It's a hot summer day, thick with humidity, when Dr. Serena Auñón-Chancellor arrives to meet me at NASA's Lyndon B. Johnson Space Center in Houston. Wearing a royal blue jumpsuit adorned with zippered pockets and badges of the US flag and her two space expeditions, she strides confidently into the massive room. Mockups of the Orion spacecraft and the International Space Station surround us, but Auñón-Chancellor isn't overshadowed by the awe-inspiring models. Her uniform gives authority, her firm posture demands attention and her warm laugh gives off positive energy.

Auñón-Chancellor, 43, has been a NASA flight surgeon for 13 years, but she's also an electrical engineer, an aquanaut and a practicing physician specializing in both internal and aerospace medicine. Oh, and she recently returned to Earth from a six-month stay, which included Expeditions 56 and 57, at the ISS.

Though only a few hundred humans have made it into space, the medical research conducted in microgravity by people like Auñón-Chancellor directly impacts the medical care of everyone on Earth. While orbiting the planet, she's performed studies that have expanded our knowledge of the human body and conducted bioscience experiments that may improve the lives of people with conditions including cancer, Parkinson's disease and osteoporosis. "People think science we do on the space station only relates to space exploration," she says. "They don't realize how much it matters to medical care of everyday living here on Earth."

She's excited to tell me the details, but she begins by telling me when she knew leaving Earth was in her future.

When Auñón-Chancellor was 15 years old, she had her first taste of "space," running mock space missions as a flight surgeon at Space Academy inside the historic US Space & Rocket Center in Huntsville, Alabama. It's a hands-on camp where students learn how astronauts train and perform space expeditions. She was instantly hooked. When her parents asked if the camp was everything she thought it would be, her response was clear. "It really solidified that this it what I wanted to do with my life."

Serena Auñón-Chancellor attended Space Academy in 1992. Space Academy

Life in microgravity

Auñón-Chancellor blasted into space on June 6, 2018, from the Russian-operated Baikonur Cosmodrome in Kazakhstan. She says the ride was surprisingly smooth, given that the Russian Soyuz MS-09 spacecraft delivered 930,000 pounds of thrust, taking her and her crewmates, Flight Engineer Alexander Gerst from Germany and Commander Sergey Prokopyev from Russia, on a ride at 1,100 miles per hour.

During the launch, Auñón-Chancellor remembers, she was completely focused on the 8 minutes, 40 seconds it took to get to an orbit of approximately 129 miles high, while making sure there weren't any malfunctions. The most fascinating part was when the shroud came off around the capsule and she saw the Earth from space for the first time.

Following 34 Earth orbits, the Soyuz connected to the ISS. She floated slowly inside with her arms wide open. "Your brain really doesn't know what to do because there's really no up or down anymore. You can move around on the ceiling or the walls or the floors," she says. "But the first time I tried to do that, I would just turn myself in circles because I wasn't sure where I was."

It wasn't long, though, before floating in microgravity felt natural. What took more acclimation was the ISS' sterile environment, where she didn't feel the air move. There are also very few windows. To make the station seem more human, she jammed to classic rock, classical music and rap tunes. "It's a very just machine-driven environment with a constant low hum," she says. "Music breaks that apart completely."

The shroud came off around the capsule and she saw the Earth from space for the first time. NASA

Aging in space

Weirder is what happens to the human body in microgravity. Astronauts lose critical minerals such as calcium, with bone mass dropping about 1% per month, according to NASA. It's a similar effect to a person with osteoporosis. As bones become brittle, people with osteoporosis disease can also experience a hunched posture or loss of height.

Those changes give researchers the opportunity to use astronauts like Auñón-Chancellor to better understand the effects of aging. She collected and saved samples of her blood, urine, saliva and even her feces. "It's not easy to collect your urine in orbit," she says. In microgravity urine droplets can float all over the place, potentially damaging equipment. "But we're constantly making changes to the kits so that we can perfect that science."

