WEBVTT - Hitting the Road with GPS 0:00:04.480 --> 0:00:12.399 Welcome to Tech Stuff, a production from iHeartRadio. Hey there, 0:00:12.440 --> 0:00:16.120 and welcome to tech Stuff. I'm your host, Jonathan Strickland. 0:00:16.160 --> 0:00:19.200 I'm an executive producer with iHeart Podcasts and how the 0:00:19.239 --> 0:00:23.720 tech are you so, y'all. I love to travel. I 0:00:23.760 --> 0:00:28.360 love to visit new places or revisit ones after I've 0:00:28.400 --> 0:00:31.240 been away for a long time. I even don't really 0:00:31.320 --> 0:00:35.160 mind the journey part of travel, which can often be 0:00:35.320 --> 0:00:38.520 you know, stressful, in a hassle if things aren't going well. 0:00:38.880 --> 0:00:41.400 One thing that does give me a huge amount of 0:00:41.400 --> 0:00:46.240 anxiety if I'm traveling is just getting lost or even 0:00:46.280 --> 0:00:48.880 the thought of getting lost. I do not do very 0:00:48.880 --> 0:00:51.159 well with that. There's some part of my brain that 0:00:51.200 --> 0:00:53.840 mistakenly believes that as long as I know where I am, 0:00:54.560 --> 0:00:58.640 nothing can go too wrong. And boy I wish that 0:00:58.720 --> 0:01:02.600 were true, but but yeah, whatever, I just need my 0:01:02.720 --> 0:01:06.360 brain to let me function properly when I'm out on holidays. 0:01:06.400 --> 0:01:11.280 So I remember traveling on my honeymoon to London. At 0:01:11.280 --> 0:01:14.600 that point, I had never been outside the United States before. 0:01:14.720 --> 0:01:18.040 This was my first trip outside the country, and I 0:01:18.080 --> 0:01:20.800 was going to a city that I had read about extensively. 0:01:21.400 --> 0:01:24.720 I knew a lot about London. My major in college 0:01:24.800 --> 0:01:27.959 was in English literature, but it was with a focus 0:01:28.000 --> 0:01:31.200 on medieval studies, so things had changed slightly by the 0:01:31.240 --> 0:01:33.760 time I got there, and reading about a city is 0:01:33.920 --> 0:01:38.600 very different from actually walking around one. Also, my honeymoon 0:01:38.640 --> 0:01:41.959 was in the nineteen nineties because I'm old, and that 0:01:42.080 --> 0:01:46.480 meant I was a decade out from the era of smartphones, 0:01:46.800 --> 0:01:49.440 so I didn't have a handy mobile device to tell 0:01:49.440 --> 0:01:52.080 me where I was as I wandered around the city. 0:01:52.280 --> 0:01:55.480 Even if smartphones had been around back then, I wouldn't 0:01:55.520 --> 0:01:58.800 have been able to rely on map apps on the 0:01:58.840 --> 0:02:03.960 smartphone because of something called selective availability. More on that 0:02:04.560 --> 0:02:07.520 in a bit, but at any rate, I had to 0:02:07.560 --> 0:02:11.800 rely on physical maps to get around and hope that 0:02:11.800 --> 0:02:14.600 I didn't mess it up too badly. Yeah, it's like 0:02:14.639 --> 0:02:17.760 the Stone Age right. Well, these days, as long as 0:02:17.760 --> 0:02:20.680 I have my smartphone with me and I'm not buried 0:02:20.760 --> 0:02:23.840 under a mountain or something, I feel fairly confident I'm 0:02:23.880 --> 0:02:26.320 not going to get lost. If I'm going somewhere that 0:02:26.320 --> 0:02:30.120 has limited connectivity, like limited view of the sky, then 0:02:30.240 --> 0:02:33.720 my anxiety starts to creep in again. But usually I'm okay, 0:02:34.160 --> 0:02:38.040 and that's thanks to the Global Positioning System or GPS. 0:02:38.360 --> 0:02:41.720 So today we're going to learn about GPS, what makes 0:02:41.720 --> 0:02:44.600 it work, how the technology has to take into account, 0:02:44.639 --> 0:02:48.679 Einstein's theories of relativity and more. And a huge thank 0:02:48.720 --> 0:02:51.839 to JP Morgan, Chase Bank, and the United Explorer Card 0:02:51.919 --> 0:02:55.400 for sponsoring this episode. We'll hear more about them later too. 0:02:55.960 --> 0:03:00.000 So GPS, well, that story begins back in the nineteen 0:03:00.000 --> 0:03:03.280 teen fifties when the United States and the then Soviet 0:03:03.400 --> 0:03:06.760 Union were locked in a Cold war, and that cold 0:03:06.760 --> 0:03:09.960 war manifested in many different ways, including an effort to 0:03:10.040 --> 0:03:13.080 launch vehicles