WEBVTT - What is a Space Elevator? 0:00:01.160 --> 0:00:04.720 Hey, welcome to Science Stuff, the production of iHeartRadio. I'm 0:00:04.720 --> 0:00:08.920 Moreham and today we are going to space. No, we're 0:00:08.920 --> 0:00:11.639 not going to strap ourselves to a giant rocket full 0:00:11.680 --> 0:00:21.200 of flammable fuel. Instead, we are going to take the elevator. 0:00:25.880 --> 0:00:29.120 It may seem like science fiction, but a space elevator 0:00:29.240 --> 0:00:33.160 is something serious scientists actually think is possible to build. 0:00:33.600 --> 0:00:35.680 And it's not just something that can take you to space. 0:00:36.280 --> 0:00:39.720 It might actually help you get to other planets. To 0:00:39.720 --> 0:00:43.720 put on some relaxing music, step inside and ride with 0:00:43.880 --> 0:00:47.120 us as we go up to answer the question, can 0:00:47.159 --> 0:00:49.919 we build an elevator to space? 0:00:56.240 --> 0:00:56.440 Hey? 0:00:56.440 --> 0:01:00.400 Everyone, Okay, today we are tackling a pretty wild idea, 0:01:00.440 --> 0:01:03.000 which is to build an elevator that can take you 0:01:03.240 --> 0:01:06.160 to space. But I promise you that by the end 0:01:06.360 --> 0:01:09.720 you're going to be thinking, my gosh, that totally makes sense. 0:01:10.160 --> 0:01:13.399 Let's build one right now. Now. To get there, I 0:01:13.480 --> 0:01:16.559 need you to imagine that you're getting into an elevator, 0:01:17.000 --> 0:01:19.480 and at each floor we're going to be answering a 0:01:19.520 --> 0:01:25.680 different question about space elevators. So step inside, perfect now, 0:01:25.760 --> 0:01:35.199 hit the button for the first floor, and we're going up. Okay, 0:01:35.319 --> 0:01:37.679 while we go up, I'll just tell you that the 0:01:37.760 --> 0:01:40.720 idea of a space elevator is that instead of taking 0:01:40.720 --> 0:01:44.720 a rocket to go to space, you just take an elevator. 0:01:45.120 --> 0:01:47.640 There would be a structure that is based here on Earth, 0:01:48.120 --> 0:01:51.280 and it would extend up past the tallest building we've 0:01:51.280 --> 0:01:56.680 ever built, past the clouds, past the atmosphere, and into space. 0:01:57.560 --> 0:01:59.520 And so if you want to go to space or 0:01:59.680 --> 0:02:02.840 take something into space, all you have to do is 0:02:02.920 --> 0:02:06.480 get on, and then you'd be in space. And if 0:02:06.520 --> 0:02:09.240 you go up high enough, when you get off, you'll 0:02:09.240 --> 0:02:13.040 actually be in orbit around Earth, meaning you wouldn't fall 0:02:13.120 --> 0:02:17.880 back down to Earth. Oh, which has got to our 0:02:17.919 --> 0:02:22.720 first stop. Okay, Here, I imagine we are ten kilometers 0:02:22.800 --> 0:02:25.800 above the surface of the Earth. This is about twelve 0:02:25.800 --> 0:02:29.000 times higher than the Birch Khalifa, which is the highest 0:02:29.000 --> 0:02:32.600 building we've ever built. Here, at ten kilometers, we're at 0:02:32.600 --> 0:02:35.560 the top of the troposphere, which is the main layer 0:02:35.760 --> 0:02:38.600 of our atmosphere. It's the lear where all the weather 0:02:38.680 --> 0:02:41.360 happens because it has most of the water that's in 0:02:41.360 --> 0:02:44.640 the atmosphere. And this is about as high as even 0:02:44.639 --> 0:02:50.720 the highest clouds go. Oh, and here joining us is 0:02:50.760 --> 0:02:55.080 our first expert, Professor Matthew Pete, come in, doctor Pete, 0:02:55.360 --> 0:02:56.440 thanks for joining us. 0:02:56.639 --> 0:02:57.840 Well, thank you for having me. 0:02:58.360 --> 0:03:00.720 Keith, Please tell us who you are and you do so. 0:03:00.760 --> 0:03:04.480 I'm a professor at Arizona State University and teach and 0:03:04.560 --> 0:03:09.360 do research in orbital mechanics and controls and dynamical systems theory. 