A historic spacewalk was scheduled to occur this week, with only women operating outside the ISS for the first time ever.
"These will be the 214th, 215th and 216th spacewalks in the history of International Space Station assembly and maintenance".
"Spacewalk assignments may be adjusted if the flight operations team deems it necessary", NASA writes on its website.
And then, it was canceled.
When McClain did a spacewalk with fellow astronaut Nick Hague on March 22, she discovered that the medium-size upper torso portion of the spacesuit fit her best.
Kristen Facciol of the Canadian Space Agency announced that she would be on console for the excursion. Soon after NASA astronaut Kathryn Dwyer Sullivan took the title as the first American women to undertake an extra-vehicular task during Space Shuttle Challenger mission.
There are six US spacesuit tops on the station - or hard upper torsos, as NASA calls them - with two considered spares. What they each need is "essentially the shirt of the spacesuit", a "medium-size hard upper torso".More news: New Zealand PM launches major inquiry into Christchurch attack
The road that leads to liftoff is a grueling one, no matter your gender.
On Earth a spacesuit can weigh up 280 pounds on the ground, without the astronaut in it.
"We've seen your comments about the spacesuit availability for Friday's spacewalk", the agency said in a Facebook post. Thus, she'll have the share the suit with Koch, who will wear the medium torso on March 29.
The plan is for the pair to lay out jumper cables between the Unity module and the S0 truss, at the midpoint of the station's backbone, during their April 8 spacewalk. While there are two medium suits on board, reps have stated it's more efficient to swap spacewalkers than to reconfigure the elements of the spacesuit.
Anne McClain and Christina Koch had been scheduled to install lithium-ion batteries at the International Space Station (ISS) on Friday.
Both McClain and Koch were members of NASA's 2013 astronaut class, 50 percent of which was made up of women, NASA said.
Perhaps this missed milestone will be a lesson for NASA to have the proper equipment prepared for crews of all shapes and sizes - something that is already important as human proportions often change as the spine lengthens slightly in microgravity. Experts say they are the assemblies of several parts put together as best adapted to each astronaut's body. NASA chose four women and four men that year.