March 29 (UPI) -- Astronauts Nick Hague and Christina Koch continued work to upgrade the International Space Station's power system during a 6.5-hour spacewalk on Friday morning, the second spacewalk of the year.
During their time outside ISS, the duo attached circuitry for newly installed lithium ion batteries on the station's starboard truss. The pair also readied the truss for future power system upgrades.
NASA TV provided live coverage of the astronauts' work.
Astronaut Anne McClain was originally slated for the spacewalk as part of the first all female spacewalk, but NASA cancelled it Tuesday because the right size spacesuit for both women to complete the mission is not available.
Friday's spacewalk is the second this month. Last week, Hague and McClain swapped out three old nickel-hydrogen batteries and installed powerful lithium-ion batteries.
When McClain did the March 22 spacewalk, she found that the medium-size upper torso portion of the spacesuit fit her best -- the same size Koch needs -- but only one is available, NASA said.
This time, Koch is working with Hague to continue the battery replacement work. The new batteries will store power produced by two of the space station's solar arrays.
The process of swapping out old batteries for new ones began in 2017.
"The spacewalking work continues the overall upgrade of the station's power system that began with similar battery replacement during spacewalks in January 2017," NASA wrote in a blog update.
During today's spacewalk, Koch prepared the truss for the arrival of another six new batteries later this year. Hague managed the robotic repair operation to replace one of the previously installed new batteries, which has failed to hold a charge, with two old batteries.
Another spacewalk is planned for April 8.