into space. For one thing, if you could 0:03:13.160 --> 0:03:17.320 launch a rocket into orbit, then you could show your 0:03:17.320 --> 0:03:20.760 technological superiority over your opponent and say, look how much 0:03:20.800 --> 0:03:23.959 further advanced we are compared to you. But you could 0:03:24.000 --> 0:03:26.480 also send the message of hey, if I can send 0:03:26.520 --> 0:03:29.200 a rocket to space, I could send a rocket to 0:03:29.280 --> 0:03:31.960 your front door, all the way from across the world, 0:03:32.200 --> 0:03:34.440 and it could be carrying a heck of a boom boom. 0:03:34.960 --> 0:03:39.360 Now this gram message underpinned what would become the space race. 0:03:39.400 --> 0:03:42.520 But the space race also meant that brilliant engineers and 0:03:42.560 --> 0:03:46.680 scientists would actually get the resources they needed to advance 0:03:46.720 --> 0:03:50.880 technology by incredible leaps and bounds over the following decades. 0:03:51.200 --> 0:03:53.920 So you got to take the good with the bad, right. 0:03:54.360 --> 0:03:59.480 The good part is you suddenly had actual financial support 0:03:59.800 --> 0:04:05.920 for or incredibly important scientific and engineering work. The bad is, well, 0:04:06.040 --> 0:04:10.480 it was all done in service of this perceived rivalry 0:04:10.760 --> 0:04:13.920 with this massive country on the other side of the globe. 0:04:14.080 --> 0:04:18.279 On October fourth, nineteen fifty seven, at approximately seven thirty pm, 0:04:18.360 --> 0:04:24.040 the USSR launched the first man made satellite into orbit, Sputnik. 0:04:24.480 --> 0:04:27.560 Non past episodes, I have referred to the satellite as 0:04:27.640 --> 0:04:31.520 the ball that went beep. That's not exactly inaccurate. The 0:04:31.560 --> 0:04:34.400 satellite was spherical in shape. It did have these long 0:04:34.440 --> 0:04:36.680 antenna extending out the back of it, so it kind 0:04:36.680 --> 0:04:39.719 of looks like a comet, like a silver comet. But 0:04:39.800 --> 0:04:43.680 the antenna transmitted short radio pulses, and these pulses could 0:04:43.720 --> 0:04:47.440 be picked up very easily by ground based audio receivers, 0:04:47.480 --> 0:04:52.360 including radio sets operated by amateurs, just an amateur radio set. 0:04:52.600 --> 0:04:56.159 This meant that Sputnik's existence couldn't be kept a secret 0:04:56.360 --> 0:04:59.520 because if you or someone you knew operated a radio, 0:05:00.040 --> 0:05:03.320 you could learn about the thing. And in the United States, 0:05:03.320 --> 0:05:07.280 it prompted no small amount of anxiety. Americans believed their 0:05:07.320 --> 0:05:10.400 country was well ahead of the Soviet Union, at least 0:05:10.400 --> 0:05:14.160 on a technological basis. But here they could see that 0:05:14.200 --> 0:05:17.760 their adversary had launched stuff into space and did it 0:05:17.839 --> 0:05:21.120 before the US could do it. That really kicked things 0:05:21.160 --> 0:05:23.680 into gear here in the United States. But I would 0:05:23.760 --> 0:05:27.200 argue that Sputnik would ultimately plant a seed that would 0:05:27.240 --> 0:05:30.720 blossom into GPS further down the line, because here you 0:05:30.760 --> 0:05:34.840 had a satellite sending regular radio signals to Earth, and 0:05:35.000 --> 0:05:38.240 those signals were pretty primitive. Essentially, the satellite was signaling 0:05:38.279 --> 0:05:41.840 that it was within range overhead, along with basic information 0:05:41.880 --> 0:05:45.720 about stuff like air pressure and temperature indicated by the 0:05:45.800 --> 0:05:48.440 length of the radio pulses. Like the pulses didn't give 0:05:48.960 --> 0:05:52.400 data the way Wi Fi does. Literally, you would measure 0:05:52.440 --> 0:05:55.279 how long the pulse lasted and that would tell you, oh, 0:05:55.360 --> 0:05:59.960 the temperature is whatever, if you happen to have the chart. 