An American astronaut and a Russian cosmonaut began a record-setting year in space Saturday, entering the International Space Station for a mission designed to study the long-term effects of zero gravity on the human body.
Scott Kelly and Mikhail Kornienko headed toward the station on a Russian Soyuz rocket that took off from Kazakhstan. They were accompanied by another Russian cosmonaut, Gennady Padalka, who is starting a six-month stay, the length of a typical mission.
"Huge thanks to all that made this beautiful launch possible," Kelly tweeted.
The U.S. space agency NASA said data from Kelly and Kornienko "will be used to determine whether there are ways to further reduce the risks on future long-duration missions to an asteroid and eventually Mars."
Kelly has a twin, former astronaut Mike Kelly, and other studies will be done to "compare data from the genetically identical Kelly brothers to identify any subtle changes caused by spaceflight," NASA said on its blog.
Conditions to watch out for include bone and immune system weakening and vision loss.
The three men joined three other crew members already at the space station: U.S. astronaut Terry Virts, Russian cosmonaut Anton Shkaplerov and Italian Samantha Cristoforetti.
NASA has been posting about the nearly yearlong mission on Twitter using #YearinSpace. In addition to photos and videos, NASA has shared facts about the expedition, including that Kelly will drink a total of 730 liters of recycled sweat and urine while in space. The agency says recycling urine is a necessity because water is "a precious and limited resource in space."
This will be the first time anyone has spent a year at the International Space Station, though several Russian cosmonauts stayed that long or longer aboard the Mir space station in the 1990s.
Russian cosmonaut Padalka, meanwhile, will be setting a record of his own, logging the most days in space of any person by the time he returns to Earth in September.
The International Space Station is a research laboratory that flies more than 400 kilometers above the Earth. It is a project of 15 nations.