"Leaving this amazing facility is going to be tough because I'll probably never see it again, and I don't expect I will," Kelly told CNN Chief Medical Correspondent Dr. Sanjay Gupta in his final round of interviews from space. "I've flown in space four times now, so it's going to be hard in that respect, but I certainly look forward to going back to Earth. I've been up here for a really long time and sometimes, when I think about it, I feel like I've lived my whole life up here."
In recent weeks, Kelly has been in the process of finishing his collection of samples, some of which will return with him in the Soyuz capsule when it lands near Kazakhstan next week. He's also been packing up because, even though there is limited space in the capsule -- it's nearly 23 feet long and nearly 9 feet in diameter -- astronauts can bring 1½ kilograms (about 3 pounds) of items back with them. Most of Kelly's items will be personal items that were given to him before he launched on March 27, 2015. The astronauts can also send other items back via SpaceX cargo spacecraft
One unexpected carry-on making that return trip? Garbage.
"We actually return garbage on the SpaceX too," Kelly said. "We've got to get rid of the stuff on the space station somehow. So we do have a pretty significant capability to bring back stuff on SpaceX that you might not imagine."
Final checks, last looks
Even though Kelly has participated in multiple missions to space, preparing for the hard landing back on Earth is key. Last week, Kelly and his one-year crewmates, cosmonauts Mikhail Kornienko and Sergey Volkov, did a fit check wearing pressure suits in the Soyuz capsule. The seats inside have liners that are customized to fit each astronaut's body.
"We checked them to make sure that they were still going to protect us if we needed to use them," Kelly said. "We have some kind of on-orbit training that covers the descent procedures, so we're fresh with those. We talked to the specialists on the ground about all operations from the time we close the hatch until the time we get pulled out of the Soyuz. So, it's a pretty busy time. It's important, clearly, when you're coming back from space that we get everything right."
Kelly's followers on Twitter
-- over 900,000 at the moment -- will no doubt miss his shared daily views from space that showcase different parts of Earth. He has captured spectacular events like snowstorms and even the Super Bowl from space, but Kelly has also witnessed Earth's fragility.
"This past summer you could notice the drought in California clearly and the fires," Kelly said, when asked about water levels on our planet. "Today we had this incredible pass over the Himalayas, and to just see all that pollution that's just kind of riding up against those mountains from the south, it's kind of heartbreaking to see that."
During his year on the space station, Kelly has been part of a twin health study comparing his condition, with the mental and physical toll of zero gravity, with that of his twin brother, retired astronaut Mark Kelly, who is on Earth.
The data collection for the twin study goes on for three years, said Julie Robinson, NASA's chief scientist for the ISS. The medical tests are measuring the impact of zero gravity on bone density, vision, the microbiome, blood, heart and cells, as well as the psychological impact on mood, stress and cognitive functions.
"For example, your bones take a long time to return to bone density. We don't know whether Scott will have lost bone or not," Robinson said.
Many of Kelly's samples will still be on the ISS until April, when they return on a SpaceX flight. Then the real work begins for lab assistants who will spend the next year analyzing the data.
Another part of Kelly's mission has served as preparation for NASA's future plans to land humans on Mars. Kelly even watched "The Martian" in space.
"There were a lot of parallels with that movie to living in space for a long period of time, including growing things in an extreme environment, which we recently finished up doing," Kelly said.
Life after landing
When Kelly lands, Kazakhstan's military search and rescue will quickly retrieve him and his fellow space travelers from the re-entry capsule. They will immediately receive a medical checkup from a flight surgeon and then carry out a set of tasks called field tests to mimic a landing on Mars, Robinson said. It's comparable to completing a time-sensitive obstacle course.
"A Mars landing makes a space landing look like a walk in the park," Robinson said. "You drop like a stone on Mars compared to how you land on Earth. We want to simulate and understand what would happen if they had just spent nine months on Mars."
Kelly will have to readjust to Earth's gravity while connecting valves and hoses, practice getting up after falling down and assess his own dizziness. Most astronauts have sensory motor deficits as their inner ears begin readjusting to Earth's gravity, and that can be disorienting, Robinson said. NASA wants to make sure that the astronauts can carry out all of the post-landing steps safely.
Kelly will also endure extra biomedical testing and continue post-flight data collection after taking a charter flight from Kazakhstan to Houston. There will be final post-flight tests 30 days after landing, as well.
Kelly's return to Earth will take less than 3½ hours. The Soyuz capsule is designed to shed heat as it re-enters the atmosphere, losing two-thirds of its mass when it reaches 400,000 feet above the Earth. The capsule will appear to streak across the sky, moving at 755 feet per second. Fifteen minutes before landing, four parachutes will release in an effort to dramatically slow it down, followed by a main chute that will slow the descent to 24 feet per second, then 5 feet per second just before landing. One second before, two sets of three engines will fire to soften the landing.
"I'm looking down at the Earth right now and it's 250 miles below me, and only a small portion of that is the atmosphere," Kelly said, when asking about preparing for re-entry. "And when that Soyuz hits that atmosphere going 17,500 miles an hour, a lot of things have to happen just right to make sure we touch down and parachute safely. So when you look at that big space between us and the speed involved, it's pretty serious. And it's something that you definitely think about and consider. But it's my second time flying the Soyuz, my fourth time flying in space. It's something I signed up to do, and we'll be ready for it next Tuesday."
CNN's Samantha Bresnahan and Debra Goldschmidt contributed to this report.