KOROLYOV (Moscow Region), December 23 (RIA Novosti) - Astronauts aboard the International Space Station successfully completed their spacewalk on Tuesday, Russia's Mission Control said.

The ISS commander American Michael Fincke and Russian engineer Yury Lonchakov, who arrived on the orbital station in October, closed the hatch to the Pirs docking station at 09:29 a.m. Moscow Time (06:29 GMT). The spacewalk, which was delayed by 37 minutes after last-minute pressure checks, lasted almost six hours.

During the spacewalk Lonchakov and Fincke, who wore Russian-made Orlan spacesuits, installed a Langmuir probe on the ISS dock to measure electromagnetic fields in an attempt to solve a problem with Soyuz landings.

Some analysts have said that these fields may have been a factor in the steeper-than-normal reentry of Soyuz capsules in April and October last year, which raised concerns of the safety of the landings.

The pair installed a device, as part of European Space Agency's EXPOSE-R experiment, on a platform of the Zvezda module to test the effects of space on a number of materials.

The astronauts also removed the second of three BIORISK-MSN experimental containers, which were installed externally in June 2007 and are designed to study the effects of space on bacteria.

It was Lonchakov's first spacewalk while Fincke has participated in five previous walks.