Three astronauts are due to land on Earth Friday after almost six months on board the International Space Station (ISS), the Russian flight control centre said on its website.

The landing capsule Soyuz TMA-22 carrying Russians Anton Shkaplerov and Anatoly Ivanishin and American Dan Burbank is due to separate from the ISS at 0818 GMT and land in the steppes of Kazakhstan at 1145 GMT, it said.

The three men will be replaced by a new crew due to take off May 15 from Russia's Baikonur cosmodrome in Kazakhstan to join current crew members Russian Oleg Kononenko, Don Pettit of the US and Andre Kuipers of the Netherlands.

The ISS, which orbits 350 kilometres (about 219 miles) above the earth's surface, is permanently occupied by a group of international researchers.

It circles the earth every 90 minutes traveling at 28,000 kilometres per hour.