First all-female spacewalk didn't happen, but not for the reason you might think

NASA announced Monday that North Carolina native astronaut Christina Koch would be joined by astronaut Nick Hague instead of Anne McClain on a spacewalk to continue the upgrade of the batteries that store power generated by International Space Station’s solar arrays. Following a similar spacewalk last week, McClain recommended to mission managers that crew assignment this week be adjusted.

The human body changes in space in ways that can be anticipated but not fully predicted. McClain, like other astronauts, trained in several spacesuits in anticipation of those changes and equipment availability. While she did grow in height by about 2 inches as the effects of microgravity allow the soft tissues between vertebrae to expand, McClain learned during her first spacewalk that the medium-sized hard upper torso of the suit fit her best. With one available in this size for the Friday, March 29 spacewalk, Koch will wear it.

Selecting a spacesuit isn’t as simple as going to the space-closet and picking out a shirt and pants. A spacesuit is essentially a personal spacecraft providing life support and enabling them to get the job done safely. Astronauts undergo 80 different measurements to configure the suit for them. There is an additional medium torso on board that could be prepped for McClain, but not in time for Friday’s spacewalk.

The suit is assembled around the hard upper torso, a vest-shaped shell made of rigid fiberglass or carbon-fiber. It serves as a connection point for the lower torso assembly (the pants), arm assemblies (the sleeves), helmet, displays and control modules. There are two each of the medium, large, and extra large sized upper torsos on station. There are also eight sizes of elbows, two waists, five knees, 65 different sizes of gloves. Each part of the spacesuit is adjustable and padding is added in the right places to make for the best fit, a process that requires 12 hours that just wasn’t available in the week’s schedule.

NASA cancels first all-female spacewalk over spacesuit sizes

Twelve hours might not seem like much, but time is the most precious commodity aboard the space station. Astronauts’ activities are scheduled in five-minute increments. Delays tend to cascade in a way that impacts everyone on board. With two resupply missions expected in the coming weeks, the crew’s schedule is very busy.

While it would have been great to make history Friday, but McClain and McClain are part of the 2013 class of astronauts, half of which are women. The first-all female spacewalk will happen, just not this week.