1 00:00:00,280 --> 00:00:05,240 Who doesn't love the idea of floating freely in the zero gravity environment of outer 2 00:00:05,320 --> 00:00:09,039 space. It looks like a ton of fun, and people will happily pay 3 00:00:09,119 --> 00:00:15,320 Jeff Bezos and Richard Branson millions of dollars just to experience zerog for only a 4 00:00:15,320 --> 00:00:18,839 few minutes at a time. But if our goal is to live in outer 5 00:00:18,879 --> 00:00:22,320 space for the long haul, then the lack of gravity is going to be 6 00:00:22,359 --> 00:00:27,480 the biggest obstacle that we face. So in order to achieve a sustainable human 7 00:00:27,480 --> 00:00:32,079 presence in space on the Moon or even on Mars, we need to solve 8 00:00:32,119 --> 00:00:38,159 the biggest logistical challenge of all artificial gravity. This is the space race. 9 00:00:38,520 --> 00:00:42,560 Of course, whenever we say something like zerog, what we actually mean is 10 00:00:42,719 --> 00:00:48,000 micro gravity, because gravity is everywhere all the time. It's the force that 11 00:00:48,119 --> 00:00:52,960 holds the structure of the Solar System and the galaxy together. Everything that has 12 00:00:53,039 --> 00:00:58,280 mass creates a gravitational effect, but it takes a very large concentration of mass 13 00:00:58,320 --> 00:01:02,840 like a planet, to actually have a discernible effect with enough force that would 14 00:01:02,880 --> 00:01:07,200 make you stick to the ground. This is an oversimplification, but I know 15 00:01:07,239 --> 00:01:10,760 you don't come to this channel for a detailed physics lesson. So we have 16 00:01:10,840 --> 00:01:15,040 to also remember that the effect of gravity tapers off very quickly from the source. 17 00:01:15,239 --> 00:01:19,519 Gravitational waves continue on infinitely into the universe. But just like heat, 18 00:01:19,760 --> 00:01:25,319 gravity is only felt intensely when very close to the source. That's the easiest 19 00:01:25,359 --> 00:01:26,959 way to think about this. I'm not going to bother you with trying to 20 00:01:27,000 --> 00:01:32,239 explain the inverse square law today. Just imagine that you are sitting very close 21 00:01:32,280 --> 00:01:34,519 to a fireplace and you hold your hand out towards the flame. If you 22 00:01:34,599 --> 00:01:40,040 move that hand either backwards or forwards by a distance of just one foot, 23 00:01:40,319 --> 00:01:44,920 that could make the difference between warm, hot, or burning. The gradient 24 00:01:44,959 --> 00:01:49,560 of the heat is very extreme at this distance. But if you move back 25 00:01:49,599 --> 00:01:52,560 and are now six feet away from the fire, and you hold your hand 26 00:01:52,560 --> 00:01:56,040 out again, you'll still feel the heat, but much less of it. 27 00:01:56,079 --> 00:02:00,480 And if you move your hand forwards or backwards by one foot, option of 28 00:02:00,480 --> 00:02:04,599 heat will be more or less the same. In all positions. At this 29 00:02:04,640 --> 00:02:08,599 distance, the gradient of heat is much softer. This is all important. 30 00:02:08,639 --> 00:02:12,960 Just stick with me and we'll get to the cool sci fi stuff very surely. 31 00:02:13,879 --> 00:02:16,879 The gravitational flame of the Earth is its core, which is a giant 32 00:02:16,960 --> 00:02:23,240 ball of solid metal that's surrounded by a thick outer layer of swirling liquid metal, 33 00:02:23,599 --> 00:02:28,520 an incredible amount of concentrated mass that creates a gravity well right in the 34 00:02:28,560 --> 00:02:31,319 middle of the planet, and that force radiates out to the surface of the 35 00:02:31,360 --> 00:02:37,439 Earth and even into space. Because the surface of the Earth is over six 36 00:02:37,520 --> 00:02:42,039 thousand kilometers away from the center of the gravity well, we do not experience 37 00:02:42,080 --> 00:02:46,919 an extreme gradient in the force of gravity out here. The effect tapers off 38 00:02:46,960 --> 