0:06:00.080 --> 0:06:05.040 Two scientists were able to adfer other information, however, from 0:06:05.279 --> 0:06:09.200 this signal, such as how the propagation of radio signals 0:06:09.200 --> 0:06:12.880 interacted in the upper atmosphere like the ionosphere, and it 0:06:13.000 --> 0:06:16.080 hinted that there could be other uses for as satellite 0:06:16.400 --> 0:06:20.640 beaming information down to Earth. Also, those signals were subject 0:06:20.680 --> 0:06:23.400 to what we call the Doppler effect. It's named after 0:06:23.640 --> 0:06:27.600 Christian Doppler effect. No, I'm sorry, it's just Christian Doppler. 0:06:27.839 --> 0:06:31.480 He first observed this effect back in eighteen forty two. 0:06:32.080 --> 0:06:35.160 And this is how the frequency of a wave changes 0:06:35.279 --> 0:06:39.360 relative to an independent observer if the thing that's emitting 0:06:39.400 --> 0:06:43.800 the wave is moving toward or away from that observer. 0:06:44.400 --> 0:06:46.920 Which was a clumsy explanation, Let's just take an example 0:06:46.920 --> 0:06:50.000 because that makes it way more clear. So let's say 0:06:50.480 --> 0:06:53.520 you're just walking down the street. You're on a sidewalk, 0:06:53.920 --> 0:06:56.159 and say one hundred feet or so in front of you, 0:06:56.440 --> 0:06:59.480 there's an emergency vehicle and it's parked. It's not currently 0:06:59.560 --> 0:07:02.880 driving anywhere, but it is running its siren. The sound 0:07:02.920 --> 0:07:06.279 of that siren is going to remain consistent relative to you, right, 0:07:06.839 --> 0:07:10.800 it may increase and decrease in pitch because the nature 0:07:10.840 --> 0:07:14.360 of the siren, but it's going to keep doing that 0:07:14.440 --> 0:07:18.120 pattern over and over again. But now let's say that 0:07:18.360 --> 0:07:21.360 it's an emergency vehicle that's rushing off away from you. 0:07:21.400 --> 0:07:24.120 It's driving off. You'll notice the pitch of the siren 0:07:24.160 --> 0:07:26.720 will start to go lower. The frequency of the sound 0:07:26.720 --> 0:07:30.680 wave decreases as the vehicle accelerates away from you, or 0:07:31.120 --> 0:07:33.840 let's say the vehicle is driving towards you, the pitch 0:07:33.840 --> 0:07:37.320 of the siren will go up as the frequency increases. 0:07:37.720 --> 0:07:39.480 You can kind of think of it like this. An 0:07:39.560 --> 0:07:44.480 approaching object emitting a wave is effectively pushing or compressing 0:07:44.520 --> 0:07:47.600 that wave as it moves closer to you. An object 0:07:47.680 --> 0:07:50.600 moving away from you is stretching out the wave it's 0:07:50.600 --> 0:07:53.960 emitting as it moves away from you. That is the 0:07:54.040 --> 0:07:58.960 Doppler effect. Scientists at the Applied Physics Laboratory or APL, 0:07:59.080 --> 0:08:03.080 at Johns Hopkins University noticed that the Doppler effect was 0:08:03.280 --> 0:08:07.720 also applicable to Sputnik's radio waves. The satellite's radio pulses 0:08:07.760 --> 0:08:11.440 were compressed as Sputnik would approach, and then they would 0:08:11.440 --> 0:08:14.600 stretch out as the satellite would move away from their 0:08:14.680 --> 0:08:18.280 point of observation, and this meant that just by listening 0:08:18.320 --> 0:08:22.400 to the pulses, the scientists could track Sputnik's movements. They 0:08:22.400 --> 0:08:24.800 didn't need to have eyes on the satellite to track it. 0:08:24.920 --> 0:08:27.400 They could just follow the pulses and observe the Doppler 0:08:27.400 --> 0:08:31.360 effect in order to know generally where it was and 0:08:31.400 --> 0:08:34.240 when it was heading away, but very generally, like they 0:08:34.240 --> 0:08:37.880 couldn't give you a pinpointed location. However, this was another 0:08:37.920 --> 0:08:41.400 important seed for what would become GPS, because it would 0:08:41.440 --> 0:08:45.160 lead to the hypothesis that a satellite could send signals 0:08:45.200 --> 0:08:48.080 to a receiver on Earth, and if that receiver quote 0:08:48.120 --> 0:08:52.000 unquote knew how far away the satellite was from the receiver, 0:08:52.440 --> 0:08:56.240 you could determine the location of that receiver on Earth. 0:08:56.679 --> 0:08:58.240 You would need to be able to get signals from 0:08:58.240 --> 0:09:00.679 more than one satellite, however, to do that, otherwise, you 0:09:00.679 --> 0:09:02.920 would really just know how far away you were from 0:09:03.000 --> 0:09:06.200 one satellite. But that's not really useful information because it 0:09:06.200 --> 0:09:08.719 doesn't narrow stuff down enough, or to put it in 0:09:08.760 --> 0:09:12.720 another way, let's say, let's take this to two dimensions. 