Sandy Magnus washes her hair aboard the space shuttle Atlantis in 2002. (Johnson Space Center/NASA)

Sandy Magnus

Flew three NASA space shuttle missions between 2002 and 2011, including the last shuttle mission

Gravity sucks. It's horrible. One of the most interesting perception changes that I had as an astronaut is one that I never expected. And that's my perception about gravity. We leave the effects of Earth's gravity because we're in free fall all the time and we adapt to this whole new environment. And then we have to come back to gravity and it's like, "Oh my gosh what the heck is this? And I can't believe we live in this all the time." I mean, it's just horrid, you know, and it's a huge force that is really pressing down on us every day, and it's astonishing when you first come back into the influence of Earth's gravity. It's astonishing to feel that and go, "Wow, I can't believe we cope with this."

Michael Collins during the translunar phase of the Apollo 11 mission. (NASA)

Michael Collins

NASA command module pilot for Apollo 11 who stayed in orbit around the moon during the first lunar landing in 1969

We had to turn sideways to the sun and rotate like a chicken on a spit and distribute the heat around a 360-degree circle around our cylindrical command and service module. Unfortunately, we could not see the Earth and moon. When we rolled out of that maneuver, we were very close to the moon. It was really awe-inspiring. I'd never seen any photographs anything like what I saw out my window. The moon was not that flat silver disk. The tummy stuck out, practically came through the glass of our window. It filled the window entirely. The sun was behind it. The periphery was suffused by a golden haze. The dark seemed darker, the light seemed lighter. There was more contrast to the surface. It was just a totally different moon than I had grown up with. It was awesome. It was certainly not inviting. It didn't offer us any invitation to go past where we were.

Pavel Vinogradov peers through a hatch window aboard the Mir space station. (NASA)

Pavel Vinogradov

Russian cosmonaut who flew to space three times aboard the Soyuz to Russia's Mir space station and the International Space Station between 1997 and 2013; conducted seven spacewalks; holds the record for the oldest person to perform a spacewalk (at age 59)

I talked to [Russian President Vladimir] Putin when he greeted us on April 12 (Cosmonautics Day) and told him, "Vladimir Vladimirovich, bring one of your colleagues along and come with us at least for a week — you will understand differently what needs to be done for the Earth." He joked back and said: "Only if I get a short vacation, but my guards will not let me go." The values that one can get after a flight into space are much higher than the goals of national politics, for example, when making money by transnational companies is considered to be a priority. When you are there, you understand very quickly that things that are happening here are so insignificant. But how can you explain that to all those important people — only if you force them all into space!

Space flights change the perception of all people regardless of their nationality, their religion, the place from which they started — South Asia or America or Russia. They realize that there is nothing to divide, that the Earth is small, you look at the atmosphere which protects us, at this very narrow blue strip above the surface of the Earth and then you realize, "What are we doing?" We try to divide religion; this religion is good and that one is bad; we start to divide resources; gas, oil. And the first thought you have is that many things which people do are not worthy of the name of the civilization called humanity.

Charlie Duke collects lunar samples as part of Apollo 16. (NASA)

Charlie Duke

Youngest person to walk on the moon during the Apollo 16 mission in 1972, when he was 36

I think the liftoff for the Saturn V was more impressive for spectators than it was riding it. The spectator gets all the vibration and the noise and the dynamics of the flames.

But inside, riding it, you're in a cockpit with the windows all covered over. And you're 363 feet above the engines. And so you don't hear any noise, but the vibration is intense. Very dynamic. And I just remembered thinking: Is this thing really working right? Is it supposed to shake that hard?

Tom Jones waves at crewmates aboard the International Space Station in 2001. (Marsha Ivins/NASA)

Tom Jones

Flew on four NASA space shuttle missions between 1994 and 2001

You can't forget the bigger picture, which is, hey, you're a spaceman! Nothing can match that. So after that I think I had a sense of being at peace with my life. I didn't have to struggle or strive to try to match the last thing that I did. I thought, I can't top those four missions. So I've been very relaxed ever since. You know, whenever I get into a stressful situation these days, I think, well, you know, compared to being strapped on a rocket, this isn't too bad.

Abdul Ahad Mohmand before the first Soviet-Afghan joint mission. (Sputnik/Alamy Stock Photo)

Abdul Ahad Mohmand

First Afghan citizen in space; flew on Russia's Soyuz in 1988

To fly to space from such a country as Afghanistan is a really big deal. Afghanistan is a country where people know nothing but war, then suddenly there was a chance to fly into space and do something. I was a pilot, then a lieutenant, and I thought that I would never have a chance to fly to space. This is an absolutely different experience. It's a different realm. When you see the Earth from space, you think globally. When you are on Earth, you think about your country, your motherland, about its borders, about your embassy. But when you are in space, you see that your home is the Earth. My first words when I got back were, "Earth is our common home."

