A U.S. astronaut and a Russian cosmonaut are headed for a year in outer space, the longest stay ever at the International Space Station.
The two men and a second cosmonaut were aboard a Russian Soyuz rocket that blasted off Saturday from the Baikonur Cosmodrome in Kazakhstan, Russia's space launch facility. The rocket launched in the very early morning local time and docked at the space station about six hours later.
NASA astronaut Scott Kelly and cosmonaut Mikhail Kornienko, both in their early 50s, will stay at the space station until next March. Scientists hope to study the physical and mental effects of living in space as the men surpass the usual six-month stay at the station.
NASA will use the information learned from the mission to plan future expeditions to Mars that could last two to three years.
Astronaut Kelly's identical twin is participating in the study on Earth. Retired astronaut Mark Kelly will undergo the same tests that his brother is subjected to in space, giving scientists a basis for comparison.
Also aboard the Soyuz capsule was veteran cosmonaut Gennady Padalka, who will return to Earth in September after racking up 878 days in space over his career, more than any other person.
The three will join the crew already at the space station.
NASA missions to outer space have never lasted more than seven months. Russia holds the world record for sending a cosmonaut into space for more than a year in the mid-1990s. But that stay was aboard the now-defunct Mir space station, which was not as sophisticated as its newer sister.
The International Space Station is a research laboratory that flies about 418 kilometers above Earth. It is a project of 15 nations.