"The human body did not evolve to live in space, and the longest any human has been off Earth is 437 days. Some problems, like the brittling of bone, may have been overcome already. Others have been identified — for example, astronauts have trouble eating and sleeping enough — and NASA is working to understand and solve them. But Kenneth Chang reports in the NY Times that there are some health problems that still elude doctors more than 50 years after the first spaceflight. The biggest hurdle remains radiation. Without the protective coc00n of Earth's magnetic field and atmosphere, astronauts receive substantially higher doses of radiation, heightening the chances that they will die of cancer. Another problem identified just five years ago is that the eyeballs of at least some astronauts became somewhat squashed. 'It is now a recognized occupational hazard of spaceflight,' says Dr. Barratt. 'We uncovered something that has been right under our noses forever.' NASA officials often talk about the 'unknown unknowns,' the unforeseen problems that catch them by surprise. The eye issue caught them by surprise, and they are happy it did not happen in the middle of a mission to Mars. Another problem is the lack of gravity jumbles the body's neurovestibular system (PDF) that tells people which way is up. When returning to the pull of gravity, astronauts can become dizzy, something that Mark Kelly took note of as he piloted the space shuttle to a landing. 'If you tilt your head a little left or right, it feels like you're going end over end.' Beyond the body, there is also the mind. The first six months of Scott Kelly's one-year mission are expected to be no different from his first trip to the space station. Dr. Gary E. Beven, a NASA psychiatrist, says he is interested in whether anything changes in the next six months. 'We're going to be looking for any significant changes in mood, in sleep, in irritability, in cognition.' In a Russian experiment in 2010 and 2011, six men agreed to be sealed up in a mock spaceship simulating a 17-month Mars mission. Four of the six developed disorders, and the crew became less active as the experiment progressed. 'I think that's just an example of what could potentially happen during a Mars mission, but with much greater consequence,' says Dr. Beven. 'Those subtle changes in group cohesion could cause major problems.'"