Tim Peake during his first spacewalk in 2015. (European Space Agency/NASA)

Tim Peake

First British European Space Agency astronaut to visit the International Space Station; flew on Russia's Soyuz in 2015 for a six-month mission

If something goes wrong on launch or landing, then it's most likely something catastrophic and it's most likely something that was completely out of your control anyway. Whereas if something goes wrong on a spacewalk it's most likely that it was your fault. Because the potential for the crew to mess up, to let go, or to get tangled up in a tether or to lose a tool or a piece of equipment — I mean it's huge. You have to be absolutely on your game with concentration for the whole time, all those hours of spacewalking.

Jim Voss is promoted to colonel aboard the space shuttle Endeavour in 1995, with the help of Kenneth Cockrell, left, and David Walker. (Johnson Space Center/NASA)

Jim Voss

Holds the world record with Susan Helms for the longest spacewalk at 8 hours 56 minutes; flew to space five times from 1991 to 2001

Floating is very special. It's wonderful. I always liken it to being like Superman because I can fly. I can move heavy things around. Every day, I think, I would — I hate to say "play" — but I would find some aspect to being in space that allowed me to do something unusual. If I was moving from one side of a module to another, I could do a flip in the middle of my transfer over there, which is a pretty abnormal thing that you could do. When you're eating, it's really hard not to play with your food or to squeeze out a ball of liquid and pluck it out of the air instead of just drinking from your straw.

Rick Hieb, left, Thomas Akers, and Pierre Thuot in 1992. (Johnson Space Center/NASA)

Rick Hieb

Flew three space shuttle missions for NASA between 1991 to 1994; participated in the first three-person spacewalk

On grabbing the satellite: On the day when Pierre [Thuot] went to put the capture bar on the line, it was very different from the ground experience. The satellite kind of twisted away from him like a scared rabbit. On the ground [during practice], the satellite sat there beautifully, stably. And in space, there's no friction, of course. So it just rotated away from Pierre each time he would just ever so barely touch it.

On solving the problem: We did everything to convince the ground that we had gone to bed because they kept nagging us. We turned off everything so they would leave us alone and we continued to work at it. We sketched up our ideas, took pictures of them with our digital camera, got our story together, and then Kevin Chilton called the ground and said, "Hey, Houston. By the way, we have some thoughts. We haven't quite gone to bed yet." And he described it. He didn't want them to interrupt him to say no, so he had his whole spiel worked out and he just kept talking until he got the whole story out. And then we sent them the pictures. We went to bed and the next day when we got up, they had been working on it, they'd had a lot of management team discussions, they'd been in the simulator, in the water tank. They'd done what NASA does — work the heck out of it. And they were coming up with a plan.

Peggy Whitson in the cupola of the International Space Station in 2016. (NASA)

Peggy Whitson

Flew to space three times as a NASA astronaut between 2002 and 2017; first woman to command the International Space Station; conducted 10 spacewalks

To me, sleeping in space is fantastic because you don't wake up feeling like you're heavy somewhere, your joints hurt or you're aching, because you're in zero gravity and it's like the perfect big bed. I distinctly remember my first mission about three weeks in. I woke up. My sleeping bag was hanging on the wall, in my little crew station, which is kind of like a phone-booth-size compartment, and it has your sleeping bag, and the computer, pictures of family and friends or whatever. But I had gotten on the computer first thing and I was still in my sleeping bag out on the computer, and I printed out something from the ground team and I floated out of my sleeping bag and I crossed the lab to the printer, and I was like, "Holy cow! I live in space!" I remember it being this kind of revelation to me: "This is home. This is so cool!"

(Virgin Galactic/Beth Moses aboard a Virgin Galactic spacecraft.)

Beth Moses

Chief astronaut instructor for Virgin Galactic; first woman to reach space on a commercial spacecraft, in 2019

I am looking over the Pacific Ocean. The top of my view is the black, black, blackness of space. The middle of my view is the blue Pacific Ocean and the coastline. And the bottom of my view is the snow on the green mountains of Southern California. And I am shocked and amazed at how clear and beautiful and sparkling and crystal it is. It blows your mind. We flew on a perfectly clear day. A lot of snow on the mountain tops. Earth was wearing her diamonds that day.

A view of oil fires in Baghdad from space in 2003. (NASA/GSFC/LaRC/JPL, MISR Team)

Mike Foale

Flew on six missions for NASA between 1992 and 2004

We came over the Atlantic going northeast toward Africa. And Africa's always dramatically red and pink and brown, extraordinary colors because of the deserts. And as we approached, I saw this great big black spot on the Earth, and it looked like a black hole had moved into the Earth and just swallowed that whole Middle East region. You could see nothing there. And I called down to Houston, where it was early in the morning, 3 a.m. or something. And I said, "Houston, has something terrible happened to Iraq?" And they said, in kind of a sleepy voice because it's the night shift, "No, Mike. There's nothing." Then I said, "Anything in the news?" They said, "No."