0:09:12.720 --> 0:09:15.200 So let's talk about a map. Let's say you've got 0:09:15.240 --> 0:09:18.200 a map of North Georgia, Okay, because that's where I live. 0:09:18.600 --> 0:09:22.520 And I could say, hey, I live twenty miles away 0:09:22.559 --> 0:09:25.480 from my parents. And let's say you happen to know 0:09:25.520 --> 0:09:28.320 where I live. Not that I'm gonna dox myself, but 0:09:28.400 --> 0:09:30.200 let's say you know where I live, so you can 0:09:30.240 --> 0:09:33.360 take that point on the map you could draw out 0:09:33.400 --> 0:09:35.960 a line that's twenty miles out and then create a 0:09:36.000 --> 0:09:40.560 circle with a radius of twenty miles but without more information, 0:09:40.679 --> 0:09:43.760 that could mean they could be anywhere along that circumference 0:09:43.760 --> 0:09:46.440 of the circle right in a radius of twenty miles 0:09:46.480 --> 0:09:48.720 from me. They could be east or west, or north 0:09:48.800 --> 0:09:51.440 or south, or any point in between, as long as 0:09:51.480 --> 0:09:54.440 it was twenty miles out from my location. We'll come 0:09:54.480 --> 0:09:58.000 back to this analogy in a little bit. Let's get 0:09:58.040 --> 0:10:00.640 back to the Doppler effect. It could all be used 0:10:00.640 --> 0:10:04.440 to get a more accurate location. If you know where 0:10:04.480 --> 0:10:07.600 the satellite is as you receive signals, you can use 0:10:07.640 --> 0:10:10.560 a series of pulses from that satellite to determine your 0:10:10.640 --> 0:10:13.440 location on Earth. This actually takes a bit, right. So 0:10:13.440 --> 0:10:15.520 if you know where a satellite is as it's beaming 0:10:15.559 --> 0:10:18.680 down these radio pulses to you, and you are able 0:10:18.760 --> 0:10:22.160 to get a sequence of measurements, and you're taking the 0:10:22.200 --> 0:10:26.000 Doppler effect into account, and you have all this information 0:10:26.040 --> 0:10:29.600 available to you, you can then use that info to 0:10:30.280 --> 0:10:33.760 reckon where you are on Earth. You have to keep 0:10:33.800 --> 0:10:36.560 receiving signals as the satellite is moving through its orbit 0:10:36.760 --> 0:10:40.400 and then use the series of data pulses to track 0:10:40.440 --> 0:10:44.080 where you are on Earth. If a satellite isn't within range, 0:10:44.320 --> 0:10:46.360 then you have to wait until one is close enough 0:10:46.400 --> 0:10:48.240 to you for you to start picking up the signals. 0:10:48.240 --> 0:10:50.640 That could be up to an hour, depending upon when 0:10:50.640 --> 0:10:53.880 the last one passed overhead, but it would work. So 0:10:54.280 --> 0:10:58.760 this would become a very early satellite based navigation system 0:10:58.840 --> 0:11:02.360 for the US Navy. So back to our history lesson. 0:11:02.720 --> 0:11:06.960 Following Sputnik's incredible impact both figuratively and then semi literally, 0:11:07.000 --> 0:11:09.760 because it would burn up upon descending through the Earth's 0:11:09.760 --> 0:11:13.440 atmosphere about three months and more than fourteen hundred orbits 0:11:13.440 --> 0:11:17.480 after initial launch, the US Advanced Research Projects Agency, or 0:11:17.720 --> 0:11:20.840 ARPA got to work on funding research for a satellite 0:11:20.920 --> 0:11:24.439 navigation system that would be called TRANSIT. Today we call 0:11:24.600 --> 0:11:28.319 ARPA DARPA, and it's a branch of the US Department 0:11:28.360 --> 0:11:31.760 of Defense that offers contracts to various organizations and companies 0:11:31.800 --> 0:11:35.480 to advance technologies that would be potentially useful in national defense. 