Washington  - Two crew members aboard the International Space Station (ISS) began a space walk late Monday to collect science experiments attached to the outside of their orbiting home.

US Commander Mike Fincke and Russian flight engineer Yury Lonchakov used the Pirs airlock to leave the space station and begin a six-hour retrieval mission.

The pair is also scheduled to install a device to measure electromagnetic potential around the station's Russian-made module. The tests are part of an investigation of misfiring explosive bolts used to detach Soyuz capsules that have carried ISS crews back to Earth.

The spacewalk began at 0051 GMT Tuesday and is expected to be completed by around 0700 Tuesday, the US space agency NASA said. (dpa)