Two humans are setting out toward the International Space Station (ISS) to spend 12 months in space aboard the low-orbit science lab.

NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko will board a Soyuz rocket in Kazakhstan Friday to attempt the longest stay ever recorded on the ISS. Cosmonaut Gennady Padalka will also board the ISS, but his tour is expected to last the standard six months.

Watch the launch LIVE via Space.com.

According to BBC News, the one-year tour on the ISS is part of the bigger picture mission to one day send astronauts to Mars. Kelly and Kornienko will provide important data on the long-term effects of living in a microgravity space such as the ISS.

"The last time we had such a long duration flight was almost 20 years and of course all... scientific techniques are more advanced than 20 years ago.'' Kornienko said in the pre-launch press conference. "And right now we need to test the capability of a human being to perform such long-duration flights. So this is the main objective of our flight - to test ourselves."

Some of the known effects of living for an extended period in time are bone loss and muscle atrophy, among others, NASA noted in a press release. But one of the more important points of study will be the psychological effect of living in relative isolation for 12 months.

Said Kelly in the press conference, "One of the differences here is that we're doing it as an international partnership, and if we're going to go beyond low-Earth orbit again, perhaps to Mars, because of the cost and the complexity it will most likely be an international mission, so we see this as a stepping stone to that."