0:11:35.840 --> 0:11:39.160 It's the agency that's responsible for bringing together the folks 0:11:39.160 --> 0:11:43.600 who actually built the infrastructure for the Internet. It's also 0:11:44.200 --> 0:11:51.400 largely responsible for the initial boom in autonomous vehicle research. Anyway, 0:11:51.679 --> 0:11:55.000 Transit would be handy for the United States Navy. The 0:11:55.200 --> 0:11:59.199 boffins over at Johns Hopkins University APL designed the satellites, 0:11:59.240 --> 0:12:03.640 which were intend to provide location information on Earth and 0:12:04.520 --> 0:12:07.600 in the Earth's socians, to an accuracy of within tens 0:12:07.640 --> 0:12:11.320 of meters, which thay sounds pretty loosey goosey, right, Like, 0:12:11.559 --> 0:12:14.840 if you were tens of meters away from your location 0:12:15.000 --> 0:12:16.960 based upon the app you would think, wow, this is 0:12:16.960 --> 0:12:21.360 not very useful. But at the time it was significantly 0:12:21.360 --> 0:12:23.720 more accurate than what we had been used to, So 0:12:23.880 --> 0:12:26.960 we were able to use this for mapping purposes and 0:12:27.040 --> 0:12:30.400 it was really handy. It would allow for far more precision, 0:12:30.880 --> 0:12:33.320 and it proved beyond a shadow of a doubt that 0:12:33.400 --> 0:12:37.199 England is not a conspiracy among cartographers and shout out 0:12:37.240 --> 0:12:40.520 to me if you actually recognize that reference. The first 0:12:40.559 --> 0:12:44.400 attempt to get a Transit satellite into orbit was a failure. 0:12:44.679 --> 0:12:47.600 As Monty Python might put it, it sank into the swamp, 0:12:47.920 --> 0:12:50.760 but it did not take four tries to get it right. 0:12:51.040 --> 0:12:55.720 Transit one B successfully achieved orbit on April thirteenth, nineteen sixty. 0:12:56.080 --> 0:13:00.320 It passed test with orbiting colors, but it would take 0:13:00.360 --> 0:13:02.760 more satellites. To create a system that would be useful 0:13:02.840 --> 0:13:05.240 and reliable, you needed a group of them, or a 0:13:05.320 --> 0:13:08.880 constellation of satellites in other words, and that's what we 0:13:08.920 --> 0:13:13.040 call a collection of satellites that collectively provide some specific 0:13:13.080 --> 0:13:16.880 information or service. It's a constellation anyway. By the mid 0:13:16.960 --> 0:13:20.800 nineteen sixties, the US launched several satellites into orbit, and 0:13:20.840 --> 0:13:24.480 this orbital path took the satellites past the Earth's poles, 0:13:24.920 --> 0:13:27.720 and once there were six satellites making up a very 0:13:27.760 --> 0:13:30.959 small constellation. The Navy would use those satellites and the 0:13:31.000 --> 0:13:34.040 Doppler effect to keep track of US subs that happen 0:13:34.080 --> 0:13:37.160 to be carrying big old boom booms on them, like 0:13:37.520 --> 0:13:40.360 the nuclear kind of boom booms. When you're on a 0:13:40.400 --> 0:13:43.600 submersible that happens to be outfitted with nuclear weaponry, you 0:13:43.679 --> 0:13:46.120 want to keep an accurate account of where you are 0:13:46.280 --> 0:13:50.120 and where you're going, and more importantly, the country that's 0:13:50.120 --> 0:13:52.400 in charge of you wants to know where you are, 0:13:52.640 --> 0:13:56.880 because if you suddenly disappear, that's a huge problem. Using transit, 0:13:56.920 --> 0:14:00.240 the subs could gain accurate location reading from satellite in 0:14:00.400 --> 0:14:03.079 just a few minutes, which again was a huge improvement 0:14:03.240 --> 0:14:08.360 over simply using map making and plotting. I mean, there 0:14:08.400 --> 0:14:11.640 are people who are phenomenal at figuring out where a 0:14:11.679 --> 0:14:16.040 submarine is based upon knowing the heading and how long 0:14:16.280 --> 0:14:19.960 a sub was traveling in that direction. I marvel at 0:14:20.000 --> 0:14:24.680 it when I see films of navigators doing those kind 0:14:24.720 --> 0:14:28.480 of calculations. But the nice thing is this would allow 0:14:28.600 --> 0:14:33.200 for relatively quick and accurate results, assuming that you were 0:14:33.280 --> 0:14:37.800 within range of receiving a satellite signal. The US Navy 0:14:37.800 --> 0:14:41.040 took over the operation of these satellites from ARPA by 0:14:41.160 --> 0:14:44.240 the mid nineteen sixties, and by nineteen sixty eight the 0:14:44.280 --> 0:14:47.720 system had a total of thirty six satellites in orbit. 