Today at 12:42 p.m. PDT/3:42 p.m. EDT, NASA astronaut Scott Kelly is scheduled to begin his year-long journey to the International Space Station — a voyage which, if successful, will surpass the U.S. record for longest-duration human spaceflight by more than 100 days.

Above: Scott Kelly sits inside a Soyuz simulator at the Gagarin Cosmonaut Training Center in Russia, March 4, 2015 | Credit: NASA

Joining Kelly aboard the ISS-bound Soyuz spacecraft are Russian cosmonauts Mikhail Kornienko and Gennady Padalka. Kornienko, too, will spend twelve months aboard humanity's orbital outpost, while Padalka will stay for six (the typical ISS mission lasts 4–6 months). In doing so, however, Padalka will set a record of his own, breaking the current record for total time in space with a cumulative mission time of nearly two and a half years.

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"Kelly and Kornienko will spend a year in space and return to Earth on Soyuz TMA-18M in March 2016," according to NASA. "By doubling the length of this mission, researchers hope to better understand how the human body reacts and adapts to long-duration spaceflight." Kelly's twin brother, retired astronaut Mark Kelly, will remain on Earth so that researchers can compare their physiologies before, during, and after Scott's year-long sojourn aboard the ISS.

"This knowledge is critical as NASA looks toward human journeys deeper into the solar system, including to and from Mars, which could last 500 days or longer," sez NASA.

Above: Mikhail Kornienko (top), Scott Kelly (center), and Gennady Padalka (bottom) wave farewell as they board the Soyuz TMA-16M spacecraft ahead of Friday's launch | Credit: NASA

Read more about today's historic mission here and here.