In 2005, astronaut John Phillips took a break from his work on the International Space Station and looked out the window at Earth. He was about halfway through a mission that had begun in April and would end in October.NASA calls this visual impairment intracranial pressure syndrome, because they think is is caused by the buildup of fluid pressure in the head under zero gravity. But that's just a guess and even if it is right they have no idea how to treat it.
When he gazed down at the planet, the Earth was blurry. He couldn’t focus on it clearly. That was strange — his vision had always been 20/20. He wondered: Was his eyesight getting worse?
“I’m not sure if I reported that to the ground,” he said. “I think I didn’t. I thought it would be something that would just go away, and fix itself when I got to Earth.”
It didn’t go away.
During Phillips’ post-flight physical, NASA found that his vision had gone from 20/20 to 20/100 in six months. . . .
Phillips case became the first widely recognized one of a mysterious syndrome that affects 80 percent of astronauts on long-duration missions in space.
Science fiction writers have made frequent use of two strategies to create false gravity on interplanetary voyages. One is giant rotating wheels, the other having the ship accelerate all the way to the halfway point, then flip around and decelerate all the way to its destination. I suppose the first requires an enormous ship to work, the second too much fuel, and neither is part of NASA's Mars plans.