Sept. 15, 2015

— One hundred seventy one (171) days ago, NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko launched on the first (almost) year-long mission aboard the International Space Station.

On Tuesday (Sept. 15), they had another 171 days to go. Not that anyone in space was counting.

"I hope I do not get to the point where I start counting the days," said Kelly in an NASA interview a few days before reaching the halfway point of his and Kornienko's mission. "Every day in space is a great day."

The pair — two out of the station's six Expedition 45 crew members — are set to come home March 3, 2016. They are spending 342 days in space to gather data about how their bodies react and adapt to long duration spaceflight in preparation for sending astronauts further out into the solar system.

Enlarge and view the video in new pop-up window. (NASA)

"I think that the legacy of this mission will be based on the science of having us in space for a year, the great data we collected, what we learned about being in space for this long and how that will help [us on] our journey to Mars someday," Kelly said.

"I hope very much our work during the year here will be of help to the next generations," Kornienko added.

During their six months in orbit so far, Kelly and Kornienko have participated in a range of scientific experiments that have focused on seven key areas of human research.

"A lot of the studies we are doing [are] on longer duration spaceflight than we've done before," Kelly noted during a live downlink with the National Press Club in Washington, D.C. Monday (Sept. 14). "This is an incredible facility that we have; the station has a lot of capability to collect data on us."

"We have an ultrasound [and] we have these devices that measure our vision. Next week we are going to do a lot of this imaging and data collection in a Russian device that pulls the blood down toward our feet," he described. "From these experiments we'll hopefully find out if there are any cliffs out there — if our vision gets significantly worse [for example], maybe after nine months or a year."

Astronaut Scott Kelly takes medical measurements as part of the Fluid Shifts investigations along with Russian cosmonaut Mikhail Kornienko, left, and cosmonaut Gennady Padalka. (NASA)

Typically, the astronauts and cosmonauts spend about six months on board the station, for which almost 15 years of data has been collected. Russian cosmonauts have spent more than a year in space before, but that was more than a decade ago.

"Even though the Russians have flown on the Mir station for a year or longer, they did not have the technology we have to figure this out," Kelly explained. "The International Space Station is also a great experiment in sustainable energy and life support equipment, and understanding how that works and how we can maintain ourselves with these systems for longer periods of time."

"Those things are going to help us go to Mars, someday, hopefully in the not too distant future," he said.

Part of the scientific studies involve Kelly and his identical twin brother, retired NASA astronaut Mark Kelly. The full analysis for the 'twins study' will begin at the conclusion of the mission once all samples have been collected.

"One thing I found somewhat interesting — maybe not too unexpected — is our microbiome, you know the stuff that is inside of us that's not us. We've more cells of bacteria that we carry around with us that isn't part of our body but they just live inside of us. One of the investigators told me that while I was up here that she found it interesting that my brother's and my microbiome are completely different," Kelly said. "I guess that it is not that unexpected because we do live separate lives, but it was kind of an interesting factoid, I guess."

"From what we understand from some of the researchers," added Mark, who was also at the press club on Monday, "one of them recently said that they're going to have more information on Scott and I — on our molecular and genetic information — than any other human ever."

This commemorative patch represents the historic, first yearlong mission on board the International Space Station. (AB Emblem)

Now at the halfway point of their space mission, Kelly and Kornienko said they were feeling good to push on.

"As far as physically, I feel good," Kelly shared. "We have some pretty good exercise equipment up here, 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 what we're studying, myself and Misha, on this one-year flight."

"I understood it is going to be challenging and it is going to be tiresome," Kornienko said. "This is not a resort, this is a workplace. At the same time, it's incredibly fun, difficult, amazing and beautiful, because not many people have the honor to be working in this amazing structure."

"I am trying not to think about March yet because we still are about just one half of the mission," he added. "When it is getting closer, then maybe we will start thinking about returning. Right now, we're just working."

"I definitely recognize I've been up here a long time and I have just as long ahead of me, but I feel positive about it," said Kelly. "I think if I manage my work, my pace of work and energy right, I'll have enough in the tank to get to the end. I'm pretty sure I will."