0:03:09.760 --> 0:03:11.640 Okay, so to thee on the program, we're answering the 0:03:11.720 --> 0:03:14.880 question what is a space elevator? So where did this 0:03:15.040 --> 0:03:15.880 idea come from? 0:03:16.120 --> 0:03:18.040 Well, you know, that's an interesting story. 0:03:18.400 --> 0:03:18.880 Arthur C. 0:03:19.000 --> 0:03:21.600 Clark had a great paper on this and he counted 0:03:21.600 --> 0:03:23.400 the number of times it had been reinvented, and I 0:03:23.440 --> 0:03:25.800 think he was at eleven. The first invention of the 0:03:25.840 --> 0:03:29.880 space elevator was by Konstancy Sokowsky. If you don't know 0:03:29.919 --> 0:03:32.320 who is you might be forgiven. But he was one 0:03:32.360 --> 0:03:36.200 of these very early rockets guys, and living in a 0:03:36.240 --> 0:03:40.280 cabin outside of Moscow back in eighteen ninety five. What 0:03:40.400 --> 0:03:43.480 he was doing inventing rockets and space elevators we could 0:03:43.520 --> 0:03:47.560 leave to our imagination. So who knows what he was 0:03:47.560 --> 0:03:50.760 doing out in his cabin. But although famous for space elevators, 0:03:50.800 --> 0:03:54.680 he's of course far more famous for inventing the rocket equation. 0:03:55.040 --> 0:03:58.360 So he laid out the basic mathematical foundations for the 0:03:58.440 --> 0:03:59.960 use of rockets back in eighteen ninety. 0:04:00.560 --> 0:04:03.160 So he sort of invented rocket signs in a way. 0:04:03.600 --> 0:04:06.360 Yeah, I would give him credit for inventing rocket scignen. 0:04:06.440 --> 0:04:07.960 So the same person who came up with the rocket 0:04:08.000 --> 0:04:10.360 equation came up with this idea of the space elevator 0:04:10.400 --> 0:04:11.040 for the first time. 0:04:11.120 --> 0:04:11.360 Yeah. 0:04:11.400 --> 0:04:14.320 He was inspired by the Eiffel Tower and how far 0:04:14.360 --> 0:04:16.560 it reached up, and he said, well, if you reach 0:04:16.680 --> 0:04:19.240 far enough, you could just drop things off the ever 0:04:19.440 --> 0:04:21.880 tower and it we'd be in orbit. So he laid 0:04:21.880 --> 0:04:24.479 out the basics and then it was invented a couple 0:04:24.520 --> 0:04:25.880 more times. 0:04:25.360 --> 0:04:27.520 Like people would just come up with it and work 0:04:27.560 --> 0:04:30.520 it out without knowing what somebody else had already done. 0:04:30.760 --> 0:04:33.520 Yeah, because it's an eminently logical and interesting idea. 0:04:34.560 --> 0:04:37.280 So this idea of a space elevator that we're writing 0:04:37.360 --> 0:04:41.920 right now came up a long time ago, back before 0:04:41.960 --> 0:04:45.240 we even had rockets, And he keeps popping up over 0:04:45.400 --> 0:04:48.279 and over again over the last one hundred and thirty 0:04:48.360 --> 0:04:51.800 years because it kind of makes sense. If you want 0:04:51.800 --> 0:04:54.320 to get to space, why not just build something that 0:04:54.400 --> 0:05:02.839 can get you there directly. Oh, we're in our next up. Okay, 0:05:03.200 --> 0:05:06.640 Here we are one hundred kilometers above the surface of 0:05:06.640 --> 0:05:09.919 the Earth, meaning about one hundred and twenty times the 0:05:10.000 --> 0:05:14.240 height of the bird khalifa. Oh, what's your step? You 0:05:14.360 --> 0:05:17.920 definitely don't want to fall from here. At one hundred kilometers, 0:05:18.160 --> 0:05:22.200 this is what's called the Carmen line. We're technically still 0:05:22.200 --> 0:05:24.680 in the atmosphere, but this is the point that people 0:05:24.720 --> 0:05:29.200 say separates being on Earth and being in space. It's 0:05:29.200 --> 0:05:32.479 a little bit of an arbitrary number, mostly chosen because 0:05:32.560 --> 0:05:35.480 one hundred kilometers is a nice round number. But at 0:05:35.480 --> 0:05:38.880 around this level is where airplanes can no longer fly 0:05:39.400 --> 0:05:42.880 or stay flying, because there isn't enough air to keep 0:05:42.920 --> 0:05:49.000 them afloat. It's also around here that there isn't enough 0:05:49.040 --> 0:05:52.560 air to burn up meteorites, so if you see shooting stars, 0:05:52.920 --> 0:05:56.160 they would be below you. It's also where the International 0:05:56.360 --> 0:06:01.680 Aeronautic Federation defines the beginning of space, which technically means 0:06:01.839 --> 0:06:06.160 you and I in this space elevator are now officially astronauts, 0:06:06.680 --> 0:06:09.719 although if you step outside right now, you would basically 0:06:09.800 --> 0:06:13.440 just fall straight down because the force of gravity is 0:06:13.480 --> 0:06:16.200 pretty much the same as on the surface of Earth. 