0:14:48.280 --> 0:14:50.480 While the primary function of the system was to keep 0:14:50.560 --> 0:14:53.920 tabs on nuclear armed submarines, researchers also used it to 0:14:53.920 --> 0:14:56.360 map out locations, including using it to get a more 0:14:56.480 --> 0:14:59.720 accurate measurement of Mount Everest's elevation, which I thought was 0:14:59.760 --> 0:15:02.920 pretty neat. Now. That was in the nineteen sixties and 0:15:03.040 --> 0:15:06.360 nineteen seventies, and transit would remain in operation until nineteen 0:15:06.440 --> 0:15:09.640 ninety six, at which point it was retired for navigational 0:15:09.680 --> 0:15:14.480 purposes anyway, in favor of GPS, which had come online 0:15:14.520 --> 0:15:18.680 not long before that, actually, but we've still got some 0:15:18.720 --> 0:15:21.960 steps in between that we're going to need to talk about. 0:15:22.000 --> 0:15:25.160 So while Transit was taking shape with occasional launches to 0:15:25.160 --> 0:15:28.560 build out its constellation, another team over at the Aerospace 0:15:28.600 --> 0:15:33.240 Corporation was developing a more advanced navigational satellite system. Among 0:15:33.280 --> 0:15:40.200 the scientists and engineers was Ivan getting Hideyoshi Nakamura, James Woodford, 0:15:40.320 --> 0:15:42.760 and Philip Diamond, and they figured out that with a 0:15:42.840 --> 0:15:46.120 large enough constellation of satellites, with each satellite carrying an 0:15:46.200 --> 0:15:50.000 incredibly accurate clock on board, you could provide even more 0:15:50.040 --> 0:15:53.720 accurate positional information to a receiver on Earth. What's more, 0:15:53.960 --> 0:15:57.280 the receiver itself wouldn't need to be a super accurate clock. 0:15:57.720 --> 0:15:59.880 The clocks would just be on the satellites, and this 0:16:00.040 --> 0:16:04.720 would dramatically reduce the cost of building out receivers on land. 0:16:04.960 --> 0:16:08.200 Like before, if the receiver on land needed to have 0:16:08.640 --> 0:16:12.920 an incredibly accurate clock as well as the satellite, then 0:16:13.080 --> 0:16:16.320 the cost would have been prohibitive for the average person. 0:16:16.760 --> 0:16:21.000 But this brought all the onus of time keeping onto 0:16:21.040 --> 0:16:23.400 the satellite site, not the receiver side, and it made 0:16:23.400 --> 0:16:27.040 it much much more affordable. So you still need those 0:16:27.080 --> 0:16:29.600 clocks in the satellites themselves, but the receivers on Earth 0:16:29.640 --> 0:16:33.200 could be drastically simplified and manageurized and again accurate reading 0:16:33.240 --> 0:16:36.320 on position. A receiver would need to connect with four satellites, 0:16:36.360 --> 0:16:39.040 so the constellation of navigational spacecraft would need to be 0:16:39.120 --> 0:16:42.000 fairly large in order to be able to receive signals 0:16:42.000 --> 0:16:45.520 from four satellites simultaneously. But those four satellites would give 0:16:45.600 --> 0:16:49.280 enough information to really hone in on the receiver's location 0:16:49.760 --> 0:16:52.200 here on Earth. So what we're going to do now 0:16:52.280 --> 0:16:54.000 is we're going to take a quick break to thank 0:16:54.080 --> 0:16:56.480 our sponsor, and then when we come back, I'll talk 0:16:56.560 --> 0:17:00.960 more about how this works, like how state lights are 0:17:01.320 --> 0:17:04.040 able to send information that a receiver on Earth can 0:17:04.080 --> 0:17:08.320 take and interpret as positional information on the surface of 0:17:08.320 --> 0:17:21.240 the planet. But first let's take this quick break, all right. 0:17:21.320 --> 0:17:23.640 I think it's best we now take time to talk 0:17:23.640 --> 0:17:27.040 about how all this works, and that's what we've been 0:17:27.040 --> 0:17:29.960 building towards. So remember when I said my parents live 0:17:30.400 --> 0:17:34.040 like twenty miles away from me, and that just tells 0:17:34.080 --> 0:17:36.800 you that they're somewhere within a twenty mile radius of 0:17:36.880 --> 0:17:40.239 my location. That's that's all it tells you. But if 0:17:40.280 --> 0:17:42.800 I gave you another data point. Let's say that I said, oh, 0:17:42.840 --> 0:17:46.400 they happen to live seventy miles from Athens, Georgia. Well, 0:17:46.440 --> 0:17:48.679 now you can take a map and draw two circles, 0:17:48.760 --> 0:17:51.640 assuming you know where I live. So one circle would 0:17:51.640 --> 0:17:54.919 be centered on my location with a twenty mile radius 0:17:54.960 --> 0:17:59.280 around it. The second circle would be around Athens, Georgia 0:17:59.359 --> 0:18:02.080 at the center. It would extend out seventy miles. So 0:18:02.119 --> 0:18:05.399 these two circles would overlap slightly. They kind of cross 0:18:05.520 --> 0:18:08.080 one another at two points, kind of like a ven diagram. 