Scott Kelly Prepares for a Year in Space on ISS

— -- Scott Kelly is about to begin an expedition that’s out of this world – literally.

The 51-year-old astronaut has signed on to live in the International Space Station for a full year on Friday. The goal of the mission is to find out how the human body responds to a prolonged stay in space. No American astronaut has spent more than six months beyond Earth’s atmosphere, and the full extent of the physical and psychological strains of space exploration are still unknown.

“There are risks and I am willing to accept that for what we are going to learn from it,” Kelly told ABC’s David Kerley.

Scott Kelly’s twin brother, Mark, who is also an astronaut, will be remain on Earth as an experimental control to help measure the changes to Scott’s body while in space.

“We need to figure out how people are going to live in space for really long periods of time, especially if we want to send somebody to Mars [and]… build a base on the Moon,” Mark Kelly said.

It takes 18 months roundtrip to get to Mars, and the data from Kelly’s expedition will help NASA determine whether a human can survive that journey. Scott Kelly recognizes the risks of the unprecedented expedition, but says he’s focused on doing what it takes to advance space travel and exploration.

“That's one of the things that makes it exciting and something I am really happy to be a part of,” he said.