In a little more than two months, American astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko will depart from Earth, not to return for an entire year. Their mission aboard the International Space Station will be the longest in more than a decade, twice as long as the normal six-moth stay.

As NASA continues to gear up for its next generation of manned deep space missions -- to the moon, asteroids and eventually to Mars -- scientists at the space agency are keen to better understand the long-term impacts of microgravity on the human mind and body.

According to NASA, the investigations "are expected to yield beneficial knowledge on the medical, psychological and biomedical challenges faced by astronauts during long-duration space flight."

Scientists will observe Kelly and Kornienko before, after and during their year-long mission in order to gain a better understanding of long-term isolation and exposure to microgravity -- including effects on behavioral health, vision, metabolism, physical stamina, microbiome makeup and more.

"What we don't know right now is what that six- to 12-month period looks like," Julie Robinson, NASA's space station program scientist, recently told reporters. "We're talking about it scientifically, but we're not really having deep discussions about it until we have the first information from the first two."

Astronauts with NASA have been calling for more one-year missions for some time now, but officials have been reluctant to plan additional 12-month stints.

"If we see something dramatic, that's going to change how everybody looks at having additional one-year missions," she added.

A recent study of space station astronauts showed that a six-month stay on ISS had a much more dramatic affect on the body's blood than previously thought. Returning astronauts showed a profound blood shift from the lower to the upper half of the body, and also had considerably lower blood pressure.

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Astronauts prepare for year-long stay on space station