Astronaut set to make history for longest stay in space

For the next year, astronaut Scott Kelly won't get stuck in traffic. He won't have to do the laundry, and he certainly won't have to worry about the weather.

At 3:42 pm ET Friday, Kelly and a Russian crewmate will blast off for new digs in outer space, not to return to Earth until March of 2016. Assuming Kelly toughs out his year in orbit, he'll smash the U.S. endurance record for the longest continuous time in space, which now stands at seven months. If Kelly and crewmate Mikhail Kornienko tough out more than 366 days together, they'll capture the record for the most enduring space crew.

The two men are bound for the International Space Station, a spacious orbiting residence and laboratory. There, more than 200 miles above the planet, they'll be free of many of the routine hassles of terrestrial life. But that doesn't mean they'll have it easy.

In the weightlessness of space, bones shrink and vision can deteriorate. Returning astronauts have a higher risk of kidney stones. The severe isolation and confinement can darken a space crew's mood, with potential implications for the ability to think clearly and work well with Mission Control.

All this is not lost on Kelly, who previously lived aboard the station from October, 2010, to March, 2011. He'll leave a girlfriend and two daughters, 20 and 11, on Earth.

"It's not going to be easy to spend a year in that kind of isolated environment," Kelly said during mission training. "But I think I'm up for that challenge."

As NASA sets its sights on Mars, the one-year mission will provide invaluable data on how humans react to a long period in space. Even better for the scientists, Kelly, 51, has a built-in control group. His identical twin Mark, a retired astronaut and the husband of former congresswoman Gabrielle Giffords, will undergo the same tests on Earth that his brother is subjected to in space.

To date only four other humans have spent a year or more at a stretch in orbit, all of them Russian or Soviet cosmonauts whose feats of longevity took place in the 1980s and 1990s. The all-time record holder, Valery Polyakov, lived 438 days in space without major incident.

But "one person being able to do this doesn't mean everyone will," says Mathias Basner of the University of Pennsylvania School of Medicine, who has studied space crews. "We know next to nothing about what will happen once we put people into space for prolonged periods of time."

NASA does know that weightlessness can be cruel, especially to bones, which weaken without the stress of gravity.

Astronauts on the station follow a grueling exercise routine but lose 3 to 4 percent of the bone density at the hip over six months, compared to 1 to 2 percent a year for postmenopausal women with osteoporosis. Crew members' bones are restored after landing. But there are worrisome hints that the bone at the hip may not regain full strength after crews return from space, leaving the hip more prone to breaking.

The downside to orbital bone loss doesn't end there. The calcium that leaks out of astronauts' bones seeps into their urine, raising the risk of agonizing kidney stones. Busy crews also tend to skimp on their fluid intake, which also promotes kidney-stone formation. All told, 20 astronauts have suffered 26 kidney stones, according to NASA statistics. The agency encourages crews to exercise and drink more to help prevent stone formation.

Space travel can take a toll on the eyes as well. Just under half of station astronauts reported that their near vision worsened in orbit. Back home, a few haven't completely recovered their pre-flight vision, though several see better than before they launched. It might be that the longer astronauts stay in space, the more likely they are to develop blurry vision and the more severe the problem will be. But no one really knows.

Perhaps the biggest unknown is how the crew will cope mentally and emotionally. Research show that after six weeks in orbit, people start to "get on each other's nerves," says Nick Kanas, an emeritus professor of psychiatry at the University of California, San Francisco, who has studied space crews. "The longer you're up and confined with the same people, the more likely you are to get tired of each other."

Kelly and Kornienko will probably reach a "steady state" in their relationship, Kanas says, but such a détente may never be reached with Mission Control. According to previous research, space crews often clash with "the ground," as astronauts call mission controllers on Earth.

"The comments he shared with me from the ground really hurt me," one space-station astronaut wrote in an anonymous journal entry shared with researchers. "I have still not recovered and am not myself."

Station astronauts average only six hours of sleep a night thanks in part to unrelenting work pressure. Mission managers must be extra careful to balance this crew's workload and their need for time off, says former station astronaut Ron Garan.

"Everyone who goes up there is of the personality type that wants to get the job done," says Garan, whose new book "The Orbital Perspective" chronicles his experiences in space and how they changed his attitude about life on Earth. "The crew really has to keep that in check." Kelly, he says, is keenly aware of that.

"This time I'm just going to have to work at a slower and more methodical pace," Kelly agrees in a pre-flight interview. "After four to five months, you do feel ready to get home. It's not because you don't like the place. … It's just because you're in one place and you can't go outside."

On his six-month mission, Garan missed "all the things that define the beauty of life on our planet," from singing birds to a breeze on the skin. A one-year flight will "just magnify" that effect, he says "We've never had an American in space for that long. … We're entering a whole new realm."