Two Russian astronauts on the International Space Station successfully completed a six-hour spacewalk, Russia's mission control said on Wednesday.

This was the second spacewalk in a week for commander Sergei Volkov and flight engineer Oleg Kononenko, who successfully fitted a docking target to the Zvezda module to allow a Russian research lab, scheduled for delivery next year, to be attached to the ISS.

The crew attached an apparatus to the Zvezda module for a new geophysical experiment designed to predict earthquakes and retrieved hardware used in previous scientific tests.

On July 11 Volkov and Kononenko, part of the 17th Expedition, made a daring exit to repair the Soyuz descent capsule, the pair removed an explosive bolt, thought to be responsible for recent reentry problems and bumpy landings on flights back to Earth.

The third crew member, U.S. astronaut Greg Chamitoff, once again had to spend the entire six hours sealed in the Soyuz capsule.

The ISS crew is scheduled to increase from three members to six in May 2009.