Can The Human Body Handle Rotating Artificial Gravity?

hello it's scott manley here today i want to talk to you about artificial gravity artificial gravity is of course a staple of science fiction partly because if you're shooting a tv show or movie it makes shooting scenes on earth a whole lot easier but in the early days of space flight there were lots of concerns about the human body's reaction to zero g to the point that yuri gagarin would have to input a three-digit code to unlock the controls on vostok1 just in case being in 0g made him space crazy while the first decade of human spaceflight showed that humans could easily adapt 0g for short missions there were many reasons to think that for longer missions say on space stations it would be a good idea to have access to artificial gravity capabilities for the sake of the long-term health of the crew specifically it was known even with a week or so of exposure that the human body will slowly lose muscle and bone mass in the absence of gravity on the engineering side of things the laws of physics give us three ways to generate gravity-style forces for a crew but only one of these is actually viable for space flight rotational artificial gravity you see gravity is a phenomenally weak phenomenon and while science fiction loves artificial gravity generators in the floors of spacecraft again because it makes it easy to shoot and because it lets you design cool spaceships there's nothing in the laws of physics that would imply or suggest that this is possible the only way that we know right now to generate a gravity field is with a huge amount of mass such as a planet planet-sized chunks of mass are great for living on but they're kind of inconvenient to carry along if you're doing space flight now another another way to do this is linear acceleration where you're going faster in a straight line and that does indeed generate the perception of real earth gravity indeed einstein built general relativity by assuming that accelerating in a straight line and planetary gravity should be identical no experiment can tell them apart and guess what that works pretty well now space flight is great for generating linear accelerations but you only get a few minutes during launch and re-entry those chemical rocket engines can deliver the g-forces you need but only for minutes before their propellant is depleted in tv shows like the expanse the spacecraft use fusion drives that can accelerate for days on end without running out propellant but that's a technology that is driven by the needs of the plot and it may never be possible with a human technology also the magnetic boots that we see in the show are again really nice if you're trying to shoot a tv show but they really just provide a way to secure your feet to the surface without actually providing the gravity loads that make the human body work out and you know decondition so rotational gravity is what's left right that's the only one that's possible and indeed the idea of large rotating space stations was around for decades before anybody ever flew in space but a lifetime later and we still don't see rotating space stations although there are many people who would love to build one such as the voyager space station so a quick reminder of the math that this involves if you have an object that is moving in a circle you need a force pushing inwards towards the middle and that force has to be proportional to the mass the radius of the circle multiplied by the angular velocity squared and in physics we measure angular velocity in radians per second so there's you know two pi radians in a complete circle in 360 degrees so now if you want to generate an earth like 9.8 meters per second of gravity with a 10 meter radius structure that's about 30 feet then you need to rotate it at about one radian per second or about nine and a half rpm if you make the radius longer then the rotation rate gets smaller and if you reduce the gravity that you want then similarly you can use lower rotation rates now at this point i should put on my physics tutor hat and explain the difference between centripetal and centrifugal forces for an object to move in a circle it has to have that centripetal force pushing it towards the center of rotation but if you are a person in a rotating space station with walls and you can't see out um what this force to you appears as the plate pushing the ground plate pushing up against you you feel a centrifugal force pulling you down towards the floor and that feels like gravity but this is different equal and opposite it look it's different enough that it can serve as a limitless source of pedantry from physicists so anyway this kind of construction is of course used in training pilots and astronauts you have the centrifuge facility this is to give pilots a high experience in high g loads on the ground you know you put them in a test cabin or a test car spin it around at high speeds and generate the g-forces that they need to learn to handle you know to make sure that the body is capable that the jeep suit works properly and just to teach them adaptation techniques to moments when they're dealing with this but this kind of training is something that lasts for hours rather than the weeks or months that astronauts might experience in the space station so you know this kind of rotational facility is well understood by the space flight community and that meant that it was also known that there were side effects from spinning humans around like this i mean it's honestly something we learn as kids right you get very dizzy if you spin around too fast and turning those childish understanding and perceptions of dizziness and falling over into quantifiable research on human physiology is a serious endeavor that requires lots of effort resources and dealing with people being sick so there's two main effects that we see when humans operate in a rotating environment firstly your body uses the semicircular canals near your ears to detect rotation and that helps you keep your balance and they do this by detecting the motion of fluid in these sort of circular um cavities and this responds to the rotation of the of your head now if you're sitting perfectly still your brain will take that as a non-moving reference frame and you'll stop getting dizzy if you're even if you're rotating but if you're returning your head then you expect a certain rotation if the room is turning and you turn your head you will get a different rotation and that will confuse your brain and that will is a great way to give yourself motion sickness one of the first things that people learn to do in rotational experiments is to stop moving their head to minimize this effect and the other thing is in a rotating environment any motion through that will frequently require forces that are different from the same motion in a non-rotating environment these are broadly described as the coriolis forces which at planetary scales affect the atmospheric motions and help make tropical storms that rotate counterclockwise north of the equator and clockwise in the south but at high rotation rates simply reaching out your hand to pick up something might result in the fictional coriolis force pushing your arm away from the path that your brain has planned for you know your brain is working with its previous experience and all your motor functions to balance this out so when this happens your motor control system needs to re-learn how to perform these basic tasks and you you can learn a specific motion really quickly minutes even but then you know in some rotational environments if you turn to face a different direction or move your hand in a different direction the coriolis force will again be different and you need further adaptation it takes days to become fully adapted to a rotating environment so one question that scientists wanted to answer was what kind