So then I showed it to Sasha Kaleri, my crewmate. So we call down to Moscow: "Has anything terrible happened in Iraq? Because we just cannot see Iraq at all. It's completely black." And the voice came back. "No, Mike. Well, hold on." And they said, "Maybe some rebels. They've been attacking oil rigs." And that was it. I suddenly realized the whole of Iraq was covered in black, absolutely opaque smoke. That's always stayed with me. It was the worst thing I've ever seen from space. And I was imagining how people were living, midday in Iraq. They could not see the sun.

Expedition One mission commander William Shepherd. (NASA)

William Shepherd

Flew to space four times as a NASA astronaut between 1988 and 2001; commander of the first crew on the International Space Station

We would get a message from Houston that would say, "That thing that you're supposed to do this afternoon at 2 o'clock? Strike that. Don't do it. But put this other activity in there." Then less than 30 minutes later, somebody from Mission Control Moscow would say: "Hey, that thing at 2 o'clock? Put this other task in there." And this kept happening for several days, and I'm going like, this is not the way we're going to do this.

Perhaps the third or fourth time this happened, I got on the radio with Moscow and I said in Russian: "This is B.S." Dead silence on the radio. I found out later that the Russians were just apoplectic because nobody had ever talked to them that way. I suppose Houston felt the same. So I switched over to English and I said, "Look. We're up here. We're flying the International Space Station program. We're doing this for a consortium of 16 nations. We're not doing a program for Houston and another one for Moscow. So you guys huddle up on the ground, and you put one plan together, and when you've got it straight send it up to us and we'll do that plan. Space Station — out." Giving the ground a piece of my mind was my best day in space.

The space shuttle Columbia lifts off in 1995. (Johnson Space Center/NASA)

Michael Lopez-Alegria

Flew on four space missions as a NASA astronaut between 1995 and 2007; retired Navy captain

On the launch: It's far more acceleration than any high-performance drag racer. But instead of lasting a quarter of a mile, it lasts eight and a half minutes. That acceleration is just unending. All you know is you are going somewhere, and you hope you are going in the right direction. At the end of that, it's like someone slamming on the brakes. The engine stopping. You go from 3 g to zero g and it transponds from this hellish, violent, exhilarating ride to this real peaceful, tranquil, magical experience where everything starts to float, including small particles of dust. It's quite a contrast. It's shocking actually, the transition.

Franklin Chang-Díaz works on the International Space Station in 2002. (NASA)

Franklin Chang-Díaz

Flew seven space shuttle missions as a NASA astronaut between 1986 and 2002; first Hispanic American astronaut

On how the Challenger explosion changed him: It had a huge impact on all of us. The Challenger was when we lost our innocence. We were all so excited and fired up about space that we had lost maybe a little bit of the perception of how dangerous it really was.

Space has come with a price. We're opening the frontier for humanity at a price and the price is a high price of human life, human sacrifice. And we want to make it worth it for those who give the ultimate sacrifice. And we believe that we're doing nothing less than ensuring the survival of the human race. When people ask , "Why are we doing this, why are we going into space?" my answer is always the same: "We're doing it to survive."

Chris Cassidy, right, and Tom Marshburn. (NASA)

Chris Cassidy

Current NASA astronaut; flew to space twice between 2009 and 2013; Navy SEAL who served several tours of duty in Afghanistan; 500th person in space

I never was a big crunchy tree hugger kind of person. But when you've seen the planet from that viewpoint, it makes you appreciate the planet. The atmosphere is so thin, and you realize that that's what keeps all 7 billion of us alive. Earth is a spaceship for all of us. It was 2013. So we're 12 years into [the war in Afghanistan]. And those guys that are down there are probably still doing the same things we were doing in 2001, and I got to imagine the overall scheme of things hasn't changed that much. But it made me think: What's the purpose of all this? Because when you look down at Earth from above you don't see borders, you don't see names of countries you just see this big blob of blue and brown and green and white clouds.

It made me feel a little bit more introspective about conflict than when I was a sledgehammer-wielding SEAL.

Anousheh Ansari aboard Russia’s Soyuz in 2006. (NASA)

Anousheh Ansari

First self-funded female astronaut; flew on Russia's Soyuz to the International Space Station in 2006

On tips she got before the trip: All of the crew members, men and women, were telling me about the launch sequence, landing sequence, if something goes wrong, tricks about if you sweat in your spacesuit, and your eyes can't see. The best thing is not to sweat. And the reason you sweat is because of the way you breathe. So, regulating your breathing, and not breathing too fast, and you know, calming yourself down, is important.

The moment I saw Earth from space was very emotional for me. I was crying and laughing at the same time. I had tear drops that had floated in front of me, which made me giggle because I realized "I'm in space." I felt the warmth and energy and life sort of coming from this incredible planet in front of me, which was my home. Somehow I was outside of it and very connected to it.

