A year is a long time to stay anyplace. But staying a year in space has some special challenges.
Kelly says NASA supplies most of what he needs but he's taking his own tool pouch, some sweatshirts and special shoes to use when he's lifting weights.
"I bought a special kind of shoes I thought would be better for that," Kelly said at a NASA briefing on Thursday.
Then there's what to do for a year in space. You get a great view of Earth, so the scenery is amazing. But the space station orbits Earth about every 90 minutes, or about 16 times a day. Could get a little repetitive. So how do you keep from getting bored?
Experiments. Lots and lots of experiments. NASA says space station crews normally work on about 200 experiments over six months, but Kelly will be doing many more. He says he's actually fascinated with the space station itself as a giant experiment in living in space.
"Building this facility that allows us to understand how to operate for long periods of time in space to allow us someday to go to Mars."
In his free time Kelly says he'll spend a lot of time talking to people on Earth, messaging on social media, reading email, watching TV and writing.
"I'm going to keep a personal journal of the experience," Kelly said. He also will share some of his journal with researchers studying the psychological impacts of long-term space flight. Will he tell all?
"I plan to be completely honest about it," he said, but ... "who knows, maybe there are some crazy thoughts I'll have at the end that I wouldn't want to share."
Kelly also might get to do a bit of singing.
British singer Sarah Brightman
will visit the station as a space tourist during Kelly's year in orbit. Will he and the other crew members sing along with her?
"It will be either all of us or none of us," Kelly joked.
One other thing Kelly has to plan for: near-zero gravity. Turns out our bodies really like gravity. Stay in orbit too long and your eyes, heart, bones, muscles -- basically everything -- change, and usually not for the better.
On the upside, you get a bit taller. At least briefly.
"You do grow when you're up there for a long time," Kelly said. "Unfortunately it doesn't last. But it did last long enough that I could stand next to my brother and look down at him a little bit."
Kelly was joking about his twin, former astronaut Mark Kelly (who is also known for being the husband of former Rep. Gabrielle Giffords). Mark Kelly has volunteered for NASA's "Twins Study" -- 10 investigations
into how the identical twins change over the year in two very different environments. Even though Mark will be on Earth getting poked and prodded by researchers while Scott makes history in orbit, Scott said his brother doesn't mind.
"He thinks it's great that he can still be a participant in this," Scott Kelly said.
The Kelly brothers' experiments should help NASA understand what happens to astronauts who spend a long time in space and help plan longer spaceflights to an asteroid or to Mars.
Despite all the health risks and personal sacrifices, Kelly said there's a big reason to stay in space a year.
"It's a lot of fun," he said. "Space station is a magical place."
The mission is a first for NASA, but not for Russia. Between 1987 and 1995, four cosmonauts spent a year or more in space. And another Russian will be with Kelly for his yearlong mission: cosmonaut Mikhail Kornienko.
Both men are space veterans. Kelly has flown on two shuttle missions and has already done two stints on the space station. In all, he's logged more than 180 days in space. Kornienko has spent 176 days in space.
The two will ride to the space station on a Russian Soyuz spacecraft along with Russian cosmonaut Gennady Padalka, who is staying for six months. The trio will launch from the Baikonur Cosmodrome in Kazakhstan on March 27.