Scott Kelly prepares to become first American to spend a year in space

Scott Kelly is preparing to do something no other American has ever done -- spend a year in space.

The 50-year-old astronaut can't wait to get there.

"The best thing is working at something that's very challenging ahead of time for a couple of years, and the challenges that space presents," Kelly said Thursday.

Kelly is no stranger to space. He already has logged 180 hours in orbit during three missions.

This time, NASA is sending him up to study the effects of long-term space travel on humans so it can better prepare for a future mission to Mars.

Kelly and cosmonaut Mikhail Korniyenko will follow a strict exercise regimen and carry out experiments on themselves while aboard the space station. The Russians have some practice at this, having conducted year-long missions in the 1980s and 1990s.

NASA plans to compare medical data from Scott and his twin brother Mark -- a retired astronaut who's married to congresswoman Gabrielle Giffords -- looking at the effects of gravity on the human body.

Kelly, Korniyenko and another cosmonaut will blast off to the International Space Station aboard a Soyuz rocket on March 27. Kelly will return to Earth in March 2016.