Video: Narrated preview of Jan. 6 spacewalk

After four years of brainstorming, custom tool development and training, two astronauts plan to venture outside the International Space Station Friday for the first of four spacewalks to repair a $2 billion cosmic ray detector. The excursions are considered the most challenging since work to service the Hubble Space Telescope.

Astronauts Terry Virts and space station commander Barry “Butch” Wilmore ventured back outside Sunday for their third spacewalk in eight days to complete initial preparations for upcoming dockings by commercially developed Boeing and SpaceX crew ferry ships.

This is a narrated animation previewing the steps and activities to be performed by the International Space Station astronauts during the battery replacement spacewalk on Jan. 13.