What does it feel like to blast off from Earth in a rocket, knowing that you will not see your family, feel the wind on your face, or taste fresh-cooked food for a whole year?

When National Geographic caught up with Kelly by phone in Las Vegas, he explained how a chance encounter with a book set him on his course to the stars, why he believes we are already capable of traveling to Mars, and how he coped in space after hearing the news that his twin brother’s wife, Gabby Giffords, had been shot. [See photos of Kelly’s triumphant return to Earth.]

View Images Courtesy of Penguin Random House

There’s an amazing moment in your book, Scott, when you lose your orientation in the dark during a spacewalk. Put us inside that moment and describe how it felt.

I was on my second spacewalk. It was long and tiring and toward the end of it, when we were heading back inside to the airlock, ground control asked me to do some other activity to check a valve. Even though I was tired, I let him know that I could do it. You don’t know what else could wind up going wrong so you’ve got to rise to the occasion.

I started heading to the work site on the other side of the truss, an area I wasn’t familiar with, and I got completely lost in space and disoriented, and turned upside down. It took me a while to figure out where I was. It’s not like you’re lost and you can’t find your way home. I never felt like I was in any kind of risk. But at the same time, it was not a great feeling.

Eventually the sun came up. [Laughs] Before that I was able to see some lights over my head which I thought was the sky, but it wasn’t. It was the Earth. When I saw them, I realized that I was flying over the Middle East. I could see the Arabian [Persian] Gulf, which is very distinctive from space, even at night.

You talk very prosaically about this. But for most of us the idea of being upside down, outside a spacecraft at night, sounds terrifying!

Yeah, but I’ve been doing this job for nearly 20 years. Even though I hadn’t done a whole lot of space walks before, I was familiar with living in this risky environment. If you took the average person, put them in a space suit and threw them outside the space station with no previous training or experience, that would be, like you said, terrifying.

RELATED: WHAT DID THIS COSMONAUT MISS ABOUT EARTH AFTER A YEAR IN SPACE? Russian cosmonaut Mikhail Kornienko spent a year on the International Space Station with astronaut Scott Kelly.

Give us a picture of what it is like outside the spacecraft.

One of the things you notice is that there are a lot of dings and, in some cases, holes going through hand rails and other metal structures, on the outside of the space station. The space station gets hit a lot! Fortunately, we have some good debris shields and nothing has ever penetrated the hull but there’s a lot of stuff flying around out there. And if one of those things hit you in the face or somewhere else on your suit, it would do some severe damage to you and your suit, which is filled with 100 percent oxygen.

The view of Earth from the outside is incredible. It makes you feel like you are experiencing the full majesty of planet Earth and it’s just incredible. Those images of sunrises and sunsets, the blue of the Earth and city lights at night, as seen through my visor, is something that will hopefully be ingrained upon my brain for the rest of my life.

On your first trip on the ISS another dramatic event occurs, but this time related to politics back on Earth. Talk us through the moment you heard your sister-in-law, Gabrielle Giffords, had been shot. Given that experience and, more recently, Las Vegas, what are your thoughts on gun control?

When Gabby was shot, on January 8, 2011, I was about halfway through my first, six-month flight. I got a call from the ground saying they were going to privatize the space-to-ground channel, which means they don’t want anyone to hear what they’re going to say. The chief of the astronaut office comes on and she says, “I don’t know how to tell you this, so I’m just going to tell you. Your sister-in-law, Gabby, was shot and a bunch of people killed.”

I was on the space station with no way to come home. The way I dealt with it was to try and do the best I could to support my brother and his family and my family on the phone. But eventually you realize you need to focus on your job, on the stuff you can control, and ignore the chaos there on Earth with my sister-in-law. Some news outlet was even reporting that she had died. But later I spoke to a good friend who said she was alive.

Since then, Gabby and my brother have been big advocates for sensible legislation to keep guns out of the hands of people that shouldn’t have them. They, as I do, believe in the Second Amendment of our Constitution. Our country was founded on this principle. But, clearly, we have a problem in the U.S. with gun violence and there’s a lot we can do. A good starting point would be having legislation that protects people from people that shouldn’t have firearms.

View Images Astronaut Scott Kelly took this photo on August 15, 2015, as the International Space Station passed through an aurora. Photograph by Scott Kelly, NASA

Little boys and girls often say they want to be astronauts when they grow up. Little in your background—poor grades at school, abusive father, blue collar neighborhood—suggests you had “the right stuff.” How, and why, do you think you succeeded?

