I'm William Brangham and this is "Horizons."

In the skies above us, an orbiting research station circles the Earth every 90 minutes.

Astronauts from around the world work shoulder to shoulder to better understand space.

Fewer than 300 people have known exactly what it's like to work, eat and sleep there in microgravity.

Life on the International Space Station, coming up next.

♪ Narrator: Support for "Horizons" has been provided by Steve and Marilyn Kerman and the Gordon and Betty Moore Foundation.

Additional support is provided by Friends of the News Hour.

♪ This program was made possible by contributions to your PBS station from viewers like you.

Thank you.

From the David M. Rubenstein Studio at WETA in Washington, here is William Brangham.

Welcome to "Horizons."

Today, we are going to get a peek inside one of humanity's most remarkable laboratories.

It's 250 miles above Earth and travels at almost 18,000 miles an hour as it circles our planet in orbit.

The International Space Station, with its huge bank of solar arrays, is as long as a football field and as tall as a 10-story building.

And since the year 2000, scientists from 26 different nations have worked there.

They've conducted experiments on everything from cancer to botany to some of the fundamental questions about our universe.

Its success has proven that humans can live and work off our planet.

And the hope is that their discoveries will help subsequent space missions, including NASA's current Artemis mission and the larger Moon-to-Mars initiative.

And today, we are so lucky to have two astronauts who have worked aboard the ISS.

Retired NASA astronaut Karen Nyberg has spent almost six months in space, including living and working on the ISS for over 160 days.

She last returned to Earth in 2013.

And NASA astronaut Don Pettit has spent almost 600 days in space, including three long stints on the ISS, the last one being roughly seven months long.

He most recently returned to Earth in April of last year.

Welcome to you both.

Thank you so much for being here.

As I'm reading that introduction, you heard me say about both of you that when you last returned to Earth, and again, to civilian ears, it's such a shocking fact that you are regularly... you are the kinds of people who leave our planet and work and live in space.

And I wonder, Karen, to you first, does that remarkable fact stick with you still to this day?

It absolutely does.

Sometimes, it feels unreal.

Living in space is such a surreal experience, because everything is just different than you experience on Earth, that if, you know, you could almost convince me that I hadn't gone if I didn't have pictures I could look at.

Brangham: Really?

Nyberg: That I had actually experienced it.

And so, you know, sometimes it's when other people start talking about it that I'm like, "Oh, yeah, I did some really cool things."

Brangham: Don, what about you?

Does it sit with you still?

To me, the amazing thing when you come back to Earth is, what are you going to miss from being in space?

Brangham: I would have thought it was the reverse, that when you're in space, you think, what are the things I miss from Earth?

Maybe, but for me, there are so many things.

You can't feel the wind on your face.

You can't eat pizza and things like that, right?

But these holes that are left from your life on Earth, you get them filled with things like you could fly around the room like Peter Pan.

You can see the Earth horizon with the atmosphere on edge in a way that you can't if your feet are on Earth.

So, the things that you miss on Earth are filled in with all these wonderful observations you can make from space.

Karen, at one point, Don, in an old interview, said that some people are born to ride a horse and be cowboys, some people are born to be in space.

And he felt that he had been born to be in space.

Did you feel that way as a young person?

Did you ever imagine, "I'm going to be an astronaut one day?"

I started dreaming that when I was about eight or nine years old.

That is what I wanted to do.

Brangham: Wow.

Eyes on the prize from that early on.

And I remember when I, on my shuttle flight, when we first got into orbit, and I had a chance to, like, really think about it and kind of look at my crewmates, and "I'm here, I did it."

And it was, it's kind of a... it was pretty magical.

And Don, for you, you did feel born to this job?

Maybe born to the opportunity presented to you in your era.

If I'd been born 150 years ago, it might be sailing wooden ships around the world or riding a horse out on the plain or something like that.

But those, you know, the opportunity for my era of existence is flying in space.

But the essential exploratory, what is out there?

How can we push the boundaries?

That seems to be the central theme you guys are talking about here.

That desire.

Pettit: I've been doing that ever since I was a little kid, watching ants walk across the sidewalk.

[Laughing] Karen, the International Space Station, as I mentioned, is principally considered a laboratory in space.

Generally speaking, are there things that are studied there that you just can't do down here on Earth?

Is it that central to be up there?

It really is.

There's the pull of gravity on fluids and flames and just about everything.

And you can learn more.

The pull of gravity is so strong, it's such a high component of the reaction that's going on in any experiment, that when you take that away, you can start to understand what other things are happening, for sure.