00:02:50,360 at a very shallow rate, So it doesn't matter if you are in an 39 00:02:50,439 --> 00:02:54,439 underground bunker or the top floor of the tallest building, your experience of gravity 40 00:02:54,479 --> 00:02:59,960 will be more or less the same, no perceivable difference. In fact, 41 00:03:00,080 --> 00:03:02,400 if you were to climb a ladder straight up into the sky all the way 42 00:03:02,439 --> 00:03:07,400 to a height of four hundred kilometers, which is the altitude of the International 43 00:03:07,439 --> 00:03:12,400 Space Station, you would still be experiencing ninety percent of the gravity that you 44 00:03:12,520 --> 00:03:15,240 left behind on the surface, and if you let go of that ladder, 45 00:03:15,599 --> 00:03:20,240 you would fall all the way back down. You might be confused at this 46 00:03:20,280 --> 00:03:23,039 point, why do people in spaceships float at the same altitude that people on 47 00:03:23,159 --> 00:03:29,680 ladders fall down. Well, that's because an orbital spaceship or space station is 48 00:03:29,759 --> 00:03:34,120 in a constant state of free fall. This is what happens to the people 49 00:03:34,159 --> 00:03:38,479 in those Blue Origin capsules. They're not weightless because they are in space. 50 00:03:38,599 --> 00:03:43,080 They've just been launched straight up at a very high speed by a rocket engine. 51 00:03:43,120 --> 00:03:46,680 But then that engine cuts off and releases the capsule to coast up for 52 00:03:46,680 --> 00:03:51,919 a little while before it starts to fall back down again. While in freefall, 53 00:03:52,000 --> 00:03:55,120 the crew will float. Same thing happens in those airplanes that NASA has 54 00:03:55,159 --> 00:04:00,680 been using to train astronauts for decades. The difference between a Blue Origin capsule 55 00:04:00,719 --> 00:04:04,560 and a real spaceship like a crew Dragon, is that the dragon has reached 56 00:04:04,639 --> 00:04:10,639 orbital velocity, where it is moving so fast parallel to the Earth's surface that 57 00:04:10,719 --> 00:04:15,560 it is literally falling around the Earth. Here's the easiest way to think about 58 00:04:15,599 --> 00:04:18,240 this. If you throw a baseball, it will eventually curve downwards and hit 59 00:04:18,279 --> 00:04:23,120 the ground because gravity pulled it down. The faster you throw the baseball, 60 00:04:23,319 --> 00:04:27,600 the further it goes before its path eventually meets the ground. We can't stop 61 00:04:27,639 --> 00:04:30,959 gravity, but we know that the Earth's surface also curves down as it moves 62 00:04:31,000 --> 00:04:35,000 away from us. So imagine if you could throw a baseball so fast that 63 00:04:35,040 --> 00:04:40,600 the downward curve of the ball match the curve of the Earth's surface. At 64 00:04:40,600 --> 00:04:43,759 this point, the ball would still be falling towards the ground, but the 65 00:04:43,800 --> 00:04:46,399 ground would be falling away from the ball at the same rate, so the 66 00:04:46,399 --> 00:04:50,839 ball would stay in the air. Of course, we know that even if 67 00:04:50,879 --> 00:04:55,519 you could throw a ball that fast, the resistance from the atmosphere would slow 68 00:04:55,560 --> 00:04:59,439 it back down again, and it would still eventually hit the ground. But 69 00:04:59,519 --> 00:05:02,199 in space, once you reach that orbital velocity, there's pretty much nothing to 70 00:05:02,240 --> 00:05:05,920 slow you back down again, so you can continue to fall around the Earth, 71 00:05:06,199 --> 00:05:11,480 moving in a circular pattern of free fall, but never getting any closer 72 00:05:11,480 --> 00:05:15,879 to the surface. So all of that to say that gravity is extremely complicated, 73 00:05:15,959 --> 00:05:20,560 yet at the same time essential to our survival. The human body evolved 74 00:05:20,600 --> 00:05:26,959 under the force of Earth gravity. Our entire muscular and skeletal structure is designed 75 00:05:27,079 --> 00:05:30,560 to resist the force of gravity. All of our internal organs are meant to 76 00:05:30,600 --> 00:05:34,920 function in step with gravity. Food goes in the top, waste comes out 77 00:05:34,959 --> 00:05:40,759 the bottom. Our entire circulatory system is meant to keep our blood moving up 78 00:05:40,800 --> 00:05:44,959 and down in spite of the force of gravity. That means when you take 79 00:05:45,040 --> 00:05:49,000 gravity out of the equation, the entire body becomes a confused mess. It 80 00:05:49,079 --> 00:05:54,360 freaks out. Nothing is functioning the way it is supposed to, And if 81 00:05:54,360 --> 00:05:58,240 you stay in that state of anti gravity for a prolonged period of time, 82 00:05:58,480 --> 00:06:01,360 then your body is going to have a very difficult struggle bringing you back to 83 00:06:01,399 --> 00:06:06,759 the natural equilibrium when you finally return to the Earth's surface. Coming back from 84 00:06:06,759 --> 00:06:13,279 weightlessness is like a full body hangover, except this one lasts for months, 85 00:06:13,600 --> 00:06:16,120 and if you stay weightless for too long, you may never get back to 86 00:06:16,120 --> 00:06:20,399 the way you were before. We're talking permanent damage. So with all of 87 00:06:20,399 --> 00:06:25,160 that in mind, we know that if humanity is ever to become a true 88 00:06:25,439 --> 00:06:30,480 space faring civilization and explore the outer reaches of the Solar System and all of 89 00:06:30,480 --> 00:06:33,160 the planets and moons in between, or even if we just want to live 90 00:06:33,199 --> 00:06:36,399 in the orbit of our own planet, then we are going to need to 91 00:06:36,439 --> 00:06:43,839 sacrifice our own bodies or develop some kind of artificial gravity replacement. Because we 92 00:06:43,879 --> 00:06:47,560 know that the only way to create true gravity is with extreme concentrations of mass. 93 00:06:47,600 --> 00:06:51,439 The best we could possibly do with something as simple as a spaceship is 94 00:06:51,480 --> 00:06:57,439 to create a force that might simulate the effect of gravity. Luckily for us, 95 00:06:57,639 --> 00:07:00,160 Albert Einstein figured out how to do this a very long time ago. 96 00:07:00,600 --> 00:07:04,360 All we need to do is accelerate at a rate that is equivalent to the 97 00:07:04,399 --> 00:07:09,839 force of Earth's gravity, which in this case would be an acceleration of nine 98 00:07:09,839 --> 00:07:14,959 point eight meters per second squared. This is also an oversimplification, but we've 99 00:07:14,959 --> 00:07:18,319 done just about enough bad physics lessons for one video. According to Einstein, 100 00:07:18,399 --> 00:07:23,800 if you could accelerate linearly at this exact rate, then the downward force you 101 00:07:23,800 --> 00:07:28,800 would experience from acceleration would be identical to the force of gravity experienced on the 102 00:07:28,800 --> 00:07:32,519 surface of the Earth. So why don't we do that? Well, Accelerating 103 00:07:32,560 --> 00:07:36,600 at nine point eight meters per second squared is incredibly rapid. It would take 104 00:07:36,639 --> 00:07:42,399 an outrageous amount of rocket fuel to achieve this kind of acceleration with a conventional 105 00:07:42,519 --> 00:07:45,439 rocket, and we have to remember that this is not a speed that you 106 00:07:45,480 --> 00:07:49,199 can coast at. This formula demands that you continuously accelerate at a rate of 107 00:07:49,279 --> 00:07:53,959 nine point eight meters per second squared, which would pretty quickly get you up 108 00:07:53,959 --> 00:07:57,920 to a velocity that approaches the speed of light. You'd enter the next galaxy 109 00:07:58,000 --> 00:08:01,240 within a few years. You could probably even reached the edge of the known 110 00:08:01,360 --> 00:08:05,079 universe within your lifetime. Meanwhile, everything not moving at near light speed would 111 00:08:05,079 --> 00:08:09,560 experience billions