It wasn’t something, like you said, that seemed a possibility for me. If you would have asked any of my teachers in school if they thought I could become an astronaut someday, I imagine they would have laughed! As I would have laughed. [Laughs] It was definitely something that interested me, like most kids are interested when they’re young and have big dreams. But it wasn’t until I was in college, still struggling academically, that by accident I walked into the bookstore and picked up the book The Right Stuff. For whatever reason, I related to it and decided that this was what I was going to do.

I wanted to be a naval aviator, to land on a ship because I thought it would be the hardest type of flying. I was absolutely right. The book was the spark I needed to get moving in a positive direction. It wasn’t easy, especially at first, when I had to teach myself how to be a good student and study. But over time I was able to learn how to compensate for my lack of attention.

It’s a giant leap if you think about it. A kid reads a book and decides he’s gonna become an astronaut. The reality is that it was a bunch of very small but positive, determined steps that eventually became a giant leap.

The title of your book references the Arctic explorer Ernest Shackleton. What similarities were there—physically and psychologically—between your voyage into space and his Antarctic odyssey?

The endurance it takes to get through a yearlong mission with the same amount of energy and enthusiasm at the end as you had in the beginning, is similar to the philosophy that I would imagine Shackleton had.

But for him that lasted well over a year, much longer than I was in space. Despite the isolation, my experience was not something you can easily compare to those guys struggling on a daily basis just to survive.

View Images Scott Kelly's one-year mission on the International Space Station was conceived as a stepping stone to a mission to Mars. This photo of the ISS was taken from the space shuttle Atlantis in 2011. Photograph by NASA

What did you find hardest?

Being separated from your family and friends and knowing that if something happened to them, there was nothing I could do to be with them. There’s the isolation from the outside world and nature, like not being in the sun or feeling the breeze on your face. There’s a lack of choice of what you’re going to do daily. You have to maintain a tightly controlled schedule for a very long period of time, which is also challenging.

I would never go as far as to say that it was as challenging as what Shackleton and his men had to deal with. But it was still a mission of endurance.

Your twin brother, Mark, is also an astronaut. Tell us about the Twins Study—and what it revealed about the physiology of space travel.

The idea of the Twins Study was that you’ve got these two guys who are almost genetically identical. They also had a lot of data on my brother because he had been an astronaut for as long as I have, going back to 1995. So comparing me in space to him on the ground at a genetic and chemical level—analyzing aspects of our physiology and psychology—was a unique opportunity.

There were some interesting results. I was, for instance, surprised to hear that my telomeres—part of our chromosomes that, as we get older, generally get shorter and more frayed—got better in space compared to his on the ground. The hypothesis was that it would be the opposite; his would do better since I was living in a radiation environment. Our microbiome, the cells that live in our digestive system, also changed in space.

View Images Twin brothers and astronauts Mark and Scott Kelly both participated in the Twin Study, which examined the effects of long-term space travel on the human body. Photograph by Robert Markowitz, NASA

The next great frontier in space is Mars. Do you think human beings will one day travel to the Red Planet? And what did your year in space tell us about the challenges we will face?

Absolutely! We could go to Mars right now if we had the money and political support. One of the challenges that needs to be solved is radiation. As you get away from the magnetic field of the Earth, you lose a lot of the radiation protection of our planet. There are ways to solve it, like shielding with water or even creating a magnetic field around the spacecraft. But it’s not easy.

Another major problem is CO2. Our ability to get CO2 levels to Earth-like levels is, technologically, very challenging in space. It requires hardware that scrubs CO2 out of the air in an efficient way and that is a challenge, as is keeping that hardware running for long periods of time. It gives you headaches and congestion. Sometimes, if the level gets too high, it also makes it difficult to concentrate. That’s something we have to solve if we want to go to Mars.

At the end of the book, you list a number of things you learned during your year in space. Give us a few of the key lessons.

The biggest thing I learned from being part of the Space Station program is that when countries work together in a cooperative way and we put our best people and resources behind something that is very difficult, we can do anything. If we someday decide we want to go to Mars, we can do that or other challenging things. We can do anything if we put our minds to it.

The other important theme of this book is that you can be struggling to find your way, but if you find something you are passionate about, some spark that gets you moving toward that goal with drive and determination, even someone who had ADD as a kid, like I did, can still be successful.

This interview was edited for length and clarity.