In order to tell the astronauts apart, Koch's helmet camera views will bear the number 18 and Meir's will be number 11. Koch's spacesuit also has red stripes on it.
This will be the fourth spacewalk for Koch and the first for Meir. Based on their position on the platform, the astronauts will be able to see the Earth pass beneath their feet.
Upon watching the spacewalk begin, NASA astronaut Tracy Dyson said she hopes this is just the first all-female spacewalk and that it becomes a normal occurrence.
The first woman to conduct a spacewalk was Russian cosmonaut Svetlana Savitskaya in 1984, followed closely by NASA astronaut Kathy Sullivan. An additional 12 US women have conducted 40 spacewalks over the past 35 years. Koch and Meir will be 13th and 14th, respectively.
Koch and Meir spoke about women working in human spaceflight during a recent news conference.
"I think it's important because of the historical nature of what we're doing and that in the past, women haven't always been at the table," Koch said. "It's wonderful to be contributing to human spaceflight at a time when all contributions are being accepted, when everyone has a role and that can lead, in turn, to increased chance for success.
"There are a lot of people that derive motivation from inspiring stories from people that look like them and I think it's an important aspect of the story to tell," Koch said.
"What we're doing now shows all the work that went in for the decades prior, all of the women that worked to get us where we are today," Meir added. "I think the nice thing for us is we don't even really think about it on a daily basis, it's just normal. We're part of the team, we're doing this work as an efficient team working together with everybody else, so it's really nice to see how far that we've come."
Fellow NASA astronaut Drew Morgan, also currently on the station, tweeted in support of Koch and Meir during the walk.
"So proud of my astrosisters @Astro_Christina and @Astro_Jessica! We've been training together since our selection in 2013, and now they're out on a history-making spacewalk! #AllWomanSpacewalk"
Koch and Meir will be replacing a faulty battery charge/discharge unit that failed to activate after a spacewalk October 11, according to the agency. Because the unit is faltering, it's keeping newly installed batteries from providing an increase in power to the station.
The space station is powered by solar arrays and four sets of batteries. Luckily, the faulty unit hasn't changed anything for the astronauts or experiments on board. The unit regulates the charge in the batteries from the solar arrays as the station orbits at night around the Earth.
Once the unit is replaced, postponed spacewalks to replace the batteries can be rescheduled.
Although floating in space looks easy, astronauts say that spacewalks are one of the most physically challenging things they can do, according to NASA.
This is the second attempt at an all-female spacewalk after the first was scrapped in March.
"However, individuals' sizing needs may change when they are on orbit, in response to the changes living in microgravity can bring about in a body," Dean said. "In addition, no one training environment can fully simulate performing a spacewalk in microgravity, and an individual may find that their sizing preferences change in space."
Koch conducted the spacewalk with fellow astronaut Nick Hague instead of McClain.
When asked about spacesuit availability this time around, Koch said there are currently two medium spacesuits on board. After the first all-female plan was shifted, Koch configured the second spacesuit herself using what was available on board.
She and Meir have trained in medium-sized suits for the past six years.
Meir arrived on the space station for her first mission at the beginning of October. She shared an image of her hugging Koch after arriving.
"This is how it feels when in addition to your childhood dream being fulfilled by arriving to @Space_Station, you're greeted by your Astro-brothers and sisters on the other side of the hatch," Meir said in her tweet.
She and Koch have trained together for the past six years because they're members of the same astronaut class. Meir is set to spend more than six months on board the station.
The upcoming spacewalks will help replace solar array batteries and upgrade them to lithium-ion batteries, as well as refurbish the Alpha Magnetic Spectrometer, a scientific instrument "that explores the fundamental nature of the universe," according to NASA.