Just like any stressful situation, a trip to the stars can cause gut upheaval in either direction. But stagnation is actually more common than diarrhea, perhaps because microgravity puts the gastrointestinal tract in an odd position. Dehydration, which can increase constipation, is also a frequent issue during the first few days on the ISS. Astronauts know that the position they sit in for launches—with their feet at the same level as their hearts—causes fluids to pool and makes them need to urinate, which is something they often try to avoid by drinking less. You can’t blame them for wanting to stay dry: On the Soyuz launch vehicles, astronauts have to pee into ultra-absorbent garments and fitted condoms.

During launches, the best way to poop is with the help of what basically amounts to a triple-layer plastic bag on a bucket. (Things were even more dire on Apollo missions, where crew members had to stick plastic bags directly to their butts and use manual pressure to make dangling turds fall inside, leading to at least one infamous floater incident). To this day, astronauts are given the option of getting an enema before they take off, just to lessen the possibility of an urgent bowel movement while they’re en route.