Mark Kelly: My twin brother Scott just blasted off for a year in space

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BAIKONUR, KAZAKHSTAN — He’s off the planet — and on his way to the International Space Station.

Earlier today, I watched as my brother, NASA astronaut Scott Kelly, and two Russian cosmonauts launched to space aboard a Soyuz rocket. They left from Kazakhstan’s Baikonur Cosmodrome, the oldest space launch facility in the world. They went from zero to 17,500 miles per hour in about 12 minutes.

After docking with the Space Station, opening the hatch, and floating out of their capsule and into the Space Station – which is about the size of a four-bedroom house – Scott will settle in for his year-long mission.

MSNBC Live with José Díaz-Balart, 3/27/15, 10:18 AM ET

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Watching the launch from nearby and feeling the roar of the Soyuz’s rocket engines, I thought of how the first manned American space flight lasted only 30 minutes. And now, we will have an American in space for a year. We have come a long way.

One thing that hasn’t really changed over the history of our space program is what it feels like to launch on the back of a rocket. It feels like the hand of God has come down, grabbed you by the collar, and ripped you off the planet. It is quite the ride. You spend years training for it and even then, as Scott likes to say, once those engines start, you know things “are about to get real.”

The day of your launch – I had four of them – you wake up knowing there are really two main possibilities for what you’ll be doing at the end of the day: you’ll either be dead, or you’ll be floating in space, looking down on our beautiful planet.

So every time we safely launch people into space, it’s a big deal. It represents the successful coming together of science, engineering, and the drive to explore. A huge number of committed individuals have to work together to support a singular event: accelerating people off the planet. It is a really challenging thing to do. And it is never, ever routine. After all, space flight is a pretty risky business.

But it is an important endeavor. The mission Scott is embarking on will push the limits of what Americans can do in space. To better understand how long-term space flight impacts humans, NASA is studying Scott and me while he’s in space and I’m on Earth. Because we are identical twins, they have a unique opportunity to study how the human body changes in space. I get the easy job, and Scott gets the fun job.

Hopefully, this will advance our knowledge of what happens when people leave the planet for a long time and help pave the way for sending Americans beyond low-earth orbit. There are a lot of exciting destinations in the universe, some not too far away. This mission is another step toward them.

But spending a year in space is a really hard thing to do. Imagine where you were a year ago – now imagine being at the Space Station for that entire time. Imagine going to your office and having to stay there for a year and not go outside once. That’s what the next year will be like for Scott at the Space Station. But take it from me: the views are pretty good.

Scott trained for a long time for this mission. He had to say goodbye to his two daughters, his girlfriend, his family, and his friends. He knows the risks. He made a huge commitment.

I am proud of him for his service to our country, and for taking on this challenge in the name of exploration, science, and advancing America’s space program.

So what’s my message to my brother Scott? “Thank you for your service. And be careful up there.”

This article originally appeared on NBCNews.com.

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Kelly: study analyzes 'details of physiology'

Identical twin astronauts Mark and Scott Kelly will be the subjects of the first-ever NASA twin study which will monitor both brothers for a year while one is in space and the other on Earth. Mark Kelly, who will remain Earthbound, joins Lawrence O…

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Mark Kelly: My twin brother Scott just blasted off for a year in space

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