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.