Pettit: I look at it, microgravity is what we call it.

Brangham: Help me understand the distinction there.

Microgravity versus zero gravity.

Okay.

On Station, we refer to it as zero gravity, but it's not really zero gravity.

It's one millionth of the gravity on Earth.

So that's why we call it microgravity.

And you remove a factor, say temperature or pH or something like that, for almost any other organism on Earth, and the nematodes shrivel up and die really quickly.

And the fact that we can send life into space where we've changed a constant environmental factor by a factor of a million, and we still seem to just keep going with secondary and tertiary effects that are oftentimes subtle.

I find that amazing and one of the more important aspects of what we're learning on this laboratory we call Space Station.

Brangham: Karen, when you see videos of space or even fictional depictions in movies, it all seems very peaceful and serene and quiet.

And yet, as you two, I'm not telling you anything you don't know, it's an unbelievably hostile environment to human beings, to us soft, fleshy people.

How much of that is in your mind when you're up there?

Are you thinking about the dangerousness of it, or does that fade into the background?

For me, it faded into the background.

I did not think about that.

But sometimes I wonder if it is kind of in the back of your mind.

I was exhausted when I came back, and I think it's kind of just as you're there, living there for six months, and all of that kind of builds.

But I didn't think of it at the time at all.

But you constantly hear the hum of your life support system, so you know there's pumps and fans and there's this constant noise in the space station, so you know that this is what's keeping us alive.

Brangham: Right.

So that quiet is only when you're outside.

Nyberg: Right.

Right.

Brangham: Right.

Don, just tell us a little bit more about what daily life is like.

I mean, again, you're a scientist up there doing scientific work, but that can't consume 24 hours of your day.

Pettit: Well, we work, we're scheduled for about 12 hours a day, starting at 7 in the morning GMT time, which is what the station runs on.

And you try to get your 12 hours worth of work done in the scheduled 12 hours worth of time, and typically things take a little longer to do than the folks on the ground think.

You end up working 13 to 14 hours a day, and we work about six days a week, and they try to give us one day a week off.

And per the schedule, they say it's one and a half days, but really, you're lucky to get one day off.

These space station missions, we're not up there to sip tea and eat bonbons.

We're up there to do the mission work.

And you just have to be prepared that, hey, you've got a heavy work environment.

Brangham: Right.

I want to hear about some of that work as well, but, like, Karen, on those days off, if you do get them, when you get them, like, what does one do with a day off on the space station?

Certainly look out the window and take pictures.

But people will bring hobbies as well.

I brought some sewing supplies.

But I found out I did not have as much time to do that as I would have liked.

You know, you're thinking you have an entire Sunday off, but even that time just goes away, and it's really hard to have that free time to do a hobby.

And also because, you know, the windows are pretty luring to go take a peek out there and grab a camera.

So, but yeah, the hobbies.

Some people watch movies and stuff.

I didn't even watch movies.

I just felt like there wasn't time.

Pettit: Yeah, I intentionally did not do anything that you could do on planet Earth, except I talked to my family so that I would have a family to return home to, right?

But you know, watching movies, surfing the Internet, I did almost zero of that and concentrated on things that you can only do in space while you are in space.

Brangham: Right.

I know, Don, that some of the scientific projects have to be, you know, you've brought the specific equipment for a specific experiment that's been through a peer review process and you're doing it up there.

Do you also have time there for improvisational science?

Are you able to do things that were not, quote unquote, "scheduled?"

You can, but you have to be very careful.

You don't want to use resources that were meant for an official experiment.

And what you could do is you could use water or food.

You could take leftover syringes and things like that.

You can take a wire and make frames.

You could take your soap solutions and make... do a study of stretched thin films.

There's a number of things that you could do just because you are there and you can.

Brangham: Right.

And that's welcome and encouraged.

Pettit: It is.

It is.

But there's the pull of the window, you know, in terms of looking out at this amazing view that you can't see any other way.

Brangham: This is something I think people may not appreciate, too, is that because you are orbiting Earth, Earth is always there out your window.

So what... Can you just give us a sense?

What do you see when you look out the window?

I know you're... I was shocked by this fact that you get something like 16 or 17 sunrises and sunsets every single day.

Nyberg: 16 every day.

And, yeah, we're only 250 miles or so above the surface of the Earth, which really isn't that far away.

And so you see... Brangham: Only an astronaut can say that.