0:06:16.640 --> 0:06:20.720 It's only three percent lower. Okay, let's keep going like 0:06:20.800 --> 0:06:22.640 the pet. Can you please press a button for the 0:06:22.680 --> 0:06:27.320 next floor, of course. Okay, our next stop is going 0:06:27.400 --> 0:06:31.040 to be one thousand kilometers above the surface of Earth. 0:06:31.360 --> 0:06:32.800 It's going to take a little bit to get there. 0:06:32.960 --> 0:06:35.599 So in the meantime, dark the peed. Can you tell 0:06:35.680 --> 0:06:38.039 us why build this space elevator? 0:06:40.080 --> 0:06:44.800 So the obvious reason is that if you're not using 0:06:44.800 --> 0:06:48.480 a space elevator, the alternative is a rocket, and rockets 0:06:48.560 --> 0:06:52.560 are dangerous and rather explosive. And there's this thing called 0:06:52.560 --> 0:06:55.680 the rocket equation, which tells you that the amount of 0:06:55.720 --> 0:06:58.479 propellant you need to get a certain amount of mass 0:06:58.560 --> 0:07:01.920 up into space grows very large the farther you go up, 0:07:02.160 --> 0:07:05.480 so that the fraction of mass to propellant would be 0:07:05.920 --> 0:07:08.680 maybe one thousand to one, right, a lot of propellant 0:07:08.720 --> 0:07:10.160 for very little mass to get up there. If you 0:07:10.200 --> 0:07:12.400 want to put a city on space, for example, it 0:07:12.400 --> 0:07:14.120 would be very difficult with rockets. 0:07:16.000 --> 0:07:19.000 Okay, what doctor P is saying is that rockets are 0:07:19.040 --> 0:07:23.440 just fundamentally inefficient, and that's because of something called the 0:07:23.600 --> 0:07:27.160 rocket equation. It tells you that the amount of fuel 0:07:27.360 --> 0:07:30.800 you need to put something in space using rockets grows 0:07:30.880 --> 0:07:34.600 exponentially the more mass you want to take to space. 0:07:35.160 --> 0:07:37.680 That's because in a rocket, you not only have to 0:07:37.800 --> 0:07:40.240 lift the thing you want to take to space, you 0:07:40.280 --> 0:07:42.480 also have to lift all the fuel you're going to 0:07:42.560 --> 0:07:45.000 need along the way, and that's going to make your 0:07:45.120 --> 0:07:48.960 rocket heavier. So you need to bring more fuel, which 0:07:49.120 --> 0:07:52.320 makes your rocket even heavier, which means you need to 0:07:52.320 --> 0:07:56.520 bring more fuel, et cetera, et cetera. This is why 0:07:56.640 --> 0:07:59.040 when you look at a rocket, most of the long 0:07:59.120 --> 0:08:02.040 cylinder that you see are the tanks for the fuel. 0:08:02.600 --> 0:08:05.040 Only the small part of the bottom is the engine, 0:08:05.200 --> 0:08:08.280 and only the very tippy top is where the astronauts sit. 0:08:08.960 --> 0:08:11.640 So if we're ever going to launch a large spaceship 0:08:11.680 --> 0:08:14.520 with food and people to other planets, it's going to 0:08:14.560 --> 0:08:17.920 take a lot of fuel, and that brings other problems, 0:08:18.360 --> 0:08:19.120 right like your beat. 0:08:19.600 --> 0:08:23.160 Yes, so recent rockets tend to use slightly different fuels, 0:08:23.480 --> 0:08:27.440 using etholocks and cara locks, which are petroleum based. So 0:08:27.440 --> 0:08:30.720 there's an environmental question which says that if you're going 0:08:30.760 --> 0:08:32.760 to put lots of things in space, well maybe it's 0:08:32.840 --> 0:08:35.480 not a great idea to burn quite that much petroleum. 