A historic spacewalk was scheduled to occur this week, with only women operating outside the ISS for the first time ever. News of the event was revealed earlier this month when a flight controller tweeted about the schedule, but as NASA noted at the time "assignments and schedules could always change." Now that has happened, as the second of three planned spacewalks will instead be performed by a man and a woman, Nick Hague and Christina Koch.
According to NASA, last week when Hague performed the first operation with astronaut Anne McClain, there was an issue with the fit of McClain's spacesuit. In what is essentially the "t-shirt" area of the Enhanced EMU suit astronauts wear on spacewalks, the Hard Upper Torso (H.U.T.) comes in three sizes: Medium, Large and XL. McClain had trained in both the medium and large sized units, but discovered that the medium size worked better for her. According to a spokesperson, there are two medium-sized units onboard, however only one can be ready in time, so Koch will go with Hague instead and history will have to be made another day.
While there's some confusion over how this could happen, it seems like there are a few issues going on. Of course astronauts are measured extensively before their trip, but there is no way to simulate the extended effects of zero gravity on their body and earlier this month McClain tweeted that she's grown by two inches since launch.
Earth will learn a lot during his busy week on @Space_Station - today he kept me company while we checked our suit sizing to account for space growth (I am 2 inches taller than when I launched!), then we did some translation adaptation. pic.twitter.com/A89tJauyQu— Anne McClain (@AstroAnnimal) March 4, 2019
As a NASA spacesuit engineer explained on Quora, the suits are modular and able to adjust between many different fits for whoever will be wearing them, and in a best case scenario, are set up for an "optimal size" for the astronaut. However that's not always possible, so someone may have to wear a suit set up for someone else, or a part may not be available on the space station.
In this case, they do have the equipment, and the suits can be reconfigured. However as described in the NASA spokesperson's tweet the team decided to swap spacewalkers instead of adjusting the various parts on the suit around a new torso.
We've seen your tweets about spacesuit availability for Friday's spacewalk. To clarify, we have more than 1 medium size spacesuit torso aboard, but to stay on schedule with @Space_Station upgrades, it's safer & faster to change spacewalker assignments than reconfigure spacesuits. pic.twitter.com/tPisBHaF2p— NASA (@NASA) March 26, 2019