[MUSIC] [MUSIC] Congratulations!

Your application to be among the next generation of astronauts has been accepted!

You’ve proven to have the right stuff.

As a member of the newest astronaut class, you’re going to take trips farther and longer than any astronaut before you.

An asteroid.

Maybe even Mars, which means you could be up there for three years, with no chance of resupply or rescue.

Naturally, we want to keep all our test subjects safe.

Did I say test subjects?

I meant international heroes!

Now in case you didn’t read all the fine print on your application, space is a risky place to go to work… your body is going to face some major challenges up there.

But we’re not going to let that stop us, are we?

We're NASA!

You might recognize NASA’s most famous test mammal: Scott Kelly.

Scott spent almost an entire year in orbit, while his astronaut twin brother stayed on spaceship Earth.

This let us do the first truly comparative study about the effects of living in space long-term.

Scott Kelly launched six minutes younger than his twin brother, but after a year zooming above the Earth at 17,500 miles an hour, he returned even younger– by a few milliseconds at least.

This is the Twin Paradox, an effect of special relativity.

Unfortunately, thanks to Scott’s telomeres, we believe he actually returned to Earth physically older than his big brother.

The ends of our chromosomes are protected by special DNA caps, which shorten as cells divide and we get older.

Living in space seems to speed up that shortening.

And since shorter telomeres are linked to physical aging, your body will age faster while you’re away from home.

Don’t worry, the effect isn’t too extreme.

But we’ll pack some dentures for you just in case.

We’re exposed to radiation every day on Earth.

Medical scans, the environment, even the food we eat.

But those tiny doses aren’t really anything to worry about.

But space?

Radiation Central.

The magnetic fields surrounding Earth and the sun shield us from the worst kinds of radiation, but out there you’ll be exposed to the Galactic Cosmic Rays.

That sounds fun, doesn’t it?

When far-off supernovas blow up, they send atoms zipping through space at near the speed of light– so fast that they get stripped of their electrons.

Those leftover particles have enough energy to pass right through a spacecraft hull… or a human body, literally changing the atomic structure of your cells on their way through, which has a handful of negative effects.

That’s bad enough, but when galactic cosmic rays collide with other matter, like the atoms that make up spaceships and astronauts, it can cause a chain reaction of secondary radiation Compared to something like a gamma ray, it's the difference between shooting something with a hair drye and a relativistic shotgun And we can’t just build a lead spaceship to protect you.

It would be too heavy to launch, and denser shields can actually create more ammo for that relativistic shotgun I mentioned earlier.

But we’re testing other shield materials that might work better, like water, nanomaterials, even the poop you’ll make on your journey.

"Captain.

Drop the shields."

We’re also packing special foods and medicines to minimize radiation damage, but you’re still gonna get a pretty good zap.

On a six-month space station mission, astronauts get radiation doses about 20 to 40 times higher than what an average person on Earth gets in a year.

But a trip to Mars might give you a dose ten times or more what astronauts receive on the ISS.

But you get to go to Mars.

Fair trade?

Fair trade.

You’re gonna feel a little bloated while you’re weightless.

Under Earth gravity, blood pools in our lower body, but in space, that fluid gets more evenly distributed, giving astronauts puffy faces, runny noses, and stuffy heads.

It actually tricks your body into thinking you’ve got too much blood, so your body makes less.

That’s why astronauts sometimes faint when they get back to Earth.

That extra pressure in your head can also press on your eyeballs and disrupt your vision.

But we’re testing drugs and negative pressure suits to redistribute that fluid back to the lower body.

In the meantime, remember to hold the camera above your head when shooting selfies for that slimming effect.

We don’t think of our bones as being “alive” but they’re constantly being broken down and rebuilt on the cellular level.

Bone is slowly reabsorbed by our body, but the strain of moving and lifting our weight stimulates the growth of new bone material to replace it.

In Earth gravity, these processes are nicely balanced, but in microgravity, the breakdown goes into overdrive.

Astronauts can lose 1 to 2% of their bone density every month, especially in places like the spine and hip.

Luckily, NASA has a new weight-lifting machine that has been shown to totally reverse this bone loss.

It hasn’t been tested on a mission as long as yours, but we don’t think you’re gonna need a walker by the time you get to Mars.

Don’t skip leg day, brah.

There’s a few things your colleagues on the space station are still working on.

Like how space might mess with your microbiome.

Or studying the effects of losing our natural day/night cycle, even how zero g might affect your epigenetics, all the chemical marks that help turn genes on and off.

Oh, and you might lose your sense of taste, but we’ll pack some hot sauce for ya.

Now, I know what you’re thinking.

With all the extreme discomfort and mortal peril that long-term space travel poses for humans, you’re afraid that we might outsource your job to robots.

Well, no need to worry!.

Robots make great explorers, but they’re not very good problem solvers.

A lot can happen up there.

New discoveries.

Emergencies.

Decisions that need to be made without a 20 minute communication lag back to Earth.

Even a simple task like dusting off solar panels requires either a dedicated robotic device or just a wave of the hand.

Long term space missions will always benefit from the bold ingenuity of humans like you.

Plus, between you and me, we want to see all those cool tweets and youtube videos you're gonna send back to Earth!

Now, before we let you go, there’s one final test we’d like to run.

When we first sent people into space,, we honestly didn’t know how their minds would take it.

There’s a sensation called the “overview effect”… the feeling of looking down and seeing your entire world, every single living thing, the blues and greens and reds and glowing lights shrinking beneath you… it can be pretty psychologically challenging.

We just want to make sure that you can handle it.

So sit back, take a look at this, and let me know what you think.

[PEACEFUL MUSIC] Hey guys!

So you can probably tell that living in space is really hard.

Astronaut Scott Kelly and cosmonaut Mikhail Korniyenko are about to return from a year on the space station.

This mission has been extreme.

Extremely difficult, extremely brave, and extremely awesome.

And if you’re like me, you want to know everything about it.

Well you’re in luck.

The folks from PBS have been filming Scott Kelly’s mission, and the months leading up to it for a special show called A Year In Space.

No space mission has been captured like this one.

You don’t want to miss this.

Year In Space is streaming at pbs.org slash yearinspace.

You can also follow along at the hashtag on like, all the social media.

And as always, stay curious.