0:08:35.520 --> 0:08:38.120 Product, it's not good for the environment. 0:08:38.320 --> 0:08:40.680 Yeah, Okay. 0:08:40.960 --> 0:08:43.559 When we come back, we're going to continue our elevator 0:08:43.640 --> 0:08:46.640 ride into space, and we're going to talk about the 0:08:46.720 --> 0:08:51.079 big question, which is how do you build a space elevator? 0:08:51.400 --> 0:08:54.640 So don't hop off, keep writing with us. We'll be 0:08:54.840 --> 0:08:55.360 right back. 0:09:02.679 --> 0:09:03.319 Welcome back. 0:09:03.960 --> 0:09:07.800 All right, we're writing an elevator to space, and you're 0:09:07.840 --> 0:09:11.559 probably wondering, how do you build an elevator to space. 0:09:11.920 --> 0:09:14.079 We'll get to that in a minute, but first we're 0:09:14.080 --> 0:09:24.520 going to make another stop right about now. Okay, right now, 0:09:24.600 --> 0:09:28.800 we are one thousand kilometers above the surface of the Earth, 0:09:30.000 --> 0:09:33.640 which is twelve hundred times higher than the tallest building 0:09:33.679 --> 0:09:37.440 in the world, the Birch Khalifa. So you can imagine 0:09:37.440 --> 0:09:40.080 to get to where we are, you'd have to stag 0:09:40.360 --> 0:09:44.200 twelve hundred of the tallest building on Earth, one on 0:09:44.320 --> 0:09:47.320 top of the other. At this height, we are still 0:09:47.400 --> 0:09:51.280 technically in Earth's atmosphere, but we're in the last layer, 0:09:51.600 --> 0:09:55.200 which is the exosphere. Below us, you can see the 0:09:55.280 --> 0:09:58.200 northern lights and there's almost no air. 0:09:59.400 --> 0:09:59.600 Now. 0:10:00.040 --> 0:10:04.800 About five hundred kilometers below us, we passed the International 0:10:04.880 --> 0:10:08.199 Space Station and you might be wondering, or hey, why 0:10:08.280 --> 0:10:10.920 didn't you stop the elevator. You could have just hopped 0:10:10.920 --> 0:10:15.160 off and boarded the space station. Uh not really. That's 0:10:15.200 --> 0:10:20.240 because the International Space Station zip past us at seventeen thousand, 0:10:20.440 --> 0:10:24.320 four hundred miles per hour, which is about eight times 0:10:24.360 --> 0:10:28.280 faster than a rifle bullet. The International Space Station has 0:10:28.320 --> 0:10:31.040 to go that fast in order to stay in orbit. 0:10:31.720 --> 0:10:34.120 If we were to step off this elevator right now, 0:10:34.480 --> 0:10:37.480 you'd still fall straight down. The force of gravity right 0:10:37.480 --> 0:10:40.360 now is still about seventy five percent of what it 0:10:40.480 --> 0:10:43.360 is on Earth, so we feel a little lighter, but 0:10:43.480 --> 0:10:46.840 you still definitely have your feet planet on the elevator floor. 0:10:47.360 --> 0:10:47.560 Now. 0:10:47.640 --> 0:10:51.720 The reason we stopped here was to pick up another passenger. Ope, 0:10:51.840 --> 0:10:57.320 here he is, Hey, doctor Wright, did you take an 0:10:57.400 --> 0:10:58.560 uber up here? Uh? 0:10:58.679 --> 0:10:59.400 No, I don't think so. 0:11:00.240 --> 0:11:01.920 Okay, I want to ask you how you got here. 0:11:02.000 --> 0:11:03.240 But thanks for joining us. 0:11:03.400 --> 0:11:05.120 You're welcome, happy you could have me on. 0:11:05.240 --> 0:11:06.680 Can you please tell us who you are and what 0:11:06.720 --> 0:11:07.079 do you do. 0:11:07.320 --> 0:11:10.559 I'm currently serving as the president of the International Space 0:11:10.600 --> 0:11:14.080 Elevator Consortium, which is basically a group of people who 0:11:14.160 --> 0:11:16.880 want to advance the development of the space Elevator and 0:11:17.120 --> 0:11:20.400 hopefully get it built within our lifetimes. We talk to 0:11:20.559 --> 0:11:23.920 people who do calculations for the space elevator, we talk 0:11:23.960 --> 0:11:27.400 to people who develop materials for it, and basically anybody 0:11:27.440 --> 0:11:31.280 who might be interested in investing in it and promoting 0:11:31.280 --> 0:11:31.960 its construction. 