Sheikh Muszaphar Shukor aboard the International Space Station. (Sheikh Muszaphar Shukor)

Sheikh Muszaphar Shukor

First Malaysian astronaut; flew to the International Space Station on Russia's Soyuz in 2007; first Muslim to spend Ramadan in space

Praying in space was magical. You're floating the whole time. You have nothing to step on, so you have to strap both your feet. You can't prostrate for too long because you start to float around. It's not difficult to pray in space, because in Islam, it's easy. If you cannot pray standing, you can even pray sitting down, you can pray moving your neck, actually — even your eyes, if it's a difficult situation. So I had no problems praying in space. Ramadan was easy for me. I didn't feel thirst, I didn't feel hunger. Definitely one of the best moments — praying in space, floating around. You feel that you're close to the creator when you're in space.

Shannon Walker during her 2010 mission aboard the International Space Station. (NASA)

Shannon Walker

Current NASA astronaut; flew aboard Russia's Soyuz to the International Space Station in 2010

I did not tell my mother before I left that we had the opportunity to make phone calls from space. You can't call to the space station, but you can call out from there. And so after she got home [to Texas] — she went to Kazakhstan to watch my launch — and after she got home, I called her from the space station. And there's of course a little time delay. So she picks up the phone, and she can't hear anything, and immediately I know and start saying, " 'Don't hang up, don't hang up! It's me, it's me!' " And she's like, " 'What? Shannon? Is that you?' " And I'm like, " 'Yeah, I'm calling from space.' "

Anna Lee Fisher works with a camera aboard the space shuttle Discovery in 1984. (NASA)

Anna Lee Fisher

Flew on a space shuttle for NASA in 1984; first mother in space

The last night, of course, our commander, his big day is ahead because he's going to have to land the shuttle the next day. But basically we're all done with the things that we are responsible for. So I can still remember Rick [Hauck] being asleep in the commander's seat because that's where he slept and the remaining ones of us were up at the overhead windows trying to be really quiet. We pretty much tried to stay up most of the night, so that we would be ready when we went home tomorrow. It felt like you were a little kid the night before Christmas, because you didn't want to wake up Dad. But there we were, holding ourselves up by the windows shoulder to shoulder, just watching the world go by.

Mark Kelly is helped with his launch-and-entry suit in 2001. (NASA)

Mark Kelly

Flew four space shuttle missions for NASA between 2001 and 2011; retired Navy captain

The wake-up music is quite the tradition. It gets a lot of attention, and it's important. It doesn't actually wake anybody up, though. We're usually up before it gets played. Sometimes it would be a surprise. In my case, when Gabby [Giffords, his wife] sent "Beautiful Day," I think I was the commander of the flight, so I knew the song was coming up. It's Gabby's favorite song. U2 is one of Gabby's favorite bands. We were at a concert about a year-and-a-half ago and Bono gave her a nice shout out in the middle of the song. It was very nice.

Steve Swanson is the subject of the first photo posted to Instagram from space. (Steve Swanson/NASA)

Steve Swanson

Flew on two NASA space shuttle missions between 2007 and 2009; flew to the International Space Station on Rusia's Soyuz in 2014

You just can't set something down and [expect] it's going to be in the same spot. It just doesn't work that way. And even if it has Velcro on it somebody can easily come by and knock it off. Velcro isn't that strong really. And so if you don't really take care and put everything back exactly where it belongs and tuck it away, you will lose it. I think it was my first trip. We get a set of silverware to eat with, and I lost my knife — a butter knife. And you can get by without it. You don't really use it for much. But I felt bad 'cause I don't want to get in anybody's way. I let people know, "Hey, if you find a knife, it's mine." You have to fess up to that. And I did not find it the whole time until we are strapped in to enter the Earth's atmosphere. We are watching the engines, I'm up on the flight deck and helping out with the whole burn to make sure it all goes correctly. And after the burn, I look up and my knife is floating right in front of me. It was just the most crazy thing.

Canadian astronaut Chris Hadfield stands on a work platform outside the International Space Station. (NASA)

Chris Hadfield

Flew three space missions as a Canadian astronaut between 1995 and 2013; retired Canadian air force colonel

When we talk about the world being four and a half billion years old, it's unimaginable. I can conceptualize the number, but I can't internalize it. But when you come around the world so often, you can start to see the age of it. You can see the ancient patterns of it, these huge swirls of a billion-year-old geology, the way that it reflects the light and the textures of the world. The transient weather, the forces reshaping the world every day, but also the permanent nature of continental drift and how this all fits together, the enormity of it.

And in my three flights total I was in space for half a year. During that time, you go from one side of the solar system to the other, halfway around the planet. And I watched the Earth go from, in the northern hemisphere, winter to summer, and vice versa in the southern hemisphere. I got to watch that entire pattern of seasons swap ends. And I realized as I was watching it that this was the world taking one breath in 4.5 billion breaths — more breaths than I will take. I got to watch the world take one regenerating breath, and it gave me a tremendous, unquenchable sense of optimism. The world is so indescribably tough and we've had life continuously here for 4 billion years without a break. Life is tough and tenacious.

