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  • In 2016, astronaut Scott Kelly returned to Earth

  • after nearly a year on the International Space Station.

  • But when he came back, he was 2 inches taller.

  • So, what exactly happened up there,

  • and what does that mean for the future of space travel?

  • If you're planning a trip to the International

  • Space Station, be prepared to feel weightless.

  • The station orbits the planet every 90 minutes,

  • moving at more than 17,000 miles per hour.

  • That's 30 times faster than a commercial jet aircraft.

  • As a result, astronauts on board live in a constant state

  • of free fall, or weightlessness.

  • Garrett Reisman: Being up there in microgravity is awesome.

  • It's, like, the coolest thing,

  • because it's like you have the power to fly.

  • Narrator: That's Garrett Reisman,

  • a former NASA astronaut who's logged 107 days in space.

  • There are a few immediate side effects, he says,

  • when you first experience microgravity.

  • Reisman: So the first thing you really feel is

  • you feel kinda sick.

  • You don't feel very good those first couple days.

  • It's kinda like being airsick or seasick.

  • We call it space-adaptation sickness.

  • Your vestibular system, your organs

  • that provide information to the brain

  • about your rotation and your acceleration,

  • they're not working that great without being in gravity.

  • Narrator: Without gravity working on your body,

  • your bones and muscles start to break down, too.

  • In fact, bone density drops by over 1% per month.

  • By comparison, the rate of bone loss

  • for elderly men and women is around 1% to 1.5% per year.

  • And, because it doesn't take much effort

  • to float through space,

  • your muscles lose strength and endurance pretty quickly.

  • Reisman: You have to work out every day.

  • So, they scheduled two hours a day pretty much every day

  • while I was on the space station for working out.

  • What we found was, if you do enough resistive exercise,

  • you can halt the effects of the bone loss

  • and the muscle atrophy.

  • Narrator: Without gravity pulling them down,

  • fluids pool in the body, tricking it into thinking

  • it's carrying too much water.

  • As a result, astronauts have to pee...

  • a lot.

  • This makes it easy for them to get dehydrated

  • and develop kidney stones.

  • Reisman: So, you have a shift in your fluid.

  • A lot of the blood volume that normally is down in your legs

  • ends up up here, and your chest kinda puffs up

  • and your face puffs up, and you can see it.

  • If you look at pictures of us on the space station,

  • it looks like we put on some weight or something

  • and we're all puffed up.

  • Narrator: Swelling in the upper body

  • puts pressure on the eyes as well,

  • which can cause vision problems.

  • Reisman: A lot of us, including myself,

  • had a shift in our vision while we're up in space.

  • You start out, everything was fine,

  • and all of a sudden things get blurry.

  • We could see the effects of it.

  • We could see swelling in the optic nerve,

  • we could see folds in the cornea,

  • but we're still not 100% sure

  • exactly what's causing it and how to stop it.

  • Narrator: With all the challenges of space travel,

  • one benefit is you actually get taller.

  • Reisman: So, yes, you do get taller when you go to space.

  • It's the whole reason I signed up for this job.

  • Your spine is being compressed by gravity.

  • So, when you go into the microgravity environment

  • and you no longer have any kind of compressive loads

  • on the spine at all, it stretches.

  • I grew about an inch.

  • Astronaut: Woo-hoo!

  • Narrator: Without gravity working against it,

  • the heart doesn't have to work as hard

  • to pump blood throughout the body.

  • Over time, this could lead to the heart

  • actually decreasing in size.

  • Reisman: There is an effect on the cardiovascular system

  • about being up in space.

  • So you do get a reduced aerobic capability.

  • You can be in great shape,

  • and after being up in space for a couple days,

  • you might get on the treadmill, and you might be like,

  • "Man, I must not have been hitting the gym."

  • Narrator: The immune system also takes a hit.

  • Researchers discovered that a lack of gravity

  • weakens the functions of T cells,

  • which play a crucial role in fighting off diseases.

  • Another concern is cosmic radiation.

  • Astronauts on the station are exposed

  • to over 10 times the amount of radiation

  • that we get on Earth.

  • Reisman: At a couple hundred miles,

  • we're well above the atmosphere,

  • but we're still well below the magnetic field of the Earth.

  • But we still get a large bit of protection

  • from that magnetic field.

  • In fact, you could tell, because when you close your eyes,

  • you see little lightning bolts,

  • and that's actually a result of some of the radiation

  • hitting your eyeballs and releasing photons.

  • Narrator: Artificial shielding on the ISS

  • only partially protects astronauts from harsh radiation,

  • leaving them more susceptible to cancer

  • and other diseases later in life.

  • Finally, astronauts must also be able to handle

  • the psychological challenges of confinement and isolation.

  • Reisman: So, there is a psychological aspect

  • to being in space, both because of the fact

  • that you're isolated from the rest of humanity,

  • it was really strange to be looking out the window

  • at billions of people down there

  • that had no way to get to me.

  • When I was there, I only had two crewmates

  • at a time on the space station,

  • so if you don't get along with somebody,

  • that could be bad, because you don't have

  • too many choices there in making new friends.

  • Narrator: And, without a 24-hour sleep cycle,

  • astronaut circadian rhythm is thrown off,

  • which can cause more stress and lead to sleep disorders.

  • Reisman: You're taking jet lag to a whole nother extreme.

  • Well, the weird thing is that you go around the planet

  • once every hour and a half.

  • So every 45 minutes, the sun is either rising or setting.

  • So you can't, like, tell what time it is

  • by looking out the window.

  • Narrator: So, what does all this mean

  • for the future of space travel?

  • Well, a trip to Mars would expose astronauts

  • to even more dangers than those

  • on the International Space Station.

  • They would face higher levels of radiation,

  • shifting gravity fields, and longer travel times,

  • which would compound all of the negative effects

  • of space on the human body and mind.

  • Reisman: I think the biggest issue we gotta deal with

  • is the radiation.

  • We don't know precisely what that exact radiation

  • does to human beings.

  • But what does gamma rays or what does heavy ions,

  • what do they do human tissue?

  • We don't really know.

  • Narrator: Right now, NASA and other research organizations

  • are working to develop better technology

  • that protects astronauts against these hazards,

  • so maybe one day humans might make it to Mars.

In 2016, astronaut Scott Kelly returned to Earth

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