NASA One-Year Mission Astronauts Blast Off On 350-Day Space Mission

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How does the human body respond to long-duration spaceflight? Does radiation present a problem? How about long periods of weightlessness? And what about the isolation?

We're about to find out.

NASA's "One-Year Mission" has officially begun , with American astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko blasting off from the Baikonur Cosmodrome in Kazahkstan at 3:42 p.m. EDT on Friday. The pair is headed for the International Space Station aboard a Soyuz spacecraft.

A new perspective. The pair will spend the next 350 days in orbit, helping the space agency gain a better understanding of the biomedical aspects of long-duration spaceflight as it gears up for a manned mission to Mars.

This won't be the longest anyone has spent in space. That record belongs to Valery Polyakov , a Russian cosmonaut who orbited the Earth from January 1994 to March 1995--almost 438 consecutive days.

But with typical ISS missions lasting four to six months, the One-Year Mission is giving these astronauts a new perspective on their time in orbit.

"On a six-month flight, your mindset is you're going to go up there, and you're going to be up there for a period of time , and you're going to come home," Kelly said at a press conference last January, according to Space.com. "When it's a whole year, I don't have that same perspective. It's almost like I feel like I'm just moving there and I'm not coming back. Or, it's going to be so long that when I come back, it's almost like I never lived here."

(Story continues below.)

I'm thinking this is about to get real. #YearInSpace pic.twitter.com/UzRtdxig6B

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I'm thinking this is about to get real. #YearInSpace pic.twitter.com/UzRtdxig6B
Scott Kelly (@StationCDRKelly) March 6, 2015

So far, scientists know that long exposure to a zero-gravity environment can affect eyesight and the immune system, and can even lead to muscle atrophy or bone loss .

It takes two. As part of the research program, researchers on the ground will compare Kelly's health to that of his identical twin, retired astronaut Mark Kelly.

We realized this is a unique opportunity to perform a class of novel studies because we had one twin flying aboard the International Space Station and one twin on the ground , Dr. Craig Kundrot, deputy chief scientist of NASAs Human Research Program, said in a written statement. We can study two individuals who have the same genetics, but are in different environments for one year.

scott and mark kelly Astronauts and twin brothers Mark Kelly (right) and Scott Kelly (left) are pictured in the check-out facility at Ellington Field near NASA's Johnson Space Center in Houston.

The researchers will compare the brothers' blood samples as well as how they perform on psychological and physical tests -- comparisons that will take place before, during, and after the mission. But according to the Associated Press, the brothers won't follow the same diet or exercise regimen . Mark Kelly said he had no desire to eat ISS food or run two hours a day on a treadmill, as his brother will be doing.

"If a mission to Mars is going to take a three-year round trip, we need to know better how our body and our physiology performs over durations longer than what we've previously on the space station investigated, which is six months. Perhaps there's a cliff out there with regards to some of these issues that we experience and perhaps there aren't," Scott Kelly told CBS News. "But we won't know unless we investigate it."

Editor's Note: This post has been updated as of Friday, March 27, following a successful launch from the Baikonur Cosmodrome.

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