So you see a portion of the Earth, but still, even at that distance, you get this very real sense of exactly what Earth is, just this ball in space.

But it's not like, you know, the Artemis two crew that was able were able to travel to the moon and then actually see the entire Earth kind of disappear and in the distance.

But I mean, it's absolutely incredible.

Not a lot of words can describe it for me.

Brangham: I know everyone always wants to ask you how you go to the bathroom in space.

I'm not going to ask you about that.

I'll spare you that.

I would urge our viewers to watch these incredible videos that Commander Chris Cassidy did about he takes you on a tour of the toilet for people who are curious about that.

I am curious, though, about sleeping.

What is it like to sleep in that gravity environment?

Is it good sleeping?

Do you dream differently?

Pettit: Oh, sleeping for me in a weightless environment is wonderful.

You feel like you're 30 years old again.

You float into your bed.

Remember, you've worked a 12 to 14 hour day.

You're tired.

You float in.

And I just conk out within two or three minutes.

And you're floating in your sleeping bag and your sleeping bag is kind of floating.

And you don't have any of these gravitational forces on you that when you wake up with a sore neck and your shoulders all rickety, all of this kind of stuff heals up after two or three weeks of being on orbit.

And you literally feel like you're 30 years old again.

So sleep is wonderful.

Nyberg: It was a little different for me because I actually missed that pull of gravity.

My back would hurt because I felt like it was arched like this.

So I would tuck my knees up with the strap that's in the sleeping bag just so my back felt like it was pushing up against the bag.

That's interesting to see the difference because I slept fine, but I wouldn't say it was great.

Pettit: Yeah.

And what Karen brings out is typical of astronauts.

They have different views of the same experience.

Brangham: Right.

I mean, one of the things about the ISS that people know is there's scientists from so many different countries there.

And that's one of the remarkable things about it, that it is this an example of international cooperation.

Karen, when you're up there, does it feel that way?

Do you feel like you are...?

Again, I know you have to work in very tight circumstances with people from all these different nations, but does it feel like you are part of that larger mission that way?

It absolutely does.

But on a day-to-day basis, it just becomes the norm, you know?

And I think it's when you... Brangham: It's just Sergei down the chute.

Right.

Exactly.

And I think when you reflect on it maybe later, and you realize what you did, or even the first time I went and I saw the space station in the distance when we were approaching on the space shuttle.

As it was getting bigger and bigger in the distance, I'm like, "Oh my gosh, "this is the most beautiful human-made thing "I've ever seen in my life."

And it was put together by people from all over the world, and it's just hanging there in the blackness of space.

And just that realization that what humanity had accomplished by putting it there in orbit.

But I think on the day-to-day, that's just what we're doing.

Pettit: My experience on the station is there's only one station, and it's not their section and nose section, it's one entity, and it doesn't matter whose side of the hatch you happen to be on.

Brangham: Do different nations do space differently?

I mean, I know that NASA is an incredible American institution, but do the Japanese do it differently?

Do the Russians do it differently?

Can you do...?

Does it feel that way?

Pettit: Food, yeah.

Is that right?

Is there a lot of cross-cultural food sharing?

Pettit: Yeah, that's one of the delightful aspects.

Nyberg: Yeah.

Yeah, well, I flew with a Japanese crew member on my first flight because we took up the Japanese lab, and he brought a big Japanese meal that we got to enjoy, and then Luca, the Italian meal, he brought up some incredible lasagna and pesto.

Yeah, and it's kind of a time to, you know, hang out with your friends and enjoy dinner, which we do all the time on Earth.

So it's a very kind of Earth-related thing that we can do and enjoy food together.

Don, I want to ask you about your photography, because in addition to your scientific work, you are really known for producing some incredible photographs.

And I understand the rationale that you've got to capture the mission, but there is also a real sense of beauty and wonder and whimsy and a sense of humor in your photography.

There's an artist at work there.

Do you feel that way?

Pettit: I'm sort of hiding in the closet as an artist among all of these fighter pilots and NASA engineers, you know, and I slowly creep out here, and then I go back into the closet and shut the door because I'm afraid to go out again.

And I've been doing photography ever since I was a little kid.

And I developed my own film, and my mother did photography.

She'd had pictures published in Life magazine.

So I grew up with this photography thing.

And anyway, you know, I just... Presented with a situation, and there's something about the situation that says, "This is interesting.

"Let me stop and take a picture," which, if you don't have a camera with you, I kind of feel naked.

Brangham: Right.

Can I ask you both a devil's advocate question?

What is the point of all of this?

