NASA’s spacesuits have a gender problem. These women are fixing it.

It was going to be a historic moment: Last spring, for the first time, an entirely female team of astronauts was to embark on a spacewalk.

But just days before Anne McClain and Christina Koch were to venture outside the International Space Station, NASA swapped Ms. McClain for a man. They’d realized there weren’t two spacesuits ready that would work for both women.

That reversal drew scorn. Instead of being a moment to celebrate the agency’s progress toward gender equality, it seemed to expose how much work remained...