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.
