LOST IN SPACE
Today we take it for granted that astronauts can function in the weightlessness of spaceflight, but at the dawn of the space age in the early 1960s, scientists weren’t sure that was possible. Some experts feared that the shape of the human eye would become distorted in zero gravity, making it difficult for astronauts to see the gauges and controls they needed to operate their spacecraft. What about eating—would astronauts be able swallow their food without the assistance of gravity? And even if they could, would their bodies be able to digest it? If not, the length of a spaceflight might be limited to the amount of time an astronaut could go without eating.
These fears proved to be unfounded, but as the years passed and the duration of spaceflights increased from less than an hour to days, weeks, and eventually months, astronauts on longer missions began to experience physiological changes that were just as worrying to scientists. For each month they spent in weightlessness, astronauts lost as much as one percent of their bone density in the hips and other weight-bearing areas of their bodies, and as much as 3 percent of their muscle mass.
Some of the first Soviet cosmonauts to spend more than 200 days in space in the early 1980s were unable to walk or even catch a ball after returning to Earth. They eventually recovered, but their experience raised the alarming possibility that if a mission was long enough, such as a three-year trip to Mars and back, an astronaut’s health might never recover. Computer models have predicted that astronauts on a mission to Mars could lose as much as half of their bone density, putting them at serious risk of bone fractures. They might land on Mars too fragile to function; if they broke a hip or some other bone…