe Passage: Astronaut Care for Exploration Missions, a study for the space agency by the National Academy of Sciences in 2001.
Without the swift, fictional propulsion systems of Star Wars and Star Trek fame, a round-trip voyage to Mars will send astronauts packing for 2 years. A tour of duty at a lunar outpost would last six months.
The trip durations lead to another worry: How does a faraway astronaut receive treatment for a medical emergency?