I'm Carla Zeus, and today's special edition of CNN 10 examines the effects of microgravity on the human body.

In a nutshell.

They're not good.

Weakened muscles, back pain.

I problems.

Astronauts say they've experienced all of these ailments after working in orbit.

Thanks to research like NASA's twin study, which will hear about in a minute, scientists are getting an idea about how extended time and space affects people.

Scott and Mark Kelly have already contributed a great deal to this kind of research.

Scott is an astronaut who spent almost a year in space.

Mark is his identical twin brother, who stayed on solid ground year in space 11 months in in a place the astronauts can never leave.

It can be tough mentally to keep things interesting, Scott Kelly decided to monkey around.

There's no such thing as a true vacation up here, and that could take a toll even on a day off, without any scheduled experiments or maintenance work.

The astronauts are always on alert.

You know, you wake up, you're at work, you go to sleep, you're at work.

You never You never leave your very busy.

I think.

You know, I think one of the underlying sze dressers of the being up there for so long is that you're always thinking Okay, we have a fire, We have a pneumonia.

Lee, you have a depressurization.

You know, I have to be able to respond to this.

And that's something that's always in your back of your mind, where you never really have a minute off from, you know, those kind of things happening.

So in San Diego, I moderated a panel with Scott and Mark Kelly.

Dr.

Stevan Gilmore also joined us.

He was Scott's flight surgeon for his past two missions.

This lack of a mental break was one of his biggest concerns.

Going into the year in space, I'd asked a few of the other astronauts that I've worked with What if they could describe what time off would be on station?

And that's kind of a difficult thing to do, because for the six month missions, you're going up there with the with an attitude of all the things that you want to get done, and it's a very achievable thing if you want to eventually get to Mars.

That mission would last roughly 30 months, two and 1/2 years for the duration of Scott's year long flight.

He would have only just arrived on Mars.

Now, in addition to being able to mentally handle it, radiation would be a big concern.

Consider this beyond low Earth orbit.

The protection of the Earth's atmosphere is gone.

NASA says astronauts are exposed to radiation anywhere from 50 to 2000.

Millie Seaver's amid receiver of radiation is equivalent to three chest X rays, so add it all up.

And that's an exposure level equal to a CZ many a 6000 chest X rays.

I'm curious with all that you've learned that you've seen.

Do you think Mars is feasible?

Yeah, I think it's, Ah, I think it's definitely feasible.

I think there are certain challenges, you know, The the radiation environment between the Earth and Mars is something that we're gonna have to I have to figure out because there is Ah, you know, we get protection here on the space station, although we get a lot more radiation than you do on Earth.

You'd get a much, much more on your way to Mars.

So that's that's a challenge.

Another aspect of being in space for so long.

Nutrition.

In 2014 I visited NASA's Johnson Space Center and got to taste some of the food.

I gotta tell you, it's come a long way.

I tried a crab cake in some fish curry.

Even still, though, I'm not sure I could eat out of a bag every meal for 340 days, let alone the time it would take for a Mars mission.

But for the twin study, NASA monitored everything Scott ate and drank while Mark continued his regular diet back here on Earth.

They also closely monitored Scott's heart in space body fluid shift from the legs to the head and upper body as much as two liters of fluid.

NASA says A natural reaction to this is a decrease in the total amount of circulating blood in the body back and result in low blood pressure upon reentry.

Back to gravity.

Some astronauts experience fainting until their blood pressure normalizes back in 2014 when I visited Johnson Space Center in Houston, Texas.

I first met Julie Robinson.

She's the chief scientist of the international space station with a critical hand in the science experiments happening during Scott Kelly's year in space.

Another element to consider about living on the space station that long is your personal space thes air the sleep quarters.

So this is your personal space.

This is it.

Julie showed me around the mock up of the station, which has 935 cubic meters of livable space.

You've got some real nice fans going blowing on you at night so you don't suffocate if I step in here.

Yes, Scott slept in this small compartment every night, so basically you have a sleeping bag.

That's Velcroed to the wall.

NASA says Ash not sleep on average, less than six hours a day and before critical mission operations, it's even less.

Twin Study is really the crown jewels of this mission.

10 studies with 10 different groups of researchers are happening almost simultaneously, using the samples from Scott and Space and Mark on Earth.

This is what we can see.

Dr.

Andrew Feinberg is a researcher with Johns Hopkins He's also one of the principal investigators of the twin study.

His focus is genetics.

But if you think about the area that the twin study was involved in things like, say, identifying what might be a genetic damage to the genome that might precede the development of mutations that could lead to cancer risk that might open the door to ways to mitigate the damage that has practical implications for here on Earth.

By studying Scott and Mark, scientists will be able to identify any links between the environment and human health.

But there is another downside in addition to the potential long term health impacts for Scott.

Because genetic information is a part of this study.

Privacy could be an issue for the Kelly twins and their families.

So before anything is published, they will have the option of withholding certain information.

Your study is going to become a well known study.

The state is gonna be out there, and obviously people gonna know it's you, too.

Because, you know, the only twins that have been study like this at that time private the security of that information, just just the privacy of it actually worry about.

I'm not worried about it for me.

I'm worried about it.

More for my kids.

Like, you know, they could potentially see that.

You know, I'm susceptible toe having this disease and basic based on the person and what kind of person they are that could have, ah, significant effect on him or not.

Maybe they would just like to know.

Did you have any reservations mark about being in a study like this?

I realize the significance of of putting that information out there and in flying in the space shuttle.

There's a lot of risk involved and it's a risk versus reward thing.

And the rule ward is really for our country and for our nation.

So same thing with the science.

There might be a little bit of a downside for us, but the benefit to the space program into the American people is enough to make it pretty obvious.

Decision.

Getting ready to depart the international space station again.

Wrapping up 340 days on board the orbiting laboratory, Scott's mission in space came to a close.

There was one big part left.

Reentry on on docking has occurred.

Perhaps the riskiest part of spaceflight happens at the very end, you described it as going over Niagara Falls in a barrel.

That also happens to be on fire.

It's pretty scary.

And I watched the video and, you know, first you seem remarkably composed, you know, you actually think about it.

So I've made it all the way through this, like, whole year.

The launch space walks the risk of being up there for a really long time.

And I'll tell you what.

You know, one of the riskiest parts is at the very end when you come, you know, blasting back into the atmosphere.

And you're relying on this, you know, parachute open in this Russian Soyuz and everything goes well when there's stuff flying by and hit the windows part of insulation that comes off and it gets hot inside.

Then as soon as the chute opens and the motion stop and you've realized it didn't kill you, it's the most fun you've ever had in your life.