The samples were later analyzed by scientists on the ground. As part of the myotomes muscle study, for example, they studied how to better understand resting muscle tone. The results could lead to new treatments for aging and for those with limited mobility. "It's interesting because they can look at us and maybe even test certain medications with the sort of bone loss that we have," Auñón-Chancellor says. "That also impacts millions of Americans on the ground who also have osteoporosis."

During expedition 57, Serena Auñón-Chancellor is mixing protein crystal samples. NASA

In addition to being the subject of study, she also conducted hundreds of experiments related to human health. For example, she examined biological samples like bovine and human sperm for a fertility study that will help scientists understand if human reproduction could possibly happen in outer space.

She also helped to crystallize a protein, leucine-rich repeat kinase 2, that's present in patients with Parkinson's disease. (During the course of the study she observed that the protein crystals grew larger and more uniformly in microgravity than they do on Earth.) Analyzing the protein's structure can help scientists better understand the role it plays in Parkinson's, which could lead to improved medicines for the disease.

Medicine in microgravity

During her 197 days aboard the ISS, Auñón-Chancellor also studied endothelial cells, the cells that line your blood vessels, to help determine if ECs grown in microgravity can serve as a good model system for cancer therapy trials. "I was most proud of the cancer research that we did because what it showed us was that cells that grow in microgravity really like to grow," she says.

Serena Auñón-Chancellor conducting a cancer therapy study inside the microgravity science glovebox. NASA

Because one of the hallmarks of cancer is its ability to form new blood vessels that feed a tumor, medication that kills that blood supply could help lead to a cure. In space, Auñón-Chancellor says, endothelial cells grow for longer than they do on Earth and in a form that's similar to how they exist in the body. That lets scientists better test chemotherapy agents or new cancer drugs.

Auñón-Chancellor is confident that what's learned in space will be useful back on the planet below. "Pretty quickly, even within the next three to five years, they could help us provide cures for cancer down here on the ground."

I love being a physician and I love practicing aerospace medicine, so I just kept moving forward and doors kept opening. Serena Auñón-Chancellor

Preparing to be an astronaut

Though her mock space mission as a teenager initially set her on the road to being an astronaut, it was her education -- earning an electrical engineering degree from The George Washington University in 1997, graduating from medical school at the University of Texas Health Science Center in 2001 and completing a residency in internal medicine and aerospace medicine at the University of Texas Medical Branch -- that led her to NASA. "There was no specific path that was laid out for me that said this is how you become an astronaut, just as it is for anybody," she says. "But I really enjoyed what I did. I love being a physician and I love practicing aerospace medicine, so I just kept moving forward and doors kept opening."

Serena Auñón-Chancellor is performing an immune blood sample draw with Alexander Gerst. NASA

NASA's door first opened in 2006 when the space agency welcomed her as a flight surgeon, or the Earth-bound personal medical physician to astronauts. Then in 2009, while Auñón-Chancellor was parked in her car at a Chinese restaurant, she got the call she'd been awaiting for years. Peggie Whitson, a former NASA astronaut and the first female commander on ISS, and former NASA Astronaut Steven Lindsey invited her to be part of the 20th NASA astronaut class.

"I remember hanging up the phone and then kind of yelling a little bit in my car," she says. "I just called my family right away."

In 2009, Auñón-Chancellor was selected to be part of NASA's 20th astronaut class. NASA

The Indianapolis native was chosen out of 3,500 applicants, becoming the second female American-Hispanic NASA astronaut after Dr. Elen Ochoa. "Serena brings so many talents to her role as an astronaut," says Ochoa, who's also a former director of Johnson Space Center. "And I was especially happy to see the second Latina in space last year, 25 years after my first flight."

One of her talents is a strong mindset for accomplishing goals, a value her parents gifted her. "Not everything is lined up for you to achieve what you want to achieve. And you have to kind of push that aside and ignore everything," Auñón-Chancellor says.

Auñón-Chancellor has a simple but powerful message for students with a similar background: Don't limit yourself. "My father came from a very humble background. He came to this country in 1960 (from Cuba) and literally had nothing," she says. "You can start with nothing and end up with everything. It's really all about what's up here, and what you envision yourself doing, and what you want to do."

