Astronauts aboard the ISS have been working on upgrading the batteries outside the space station for a few years. The task is much more complicated than it may sound because of the need for astronauts to wear spacesuits and work outside the space station. The replacement battery program took eight years of research and development and 14 spacewalks to replace the aging batteries that store electricity generated by the ISS solar panels.
NASA says the new battery upgrade will help continue research aboard the ISS, which has been operating for two decades of continuous human presence. One of the challenges of changing the ISS batteries is that the space station orbits the earth at 17,500 miles per hour. That means every 45 minutes, the station enters sunlight and returns to darkness.
During its time in the sun, the massive solar arrays attached to the space station truss structure store power in the batteries. Each time the station crosses the “Terminator line,” which is the point where it passes between day and night. The batteries provide stored power to the space station to power everything from life support systems down to the vacuum used for cleaning inside during the night.
The primary power system originally used nickel-hydrogen batteries for electricity storage. The ISS Program began conducting a preliminary risk and feasibility study to evaluate the use of lithium-ion batteries in 2009. The program was approved in 2011, and production of the new batteries started in late 2014.
NASA and crew aboard the space station began replacing aging batteries with new lithium-ion batteries in December 2016. The new batteries were sent to the space station aboard a Japanese H-II Transfer Vehicle cargo spacecraft over four flights. Since then, 13 different astronauts have conducted 14 spacewalks upgrading the batteries. NASA says the primary power system has now been fully upgraded to lithium-ion technology.