(CNN) If NASA had allowed it, astronaut Scott Kelly would have loved to climb out of the Soyuz capsule after landing on Tuesday and walked on his own, Kelly's brother, Mark, said during a news conference on Friday.
This is exactly what would have taken place if Scott Kelly had been on a mission to Mars and landed on the red planet after six months of space flight. So far, since landing after 340 days in space, he has successfully completed every field test he's taken, with those tests designed to simulate what astronauts landing on Mars would experience. Part of Kelly's year-long mission in orbit consisted of experiments that will determine the program for landing humans on Mars in the future.
Scott Kelly's takeaways from his recent mission for a successful trip to Mars involve having a robust life-support system in place, protecting the crew from radiation and creating a propulsion system that reduces the trip time.
"Going to Mars is doable," Scott Kelly said during the NASA news conference that was also attended by his astronaut twin brother. "We're close enough that if we make the choice, I think we can do it."
Kelly's capsule landed upright on dry land, meaning he had to maneuver himself halfway out of the capsule before he could be helped out, but he's convinced that leaving the capsule would be easier on Mars due to the fact that the planet has less gravity.
Kelly estimates that during his near year on the International Space Station, he spent six months of that time in the personal crew quarters and talking on the phone, emailing, taking photos of Earth, reading and catching up on TV shows and movies. Those normal activities and keeping himself task-oriented each day were key to maintaining his sanity, he said. The craft that takes the inaugural crew to Mars will involve even tighter quarters than the ISS.
"If you're going to Mars in a smaller vehicle than the space station and living practically on top of one another, having that space that (the astronauts) spend so much time in is very, very important," Scott Kelly said. "You have to make it as perfect as you can, including the environment, air temperature, interfacing with the system, communication, entertainment and noise abatement because you're sleeping, living, exercising and eating right next to each other."
Dr. Julie Robinson, ISS program chief scientist, said that NASA would like to see 10 or 12 crew members with long-term data to be confident in knowing the risks and what's involved for a trip to Mars. Studying the data from all of the physiological and medical tests from Kelly's duration in space and the months after is just the first step in this direction.
Of the 450 investigations that took place on the ISS during Kelly's mission, 18 were research on human reactions and functions. The others covered everything from how stem cells and worms respond to space to technology demonstrations to the burning of various fuels and liquids.
These findings paired with Kelly's data, along with that from his brother, Mark, who served as the control on Earth in NASA's twins study, will help in addressing some of the concerns about the Mars mission.
Many of the concerns center on the well-being of the astronauts themselves: being confined in a small vehicle, medically taking care of astronauts who are so far from Earth, providing nutritious and long-lasting food, determining the right circadian rhythms for proper sleep and managing bone and calcium loss.
"Every body system you can imagine is impacted by spaceflight," said Dr. John Charles, Human Research Program associate manager for international science. "At the end of the ISS era, we can give our findings to the Mars mission program with how to keep our astronauts happy, healthy and performing at a high level for the duration."
After landing, Kelly was immediately carried to a medical field tent for testing and evaluation by flight surgeons. He said he felt great when he emerged from the capsule -- even better than after a previous six-month mission -- but is now starting the feel the effects of gravity once again.
"Adjusting to space is easier than adjusting Earth for me," Kelly said Friday. "I never felt completely normal up there, but coming back to gravity is harder than leaving gravity."
Kelly said his muscle soreness and fatigue is a lot greater than after his previous missions. He is also experiencing sensitive skin, which he described as almost a burning sensation, when he is sitting, lying down or walking. Kelly believes it is due to the fact that his skin hasn't touched anything for such a long time.
He also joked about not being able to throw and aim things the way he wants after getting used to letting go of things on the ISS and allowing them to float.
And as Kelly has said, the 1.5 inches he gained in height in zero gravity have already disappeared.
"Gravity pushes you back down to size," he said.
During his time in space, Kelly was a prolific user of social media and continues to post about what it's like to be back on solid ground. The popular posts have pushed his number of followers to over a million, but he won't take full credit for them. His longtime girlfriend and NASA public affairs officer Amiko Kauderer worked on them as a project with him.
"This was something we could share together and it made the experience more rewarding, rather than just our conversations on a daily basis," he said.
While his unique view of our planet captivated hundreds of thousands of people, it also gave Kelly an insight into the fragility of Earth.
"Earth is a beautiful planet. It's everything to us and important to our survival and the space station is a great vantage point to share our planet in pictures. But you also notice how fragile the atmosphere looks and it makes you more of an environmentalist after seeing that. We need to take care of the air we breathe and the water we drink. We do have an impact on that and the ability to change it if we make the decision to."
When asked if he's finished with missions to space, Kelly said that would be up to NASA, at least in part. He's flown multiple missions for the space agency -- and it's time to give other, talented astronauts a chance, he said. But he's hopeful for the future of commercial spaceflight and sees opportunities for himself in that field.
"I will never be done with space, I will always be involved," Kelly said. "I think everyone should be able to go to space. It depends on the person and what experience they would want. It would be great to have a variety of ways to get to space or near space for the view. Maybe in the next 20 years, you can buy a cheap ticket for a little visit."
He also highlighted the importance of focusing on space exploration.
"It's our future, helps the economy grow and improves technology. There are things we will discover about the ISS experience that we don't even know now. When the guys were walking on the moon, they were trying to develop more advanced computers and technology. They didn't know how important it would be in the future."