For people who might be skeptical about all the money that is being spent to go to space, to learn all of these techniques to then go to the moon, to then go to Mars, help me, from your perspective, what's the point?

Nyberg: First of all, you know, when you look at the amount of money, it really isn't that much, the amount of money that NASA gets to do this exploration.

And that's exactly what it is, exploration at the core.

It's going out and doing things from, you know, in all of humanity, people explored and looked over the horizon and what's there.

And also, I mean, some of the science we're doing, it can be very valuable for things on Earth.

And so I think there's a number of aspects to it.

Pettit: Exploration is a metric for how viable a culture you come from.

And it pays off dividends on the multi-decade to hundreds of years kind of scale.

Exploration ultimately gives you places to live and resources to use.

However, from what we know now about the dynamics in our solar system, a single planet species is going to have trouble living for a long time.

So I like to say that, if the dinosaurs had explored space, if they'd colonized other planets, they would still be alive today.

Brangham: As you both know, the ISS is being decommissioned, deorbited, I think is the technical term, in a couple of years.

NASA says that they're going to try to do some other smaller low-Earth orbit research stations.

I wonder, Karen, what you think, how that will feel when that station is finally disassembled and brought down to Earth?

Nyberg: That's going to... That will be hard.

You know, it was designed for, what, till 2015?

The original design of space station was about 15 years.

So it's done incredibly well, and it's way outlasted what was originally designed.

You know, I think any place you lived and loved when it's no longer functioning, it will be sad, for sure.

And I'm hoping by that point we have a couple, at least one commercial space station that can kind of take its place.

Brangham: We have about a minute left.

Pettit: One thing about the commercial stations coming up, they're all significantly smaller capability platforms.

If you look at what the International Space Station could do, from crystal growth, high-temperature furnace, DNA, human research, the chemistry research, engineering research for a platform to test out our machines before we go further from Earth.

We will not have this capability built for a long, long time in any follow-on space station.

And I like to look at the B-52 Air Force bomber.

By the time the Air Force retires that airframe, it will have been flying for almost 100 years.

You could have great-grandchildren of pilots that initially flew in that airplane still flying the B-52.

And space station, I believe, could be in that category so long as we are willing to fund the maintenance and the repair work and keep space station going.

Brangham: Don Pettit and Karen Nyberg, thank you both so much for being here.

Really appreciate it.

Nyberg: Thanks for having us.

Pettit: It's been a pleasure.

Before we go, we wanted to touch on another one of the unusual kinds of experiments that have come out of the ISS.

It's what's known as the twin study.

NASA, of course, needs to know what living in space for long periods of time does to the human body.

And while NASA has lots of individual examples of people living in space, it's hard to know whether any effect was just caused by that person's unique physical or genetic makeup.

Well, back in 2015, NASA realized they had the good luck to have two people with nearly identical bodies and genetics, twin brothers Mark and Scott Kelly, who are both retired astronauts.

So NASA devised an experiment.

After doing extensive testing on each of the brothers, Scott Kelly went and spent a year up at the ISS, living, working, eating and sleeping in space, subject to the same microgravity and radiation exposures that most astronauts there experience.

Meanwhile, his brother, Mark Kelly, went about his daily life here on Earth.

He ran a company, helped care for his wife, former Congresswoman Gabby Giffords.

After a year, Scott returned from space.

The brothers were reunited and tested even more.

The overall finding was that the human body is remarkably resilient.

A lot of the subtle changes that happened to Scott Kelly, like the changes to his gut microbiome or the unusual finding that the tips of his chromosomes got a little bit longer, those things quickly returned to normal once he was back on Earth.

But some changes were more notable.

There were some changes to his eyes, to his cardiovascular system.

And upon his return, some cognitive skills were a bit diminished compared to his brother.

These effects and what can be done to minimize them are being studied and worked on to this day.

In classic sibling fashion, though, Scott Kelly, when he heard about some of the subtle temporary changes to his DNA, he couldn't help but tease his brother, writing, "What?

"My DNA changed by 7 percent?

"Who knew?

This could be good news.

"I no longer have to call Mark Kelly "my identical twin brother anymore."

That's it for this episode of "Horizons."

Thank you so much for watching.

We will see you next week.

Narrator: Support for "Horizons" has been provided by Steve and Marilyn Kerman and the Gordon and Betty Moore Foundation.

Additional support is provided by Friends of the News Hour.

♪ This program was made possible by contributions to your PBS station from viewers like you.

Thank you.

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