0:11:32.520 --> 0:11:34.680 Great, hold on, let me press the button for the 0:11:34.679 --> 0:11:37.960 next top, which is going to be thirty five thousand, 0:11:38.320 --> 0:11:41.560 seven hundred and eighty six kilometers from the surface of 0:11:41.559 --> 0:11:47.560 the Earth. We'll explain why we're going to that height 0:11:47.679 --> 0:11:50.320 in a minute. But docked right, I want to ask 0:11:50.360 --> 0:11:53.920 you most people listening probably assume that to build a 0:11:53.960 --> 0:11:57.000 space elevator like the one we're writing right now, you 0:11:57.080 --> 0:11:59.679 have to build it from the ground up, like you 0:11:59.760 --> 0:12:02.680 start building a base on Earth, and you just keep 0:12:02.720 --> 0:12:05.000 building up higher and higher and higher. 0:12:05.600 --> 0:12:09.559 Yeah, pretty much, the ground up way is impractical. So 0:12:09.880 --> 0:12:12.720 Konstantin Sarkowski he came up with the idea of building 0:12:12.760 --> 0:12:15.520 a tower. He was thinking that of a rigid structure 0:12:15.920 --> 0:12:19.360 fixed to the equator, and he figured, well, if you 0:12:19.360 --> 0:12:21.440 build it high enough, yeah, you can get something into 0:12:21.520 --> 0:12:24.320 orbit that way, and it would be very efficient. 0:12:24.280 --> 0:12:29.080 Right, like basically building a super gigantic Eiffel tower, or 0:12:29.200 --> 0:12:33.280 like a Birch Khalifa. But on steroids. But that wouldn't work, right, Like, 0:12:33.600 --> 0:12:36.440 you can't build a tower that tall exactly. 0:12:36.960 --> 0:12:39.680 He realized that would not be practical because he was 0:12:39.679 --> 0:12:42.520 thinking of a compressive structure, in other words, a tower 0:12:42.920 --> 0:12:47.360 based on Earth, and so calculating the strength of steel 0:12:47.600 --> 0:12:51.079 and the mass of such a long structure it would 0:12:51.080 --> 0:12:53.120 take I think he estimated the mass of all the 0:12:53.160 --> 0:12:54.360 steel in the Solar System. 0:12:54.800 --> 0:12:57.240 Okay, what doctor Wright is saying here is that to 0:12:57.280 --> 0:13:00.520 build a space elevator you can't build it from the 0:13:00.559 --> 0:13:04.000 ground up. That's because at some point the weight of 0:13:04.040 --> 0:13:07.439 the tower is too much and the whole thing which 0:13:07.559 --> 0:13:10.320 just collapse. You'd have to build a structure that is 0:13:10.400 --> 0:13:14.240 so ginormous you would use up all the steel in 0:13:14.280 --> 0:13:18.920 the Solar System, which is impossible. So then how do 0:13:18.960 --> 0:13:20.840 you build a space elevator? 0:13:21.559 --> 0:13:24.800 The way we like to think of deploying it is 0:13:24.880 --> 0:13:28.560 starting with something in orbit. In geosynchronis orbit sending a 0:13:28.559 --> 0:13:31.560 cable down until you have a cable that reaches the Earth. 0:13:31.720 --> 0:13:34.439 In other words, the way to build a space elevator 0:13:34.840 --> 0:13:39.000 is from the top down. But how do you do that? 0:13:40.840 --> 0:13:45.439 And that brings us to our next stop. We are 0:13:45.520 --> 0:13:50.680 now thirty five thousand, seven hundred and eighty six kilometers 0:13:50.920 --> 0:13:53.960 from the surface of the Earth. In other words, we 0:13:54.080 --> 0:13:58.160 are standing on the equivalent of forty three thousand, one 0:13:58.240 --> 0:14:03.000 hundred and fifteen birds, which khaliphas stacked one on top 0:14:03.080 --> 0:14:06.040 of the other. At this point, we are about three 0:14:06.280 --> 0:14:10.360 earth diameters away from the surface of Earth and about 0:14:10.400 --> 0:14:12.880 a tenth of the way to the Moon. If you 0:14:12.920 --> 0:14:16.160 look down, you'd see the whole Earth about the size 0:14:16.200 --> 0:14:20.240 of a basketball held at arm's length. Now, why do 0:14:20.400 --> 0:14:23.200 we make a stop here. The reason is that at 0:14:23.200 --> 0:14:29.080 this distance from Earth, you