Leland Melvin watches a water bubble float aboard the space shuttle Atlantis. (NASA)

Leland Melvin

Flew two space shuttle missions for NASA, in 2008 and 2009; the only person who has both been drafted into the National Football League and flown in space

On my first mission, I felt like I was about to throw up, and it was like slowly building and so I grabbed the emesis bag. It's like a plastic bag, but it's got this bit of fabric on it so you throw up in the plastic bag and then you can wipe your mouth or whatever, then you seal it up and you throw it away. On my second mission, I missed the bag. All of that vomit was suspended in front of my face.

The Soyuz takes Oleg Artemyev, Richard Arnold and Andrew Feustel to the International Space Station. (Dmitri Lovetsky/AP)

Andrew Feustel

Current NASA astronaut; veteran of three spaceflights between 2009 and 2018

You've made all those choices to get to where you are. There's no backing out, right? So you have to, I think, be a little bit fatalistic and just realize that there's two outcomes to what's happening next when the rocket lights: you're either going to space or you're not going to space, and if you're not going, you're probably not coming back. So that's just the way it is. You know that's the job we do, we're lucky to have the opportunity, and, heck, if we don't come back, it doesn't matter for us. It matters for our families, and it's a great tragedy for everybody, but that's it. You're riding the rocket, so keep your fingers crossed.

Oleg Kotov uses a digital camera in 2007. (NASA)

Oleg Kotov

Russian cosmonaut who flew on three missions to the International Space Station between 2007 and 2013

There is a task for every spacewalk, a list of things you are supposed to do. The crew trains for every spacewalk. When you are out in the open space you usually work in pairs, you work and help your colleague. You can fly from the station for the length of your support rope — not further. If you don't attach yourself to the station, there is a risk that you would fly away and nobody will be able to bring you back. And when your oxygen is over, that's it for you — end of story. So you move like a mountain climber, you do the tests, accomplish other tasks, collect the equipment and so on, and then get back to the station. You are always happy when you return, and it is such a pleasure to get out from the spacesuit. Because your hands are tired, your legs do not work, and you have to hold yourself in a spacesuit plus all the equipment. It is physically very hard.

Soichi Noguchi sits in a chair outside the Soyuz minutes after it landed in 2010. (Bill Ingalls/NASA/Getty Images)

Soichi Noguchi

Current Japanese astronaut; flew to space twice between 2005 and 2010; selected to fly to the International Space Station in 2019

You feel really sad as the final day comes near. And you try to find a rationale to stay longer but obviously most of the time it's in vain. You have to pack up, and then when the day comes you say goodbye to your friends on orbit and get yourself seated on the capsule. And then up to the moment that the capsule touches down on the ground and the hatches open and you feel the fresh air, you feel like you're still space traveling. It's a mixed feeling. It's good and bad, but all I feel is: Now we are back to reality — and sometimes reality bites.

Sergey Ryazansky speaks to his family in 2013 before his flight to the International Space Station. (Carla Cioffi/NASA)

Sergey Ryazansky

Russian cosmonaut who flew twice to the International Space Station on the Soyuz between 2013 and 2017

After four or five months at the station, you realize that yes, space is great, but there are things that you want to go back for. Your beloved children, your beloved wife, your friends whom you really miss. And we are at a modern station, we can write emails, we can have space Skype once a week. You can talk to your family and you see them. But at some point, it becomes insufficient. We are people, and we have our roots on the Earth. Your parents are getting old and you need to spend time with them, you need to take care of your children. When I flew, my youngest son could say just a couple of words: papa, mama, baba. And when I returned, he came into my room and said, "Dad, your phone rang. I wanted to pick up but couldn't." And I look at my kid and understand that I missed something. During half a year, he turned into a little person who could speak in sentences. Yes, I did talk to my family, but he was not interested — I was an iPad dad for him. But children need a dad who plays with them and talks to them.

The space shuttle Discovery lifts off, carrying the Hubble Space Telescope, Charlie Bolden and four other crew members. (NASA)

Charlie Bolden

Flew on the space shuttle four times for NASA between 1986 and 1994; retired Marine Corps major general and former NASA administrator

Somewhere between 10 and 15 minutes after my first launch, when I raised my seat and had an opportunity to look out the windows in the shuttle, I saw this series of land masses coming up. And it didn't take me too long to figure out: Okay, that's the British Isles and Europe. And then I looked up a little bit farther and saw this massive — what looked like a big island. And it took me a few seconds to realize that that island was the continent of Africa.

And you know, being an African American, I had done a lot of study of African geography. I wanted to be able to look down and identify some of the potential countries from which my ancestors had come on the west coast of Africa. And it may sound stupid because I thought I would be able to distinguish one country from another. And what absolutely amazed me was this massive land mass that went from the Mediterranean all the way down to the tip of South Africa with no borders or boundaries. Going from the beautiful Mediterranean coast through the Sahara Desert all the way down through the jungles in the equatorial region and then down into South Africa, and not a single sign of an individual country. This one big mass. And I actually got tears in my eyes because that was my big wake-up call to the fact that we are all on this one planet together. We're not really divided and separate the way we had been taught to believe.

