NASA plans to conduct its first all-female spacewalk later in March during Women's History Month.
NASA didn't originally intend to make the March 29 spacewalk historic, a spokesperson told HuffPost.
McClain launched to the International Space Station in December for Expedition 58 and will continue on Expedition 59's crew.
There have been 213 spacewalks at the ISS since 1998 for the purposes of maintenance, repairs, testing of new equipment or science experiments, according to Nasa.
Fewer than 11% of the more than 500 people who have been to space have been female, and spacewalk teams have either been all-male or male-female.
"The March 29 spacewalk will be the first with only women", NASA spokeswoman Kathryn Hambleton said, hedging that "assignments and schedules could always change".
Both were members of NASA's 2013 class of astronauts, where four of the eight members were female, and traveled to the ISS over the previous year as part of expedition 58 and 59, respectively. "It is the second in a series of three planned spacewalks".
Koch and McClain's spacewalk is set to last for about seven hours and will be broadcast on NASA TV. She happens to be the Canadian Space Agency Controller and will be stationed at the Nasa's Johnson Space Centre in Houston.
A spacewalk, also known as "extravehicular activity" (EVA), is a broad term that applies to any time an astronaut exits a vehicle while in space.
Nasa has kept the world on its toes by announcing that they have organized and will execute an All woman Space Walk on the 29th of March 2019. This is going to be the first time in space for McClain and the first spaceflight for Koch.