Before going to space, Auñón-Chancellor trained for two years at the Johnson Space Center. She performed extravehicular activities combined with robotic operations simulations at NASA's Virtual Reality Laboratory, according to Evelyn R. Miralles, the associate vice president for Strategic Information Initiatives & Technology at the University of Houston-Clear Lake and a former NASA chief principal engineer.

One lesson covered what Auñón-Chancellor should do if she became detached from the ISS while performing a spacewalk. Using a VR headset, real-time graphics and motion simulators, Miralles showed her how to manipulate the inputs from the spacesuit's SAFER (Simplified Aid for EVA Rescue) hand controller. Worn like a backpack, it's like a spacewalk life jacket with nitrogen thrusters that allows astronauts to move around space.

Auñón-Chancellor trained at NASA's virtual reality lab. Evelyn Miralles

Miralles describes Auñón-Chancellor as a smart, dedicated professional. "She was very aware of her environment and the complexity, being a flight surgeon," she says. "She had a lot of stamina, strength and resiliency. "

Shortly after she graduated as an astronaut, Auñón-Chancellor's adventure in extreme environments started at the world's only undersea laboratory. She splashed down to the National Oceanic and Atmospheric Administration's Aquarius habitat, located 60 feet below the coast of Key Largo, Florida. Living in a confined environment for 17 days as part of NASA Extreme Environment Mission Operations (Neemo 20), she performed Earth science experiments, including taking samples of Siderastrea siderea, a coral found in both the shallow (17 meters below water) and deep (27 meters below water) parts of a reef. "It's quite an honor to live under the sea for that period of time," she says.

Scientists then analyzed the samples to see how the fungi, bacteria and algae associated with the coral changed between the shallow and deep areas. These microbe communities may give insight as to how coral acclimate to different depths, explains Daniel Merselis, postdoctoral researcher at the University of Florida International, who worked with Auñón-Chancellor during the Neemo 20 mission. "She learned to identify coral species at a remarkable rate and sample them with precision, Merselis says. "Her leadership abilities and great competence was really appreciated by us coral biologists."

The Neemo 20 team also tried to solve potential problems for future Mars missions. The crew simulated the one-way communication time delay of 10 minutes that's expected when astronauts on Mars communicate with mission control on Earth, says Auñón-Chancellor. "We did experiments where we would talk for half a day or an entire day and insert that time delay to see how it impacted science operations and if we had any problems that arose."

Auñón-Chancellor lived beneath the sea for 17 days as part of NASA Neemo 20. NASA

The moon and beyond

Before a Mars mission, though, NASA plans to return to the moon by 2024 in the Orion spacecraft. Auñón-Chancellor says it'll happen on time. "People think that's impossible," she says. "It's not impossible."

NASA's Artemis mission, named after the goddess of the moon in ancient Greek mythology, will return astronauts, the first woman included, to the moon's south pole. Auñón-Chancellor is one of 12 active female NASA astronauts ready to go. When I asked whether it could be her going, she smiled and briefly paused before answering. "It can certainly be anybody," she says. "I'm excited because for the first time we are going back to the moon not just to say we went back there, but with a purpose. I think folks should be excited."

Though the short-term goal of Artemis is to begin creating a sustainable NASA presence on the moon, the long-term goal is to use the moon as a stepping stone to Mars. NASA will place the Lunar Gateway spaceship in orbit around the moon to train astronauts on living in deep space for long periods. (A one-way journey to Mars, about 34 million miles from Earth, is expected to take six to nine months.) Also, because a Mars-bound spacecraft will need to change its orbit on the way to the red planet, NASA will use the Lunar Gateway to train astronauts on how to perform deep-space maneuvers.

The point is to know how to live away from Earth before heading to Mars. "We want boots-on-the-ground with a minimal configuration ... that's our start," Auñón-Chancellor says. "Then we create the sustainable presence on the lunar surface. It may take some time, but I would rather be ready to go to Mars than take a big guess and hope that things work."

