Spacewalking astronauts upgrade antenna

Russian astronauts have replaced an antenna on the International Space Station in a spacewalk that lasted for more than four hours.

Cosmonauts Alexander Misurkin (L) and Anton Shkaplerov successfully replaced ISS electronics. (AAP)

Spacewalking Russian astronauts have replaced an electronics box as part of an antenna upgrade at the International Space Station, tossing the old unit overboard as a piece of junk.

Commander Alexander Misurkin used both gloved hands to shove the obsolete device away from the Russian side of the orbiting complex. The bundle - bearing white insulation, with straps dangling - tumbled harmlessly away, high above the North Atlantic.

"There it goes," NASA's Mission Control reported from Houston. The 27kg box - measuring less than a metre - was hurled in a direction that will not intersect with the space station, according to NASA officials.

With the obsolete unit finally out of the way four hours into the spacewalk, Misurkin and Anton Shkaplerov set about installing the new electronics box. Once everything was hooked up, Russia's Mission Control declared the revitalised communication system in good shape.

Original to the 400km-high outpost, the antenna and associated equipment have been up there since 2000. The new electronics box will improve the communications with Russia's Mission Control outside Moscow.

The discarded electronics box will re-enter the earth's atmosphere and burn up. Mission Control said it did not know when that will occur.

The space station is home to two Russians, three Americans and one Japanese.