Two space travelers have been selected for a yearlong mission aboard the international space station.

NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko will be launched aboard a Russian Soyuz spacecraft from the Baikonur Cosmodrome in Kazakhstan in spring 2015. They will return to Kazakhstan only in spring 2016.

The main objective of this yearlong mission is to study the effects of zero-gravity on the human body and to find out how it adapts to extreme harsh conditions. The veteran crew will also be collecting data required for future human exploration of our solar system, announced NASA.

"Congratulations to Scott and Mikhail on their selection for this important mission," William Gerstenmaier, associate administrator for Human Exploration and Operations at NASA Headquarters in Washington, said in a statement.

"Their skills and previous experience aboard the space station align with the mission's requirements. The one-year increment will expand the bounds of how we live and work in space and will increase our knowledge regarding the effects of microgravity on humans as we prepare for future missions beyond low-Earth orbit," Gerstenmaier said.

Both Kelly and Kornienko have been skilled crew members. Kelly, a retired captain in the U.S. Navy, has served as a flight engineer on the space station's Expedition 25 crew in 2010 and as a commander of Expedition 26 in 2011. He has logged more than 180 days in space.

Kornienko from Russia was a former paratrooper officer who has trained as a space station Expedition 8 backup crew member. He has also served as a flight engineer on station's Expedition 23/24 crews, for which Kelly trained as a backup crew member. Kornienko has logged more than 176 days in space.

The two veteran spacefarers will begin a two-year training program from 2013 to help themselves prepare for the one-year mission. There has been a continuous human presence aboard the space station for the last 12 years. Until now, astronauts have been sent to the space station for a period of three to six months. This will be the first time that space travelers are sent on a yearlong mission. 

The space station is a research laboratory, orbiting some 250 miles above Earth. The space station is a joint project by space agencies from five different nations including NASA, Russian Federal Space Agency, the European ESA, the Japanese JAXA and the Canadian CSA, to carry out various research experiments.