On Wednesday, Jan. 15, NASA astronauts Jessica Meir and Christina Koch will step outside of the International Space Station into the vacuum of space together. The duo will replace old nickel-hydrogen batteries with newer, more powerful lithium-ion batteries to continue upgrading station power systems on the Port-6 truss structure. The spacewalk is scheduled to begin at 6:50 a.m. EST and last about six-and-a-half hours.