Moscow  - Two crew members aboard the International Space Station (ISS) opened the hatches to the vacuum Tuesday to set up a bio experiment outside their orbiting home.

US Commander Mike Fincke and Russian flight engineer Yury Lonchakov began the six-hour space walk at 7:20 Moscow time (4:20 GMT).

"We have an important and very interesting mission. Today we will set up European scientific equipment, also we will undertake repairs and photograph various parts of the ISS," Lonchakov was quoted by news agency Interfax as saying during an exchange with the mission control centre Tuesday.

The third ISS crew member, US astronaut Sandra Magnus will monitor the mission from onboard the space station.

"This is an unplanned sortie. It was added in order to successfully carry out an international experiment on the impact of cosmos on microorganism," a spokesman for the mission control centre in Star City oustide Moscow told Interfax. dpa