This was supposed to be a history-making week for NASA, with the first all-female spacewalk originally scheduled to take place on Friday. Unfortunately, a last-second swap has led to one of the expected participants, Anne McClain, being replaced by a fellow ISS resident Nick Hague.
NASA's explanation was that McClain would not have a space suit available to her for the spacewalk due this sizing, since Christina Koch will be wearing the medium-sized suit that McClain wore during her previous spacewalk last week. This left a lot of people scratching their heads. After all, NASA says there's two of every size space space on the ISS, so why can not both McClain and Koch wear the same sized suits? Speaking with CNN NASA representatives offered a deeper explanation.
The lengthy discussion reveals some of the quirks of life onboard the International Space Station, as well as some insights into how human bodies change once they are in space
While still back on Earth, McClain had trained in both the large and medium sized suits. Originally, NASA was planning to have McClain wear the bigger suit while Koch would wear the medium rig. However, during McClain's recent spacewalk it became clear that the medium sized fit fit her body better in space, which left NASA in a bit of a pickle
NASA has two of every size space space on the ISS but only one of them is fully outfitted and ready to use at any given time. The other suits, which are considered backups, can not be pulled out and used immediately, and they have to be prepped for use in space
NASA's Brandi Dean explains it like this:
We do our best to anticipate the space-sized sizes that each astronaut will need, based on the size of the spacesuit they wore in training on the ground, and in some cases (including Anne McClain's) astronauts train in multiple sizes. However, individuals' sizing needs may change when they are on orbit, in response to changes in living in microgravity can bring about in a body. In addition, no training environment can fully simulate the performance of a spacewalk in microgravity, and an individual may find that their sizing preferences change in space
Training in various space suits on Earth can not adequately predict what suit will fit you better in space, and in this case the time crunch between the two spacewalks has forced NASA to replace McClain with Hague. It's obviously a bummer for McClain, but nobody wants to be floating around in space in a suit that does not fit