fall into a geosynchronous orbit. Look, 0:14:29.080 --> 0:14:31.480 you're right, Can you explain that for us? 0:14:31.960 --> 0:14:34.840 So this is a particular kind of orbit in which 0:14:34.960 --> 0:14:38.360 the object in the orbit at that altitude seems to 0:14:38.720 --> 0:14:40.960 keep the same position over the Earth when you're at 0:14:41.000 --> 0:14:46.080 the equator. So essentially, the velocity at geosynchronous orbit is 0:14:46.120 --> 0:14:48.520 the same as the angular velocity at the Earth, and 0:14:48.560 --> 0:14:50.680 it would just look like it's staying there. In fact, 0:14:50.840 --> 0:14:53.000 it's really moving at a pretty significant clip. 0:14:54.200 --> 0:14:57.440 Okay, Remember I told you that the International Space Station, 0:14:57.880 --> 0:15:00.800 which was in orbit about four hundred klumter from Earth, 0:15:01.080 --> 0:15:04.600 had to go at about seventeen thousand miles per hour 0:15:04.880 --> 0:15:08.360 to stay in orbit, otherwise it would just crash down 0:15:08.400 --> 0:15:11.800 to Earth. Well, as you go further away from Earth, 0:15:12.120 --> 0:15:16.520 that speed gets slower and slower, and at some point 0:15:16.720 --> 0:15:18.920 the speed you have to keep to stay in orbit 0:15:19.320 --> 0:15:22.720 it's the same speed as the rotation of the Earth, 0:15:23.440 --> 0:15:28.640 and that orbit at that altitude is called the geosynchronous orbit. 0:15:29.240 --> 0:15:32.600 So the Earth is rotating and we're flying around the Earth, 0:15:32.960 --> 0:15:35.840 but it looks like we're just floating because the two 0:15:35.960 --> 0:15:40.040 speeds match each other, and so we're always above the 0:15:40.160 --> 0:15:43.680 same spot on Earth. Okay, I think you know where 0:15:43.720 --> 0:15:46.280 this is going. What happens next, doctor B. 0:15:48.120 --> 0:15:50.320 And So the idea of a space elevator is if 0:15:50.320 --> 0:15:53.480 you put like a really big spool of cable right 0:15:53.560 --> 0:15:56.440 at that geosynchronous altitude and just sort of let it 0:15:56.480 --> 0:16:00.440 down very gradually and slowly, it would just come all 0:16:00.440 --> 0:16:02.880 the way down to the surface of the Earth, and 0:16:02.920 --> 0:16:05.080 you could just tie it down and have a very 0:16:05.240 --> 0:16:08.040 long cable which you can then run some mechanical device 0:16:08.120 --> 0:16:10.360 up to get things up into geosynchronous orbit. 0:16:10.920 --> 0:16:13.240 It's like if you were trying to build an elevator 0:16:13.280 --> 0:16:15.680 to a cloud. One way to do it is to 0:16:15.720 --> 0:16:19.880 build a huge tower from the ground that reaches the cloud, 0:16:20.200 --> 0:16:22.800 or you could just fly a balloon up to the 0:16:22.800 --> 0:16:26.480 cloud and once you're there, lower a rope or a 0:16:26.560 --> 0:16:29.760 cable down to the ground and use that to climb 0:16:29.880 --> 0:16:33.239 up to the cloud. The idea for this space elevator 0:16:33.560 --> 0:16:37.320 is the same, except instead of a balloon, you're putting 0:16:37.320 --> 0:16:40.160 something in geosynchronous orbit. 0:16:40.520 --> 0:16:43.520 And then you have this straight or mostly straight cable 0:16:43.560 --> 0:16:45.520 that goes from the surface of the Earth, so it's 0:16:45.520 --> 0:16:50.400 a big stationary cable. And on this cable you would 0:16:50.440 --> 0:16:53.960 put a climber or an elevator car or something which 0:16:54.040 --> 0:16:57.160 lifts your payload up to whatever altitude you want. 0:16:57.760 --> 0:17:00.280 And at this distance from Earth, if you s depth 0:17:00.320 --> 0:17:04.560 outside the elevator, you would just float. You wouldn't fall 0:17:04.600 --> 0:17:07.800 back down because the gravity would be weaker, and it 0:17:07.840 --> 0:17:11.760 would exactly match this interpretal force you get from going 0:17:11.840 --> 0:17:15.119 in a circle around the Earth. And the idea is 0:17:15.119 --> 0:17:17.960 that at this point you could bring materials up to 0:17:18.000 --> 0:17:21.879 the elevator and build a whole city up there in space. 