One thing that nearly all spaceship-based sci-fi movies have in common is their portrayal of an artificial gravity system. People walk around the deck of the USS Enterprise or the Battlestar Galactica like they would on Earth; they aren't floating about the cabin like astronauts aboard the International Space Station. Artificial gravity makes science fiction more relatable, and easier to shoot—the zero-g sequences in Apollo 13, for example, were filmed 23 seconds at a time in the infamous "Vomit Comet").
As a result, it's easy to forget just how much the lack of gravity dictates life for today's space explorers. Motion sickness, difficulty remaining stationary and oriented, and bone and muscle deterioration are just a few of the problems astronauts can face. So why don't we have artificial gravity on ISS?
The most realistic method of producing artificial gravity aboard a space station is using centripetal force to produce a pulling sensation toward the "floor" that would mimic the effects of gravity. Physics blogger Matthew Francis tells PM that it's a lot like one of our favorite boardwalk attractions. "If you've ever ridden on a carnival ride," he says, "you know that spinning very fast makes you feel heavier, and can even hold you against the wall of the ride if the floor drops—like in the old Gravitron ride." In a rotating spaceship, objects inside would be pushed toward the hull.
In a spaceship designed to produce artificial gravity, you'd walk around perpendicular to the "wall" you were stuck to, and parallel to what would, in a Gravitron, be the floor. The wall would become the floor, and the floor would become the inner wall of the ship. A person can get a pretty good idea of what it would look like from 2001: A Space Odyssey's iconic jogging scene, or from this old NASA test video.
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Why haven't we built ourselves a centripetal space station yet? One problem is size. John Page, a lecturer on aerospace design for University of South Wales, told ABC Science that the scale of such a craft would pose some problems. "The smaller the spacecraft is, the faster it has to rotate," he says, "so if you're going to generate gravity, it's got to be done with a very large spacecraft that spins very slowly. The bigger the disk, the slower you can rotate it. Plus, says Francis, "it'll be disorienting if your ship has any windows in it." And what would an ISS mission be without Chris Hadfield sending back pictures of Earth?
Besides, a lack of windows wouldn't make dizziness a nonissue: If a spacecraft's rotating portion were too small, residents would feel a huge difference in the force imposed on their heads and what they felt on their feet. They'd end up dizzy and lightheaded because blood would be drawn down, away from the brain. "At this stage," Page said, "there's no spacecraft on the drawing board big enough to do this. It would have to very large—much larger than a football field." ISS, in comparison, is basically the size of a small apartment. Francis points out that at a viable scale, a rotating spacecraft becomes one heck of an added expense. "Making a really big spaceship is an expensive problem too," he says, "since every piece of it has to be boosted from Earth into orbit."
Short-term space travel doesn't really need artificial gravity. In fact, most of the research done on ISS relies on the lack of gravity. And on a long-term mission, say, to Mars, the last thing NASA wants is an even bigger, fuel-hungrier, more expensive spacecraft.
As far as alternatives to a spinning ship, Star Trek credits its ships' artificial gravity to the use of "gravity plating" under the decks. Without that kind of gee-whiz sci-fi tech, modern astronauts exercise with pulleys and gizmos that simulate gravity (albeit pretty awkwardly), and NASA is researching the use of an astronaut-size centrifuge that you could spend a certain amount of time in every day. It's nausea-inducing and far from as good as the real thing, but for now a spinning gurney is the cheapest, most practical, and most realistic option for simulating gravity in space.
Rachel is a freelance writer, editor and content strategist and host of the hit podcast The Weirdest Thing I Learned This Week. Her first book, "Been There, Done That: A Rousing History of Sex" came out in May 2022. She loves reading about weird history, sharing weird science facts and writing weird ghost stories.
