Meanwhile, in Russia, Kornienko's wife wept at the news. The 52-year-old cosmonaut, a rocket engineer with one daughter, said he initially had some doubts about taking on such a challenge. He previously spent six months in space.
"A year is a serious time," Kornienko said in Russian. But he said his doubts did not last long, "and actually it was my initiative."
Kelly was among four astronauts on NASA's short list for the assignment. Each had served as a commander aboard the space station, and was able to perform spacewalks and robot arm operations. Medical information also went into the selection: A crew member could not have exceeded his limit for exposure to cosmic radiation, for instance.
Kelly said he has no idea how or why he ended up being chosen. He will set a U.S. space endurance record with this mission. No American has spent more than seven months in space at a time.
Russia, on the other hand, already has experience with yearlong space travel. But it's limited to the old Mir space station and more than a decade has passed.
Four Russian cosmonauts have spent at least one uninterrupted year in space. Another two came close.
The world record — 14 months in a single mission — is held by Dr. Valery Polyakov.
"They all are alive and well today. Their health status is quite good for their age," said Dr. Igor Ushakov, director of the Institute for Biological Problems in Moscow.
Ushakov warned that the medical risks will be at least double what they are on the more typical six-month mission.
NASA space station program scientist Julie Robinson expects the two men to come back just fine. They will watch an assortment of multinational crews come and go during their tenure; up to six people live on the orbiting outpost at any one time.