0:18:08.200 --> 0:18:10.600 And now you've narrowed down my parents' house to one 0:18:10.720 --> 0:18:14.199 of two possible points. Because where they live needs to 0:18:14.200 --> 0:18:16.880 be within twenty miles of me and seventy miles of Athens. 0:18:16.920 --> 0:18:19.880 That only leaves two locations on the map. Now, unless 0:18:19.880 --> 0:18:21.840 one of those points happens to be somewhere where a 0:18:21.880 --> 0:18:24.840 house could not possibly be located, like in the middle 0:18:24.880 --> 0:18:28.120 of a lake or something, they're still ambiguity. You don't 0:18:28.160 --> 0:18:31.320 know if they're in location one or location two. Ah. 0:18:31.560 --> 0:18:34.240 But what if I also said my parents live within 0:18:34.760 --> 0:18:38.080 or ten miles away from the amusement park six lags 0:18:38.080 --> 0:18:40.800 over Georgia. Well, you could draw a third circle with 0:18:40.880 --> 0:18:43.720 a radius of ten miles around that park, and you 0:18:43.760 --> 0:18:46.440 should see that this circle intersects with the other two 0:18:46.600 --> 0:18:50.480 already drawn at a single point. They three circles meet 0:18:50.600 --> 0:18:53.639 only in one location, and that is where my parents 0:18:53.680 --> 0:18:56.359 would live, or it would be if I weren't giving 0:18:56.840 --> 0:19:00.800 total made up answers to these different distances. For one thing, 0:19:00.880 --> 0:19:03.760 I don't think you could have circles that overlap seventy 0:19:03.840 --> 0:19:06.280 miles out from Athens and ten miles out from six Legs. 0:19:06.280 --> 0:19:09.720 They're too far apart. But you get the idea. GPS 0:19:09.760 --> 0:19:12.199 satellites work in a similar way, except we need to 0:19:12.200 --> 0:19:15.720 think about spheres rather than circles. We have to go 0:19:15.760 --> 0:19:19.280 into three dimensions, right, So a GPS satellite essentially sends 0:19:19.280 --> 0:19:22.200 out a pulse of data and it indicates a time 0:19:22.320 --> 0:19:26.400 stamp and the satellite's location. A receiver on Earth receives 0:19:26.480 --> 0:19:28.840 this message and by doing a little math, figures out 0:19:29.040 --> 0:19:33.280 how far away it is from the satellite by knowing 0:19:33.320 --> 0:19:35.879 how long it took the message to travel from the 0:19:35.920 --> 0:19:38.800 satellite to the receiver. These pulses are traveling at the 0:19:38.800 --> 0:19:41.560 speed of light, so we actually do know the velocity 0:19:41.720 --> 0:19:44.680 or the speed rather of those signals. So we've got 0:19:44.800 --> 0:19:48.360 time and we've got speed. We need to figure out 0:19:48.480 --> 0:19:52.680 the distance to know how far the receiver is from 0:19:52.720 --> 0:19:56.919 the specific satellite, and we can eliminate all the positions 0:19:57.240 --> 0:20:00.880 that aren't on Earth. Right once we figure out, oh, 0:20:00.880 --> 0:20:03.320 it took x amount of time to get here, that 0:20:03.359 --> 0:20:06.800 means where why number of miles away from the satellite 0:20:06.880 --> 0:20:09.600 we happen to know where the satellite is located, you 0:20:09.640 --> 0:20:14.480 could create a sphere representing all the points around the 0:20:14.480 --> 0:20:17.480 satellite that are the proper distance away. A lot of 0:20:17.520 --> 0:20:19.600 those points are going to be out in space. We 0:20:19.680 --> 0:20:23.359 can disregard those because obviously we're not in outer space. 0:20:23.720 --> 0:20:26.439 But for the ones that are on Earth, there's going 0:20:26.480 --> 0:20:28.320 to be a lot, right, Some are going to actually 0:20:28.320 --> 0:20:32.359 extend into the Earth. We can probably dismiss those as well. 0:20:32.640 --> 0:20:34.640 So we're just looking at the ones that actually intersect 0:20:34.680 --> 0:20:37.439 with the surface of the Earth. But there's still a lot, 0:20:37.600 --> 0:20:39.840 so we have to narrow it down. We do that 0:20:40.240 --> 0:20:46.480 by receiving multiple signals from multiple satellites, preferably for satellites 0:20:46.560 --> 0:20:49.679 to really get rid of any ambiguity. If the receiver 0:20:49.760 --> 0:20:52.920 does this with at least three but typically four satellites. 