The Orion crew module mockup at NASA Johnson Space Center in Houston. Erica Argueta

Mission to Mars

NASA's plan to send humans to Mars is a grand vision, but will the human body be able to handle a multiple-month trip there and a deep space mission? Not quite yet, Auñón-Chancellor says. "We're pretty well protected in our little bubble close to Earth here, but as we go out past that, it's gonna impact our body more -- and also behaviorally."

Currently, astronauts living in the ISS about 254 miles above Earth's surface are well protected from solar radiation (energy packed in electromagnetic waves) by the station's thick walls and the Earth's magnetic field. But as they travel farther into outer space, the radiation will be stronger and humans will need better protection. According to NASA, data collected from the Curiosity Mars rover showed that it was exposed to an average of 1.8 millisieverts of galactic cosmic rays, which is like a human getting a whole body CT scan every five days or 18 chest X-rays per day.

Auñón-Chancellor says another risk astronauts may face while traveling to Mars is an encounter with a large solar particle event. Hazardous to humans, the events are made up of radioactive particles moving at 99% of the speed of light following a solar flare. "You can get something called sort of acute radiation sickness, where you don't feel very well for a period of time," she says. "That can also decrease the body's immune system and provide problems later on down the line."

To protect astronauts from harsh radiation, NASA is working on developing radiation shields. One of them will be the Orion itself. At Johnson Space Center, I went inside the Orion crew module mockup, where astronauts will train. At 16.5 feet in diameter and 10.10 feet in length, the crew module felt tiny, even for a 5-foot 4-inch woman. When I crawled inside, I couldn't even stand up. And remember that four astronauts will be riding inside.

The interior of the Orion crew model mockup. Erica Argueta/CNET

Though it looks similar to the Apollo 11 command service module, it won't act the same. Nujoud Marancy, chief of NASA's Exploration Mission Planning Office, says the agency took a lot of what it learned from the Apollo mission about protecting a crew and applied it to Orion. For starters, the crew module will be equipped with thermal protection made with carbon fiber material. The crew module also has an improved heat shield that'll be the largest one ever built, measuring 16.5 feet in diameter.

"We use a lot of carbon composites that they didn't have during the Apollo era. Most of the Apollo capsule was full of computers with very low computing capacity," Nujoud says. "What we can do with our computers is to fly four redundant computer systems that can survive radiation."

The Orion spacecraft also be equipped with a radiation-sensing instrument designed to warn astronauts to take shelter in the center module, where the spacecraft's greater mass will better protect them from the harmful particles.

Other teams at NASA are developing technology for protective vests and electrically charged spacecraft surfaces that would divert radiation. But there's still a lot to learn, so NASA will be collecting data for developing radiation protection strategies during the Artemis mission. One thing's for sure: Sending humans to the moon or Mars will push the human body to a new limit. How much? It's unclear, but NASA hopes to find out in 2024 with that first step to the moon.

Auñón-Chancellor poses in the windowed cupola of the ISS mockup. Erica Argueta/CNET

What it is clear to Auñón-Chancellor is that the Mars mission will require a global effort. "One of the most important takeaways from what the space program is doing right now is that it's continually trying to advance human presence in space," she says. "Whatever your background is, whether it's science, chemistry, engineering, you're a physician, you're in the military, get involved with your country's space program wherever you are across the world."

Toward the end of our time together, Auñón-Chancellor and I walk the floor of the famous Building 9 where astronauts train. Though it feels like the size of a football field, she shows me around as if we were in her home. In the ISS mockup, she points out the station's windowed cupola and she takes me into the Kibo Laboratory (where, in space, she conducted her experiments). When we bump into her colleagues, they greet her with hugs. I soak up the experience of this real-life classroom, an innovative space that's training future astronauts who'll go to the moon. That's a real possible future for Auñón-Chancellor.

For now she's traveling the world and sharing her unique experiences with biomedical research in microgravity. "I enjoy doing that because I find out a lot of folks are kind of in the dark," she tells me. "I like opening that up, I like telling that story, so that people better understand it."