0:17:22.600 --> 0:17:24.000 So there are a lot of things we can do. 0:17:24.480 --> 0:17:27.800 So that's a perfect place to build solar power satellites. 0:17:28.080 --> 0:17:32.080 Rather large habitats could be built there. Okay, colonies things 0:17:32.160 --> 0:17:33.879 like that, orbibal factories. 0:17:36.040 --> 0:17:38.359 Okay, when we come back, we're going to talk about 0:17:38.480 --> 0:17:41.879 another really cool thing you can do with a space elevator, 0:17:42.200 --> 0:17:45.000 and we're going to answer the question you're probably thinking 0:17:45.280 --> 0:17:49.280 right now, which is why haven't we built them? If 0:17:49.320 --> 0:17:52.679 space elevators are so great, why are we still sending 0:17:52.720 --> 0:17:56.760 things to space using rockets? Well, answer that question after 0:17:56.920 --> 0:18:09.240 the break. You're listening to science stuff and we're back. Okay, 0:18:09.600 --> 0:18:13.399 you and I are currently in space thirty five thousand, 0:18:13.720 --> 0:18:17.800 seven hundred and eighty six kilometers above the surface of 0:18:17.840 --> 0:18:22.600 the Earth. At this point, we are definitely outside Earth's atmosphere. 0:18:22.920 --> 0:18:25.800 We left that at ten thousand kilometers, but we're still 0:18:25.880 --> 0:18:31.040 under the influence of Earth's gravity barely. At this height 0:18:31.119 --> 0:18:34.879 and at this speed, we are logged in geosynchronous orbit, 0:18:35.320 --> 0:18:38.600 which means we're always above the same point on the 0:18:38.680 --> 0:18:42.640 surface of Earth as it rotates. And I should mention 0:18:42.840 --> 0:18:46.960 this only works of our orbit goes around Earth's equator. Now, 0:18:47.000 --> 0:18:49.199 if we were to lower a cable down to the 0:18:49.240 --> 0:18:52.440 surface of Earth thirty five thousand, seven hundred and eighty 0:18:52.480 --> 0:18:56.520 six kilometers, we would create a link between us and 0:18:56.720 --> 0:19:00.800 Earth that we could use as an elevator. You could 0:19:00.800 --> 0:19:04.160 attach a platform that climbs up the cable to bring 0:19:04.240 --> 0:19:08.880 things to space without having to use expensive, dangerous and 0:19:08.960 --> 0:19:14.199 polluting rockets. That's the idea of a space elevator. And 0:19:14.240 --> 0:19:16.119 what school is that you can use it not just 0:19:16.160 --> 0:19:19.480 to put things in space, but to fling them to 0:19:19.720 --> 0:19:21.919 other planets, right the repete. 0:19:22.200 --> 0:19:25.400 Yeah, And the final argument that people put forward is 0:19:25.440 --> 0:19:29.880 that you know, there's this balance between centripetal and gravitational acceleration, 0:19:30.680 --> 0:19:33.840 and when you're in geosynchronous they're precisely balanced and you're 0:19:34.000 --> 0:19:38.520 precisely above the Earth. But everything beyond that centripetal acceleration 0:19:38.640 --> 0:19:42.120 is actually larger than gravitational force. So if you run 0:19:42.160 --> 0:19:45.320 a cable beyond the space elevator, if you run some 0:19:45.400 --> 0:19:48.720 kind of structure beyond the space elevator, at some point, 0:19:48.880 --> 0:19:52.280 if you go an additional three thousand kilometers, that tip 0:19:52.600 --> 0:19:55.920 the apex of the space elevator is actually moving faster 0:19:56.400 --> 0:19:59.320 than the velocity you need to escape the Earth's gravitational influence, 0:19:59.359 --> 0:20:00.680 so you could go to other planets. 