BAIKONUR, Kazakhstan (AP) — American astronaut Scott Kelly and Russian counterpart Mikhail Kornienko blast off early Saturday to begin a year away from Earth.

Gennady Padalka of Russia also is to be aboard the Soyuz space capsule; he is scheduled for the standard six-month tour of duty aboard the International Space Station.

The trip is NASA's first stab at a one-year spaceflight, anticipating Mars expeditions that would last two to three years.

The Soyuz sets off from Russia's manned space launch facility on the steppes of Kazakhstan and docks with the space station hours later.

Kelly's identical twin Mark, a retired astronaut, agreed to take part in many of the same medical experiments as his orbiting sibling to help scientists see how a body in space compares with its genetic double on Earth.