Christina Koch (centre) assists fellow astronauts Nick Hague (left) and Anne McClain to prepare for a spacewalk last week NASA

The first all-women spacewalk has been cancelled. NASA astronauts Christina Koch and Anne McClain were scheduled to stroll into the vacuum of space on 29 March to change the batteries for some of the International Space Station’s solar panels. Now Nick Hague will replace McClain, because there wasn’t time to put together a spacesuit that would fit her.

Spacesuits are modular, with the torso, legs and arms all sized separately and then fitted together in the best configuration for the individual astronaut.

According to NASA spokesperson Stephanie Schierholz, McClain trained on Earth using both medium and large-sized spacesuit torsos. After conducting her first spacewalk on 22 March wearing a large-sized torso, she realised that the medium fit better.


This may partially be due to physical changes that happen in space. Astronauts tend to lose both fat and muscle mass in microgravity, and can get taller as the spinal column stretches out. McClain tweeted earlier this month that she had gained 5 centimetres in height since arriving on the ISS in December.

There is another medium torso aboard the ISS, but it takes time to fit together and test a full spacesuit, so only one suit with a medium torso will be available by 29 March. Rather than delay, NASA switched out one of the astronauts. Christina Koch will wear the one medium-sized spacesuit. NASA’s overall spacesuit shortage won’t be helping.

This all-women spacewalk came about through a coincidence of scheduling, but it was fairly unlikely. Of 223 astronauts who have been on a spacewalk (not counting Koch, because the walk on 29 March will be her first), only 13 have been women. It may be years before this happens again, unless NASA purposefully selects a pair of women to walk together.