0:20:52.920 --> 0:20:55.080 Then it can pinpoint where on the surface of the 0:20:55.119 --> 0:20:58.200 Earth the receiver happens to be. It's a clever way 0:20:58.200 --> 0:21:01.040 to figure out locations because once we do figure out all, right, 0:21:01.080 --> 0:21:05.159 where why number of miles from satellite A, where Z 0:21:05.359 --> 0:21:08.439 number of miles from satellite B, where AA number of 0:21:08.480 --> 0:21:13.840 miles or satellite three and BB from satellite four, you 0:21:14.080 --> 0:21:16.600 create the spheres around all four of those satellites. You 0:21:16.640 --> 0:21:18.440 know where they are, they've told you where they are. 0:21:18.480 --> 0:21:21.080 You know what time stamps you're looking at. The time 0:21:21.119 --> 0:21:24.720 stamps also need to be in sync with the receiver's clock, 0:21:24.800 --> 0:21:27.040 but the receiver's clock can be modified here on Earth. 0:21:27.040 --> 0:21:29.080 We don't have to worry about the satellites doing that, 0:21:29.480 --> 0:21:33.520 and collectively that will end up giving you a single 0:21:33.520 --> 0:21:37.040 location where it's the only place on the surface of 0:21:37.040 --> 0:21:40.399 the Earth where all of those points of data converge. 0:21:40.640 --> 0:21:43.960 And that's how GPS works. So the scientists work fed 0:21:44.080 --> 0:21:46.720 nicely into work that was already being done at the 0:21:46.800 --> 0:21:50.320 US Naval Center for Space Technology, where other brilliant people 0:21:50.320 --> 0:21:53.480 were hard at work developing atomic clocks. So let's talk 0:21:53.480 --> 0:21:57.120 about that for a second too, because this timekeeping element 0:21:57.359 --> 0:22:02.199 is absolutely vital for navigation purposes. Remember, all of our 0:22:02.280 --> 0:22:06.480 navigation calculations are based upon how far we are from 0:22:06.520 --> 0:22:10.280 these satellites. But if the timekeeping is off, then our 0:22:10.320 --> 0:22:13.080 distance is going to be off, which means we're going 0:22:13.119 --> 0:22:15.600 to think we're somewhere else on the surface of the 0:22:15.600 --> 0:22:18.199 Earth and where we actually are. So let's take quartz 0:22:18.280 --> 0:22:21.480 based risk watches as sort of a starting point. Quarts 0:22:21.600 --> 0:22:25.920 will vibrate physically when subjected to a voltage. This relates 0:22:25.960 --> 0:22:29.200 to piezo electricity, which is the ability for certain materials 0:22:29.200 --> 0:22:32.040 like quartz to store an electric charge in response to 0:22:32.080 --> 0:22:35.720 mechanical force that's been applied to that substance. In other words, 0:22:35.720 --> 0:22:39.680 like if you'll whack quartz, it'll build up an electric charge. 0:22:39.840 --> 0:22:43.679 But the other effect can also be true. Certain materials, 0:22:43.720 --> 0:22:47.280 when exposed to an electric field, will produce physical vibrations, 0:22:47.320 --> 0:22:50.720 and quartz is one of those materials. What's more, it 0:22:50.760 --> 0:22:54.360 will always produce the same frequency of vibrations in response 0:22:54.400 --> 0:22:58.159 to specific applied voltage. So if you apply the same 0:22:58.280 --> 0:23:01.600 voltage over and over, is going to vibrate at the 0:23:01.640 --> 0:23:05.400 same frequency over and over. It does not vary, at 0:23:05.480 --> 0:23:09.320 least not for the purposes of wristwatches. As it turns out, 0:23:09.359 --> 0:23:13.760 for the purposes of space navigation, it's not nearly precise enough. 0:23:13.920 --> 0:23:16.479 But if you apply specific voltage to a quartz crystal, 0:23:16.480 --> 0:23:19.200 the crystal will produce a vibration of a specific frequency, 0:23:19.240 --> 0:23:21.240 which you can then use as if it were the 0:23:21.280 --> 0:23:24.760 swinging pendulum of an old timey grandfather clock, and you 0:23:24.800 --> 0:23:28.560