of years of passing time, So the Earth, the Sun, 112 00:08:09,600 --> 00:08:13,720 and even the entire Milky Way galaxy would all have grown old and died. 113 00:08:13,160 --> 00:08:18,600 You'd have accelerated yourself right to the end of infinity, whatever that is. 114 00:08:18,480 --> 00:08:24,160 But time is even weirder than gravity, so let's stop talking about it before 115 00:08:24,160 --> 00:08:28,759 we all have an existential meltdown. So with Einstein's theory out, that leaves 116 00:08:28,800 --> 00:08:33,399 us with one final way to mimic the effect of Earth's gravity spinning in a 117 00:08:33,440 --> 00:08:37,679 circle. I'm pretty sure these things are illegal now, but if you're an 118 00:08:37,720 --> 00:08:41,679 adult over the age of thirty, then you've probably experienced one of these playground 119 00:08:41,679 --> 00:08:46,039 merry go round things. A bunch of sadistic children would spin this nightmare up 120 00:08:46,039 --> 00:08:50,279 to terminal velocity until kids started flying off and vomiting everywhere. It was great 121 00:08:50,360 --> 00:08:54,279 fun, and that is the exact kind of effect that we are trying to 122 00:08:54,320 --> 00:09:00,639 replicate in space, just hopefully with less crying and vomiting. This is where 123 00:09:00,759 --> 00:09:03,840 rotating space stations come into the picture. We've seen a ton of these things 124 00:09:03,840 --> 00:09:09,639 in science fiction media over the years, but would they actually work as advertised 125 00:09:09,639 --> 00:09:13,279 in the real world. The reason that those old playground toys had such devastating 126 00:09:13,279 --> 00:09:18,639 effects on our tiny little bodies was down to the radius being too small and 127 00:09:18,679 --> 00:09:22,519 the rate of rotation being too fast for the brain and the inner ear to 128 00:09:22,639 --> 00:09:26,600 handle. Very smart people have done a bunch of really interesting studies where they 129 00:09:26,639 --> 00:09:31,759 stuck people into centrifuge machines, which are basically very large equivalents of our playground 130 00:09:31,759 --> 00:09:37,799 merry go round, and they monitor what happens to the lucky subjects. From 131 00:09:37,840 --> 00:09:41,080 that, we've figured out that the average person can sustain around one revolution per 132 00:09:41,120 --> 00:09:48,039 minute without becoming nauseous or disoriented, So that's not very fast. If we 133 00:09:48,080 --> 00:09:50,759 know the desired revolutions per minute and we know the target force of one G, 134 00:09:52,279 --> 00:09:54,799 then all we need to do is find our radius for our circular space 135 00:09:54,799 --> 00:10:00,279 station and we should be all set. The biggest problem we face is that 136 00:10:00,320 --> 00:10:03,159 the slower the desired rotation, the larger the space station needs to be. 137 00:10:03,559 --> 00:10:09,000 For example, if we wanted to spin something the size of the existing iss 138 00:10:09,039 --> 00:10:11,840 to generate one g of force, then it would need to rotate once every 139 00:10:11,919 --> 00:10:16,919 ten seconds, so obviously the result would be a vomit comet. It's generally 140 00:10:16,960 --> 00:10:20,440 accepted that to achieve a force of around one g at around one rpm, 141 00:10:20,639 --> 00:10:26,120 we would need a structure that is at least one kilometer across, So this 142 00:10:26,200 --> 00:10:30,279 is one gigantic circle. But that's not even all that we have to consider 143 00:10:30,320 --> 00:10:35,159 here. Remember we figured out that the Earth's surface is over six thousand kilometers 144 00:10:35,159 --> 00:10:39,000 away from its gravity well, and that's why we don't experience different amounts of 145 00:10:39,039 --> 00:10:43,799 gravity at different elevations on the surface. Even in a one kilometer diameter ring, 146 00:10:45,039 --> 00:10:48,840 you are now relatively close to your center point, which in that case 147 00:10:48,879 --> 00:10:52,720 the center of the ring would be a point of zero gravity and the full 148 00:10:52,759 --> 00:10:56,679 one G force would be located on the outside of the ring. That means 149 00:10:56,679 --> 00:11:00,559 that the gradient between zero G and one G is going to be steep. 