0:20:02.119 --> 0:20:04.840 Okay, this is pretty cool. So where we are now 0:20:05.040 --> 0:20:09.040 in geosynchronous orbit, it's sort of perfectly balanced. But if 0:20:09.080 --> 0:20:12.359 I were to extend the space elevator further out, like 0:20:12.600 --> 0:20:15.040 if I were to not just drop a cable down 0:20:15.080 --> 0:20:17.760 to Earth, but also let loose a cable the other 0:20:17.840 --> 0:20:21.480 way away from Earth, you could use that cable to 0:20:21.680 --> 0:20:26.159 fling things out into space. So, for example, if I 0:20:26.200 --> 0:20:29.600 attach a dumbbell to that cable above us, we would 0:20:29.640 --> 0:20:33.000 see that dumbell start moving away from us because of 0:20:33.160 --> 0:20:37.240 centripetal acceleration. That's the force that pushes you out when 0:20:37.520 --> 0:20:40.159 say you're going around a Narry go round, or the 0:20:40.160 --> 0:20:42.760 force that pulls your arms out if you spin in place. 0:20:43.520 --> 0:20:46.720 So we'd see the dumbbell move away from us, going 0:20:46.840 --> 0:20:50.439 faster and faster, and then if the cable ends, the 0:20:50.520 --> 0:20:54.359 dumbo would get flung out into space. And that's how 0:20:54.400 --> 0:20:57.560 you can use a space elevator to launch things to 0:20:57.760 --> 0:20:58.800 other planets. 0:21:00.440 --> 0:21:02.760 Yeah, you could let it go off the end of 0:21:02.800 --> 0:21:06.560 the cable and that would have its maximum release velocity. 0:21:06.640 --> 0:21:10.080 So if you release at one hundred thousand kilometers, then 0:21:10.119 --> 0:21:12.520 you can reach the inner edge of the asteroid belt 0:21:12.640 --> 0:21:16.720 without any extra rocket thrust. If you want to go 0:21:16.760 --> 0:21:21.280 to Mars, you can release at that altitude or a 0:21:21.320 --> 0:21:24.120 lower one. But if you release at that altitude, then 0:21:24.160 --> 0:21:26.639 you can get to Mars in about sixty one days 0:21:26.640 --> 0:21:29.480 as oppose to you know, they're talking about one hundred 0:21:29.480 --> 0:21:31.280 and eighty days for a typical mission. 0:21:31.680 --> 0:21:35.320 Exactly, you wouldn't need any rockets at all. Presumably once 0:21:35.320 --> 0:21:37.399 you got to Jupiter, you wouldn't want to like crash 0:21:37.440 --> 0:21:39.719 into one of the moons, so there'd have to be 0:21:39.720 --> 0:21:42.680 some aerobraking, or you might want to like have a 0:21:42.760 --> 0:21:44.480 rocket to slow down at some point. 0:21:44.640 --> 0:21:48.320 Yeah, so this space elevator wouldn't just get you to space. 0:21:48.720 --> 0:21:50.960 If you want to, say, live in a space station 0:21:51.160 --> 0:21:56.280 in geosynchronous orbit, you could also sling you to other planets. Okay, 0:21:56.280 --> 0:21:59.720 you're probably thinking, now this sounds great, Jorge, but why 0:21:59.760 --> 0:22:02.440 haven't we built one? What's the catch? 0:22:03.080 --> 0:22:03.199 All? 0:22:03.280 --> 0:22:07.760 Right, there are two caveats. The first one comes if 0:22:07.760 --> 0:22:10.639 you think about where the energy is coming from in 0:22:10.720 --> 0:22:13.720 a space elevator. I mean, you get to put things 0:22:13.720 --> 0:22:16.720 in space and even fling them to other planets without 0:22:16.840 --> 0:22:21.000 needing rockets. It sounds too good to be true, doesn't it, 0:22:21.040 --> 0:22:21.760 doctor Pete. 0:22:22.040 --> 0:22:26.280 Yeah, now that's a great insight. So there's no free launch, 0:22:26.359 --> 0:22:29.680 I guess, But weird things happen in space because it's 0:22:29.680 --> 0:22:34.200 an energy conserving field, So where is the energy coming from. 0:22:34.320 --> 0:22:38.040 It's interesting because once you get beyond geosynchronous, the acceleration 0:22:38.200 --> 0:22:41.080 to get to the velocity to get to Jupiter is 0:22:41.480 --> 0:22:45.640 coming from actually the rotational inertia of the Earth itself. 0:22:46.119 --> 0:22:49.760 So the Earth is spinning and pulling the space Elevator 0:22:49.800 --> 0:22:53.960 along with it, and so that acceleration is transferred to 0:22:54.000 --> 0:22:56.720 the base of the space Elevator, and every launch would 0:22:57.080 --> 0:23:00.359 very slightly slow down the spin of the Earth. So 0:23:00.520 --> 0:23:03.879 presumably we wouldn't launch too much or people would have 0:23:03.920 --> 0:23:08.120