of rotation rates can the human body handle for long durations long enough to get over that initial sickness long enough that the gravity would need to be would be needed to avoid deconditioning of the body can people perform at the same levels as they do in a non-rotating environment or is there some penalty that can't be eliminated by training at any rotation rate is there an upper limit on the rotating conditions that human can handle um because that in turn if you've got a limit on your rotation rates that will set the minimum radius for a spacecraft that is using rotational artificial gravity now one of the problem with all the studies like this is that they're interested in hypothetical rotating structures in space but they have to take place on earth and you can't subtract earth's gravity because we don't have anti-gravity so one type of test is the rotating room where a room is rotated around its vertical axis like this and you might actually have seen this on youtube there's a video with tom scott that does this but these have been around for a long time the us naval medical research laboratory built the slow rotating room facility in 1958 that was like 10 meters across and they had living quarters in there for long duration testing so people would live in there for weeks on end at 1 rpm people could operate with very little adaptation but most subjects would begin to suffer motion sickness initially when the room was spinning at about 3 rpm again turning your head was the thing that would really trip off motorcycle motion sickness but from that people could adapt as you spun the room faster and faster and they could learn to handle much higher rotation rates even up to 10 rpm although quite a few people couldn't adapt and ended up making frequent use of the sick bags yeah now in the soviet union again they did similar experiments using rotating rooms and they came to the same conclusions but the rotating room isn't the same as a spacecraft rotating to provide artificial gravity because the axis of rotation is in the spacecraft is parallel to the floor but you can't do that on earth because of the ever-present gravity of the earth however there have been tests on large centrifuges with whole living spaces at the end with a rotation rate fast enough to incline the floor to provide a non-sloping surface for the occupants and this means not only is the space rotating but you're also dealing with stronger gravity so you had better be sure that you are not going to fall over because if you fall over due to your lack of balance you're going to hit the ground a lot harder in these environments so this footage here is from a soviet experiment where again people would live for about a week at a time and one of the more amusing demonstrations is the arrow throwing where they curve around thanks to the coriolis force although the elevator system is also another interesting thing because you know you want to bring out the doctor to the crew to study them but moving radial is really hard because you know your gravity forces and everything are rapidly changing as you move down this arm it's one of the more disorienting experiences nasa also had a very large centrifuge system it's called the rotating test facility and it was built by rock well out in california so on one side there was this living area it was like 40 feet long by 10 feet wide was actually a section of an aircraft apparently and people would live in this for about a week at a time the other side they counterbalanced this by having the walking wall and this was a vertical wall and they had straps to support people so they could actually stand sideways on this and test walking like let you prograde and or counter rotation right they could also use the same support harness system to simulate ascending and descending ladders because again that's another thing that was quite complicated for your body to learn but the only experiment i've seen that's really flown in space and provided artificial gravity is the soviet bion 3 or cosmos 782 mission so that had a small centrifuge on board it and they had plants and animals in containers at different distances from the rotation axis and that allowed them to compare different simulated gravitational environments and as far as i can tell this is the most significant test of artificial gravity ever flown in space it's also notable as the first time a u.s experiment flew on a soviet space mission the spacecraft was actually based on the zenith design which was a soviet photo reconnaissance satellite that shared a lot in common with vostok because back in the 50s and 60s when sergey corralev was developing this he realized he could get money from the people that wanted a human spacecraft and from the people who wanted a spy satellite and build them one spacecraft right um so yeah all of this stuff went on for decades and huge reports that were compiled for all these experiments and what they all basically say is slower is better but rotational artificial gravity is possible in structures are comparable to the size of the international space station there would be a few engineering problems to solve to make sure like the thing remained balanced and you have your proper seals and transitions but there's nothing insurmountable there instead we don't see rotating space stations because there's no real selling point since the same intense medical research has helped develop ways to stave off the deconditioning associated with zero g through consistent exercise to make up for the body not supporting your weight doing mundane things in zero g the iss is primarily concerned with zero g research and that kind of research is hard to do in a rotating station you would need a non-rotating section but the iss does miss out on the ability to perform experiments at lower gravity levels than those on earth i mean at one point there was a centrifuge facility planned for the iss very similar to that found in the bion 3 satellite and that would allow small biological payloads to be exposed for lower gravity for long periods of time but ultimately this was cut to make the state space station more affordable but you know with the new wave of space tourism there's suddenly a number of people who are interested in going into space and may find the idea of staying in space for a while taking in the views and who don't need experiments that are in carefully controlled microgravity so maybe the idea of a rotating space station will finally return in the movie 2001 a space odyssey the rotating space station 5 at the start the interiors we get to see lounges restaurants and a hotel it's not a science facility so maybe the only thing arthur c clarke got wrong was the date i'm scott manley fly safe [Music] you

Channel: Scott Manley

Views: 1,589,609

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Id: nxeMoaxUpWk

Length: 15min 27sec (927 seconds)

Published: Tue Aug 17 2021

Reddit Comments

[u/venusiancreative]

One way rotating space stations could work is by having a large factory with no gravity with a rotating section attached for better long term living facilities. Varda has recently made a deal with Rocketlab; maybe they should look into something like this down the line.

[u/Wise_Bass]

I suspect artificial gravity via rotation in space will be a lot easier to adapt to than it has been on Earth, because you'll only feel the effective "pull" of it in a narrower set of directions. As Manley points out, you can't get rid of Earth's gravity no matter how you orient your rotating module.

You don't really need to go above 10 RPM, because at that point you've got Earth-like gravity with a radius of only 9 meters, and you'll really notice a difference in gravity depending on which direction you walk in a rotating ring.

[u/AuntyProton]

Normally I'm an all out Scott Manley fan but he didn't even mention Dr. O'Neill. 😲😮😕