Mark Vande Hei exits the International Space Station in 2017 for a spacewalk. (NASA)

Mark Vande Hei

Current NASA astronaut; flew on Russia's Soyuz to the International Space Station in 2017; retired Army colonel

There was a moment: As we we're approaching to dock with the space station. out this little portal is a window near my left shoulder, and I could suddenly see one of the solar arrays. It was bright orange and huge. The Russian commander was very focused on making sure the automatic docking system is working right and, if it stops working correctly, we don't want to collide in the wrong spot with the space station. Basically, what we're doing is trying to collide with the space station in exactly the right spot, at exactly the right speed. That's how we dock. So, I wasn't supposed to be saying anything, but as soon as I saw that view, I just said: "Whoa!" And then he looked at me and put his finger to his lips, like "please be quiet."

Chiaki Mukai tends to an experiment in the Spacehab module in a space shuttle. (NASA)

Chiaki Mukai

First Japanese woman in space; first Japanese citizen to have two spaceflights, in 1994 and 1998

My flights were very short — one was two weeks, and the other one was 10 days. It's not six months like the International Space Station's astronauts do. It's more like a business trip. I actually really wanted to work more in space. On the way back, when the orbit happened, the gravity increased more and more and then my body became heavier and heavier and heavier. It made me feel like, "Oh, I'm getting closer to my home." Which is Earth. So psychologically somehow I actually wanted to stay longer. At the same time, I was very glad that after the successful work I'm now going back to my home.

Pam Melroy, left, and other astronauts sleep aboard the space shuttle Discovery while docked with the International Space Station. (NASA)

Pam Melroy

Flew on three space shuttle missions for NASA between 2000 and 2007; retired Air Force colonel

On my first flight I did feel discomfort. I just got super sleepy. The way the doctor described it to me later was like your brain just pulls all the circuit breakers and says, "Does not compute." And so I got really, really sleepy. My commander just basically stuffed me in a sleeping bag and said, "Just go to sleep." And I woke up the next morning and I felt great. For me, the subsequent flights, I don't know if my body remembered everything, but it was very easy after that. That's pretty typical. I would say 80 percent of people feel at least some minor discomfort all the way up to being sick.

Shannon Lucid, with Yury Usachov, left, and Yuri Onufrienko. (NASA)

Shannon Lucid

Part of the first class of female astronauts; only American woman to serve aboard Russia's Mir space station, in 1996

On working with Yuri Onufrienko and Yury Usachov aboard Mir: I was so fortunate to work with Yuri and Yury. They were probably the most perfect people that I could have worked with, the most compatible people. I did not know them very well at all because we hadn't had much interaction before I launched. I was also just a little apprehensive because, you know, my Russian was — shall we say — weak to nonexistent. And, anyway, when the shuttle docked with Mir, then I went across into the Mir space station and started working with them, and right away — I do like to talk. So I was talking in my broken Russian because they did not speak English. And I sort of cracked a joke, and they laughed! And I thought, "Okay! This is gonna be great."

John Herrington aboard the International Space Station. (NASA)

John Herrington

Flew on a space shuttle for NASA in 2002 to visit the International Space Station; retired Navy commander

On the flight deck, it was easy for me to take a nap. It was very hard for me to get long restful sleep. You're floating, and if you imagine not touching anything for the very first time in your life and trying to sleep, it's really bizarre. And then when you close your eyes, you see little flashes of light, cosmic particles coming and whacking you in the eyeball. So I'm taking this nap, and when I wake up I end up in a different location on the flight deck. I just happened to be looking out the overhead windows and — "Where am I?" Well, it was at night and I could see the coast of England, and London, the coast of France, and Paris, all in one fell swoop. It was intriguing to be able to see that in that manner, and be able to figure it out without referencing a computer. That was fun.

Earth seen from lunar orbit during the Apollo 15 mission. (NASA)

Al Worden

Command module pilot for Apollo 15 in 1971; retired Air Force colonel

There's about a quarter section of the trajectory where you are shadowed. So there's absolutely no solar light on you. The only light that comes to the spacecraft is from stars out there in the universe. We found that there were millions of times more stars we could see from that vantage point than you can looking through the atmosphere here on Earth. There were so many stars that I couldn't even find my 37 brightest stars which I use for navigation. They were completely washed out by all the starlight in the universe. And that makes you really think about what is the universe. What is it all about?

Frank Culbertson Jr. took this image of Ground Zero from the International Space Station on Sept. 11, 2001. (NASA)

Frank Culbertson Jr.

Flew three missions for NASA between 1990 and 2001; retired Navy captain

I was the commander of the space station during 9/11. As we were flying over New England, I could look back and see New York very clearly. Over Manhattan, I saw this thick gray cloud enveloping the southern half of the city. What I was seeing, I determined later, was the second tower coming down. I just assumed tens of thousands of people were dying.

