American astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko mark the halfway point of on Tuesday, Sept. 15.

The year-long literal trip around the world will study the physical and mental effects of sustained time in space. Kelly's identical twin, retired astronaut Mark Kelly, is also being examined as part of the research to determine the subtle impact of space flight on individuals with the same genetics.

On Monday, Sept. 14, Scott Kelly said during a NASA press conference that he feels “pretty good overall.”

"I definitely recognize that I've been up here a long time and have just as long ahead of me. But I feel positive about it. I think if I manage my work, pace of work, and energy right I'll have enough in the tank to get to the end. I'm pretty sure I will,” he said. "… But there are a lot of effects of this environment that we can't see or feel, like bone loss, effects on our vision, effects on our genetics, our DNA, RNA and proteins, things like that. And that's why we're studying this, myself and Misha, on this one-year flight."

As part of Scott Kelly's year among the cosmos, he has served as the unofficial photographer of the International Space Station, delighting Earth-bound followers with his one-of-a-kind images. Occasionally he zooms in on certain locations, such as Soldier Field, the home of the Chicago Bears, as he did at the start of the NFL season. Other times, he turns his lens on the weather, such as Tropical Storm Grace, shown at the beginning of the slideshow above, or on atmospheric phenomena, such as the Aurora Borealis.

See these and other images from his 170-odd days in space in the slideshow above.

On the ground on Monday, Mark Kelly said the mission will help determine the physiological and mental-health challenges that stand in between today's understanding of sustained space flight and what would be needed to send a manned mission to Mars.

Using the current technology — a traditional chemical rocket engine — it could take six months to reach Mars, he said, meaning astronauts would need to plan for a three-year round-trip to the Red Planet. Currently, there's a good bit of data on what happens to the human body after six months in space, but we're limited beyond that period, he explained.

As far as when this maiden voyage to Mars might be, Mark Kelly told the assembled crowd at the press conference that we could develop the technology for the trip. The limiting factor is the “public desire to do it.”

NASA astronaut Terry Virts, who just returned from a 200-day mission aboard the International Space Station, echoed this. “It could be done in a decade or two, but it's more a question of political science than it is rocket science,” he said.

Watch a full video of the press conference .

MORE: The ESO's Best Space Photos of the Week

Resembling an optical illusion or an abstract painting, stars arc around the south celestial pole in this time-lapsed photo, taken at the European Southern Observatory's La Silla Observatory in Chile. Each week, the ESO releases its favorite image of the week — click through to see the highlights. (ESO/A.Santerne)