Engineering Artificial Gravity Solutions

The human body was built for gravity, taken away and bones weaken, muscles shrink, fluids shift, and even your vision can change. For astronauts spending months in orbit, zero gravity isn't just strange, it's one of the greatest obstacles to living and working in space . Yet there are solutions . It might just be a matter of exercise, or in the future the solution might be to create artificial gravity by spinning a spacecraft. Learn more about dealing with zero gravity on this episode of Everything Everywhere Daily This episode is sponsored by Hexclad. Over a year ago, I invested in a set of Hexclad cookware. I got a griddle, a stock pot, and two frying pans, and I have been loving it, and I use it almost every single day in my house. Hexclad completely changed the game by combining the performance of stainless steel with the convenience of non stick in a single pan. Hexclad gives you a proper sear, great heat control, and clean up that doesn't turn to a whole second job after dinner. 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Let me start right out by noting that while the term zero gravity is the common term used for the condition that astronauts experience in orbit , it is technically incorrect. A better term might be microgravity or weightlessness . Gravity is not absent in orbit . In fact, astronauts aboard the International Space Station are still strongly affected by the Earth's gravitational field. At the International Space Station's altitude roughly two hundred fifty miles above the surface of the Earth, gravity is still about ninety percent as strong as it is at the surface. If gravity vanished, the station would fly off in a straight line in space. What's really happening is that the spacecraft and everything inside are all falling around the Earth together . An orbit is basically a continuous fall. Imagine throwing a ball horizontally. It will eventually fall to the ground, but if you throw it faster, it lands further . But if you throw it fast enough, as it falls, the curvature of the earth drops away beneath it at the same rate. The object keeps falling, but it will never hit the ground , and that is all it means to orbit something . What astronauts experience is the same thing that you would experience if you were to go skydiving . So zero gravity is a misnomer because gravity is still very much present . What is missing isn't gravity itself, but the sensation of weight . By all accounts, weightlessness is fun , at least initially. Outside of a few seconds of bungee jump ing, I can't claim to have experienced it. However, the longer you are in a weightless environment, the more problems can arise . And the first problem that many astronauts experience is space sickness. Spaceness is the nausea, dizziness, headaches, and disorientation that many astronauts feel during their first hours or days in microgravity. It happens because the brain receives conflicting signals. On Earth, the inner ear's vestibular system uses gravity to help determine balance and direction. In orbit, that gravity cue disappears, while the eyes still report motion and orientation. The brain has to recalibrate to a world with no true up or down . Symptoms can include nausea, vomiting, cold sweating, loss of appetite, fatigue, and trouble concentrating. It's similar to motion sickness, but it's caused by weightlessness rather than by a carboat or airplane. Most astronauts adapt within a few days, although they can experience a similar readjustment problem when they return to Earth's gravity. Long term weightlessness has problems beyond just being nauseous. It's a serious biological problem because the human body is built around constant mechanical loading. Gravity tells your bones, muscles, blood vessels, balance organs, and even fluid distribution how to behave . Remove it for months or years, and the body adapts in ways that are useful in orbit but can be dangerous when returning to Earth. In weightlessness, the body no longer has to support itself. The legs, hips, and spine stop doing much of their normal work. Bones no longer receive the same stress signals that tell them to maintain density . Fluids no longer settle towards the lower body, so blood and cerebrospinal fluids shift upwards towards the head. The cardiovascular system, vestibular system, eyes, immune system, and kidneys all respond to this new environment. NASA summarizes the major effects as muscle loss, bone loss, upward fluid shifts, vision problems, increased risk of kidney stones, and cardiovascular deconditioning. In microgravity, astronauts can lose bone density, and NASA's twenty twenty five risk summary estimates a typical loss rate of about one to one and a half percent per month during four to six month missions if not adequately countered . Astronaut Scott Kelly spent three hundred and forty days aboard the International Space Station in twenty fifteen and twenty sixteen . After returning to Earth, he reported sore skin, rashes, flu like symptoms, sw ollen legs, balance issues, and other difficulties readjusting to Earth's gravity. He also has a twin brother, and NASA did a study of him and his twin to compare what happened to him after his flight. They found chang es involving gene expression, immune response, bone metabolism, body mass, and cardiovascular function , although many of these returned towards baseline after he came home. The main thing currently used to offset these problems is exercise . ISS astronauts typically use a treadmill with a harness, a stationary cycle, and a resistive exercise device that mimics weightlifting. And this helps a lot. Modern crews return in far better condition than early long duration crews did. Diet, vitamin D, medication, hydration monitoring, and medical imaging also help. However, exercise is an imperfect substitute . It takes time, requires bulky equipment, stresses joints in unnatural ways, and does not reproduce gravity's continuous whole body effects , and it also does absolutely nothing to solve the problem of fluids shifting to your head. The ultimate solution would be to try and replicate gravity . In many science fiction movies and TV show s, artificial gravity is used as a plot device because filming weightlessness would be challenging and expensive. Many times it isn't even explained and people just