Nicole Stott in 2009. (NASA)

Nicole Stott

Flew on a space shuttle for NASA twice between 2009 and 2011

To paint with watercolors in space — you know, everything floats. So instead of dipping my brush in a cup of water, I would use a little ball of water from a drink bag. I thought I'd be dipping [the brush] into the ball of water at the end of the drink bag, but just before the brush would touch the water, the water would move over to the brush. Some super fancy magnetism or something. Then you'd have this ball of water floating around the end of the brush and then as you got it close to the solid paint, it would move from the brush to the paint. You didn't even have to really touch the brush to the paint; it was like it was attracted. It was the weirdest thing.

Yury Usachov aboard Mir, as seen from Atlantis in 1996. (NASA)

Yury Usachov

Russian cosmonaut who flew to the Mir space station and the International Space Station (ISS) between 1994 and 2001; former commander of the ISS and the Soyuz; conducted seven spacewalks

When I saw the Earth for the first time, I was shocked with its size. You think that you would see it very small and fragile like a Christmas decoration, but when you saw it from the distance of 200 kilometers you are so impressed with its huge size — one circle around the Earth takes one and a half hours at a speed of 8 kilometers per second. And you are also impressed with its beauty. This is stunning, you can stay at the window for hours and enjoy wonderful views. Nobody can remain indifferent. Because the view of the Earth from space is something really amazing. I had a thought that it is a live organism and it lives according to its own laws. I am not a religious person, but I got a thought that such beauty could be created by a very big love.

Mike Massimino is seen from an aft flight deck window of the space shuttle Atlantis. (NASA)

Mike Massimino

Flew on two space shuttle missions for NASA, in 2002 and 2009, to service the Hubble Space Telescope

It was probably my third day back, and I was taking groceries out of the minivan, and I wasn't sure where to put them. I had all these plastic bags from Kroger's and I had to get them out of the car and into the house. So I thought, why don't I just float this one here? And I just dropped it, thinking it was going to float.

The Soyuz ferries Richard Garriott to the International Space Station in 2008. (NASA)

Richard Garriott

Went to space as a civilian who paid to fly on Russia's Soyuz to the International Space Station in 2008

You notice how the impact of humanity is everywhere. The Sahara is crisscrossed by roads and has farms all over it, deep-wooded areas like the Amazon are also still full of roads and civilization. You see the same thing happening all through the green areas of Africa. You can see that forest fires or the fires that we're clear cutting in the Amazon create enough soot that it rises up through the very thin atmosphere. It spreads out and covers whole states with soot. We're well past the point of creating enough pollution to fill the entire air bubble, the thin atmosphere that sits around the Earth.

Terry Virts Jr. captured this image of Europe in 2015. (NASA)

Terry Virts Jr.

Flew on two space shuttle missions for NASA between 2010 and 2015; retired Air Force colonel

You're floating in space and you look out of a hatch and there's a planet over there, like you're not on your planet anymore. And that's pretty profound. It surprised me, the emotional impact that that had on me. I'm not an idealist, and I'm very much a realist. I spent 30 years in the Air Force, and I'm not a pie-in-the sky guy. But I just go, "Why the hell are we having these conflicts down there?"

Walt Cunningham works inside the Apollo 7 command module in 1968. (NASA)

Walt Cunningham

Pilot of the 1968 Apollo 7 mission, which orbited the Earth 163 times; retired Marine Corps colonel

I think the first question people really want to know (though they usually ask it second or third) is how do you go to the bathroom in space? And that was a different job then than it is today. In fact, I think I was the first one in the crew after about two and a half days, I had to go first. I remember when I got back it took me an hour and a half to write up how to handle things and how to avoid this and avoid that. Today, it's a different world. They have kind of bathrooms today. You've also got men and women. That creates a problem, too.

Scott Kelly wears a gorilla costume aboard the International Space Station in 2016, a gift from his twin, Mark, a former astronaut. (NASA/AP)

Scott Kelly

Flew four missions for NASA between 1999 and 2016; spent almost a year on the International Space Station; retired Navy captain

On the gorilla costume he wore in space: I was this kid that couldn't pay attention in school. So you're always look for the little thing that gets some people to pay attention and be inspired or motivated. I'll go up sometimes in front of a class of hundreds of kids and there's always a few outliers who don't want to pay attention — they're looking out the window. You know it's just like you when you were in school. Sometimes even the astronaut can't command full attention. You know what does command full attention from everybody? Space gorilla. You put a gorilla flying around in space, and there's nobody that doesn't pay attention to that.

Kathryn D. Sullivan uses binoculars to view the Earth through the space shuttle Challenger's forward cabin windows. (NASA)

Kathryn D. Sullivan

Flew three space shuttle missions for NASA between 1984 and 1992; first American woman to perform a spacewalk

Probably the distinctive visual memory for me is on a spacewalk, I had a moment to shift my gaze from watching where I was carefully placing my hands to looking down to my toes and seeing Venezuela slide by below my feet. I instantly felt like a kid at the jungle gym hanging upside down by my toes.

