To answer these questions, it helps to start at the beginning. Not the Big Bang—we’ll save that for another day—but the 1960s, when NASA first started launching astronauts to space.

Read: 5,200 days in space

Back then, women weren’t wearing space suits; they were making them. The Apollo space suits were manufactured by the International Latex Corporation, the maker of Playtex bras and girdles. Seamstresses went from sewing undergarments to stitching together thin layers of high-tech fabric on their noisy Singer sewing machines. The space suits were custom-made for individual astronauts, all of whom were men.

After astronauts planted the American flag on the moon, NASA turned its focus toward the next phase in space travel, the space-shuttle program. The shuttles were designed for a future of frequent flights to and from the space above Earth, with more astronauts than ever before.

Tailoring custom space suits for so many passengers would be too expensive and time-consuming. So in the 1970s, NASA took a Mr. Potato Head approach and developed pieces for arms, legs, and torsos that astronauts, from the smallest women to the largest men, could mix and match. The spacewalking suits—known as extravehicular mobility units, or EMUs—came in five sizes: extra small, small, medium, large, and extra large.

Space-suit engineers thought that outfitting the new space travelers would be simple. “Some groups initially assumed that women could fit in the same sizes as small men—or at worst, that some of the men’s sizes would have to be scaled down proportionately to fit women,” Elizabeth Benson, a NASA design engineer, wrote in a 2009 paper on sizing considerations in space-suit design.

This approach doesn’t account for differences in the body shape of men and women. “For the same height and weight, women can have significantly wider hips and narrower shoulders than men,” Benson wrote. “If, for example, a one-piece coverall designed for a man is meant to fit at the shoulders and the hips, then one of these fit areas is likely to be compromised for a woman.”

Extra room can actually make space walks more difficult. “As a woman, doing space walks is more challenging mostly because the suits are sized bigger than the average female,” Peggy Whitson, a NASA astronaut who helped build the ISS and who holds the American record for time spent in space, said in a recent documentary interview. And Whitson would know: She also holds the record for the most space walks for a female astronaut, 10.

In the 1990s, several years after the first American women flew to space, budget cuts forced NASA to trim its space-suit program. Extra small was the first to go, and small followed soon after. Most astronauts fit into the mediums and larges, but not all.

“People my size are in fourth grade. Literally, I mean, some fourth graders are bigger than me,” Nancy Currie, a NASA astronaut who is 5 feet tall, told NPR in a 2006 interview.