This morning, NASA astronauts Peggy Whitson and Shane Kimbrough will take a stroll outside of the International Space Station to help upgrade the orbiting lab’s power systems. Specifically, the duo are going to help swap out the old nickel-hydrogen batteries the ISS has been using with new, more efficient lithium-ion batteries. The duo are veterans of venturing out into space, as today’s journey will mark Kimbrough’s third spacewalk and Whitson’s seventh. Their trip also will be the first of two spacewalks this month to install the batteries on the ISS.

A lot of the preparation for this battery swap has already been done

Fortunately for the two astronauts, a lot of the preparation for this battery swap has already been done. Six lithium-ion batteries and six adaptor plates were launched to the station at the end of last year on a Japanese HTV cargo vehicle. NASA likes the new lithium-ion batteries because they have lighter mass, making them easier to get to orbit, and they’re supposed to last much longer than the older batteries. So one battery and one plate will be used to replace one pair of the old nickel-hydrogen batteries near the station’s solar panels. A data-link cable will connect each adapter plate and battery pair, and the plates will also be used to store some of the old batteries that won’t be used anymore.

Additionally, everything is more or less in position for today’s walk. On New Year’s Eve, teams on the ground remotely controlled Canada’s robotic arm and a robot called Dextre, moving many of the old nickel-hydrogen batteries out of the way and getting the new lithium-ion ones in the right spot for installation. These robotic operations were meant to help cut down considerably on the number of spacewalks needed to perform the full battery operation. “When we go outside, [spacewalks] are one of the most dangerous things we do as a program,” Kenneth Todd, the ISS Operations Manager, said at a press conference. “So any time we can use station assets that are not the crew to go do a task, then that’s certainly something we want to endeavor to do.”

The ground crew used Dextre to remove the new batteries from a storage pallet that was carried to the station in the HTV cargo spacecraft. That same pallet will be used to store some of the old nickel-hydrogen batteries, too. Eventually the pallet along with nine old batteries will be destroyed when the HTV cargo vehicle leaves the station and burns up in Earth’s atmosphere.

Today, Whitson and Kimbrough’s jobs are mostly to install the new batteries and plates by bolting them down and attaching the data cables. They’ll also store some of the old nickel-hydrogen batteries on top of the new adaptor plates. The entire operation should take about 6.5 hours, the standard duration for spacewalks. Once they’re finished, it’ll be time to prep for next week’s trip, in which Kimbrough and French astronaut Thomas Pesquet will complete the rest of the battery installation.

But once that’s over, the full battery swap on the ISS isn’t truly done

But once that’s over, the full battery swap on the ISS isn’t truly done. The station’s eight power channels each use three strings of batteries, and each string has a pair of nickel-hydrogen batteries. So this months’ installation is only replacing a fraction of the full battery supply. NASA still has a few more sets of lithium-ion batteries and adaptor plates it needs to send up to the station for replacement. It’s a process that’s going to take a couple of years, with the next set of batteries slated to be installed later this year.

Things get underway this morning when Whitson and Kimbrough exit the station around 7:10AM ET. You can watch the entire spacewalk on NASA TV, embedded above.