"Later today, a Russian rocket is scheduled to carry a Russian cosmonaut and an American astronaut to the International Space Station, where they will live for a full year, twice as long as people usually stay."

"No American has lived in space for longer than 215 days. Only a few people have ever gone on space trips lasting a year or more — the longest was 437 days—and they're all Russian cosmonauts. The last year-plus stay in space occurred nearly two decades ago."

"What's more, NASA's upcoming mission offers scientists a unique opportunity to study the effect of spaceflight on the human body. That's because the astronaut making the trip, Scott Kelly, has an identical twin brother, Mark Kelly, who's a retired NASA astronaut."