Enlarge / Cosmonaut Mikhail Kornienko climbs the stairs to enter the Soyuz TMA-16M spacecraft during the final check of the spacecraft, with NASA Astronaut Scott Kelly. (credit: NASA)

Eight months have passed since NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth from a nearly year-long mission aboard the International Space Station. During that time, the long-duration fliers completed a battery of follow-up tests, and US and Russian scientists have busily crunched away at data collected before, during, and after the extended space mission. Researchers plan to present preliminary results at a scientific meeting in January.

The one-year mission was just the beginning, however. NASA’s Human Research Program, which supports safe and productive space travel, has begun devising follow-up missions to ensure it knows enough about prolonged stays in microgravity before astronauts venture into deep space for extended periods of time. And as important as Kelly’s and Kornienko’s data is, a study with just two participants doesn’t allow scientists to draw meaningful conclusions.

“It’s just not enough,” said William Paloski, the director of human research program at NASA’s Johnson Space Center. “To extrapolate we need to have more time in space, and more observations. We started working on additional missions two years ago.” The question is how best to collect that additional data.