JUDY WOODRUFF: Finally, a conversation about an out-of-this-world experience: living in space.

Astronaut Scott Kelly arrived this weekend at the International Space Station. He will stay there for almost a year, the longest duration an American has ever spent in space. Hes the identical twin brother of former astronaut Mark Kelly. And both will participate in a study to see the effects of living in space.

After Scott Kelly lifted off on Friday, Jeffrey Brown spoke with a former astronaut, Chris Hadfield, whose final stay on the space station lasted five months.

JEFFREY BROWN: Chris Hadfield, welcome to you.

The twin study is especially interesting this time, right, the research on the two brothers, Scott and Mark Kelly, one in space, one on the ground. What kinds of things are being looked at?

CHRIS HADFIELD, Canadian Space Agency: Yes, it sounds like science fiction, doesnt it, to have an identical twin on a space ship and another one down on the ground?

But its just luck, but, boy, it sure provides some interesting medical and scientific opportunity. You take two people that are as identical as they can be. You put them in wildly different environments, one of them that is really brand-new for humanity, living in weightlessness off the planet, and then you watch how they change over a year. You measure all of those subtle things, bone density, muscle strength, psychology, vision, blood pressure, blood pressure regulation, all of those, liver function, everything.

And it is really going to help us not only understand spaceflight for long-term flight, for going from here to the moon and Mars and beyond, but also just understand the effects on the body of flight itself, the subtle changes that happen within the body, and teach us inherently about physiology. Its a really cool thing. Its never been done before.

JEFFREY BROWN: Well, so, then, of course, there is the length of time. This would be twice as long, I think, twice longer than any American up to this point.

Whats the why go longer? And lets start to talk a little bit about the new difficulties that that presents in staying up that long.

Go here to read the rest:

Astronaut Scott Kelly sets out to break an American record in space