(Intro)

Reid Reimers: You see it at, like, all the movies.  Either there's a space station that's a big spinning wheel or there are spaceships that use some invisible technology so that somehow, even though the characters should be floating around because they're in space, they're sticking firmly to the floor.  

Artificial gravity is more than just convenient.  Weightlessness is bad for humans.  It makes bones and muscles degrade, causes heart and vision problems, the list goes on.  So you'd think, after more than 50 years of spaceflight, we'd have come up with a way to make artificial gravity.  But we haven't, 'cause it's hard.  The only practical way to make you feel like you're experiencing the full effects of gravity is by spinning.

You've probably seen this effect at an amusement park.  A ride spins really fast like a centrifuge, making you stick to the walls?  That's because as the ride spins, centripetal forces are constantly pushing the wall towards you.  They're making you turn instead of just zoom off in a straight line.  So if you sent a disc into space and set it up carefully enough, you could make it so that the centripetal acceleration was 9.8 meters/second squared, the same as Earth's gravity.

That might sound pretty simple, but it's really not.  For one thing, the smaller your disc is, the faster you have to make it spin to achieve the same centripetal force, but as you can probably imagine, living in a disc whirling around like a spinning top is not super comfortable.  If you want a useful artificial gravity habitat that spins slowly enough to be habitable, scientists estimate that it would have to be around 100m in radius.  I'm talking about a structure that would be twice as big across as the International Space Station is long, which would be incredibly expensive and time-consuming to build.  

Even if you could build it, there would still be problems, because standing inside a spinning disc isn't exactly like standing on the ground.  For one thing, your head would be closer to the center of the disc, so it would feel less of those centripetal forces.  It would be like your head was experiencing less gravity than your feet, and the human body didn't evolve to handle that kind of thing.  Your heart, for instance, would have to work harder to make sure that all your blood was distributed properly and not spending extra time drifting around in your head.  And if you bent down or even tilted your head to the side, you'd get super disoriented, because the fluids that fill the internal gyroscope of your inner ear would suddenly be swirling in a different direction, which makes me nauseous just thinking about it.  

Still, figuring out a way to safely simulate gravity would be useful, especially if we wanna send humans on long-distance trips to places like Mars.  So researchers have been working on it for a long time.  In 1966, astronauts of the Gemini 11 capsule actually tethered their craft to another ship, called the Agena Target Vehicle and set them spinning very slowly, like one rotation every seven minutes, to see what would happen.

Turns out, it was enough to simulate only 5 ten-thousandths of Earth's gravity, too small for the astronauts to even feel.  Much more recently, a mission concept was proposed in 2011 called Nautilus X, a spacecraft that included a spinning disc designed to simulate gravity for astronauts onboard.  But the mission was cancelled because of its costs, before the team could develop an effective centrifuge, and in July 2015, engineers at MIT built a very small centrifuge meant to fit inside the ISS and be used mainly for exercise.

The researchers tested it on twelve people on Earth who used an exercise bike while being spun around at up 32 revolutions per minute.  They did experience motion sickness, as you might imagine, but it was mostly while the centrifuge was speeding up or slowing down.  

With so many complications and so much research left to do, it'll probably be a while before we see spinning spaceships that can produce artificial gravity, but when we do, astronauts will be in for a wild ride.  Thanks for watching this episode of SciShow Space, and especially to our Patrons on Patreon, who help make this show possible.  If you wanna help support the show, go to Patreon.com/SciShow to learn more, and don't forget to go to YouTube.com/SciShowSpace and subscribe.

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