U.S. and Russian medical experts will draw from seven broad areas as they establish a research agenda in early 2013 for a one-year mission aboard the International Space Station (ISS) flown by NASA astronaut Scott Kelly and Mikhail Kornienko, test cosmonaut from RSC Energia.

The ISS veterans were selected in late November by the U.S. and Russian space agencies to train for the long flight expected to launch in March 2015 and potentially reveal health or performance concerns for deep-space exploration by humans.

The flight, the first of its kind since cosmonaut Sergei Avdeyev returned from a 380-day mission to what was Russia's Mir space station in August 1999, will serve as a “checkpoint” for the studies now carried out on the multinational crews that spend 4-7 months aboard the six-person ISS, according to Julie Robinson, NASA's ISS program scientist, and Igor Ushakov, director of the Institute for Biomedical Problems in Moscow.

Kelly, 48, and Kornienko, 52, will be monitored closely for the emergence of health issues not seen in their previous shorter-duration missions—impairments that could influence discussions over expeditions to the Moon, a near-Earth asteroid and Mars. An expedition to Mars, the most challenging of those destinations, would require 2-3 years roundtrip, using current propulsion technologies.

The focus areas include an intracranial pressure rise blamed for blurred vision—a recent concern discovered by U.S. researchers and affecting one-third to one-half of astronauts logging an average of 108 days in space—as well as nutrition and bone loss. The latter, first noted among NASA's Gemini crews, appears to have been overcome through diet, adequate vitamin D intake and regular, vigorous, in-space, load-bearing exercise involving resistive exercise devices.

Other focus areas include degraded immune function; neuro-vestibular changes that affect astronauts as they re-adapt to gravity; behavior, performance and interpersonal interactions; radiation exposure; and the ability to retain preflight training on missions lasting many months.

The merits of a “checkpoint” mission have yet to fully emerge. There are no plans to repeat the marathon prior to 2020, the scheduled end of station operations agreed to by the U.S.-led, 15-nation ISS partnership.

“Virtually all research data for ISS are based on regular six-month missions. It is important that we continue to collect data at these intervals so that we can begin to draw statistically significant conclusions [from a significant sample size],” says Leroy Chiao, who commanded a 6.5-month mission to the ISS in 2004-05 and currently chairs the National Space Biomedical Research Institute's (NSBRI) user panel, a group of 20 former flight surgeons and astronauts that assesses research on space health issues.

The source of the blurred vision issue and an effective countermeasure, a new NSBRI focus, are among the issues in need of a significant sample size, he notes.

“A one-year mission would have some value,” Chiao says. “Data could be used to compare to extrapolations made from six-month flights.”

Russians account for all four space missions of a year or more, each flown on Mir between 1987 and 1999. Since then, the ISS has greatly advanced opportunities for peer-reviewed medical research, a factor in Russia's enthusiasm for undertaking at least one more marathon flight while the ISS is in orbit.

“We would like to renew this experience,” says Alexey Krasnov, director of piloted space programs for Russian federal space agency Roscosmos. “The time is short. There are many things we don't know in spite of the fact that we have a lot of experience in spaceflight.”

Kelly and Kornienko will face twice the usual 7% chance that one of them will require a minor or major medical intervention during their flight, yet another opportunity for lessons learned, according to Ushakov.

Nonetheless, Avdeyev; Vladimir Titov and Musa Manarov, who ended a 366-day stay on Mir in late 1988; and Valery Polyakov, who completed a world-record 438-day mission to Mir in 1995, are alive and well.

“Their health status is quite good for their age,” says Ushakov, whose institute keeps up with their status. “So, the flights that happened 13-24 years ago did not negatively impact their health.”

Kelly's three space flights include a 160-day ISS mission in 2010 in which he served as commander for much of the stay. Kornienko served as an ISS flight engineer in 2010. NASA expects to name a backup for Kelly within several months; Kornienko identified cosmonaut Sergei Volkov as his backup,

“It's definitely a challenge,” says Kelly, a retired U.S. Navy aviator. “It's fun when you are done with it, not while you are doing it. It's like climbing Mt. Everest, not the kind of fun you have riding a roller coaster.”

“It's a unique opportunity for me,” says Kornienko, an experienced climber who includes Mt. Kilimanjaro among his summits. “I'm very eager to do this. I understand it will not be easy.”