Dorothy Metcalf-Lindenburger, in the cupola of the International Space Station while the space shuttle Discovery remains docked. (NASA)

Dorothy Metcalf-Lindenburger

Flew on the space shuttle for NASA to the International Space Station in 2010

The first day itself is like a big blur, because you're going from this incredibly powerful launch to turning your vehicle into a place to live for the next couple weeks. We have to get out of the big orange suits, and there's a whole system for doing these things, so you're not all crowding the deck at once. So we had choreographed this, and planned it, and practiced it in simulators. And for the most part, it goes pretty well. The part that you can't anticipate is: I got space sickness, which is pretty common for rookies in space. It's kind of a bummer. It's not like the whole first day that you're puking or anything. It's just that, occasionally, you'll be working and trying to focus and then all of a sudden I'd be like, "Oh, I gotta get that emesis bag." You need to take care of that, get yourself cleaned up and then get back to work.

Rakesh Sharma, left, was the first Indian in space. (Sputnik/Alamy Stock Photo)

Rakesh Sharma

First Indian citizen in space; flew to the Soviet Union space station Salyut 7 on the Soyuz in 1984 as part of the Interkosmos program

On doing yoga in space: The lack of gravity made it different. A purist would have frowned somewhat, because to maintain your vertical position during the asanas [yoga positions] you need an elaborate harness system. That is what negates the effect of the lack of gravity. And it was the very first time such a harness was being tried out, after it was designed on Earth. There were, naturally, some shortcomings so you did have to work pretty hard to maintain a balance. It took some trial and error.

Christina Koch posted this image of the Earth on Facebook in late May. (NASA)

Christina Koch

NASA astronaut serving on the International Space Station; launched on Russia's Soyuz in March 2019

One interesting thing that I've come to realize in being here and having time to look at the Earth, is how small the area that I'm familiar with is compared to the entire area of the Earth. Very rarely are we actually flying over a place that I have lived, or that I know well, and more often we're flying over a place that's unfamiliar to me, unexplored territory. And it's really just brought the perspective of how big the Earth is and how special those places are that I have spent time.

Nick Hague floats in Europe’s Columbus lab module during a ham radio session aboard the International Space Station. (NASA)

Nick Hague

NASA astronaut serving on the International Space Station; launched on Russia's Soyuz in March 2019

You continually wash up here, and so slowly, the dead skin off the bottom of your feet goes away and they become fairly smooth. But we're constantly hooking our toes underneath handrails to hold us down, just like we are right now. I've got my feet underneath a handrail. And because I'm hooking up with my toe, the top of my big toe is in constant contact throughout the day with these hard metal handrails. And so slowly, the tendon on top of my toe has gone through spurts of pain as it's adjusting to all of this, and the skin has started to thicken on top, and everything started to adapt. But it's taken a good two months to get to that point.

George Zamka sits at the pilot’s station aboard the space shuttle Discovery in 2007. (NASA)

George Zamka

Flew two space shuttle missions, one in 2007, the other in 2010; retired Marine Corps colonel

As you can imagine, it's a transition from a warrior culture in the Marine Corps, where you prepare your skills and your leadership ability to be ready for combat. On the NASA side, it's much more of an academic type of situation where you are part of a group. There aren't ranks.

That's the most obvious thing: You don't look at a collar or on a shoulder to determine who is in charge here. It's more of a peer-type relationship — with flight controllers, with engineers, with the folks that work on the rockets itself. So going from a very hierarchical organization to a flatter organization at NASA, being a test pilot helps because when you are doing that job you're also working with engineers, and it's also kind of a peer relationship. So that helped ease that transition.

Front, from left: Thomas Reiter, Nicholas Patrick, Joan Higginbotham and William Oefelein. Center row: Robert Curbeam Jr., Christer Fuglesang and Mark Polansky. Back row: Michael Lopez-Alegria, Mikhail Tyurin and Sunita Williams. (NASA)

Joan Higginbotham

Flew on a space shuttle mission for NASA to the International Space Station in 2006

The shuttle crew was probably one of the most, if not the most, diverse crew ever. It just kind of happened that way. The crew was made up of two African American astronauts. That's the first time two African American astronauts have ever flown together. We had one person of Russian-Korean descent, although he was American, but that was his heritage. Suni [Williams] — her parents are from India. Nick [Patrick] was British-born but became a U.S. citizen so he could become an astronaut. We have Christer [Fuglesang] who was the first Scandinavian astronaut. And then when we attached ourselves to the station, the station crew consisted of a Russian cosmonaut, a German astronaut, and then Mike L.A. [Lopez-Alegria], who is a U.S. astronaut but he's of Spanish descent, and it dawned on me: Oh my gosh, we have literally like seven nationalities, we have four countries and we're speaking like seven languages. And I'm thinking: If we can all get along and accomplish this mission in this little sardine can, why can't we all get along on Earth?