 Ladies and gentlemen, welcome to my period piece, a.k.a. menstruation in space, today on Vintage Space. In the 1960s, nobody was really sure what was going to happen to a human body in space. It was possible that once in zero gravity, a man wouldn't be able to swallow so he couldn't eat or drink. It's possible that without gravity, his eyes would distort and he wouldn't be able to see the controls in front of him. These were serious questions that NASA answered with the Mercury program. And as space flights got longer, there were new questions about physiology. One thing flight surgeons did a lot of research into in the 1960s and 70s was the cardiovascular system. And it turns out that this system is greatly affected by microgravity. The heart almost gets lazy when it's in space. Because humans developed in a 1G environment on the Earth, our bodies are very good at pumping blood from the lower extremities and the lower body up to the heart where the blood is re-oxygenated and then circulated back through the body. In space, the cardiovascular system isn't fighting gravity, and so more fluid pools in the upper body and in the head than in the legs. And prolonged exposure to microgravity does impact heart rates because the heart and the cardiovascular system doesn't need to work quite the same way it does on Earth. When NASA started allowing women into the astronaut corps in the 1970s, this opened up a whole new realm of physiological problems to dig into, and one of the biggest unknowns was what would happen to a woman menstruating in space. As if drawing analogy from the cardiovascular system which changes drastically in microgravity, a lot of people thought that there would be a problem with retrograde menstrual flow with a woman menstruating in space. Basically, flight surgeons were worried that instead of the blood flowing out of a woman's body, it would flow upward into the abdomen, causing a condition known as peritonitis. Peritonitis is an inflammation of the peritoneum, which is the membrane that lines the inner abdomen and covers the organs inside the abdomen. If left untreated, this can become a life-threatening condition, and so nobody wanted to send a woman up into space only to have her die because of her natural body cycles. But there's a difference between the cardiovascular system and menstruation, obviously. The cardiovascular system relies on series of arteries and veins with valves to pump blood throughout the body. Menstruation is simply regulated by hormones. While male engineers and flight surgeons were very concerned about what was going to happen to a menstruating woman in space, none of the female astronauts were too concerned. To them, they couldn't imagine that menstruating in space would be any different than menstruating on Earth. The problem was there was no way to prove it unless somebody just went up there and did it. It's unclear who the first woman to menstruate in space was, but ultimately, the answer was exactly as the female astronauts predicted. There's no difference to menstruating in space as there is to menstruating on Earth. There is a difference, though, in how NASA deals with menstruating astronauts. No two women menstruate the same, and no two women have the same preferences. So NASA has to deal with packing personal kits based on every astronaut's own needs and preferences. Astronauts can also choose to stop their menstrual cycles altogether using hormonal birth control methods. Something that could be useful on a long-duration mission, say a mission to Mars, where there is just no room to take extra stuff with you. Ultimately, the question of menstruating in space is more interesting when you look at it historically and socially, and that women became this weird unknown that NASA just didn't know how to deal with. The agency even considered making makeup kits for the astronauts to take in space because that's something that you need in orbit. I've got more on that, including some great anecdotes on my latest blog post at Vintage Space over on Popular Science, so definitely check that out if you would like to know more. The link is in the description below. This seems to be the weird taboo topic that nobody really wants to deal with, but it is pretty interesting. Do you guys have more questions about menstruation in space or anything else relating to the female reproductive cycle and spaceflight? Let me know in the comments below, and, of course, leave me your questions about anything space-related and things you would like to see covered in future episodes. Be sure to follow me on Twitter for daily Vintage Space content and of new videos going up every Friday. Subscribe right here, so you never miss an episode.