150 00:11:00,679 --> 00:11:05,240 So just standing up straight on the floor, you may experience a perceptible difference 151 00:11:05,279 --> 00:11:07,879 in the force of gravity acting on your head than what you feel at your 152 00:11:09,000 --> 00:11:13,240 feet. Best case scenario, this could be very strange, but worst case 153 00:11:13,320 --> 00:11:16,720 it could be straight up disorienting. This is also problematic if you want to 154 00:11:16,759 --> 00:11:20,919 have multiple levels in your space station, as each level would have a reduced 155 00:11:20,919 --> 00:11:26,159 force of gravity as you went up, and even more extreme gradient between the 156 00:11:26,200 --> 00:11:30,240 force of gravity at the ceiling and g force at the floor. Though climbing 157 00:11:30,279 --> 00:11:33,720 any kind of stairs or ladder would be nearly impossible. Yet another force that 158 00:11:33,720 --> 00:11:37,360 we have to consider here is the Coriolis effect, which is pretty much the 159 00:11:37,399 --> 00:11:43,159 effect of our rotational momentum on objects inside the station. We have this on 160 00:11:43,200 --> 00:11:46,240 the Earth, but because the Earth rotates so slowly, the Coriolis effect is 161 00:11:46,279 --> 00:11:52,480 imperceptible in our daily lives. The force of gravity significantly overpowers the rotational momentum, 162 00:11:52,759 --> 00:11:56,720 so it only really has an effect on high level weather patterns. This 163 00:11:56,840 --> 00:12:01,159 is what causes storm clouds and hurricane to rotate. But on a much smaller, 164 00:12:01,240 --> 00:12:05,440 much faster spinning station, the Coriolis effect is going to be a regular 165 00:12:05,480 --> 00:12:11,240 force to contend with. It basically means that nothing will ever go in a 166 00:12:11,279 --> 00:12:15,480 straight line. So if you tried to throw a baseball inside a rotating space 167 00:12:15,519 --> 00:12:20,080 station, the ball would immediately curve over to the side. If you tried 168 00:12:20,120 --> 00:12:22,679 to pour a drink into a glass, the liquid would go flying out at 169 00:12:22,679 --> 00:12:26,799 an angle, trying to take a shower would be a major challenge because the 170 00:12:26,840 --> 00:12:33,200 water would never fall straight down. Now you've probably already noticed that building a 171 00:12:33,200 --> 00:12:37,600 gigantic space station ring one kilometer across is going to be nearly impossible from a 172 00:12:37,639 --> 00:12:43,679 logistical standpoint. That's the kind of thing that will definitely require some asteroid mining 173 00:12:43,879 --> 00:12:48,080 and a whole manufacturing industry on the Moon and stuff like that. But we 174 00:12:48,159 --> 00:12:52,000 could have a more feasible solution. We don't actually need the entire ring. 175 00:12:52,120 --> 00:12:56,360 All we need is the diameter and the rotation. So you could have two 176 00:12:56,399 --> 00:13:01,759 space station modules that are connected together by a one kilometer long truss and then 177 00:13:01,879 --> 00:13:07,480 set it into rotation. This would achieve that force of roughly one G in 178 00:13:07,559 --> 00:13:11,759 each of the modules. So in theory, all we would really need to 179 00:13:11,759 --> 00:13:16,480 figure out is a relatively basic microgravity three D printing operation to build out that 180 00:13:16,720 --> 00:13:22,720 trust structure. We could then use two large vehicles like SpaceX starships or cr 181 00:13:22,759 --> 00:13:26,759 space inflatable life modules, and we could have the first artificial gravity station. 182 00:13:28,279 --> 00:13:33,879 This is at least conceivable with the technology that we have available right now.