Two astronauts of the International Space Station walked in space Tuesday to set up a biology experiment outside the orbiting laboratory and fix a docking port.

American Michael Fincke and Russian Yuri Lonchakov reinstalled the European Space Agency's Expose R biology experiment container. Plant seeds and spores of bacteria and fungi inside the container will be exposed to weightlessness, sun rays and temperature extremes for 18 months as part of a scientific study to determine if life forms originated on Earth or in outer space.

The experiment failed to activate in December due to an electrical glitch and had to be fixed inside the space station.

To ease the docking of the U.S. Space Shuttle Discovery on Wednesday and other spacecraft in the future, Fincke and Lonchakov cleared straps in the docking port. They also repositioned a Russian biology experiment and photographed the Russian portion of the space station for study by structural engineers.

The tasks were completed in four and a half hours, about 90 minutes ahead of schedule.