During the first spacewalk of the series, on March 22, McClain became the 13th woman to perform a spacewalk. And, while the comfort and safety of the astronauts remains the most important aspect of any space mission, this last-minute reassignment seems to highlight the reality that many women will have to overcome additional career roadblocks working in a world created to accommodate men.
The spacewalk is still set for Friday, though the work of installing lithium-ion batteries on the station's solar panels will continue with NASA astronauts Nick Hague and Anne McClain switching places.
In response, NASA declared that it was faster and safer to swap astronauts, rather than reconfigure a suit to properly fit Koch, seeing as there wasn't another size medium readily available.
McClain worked with both the medium and small suits during training sessions on Earth and initially believed the larger suit would work well for her.
Given that they are outside, in the unsafe environment of near-Earth orbit, for over 6 hours, with no break, the astronauts being comfortable with the equipment they are using is extremely important for their safety.
"Gee, if you ever hoped to do another spacewalk, it would pay to do the first one really well", Sullivan said about her focus on the mission.
She will wear the medium-size suit used by McClain on a spacewalk with Hague last week.
Anne McClain shared this on Twitter, a brilliant image of her in space, and it just makes me want the all-female walk that much more.
She said not having enough spacesuits available to fit women was a problem years ago, "and obviously nothing has changed".
For safety reasons, she had no choice but to pull out and be replaced, due to the length of time it would take to produce the new spacesuit.
NASA spokesperson Stephanie Schierholz elaborated in an email to Gizmodo.com's George Dvorsky. However, after completing the walk, she noted how hard it was to maneuver in the large suit and requested a medium suit for this week's spacewalk. "It would take hours of crew labor - not to mention some additional risk - to fix that in time" for Friday's mission.
McClain will still get to do another spacewalk on April 8, NASA said, but she'll also be joined by a male astronaut.
McClain, Koch and Hague are part of NASA's Astronaut Class of 2013, the only time there have been the same number of women accepted as men.
Delaying the spacewalk would pose other schedule challenges as well.
NASA said in a statement: "Koch had been scheduled to conduct this spacewalk with astronaut McClain, in what would have been the first all-female spacewalk".