Two Russian cosmonauts and an American astronaut on Wednesday boarded a Soyuz space capsule in preparation for their return to Earth after spending six months at the International Space Station.

Yelena Serova, Alexander Samokutyaev and Barry Wilmore said farewell to their three crewmates who are staying at the orbiting lab, and floated into the Soyuz, closing the hatch behind them at 3:36 pm Eastern time (1936 GMT).

The Soyuz will undock from the space station at 6:44 pm (2244 GMT), then perform an engine burn a couple of hours later to help the spacecraft drop out of orbit.

Aided by a parachute, the spacecraft is expected to land on a snow-covered steppe in Kazakhstan at 10:08 pm (0208 GMT Thursday).

The trio left Earth on September 26. They spent 167 days in space and traveled more than 70 million miles (112 million kilometers) during that time, NASA said.

The next crew launches from Baikonur, Kazakhstan on March 28.

The men on board will be US astronaut Scott Kelly and Russian cosmonauts Mikhail Kornienko and Gennady Padalka.

Kelly and Kornienko will stay at the research outpost for an entire year instead of the usual six months, "collecting valuable biomedical data that will inform future deep space, long-duration missions," NASA said.