walk around on the decks of spaceships like they were on the surface of a planet. In reality, the only solution to artificial gravity that we know of is rotation . There's no known practical machine that can generate gravity like a planet , but a rotating structure can create an outward app arent force . Stand inside the rim of a spinning station and the floor pushes against your feet. And to you that feels very much like weight . The basic equation for creating artificial gravity is very simple . It's angular velocity squared times the radius . And that means a station can get earth like gravity by either spinning fast , by being very large , or by some combination of the two . There have been some movies that have depicted such space stations. There was a rotating space station in the movie two thousand one of Space Odyssey, as well as in the series for All Mankind These are usually depicted as large rotating wheels with spokes and a central docking hub. However, there's a problem with this. A rotating station is not exactly the same as standing on Earth. When you move your head, throw an object, pour water, or climb a ladder, or walk inwards towards the hub, you experience the coriolis effect . This makes moving objects appear to curve from the perspective of people inside the station . At low rotation rates, this is manageable, but at high rotation rates it can become nauseating. The rule of thumb that's often cited in artificial gravity design is that around one to two revolutions per minute would be comfortable for almost everyone, while three to four RPM may be tolerable after adaptation and higher rates become increasingly unpleasant. The exact limit is debated because we've never actually built such a space station , but the lower the RPM the easier it would be to adapt to, but it also means the space station has to be larger . To be able to support Earth like gravity at only one RPM , you would need a rotating space station with a radius, not a diameter of eight hundred ninety five meters or a little more than half a mile. And that's the radius. Double it for the diameter . At two RPM, which is also reasonable, you'd need a radius of only two hundred twenty four meters . And at four RPM, which might require some adjustment, you'd need a radius of about fifty six meters . Of course, it might not be necessary to experience the full gravity of Earth. If you wanted to simulate the Moon's gravity at one RPM, it would only require a station with a radius of one hundred and forty eight meters or four hundred and eighty five feet. And if you're willing to spin it at four RPM, you'd need a radius of a reasonable nine point two meters or about thirty feet . This really isn't a question of physics, it's more a matter of engineering and how you could actually build such a thing in orbit. The first one would be extremely difficult to build and would most likely be extremely expensive . A rotating space station is currently possible but difficult, and it might be more plausible if we can reduce the cost of transporting cargo to orbit even further . But that doesn't stop people from thinking even bigger. There have been proposals for some truly enormous space stations that use rotational motion to create artificial gravity. The Stanford Taurus is a more ambitious version of the wheel, a large donut shaped habitat usually imagined as a space colony rather than just a space station . People live on the inner surface of the Taurus with the ground curving up in the distance . Its major advantage is livability. A taurus can provide a large continuous landscape, neighborhoods, agriculture, and a more earthlike environment , and its large radius allows for a much slower rotation. A Stanford Taurus would start at maybe about one RPM and go down from there if it were even larger . However, a Stanford Taurus would simply have people living on the rim of a wheel. Something that would radically expand the amount of living space that people could have is an O'Neill cylinder. An O'Neill cylinder, as the name would suggest, is a gigantic rotating cylinder with its entire interior available for use . Princeton physicist Gerard K O'Neill proposed enormous counter rotating cylinders with people living on the inside surface. A cylinder could provide a vast habitable area . The classic concept features alternating strips of land and windows with mirrors reflecting sunlight into the interior. A big advantage is scale. A cylinder can in theory support citiess, farmland and industry. It also has better land use geometry than a wheel does because its inner surface can be very large. O'Neill cylinders have been shown in the movie Interstellar and in the TV show The Expanse. An alien O'Neill cylinder also plays a central role in Arthur Clark's book rendezvous with Rama . There's supposedly a movie in the works that is to be directed by Denny Villenux, but production hasn't started yet. The theoretical length of an O'Neill cylinder could be miles long, although we have absolutely no clue how to build such a thing to say. However, this theoretical idea can be taken to an even higher level , a Dyson sphere is a proposed megastructure that would completely surround a star and capture all or some of its energy output . The usual popular image is a solid shell surrounding a star, but physicist Freeman Dyson did not originally propose such a rigid sphere. His more plausible idea was a vast swarm of orbiting solar collectors, habitats, or satellites that were surrounding a star. The best fictional representation of Dyson's idea was in Larry Dimmon's nineteen seventy novel Ring World . It's an enormous artificial ring built around a star with its inner surface serving as habitable land . Unlike a rotating space station, it's not a small wheel in orbit, it's more like a slice of a Dyson sphere. A band millions of miles across that completely encircles a star at roughly the orbit of Earth. The ring rotates to create artificial gravity through centrifugal force while the star provides light and heat . Even with such a gigantic ring, it would still be required to rotate once every nine and a half days . It would have to move more than thirty eight times faster than the Earth's orbital speed around the Sun in order to produce the same gravity. We have yet to build a single artificial gravity system for humans in space