Spacesuits are made of several components, but the issue for McClain was that the large-sized hard upper-torso was too big for her.
"In this case, it's easier (and faster!) to change spacewalkers than reconfigure the spacesuit", Schierholz said. The reason that McClain was pulled off the roster for the walk has to do with space suit availability.
McCain was the 13th women in Space history to complete a spacewalk and Koch will become the 14th.
This is obviously a rather disappointing development but, as NASA has warned in the weeks leading up to the spacewalk, plans often change rapidly. Last week, McClain tweeted a video of her performing a "loop scrub" on a spacesuit to keep its cooling system running correctly.
"I'm super disappointed about the all-woman spacewalk not happening as scheduled this Friday but I'm also super supportive of astronauts having the authority to say "I would be safer using a different piece of equipment", wrote Emily Lakdawalla, a senior editor at the USA non-profit The Planetary Society. She said two upper parts in each of the three available spacesuit sizes are now held at the space station: medium, large and extra large.
NASA opened the space program to female applicants in 1978.
Anne McClain and Christina Koch were scheduled to both walk outside the ISS to install new batteries.
In 54 years of spacewalking, women have only gone outside with men. "NASA looks forward to being able to celebrate the first all-female spacewalk, and other firsts for females in the future", Dean adds.
McClain is tentatively scheduled to perform her next spacewalk on April 8 alongside Saint-Jacques from the Canadian Space Agency.
NASA astronaut Anne McClain (R) poses during her final exam at the Gagarin Cosmonauts' Training Centre in Star City outside Moscow on November 14, 2018.
Christina Koch will be walking on space as scheduled on March 29, but not with another female astronaut.
When asked whether girls can be astronauts, US astronaut Anne McClain tweeted that while there are many obstacles on the journey to space, your gender isn't one of them.