Welcome to Tech Stuff, a production from iHeartRadio. Hey there, and welcome to tech Stuff. I'm your host, Jonathan Strickland. I'm an executive producer with iHeart Podcasts and how the tech are you so, y'all. I love to travel. I love to visit new places or revisit ones after I've been away for a long time. I even don't really mind the journey part of travel, which can often be you know, stressful, in a hassle if things aren't going well. One thing that does give me a huge amount of anxiety if I'm traveling is just getting lost or even the thought of getting lost. I do not do very well with that. There's some part of my brain that mistakenly believes that as long as I know where I am, nothing can go too wrong. And boy I wish that were true, but but yeah, whatever, I just need my brain to let me function properly when I'm out on holidays. So I remember traveling on my honeymoon to London. At that point, I had never been outside the United States before. This was my first trip outside the country, and I was going to a city that I had read about extensively. I knew a lot about London. My major in college was in English literature, but it was with a focus on medieval studies, so things had changed slightly by the time I got there, and reading about a city is very different from actually walking around one. Also, my honeymoon was in the nineteen nineties because I'm old, and that meant I was a decade out from the era of smartphones, so I didn't have a handy mobile device to tell me where I was as I wandered around the city. Even if smartphones had been around back then, I wouldn't have been able to rely on map apps on the smartphone because of something called selective availability. More on that in a bit, but at any rate, I had to rely on physical maps to get around and hope that I didn't mess it up too badly. Yeah, it's like the Stone Age right. Well, these days, as long as I have my smartphone with me and I'm not buried under a mountain or something, I feel fairly confident I'm not going to get lost. If I'm going somewhere that has limited connectivity, like limited view of the sky, then my anxiety starts to creep in again. But usually I'm okay, and that's thanks to the Global Positioning System or GPS. So today we're going to learn about GPS, what makes it work, how the technology has to take into account, Einstein's theories of relativity and more. And a huge thank to JP Morgan, Chase Bank, and the United Explorer Card for sponsoring this episode. We'll hear more about them later too. So GPS, well, that story begins back in the nineteen teen fifties when the United States and the then Soviet Union were locked in a Cold war, and that cold war manifested in many different ways, including an effort to launch vehicles into space. For one thing, if you could launch a rocket into orbit, then you could show your technological superiority over your opponent and say, look how much further advanced we are compared to you. But you could also send the message of hey, if I can send a rocket to space, I could send a rocket to your front door, all the way from across the world, and it could be carrying a heck of a boom boom. Now this gram message underpinned what would become the space race. But the space race also meant that brilliant engineers and scientists would actually get the resources they needed to advance technology by incredible leaps and bounds over the following decades. So you got to take the good with the bad, right. The good part is you suddenly had actual financial support for or incredibly important scientific and engineering work. The bad is, well, it was all done in service of this perceived rivalry with this massive country on the other side of the globe. On October fourth, nineteen fifty seven, at approximately seven thirty pm, the USSR launched the first man made satellite into orbit, Sputnik. Non past episodes, I have referred to the satellite as the ball that went beep. That's not exactly inaccurate. The satellite was spherical in shape. It did have these long antenna extending out the back of it, so it kind of looks like a comet, like a silver comet. But the antenna transmitted short radio pulses, and these pulses could be picked up very easily by ground based audio receivers, including radio sets operated by amateurs, just an amateur radio set. This meant that Sputnik's existence couldn't be kept a secret because if you or someone you knew operated a radio, you could learn about the thing. And in the United States, it prompted no small amount of anxiety. Americans believed their country was well ahead of the Soviet Union, at least on a technological basis. But here they could see that their adversary had launched stuff into space and did it before the US could do it. That really kicked things into gear here in the United States. But I would argue that Sputnik would ultimately plant a seed that would blossom into GPS further down the line, because here you had a satellite sending regular radio signals to Earth, and those signals were pretty primitive. Essentially, the satellite was signaling that it was within range overhead, along with basic information about stuff like air pressure and temperature indicated by the length of the radio pulses. Like the pulses didn't give data the way Wi Fi does. Literally, you would measure how long the pulse lasted and that would tell you, oh, the temperature is whatever, if you happen to have the chart. Two scientists were able to adfer other information, however, from this signal, such as how the propagation of radio signals interacted in the upper atmosphere like the ionosphere, and it hinted that there could be other uses for as satellite beaming information down to Earth. Also, those signals were subject to what we call the Doppler effect. It's named after Christian Doppler effect. No, I'm sorry, it's just Christian Doppler. He first observed this effect back in eighteen forty two. And this is how the frequency of a wave changes relative to an independent observer if the thing that's emitting the wave is moving toward or away from that observer. Which was a clumsy explanation, Let's just take an example because that makes it way more clear. So let's say you're just walking down the street. You're on a sidewalk, and say one hundred feet or so in front of you, there's an emergency vehicle and it's parked. It's not currently driving anywhere, but it is running its siren. The sound of that siren is going to remain consistent relative to you, right, it may increase and decrease in pitch because the nature of the siren, but it's going to keep doing that pattern over and over again. But now let's say that it's an emergency vehicle that's rushing off away from you. It's driving off. You'll notice the pitch of the siren will start to go lower. The frequency of the sound wave decreases as the vehicle accelerates away from you, or let's say the vehicle is driving towards you, the pitch of the siren will go up as the frequency increases. You can kind of think of it like this. An approaching object emitting a wave is effectively pushing or compressing that wave as it moves closer to you. An object moving away from you is stretching out the wave it's emitting as it moves away from you. That is the Doppler effect. Scientists at the Applied Physics Laboratory or APL, at Johns Hopkins University noticed that the Doppler effect was also applicable to Sputnik's radio waves. The satellite's radio pulses were compressed as Sputnik would approach, and then they would stretch out as the satellite would move away from their point of observation, and this meant that just by listening to the pulses, the scientists could track Sputnik's movements. They didn't need to have eyes on the satellite to track it. They could just follow the pulses and observe the Doppler effect in order to know generally where it was and when it was heading away, but very generally, like they couldn't give you a pinpointed location. However, this was another important seed for what would become GPS, because it would lead to the hypothesis that a satellite could send signals to a receiver on Earth, and if that receiver quote unquote knew how far away the satellite was from the receiver, you could determine the location of that receiver on Earth. You would need to be able to get signals from more than one satellite, however, to do that, otherwise, you would really just know how far away you were from one satellite. But that's not really useful information because it doesn't narrow stuff down enough, or to put it in another way, let's say, let's take this to two dimensions. So let's talk about a map. Let's say you've got a map of North Georgia, Okay, because that's where I live. And I could say, hey, I live twenty miles away from my parents. And let's say you happen to know where I live. Not that I'm gonna dox myself, but let's say you know where I live, so you can take that point on the map you could draw out a line that's twenty miles out and then create a circle with a radius of twenty miles but without more information, that could mean they could be anywhere along that circumference of the circle right in a radius of twenty miles from me. They could be east or west, or north or south, or any point in between, as long as it was twenty miles out from my location. We'll come back to this analogy in a little bit. Let's get back to the Doppler effect. It could all be used to get a more accurate location. If you know where the satellite is as you receive signals, you can use a series of pulses from that satellite to determine your location on Earth. This actually takes a bit, right. So if you know where a satellite is as it's beaming down these radio pulses to you, and you are able to get a sequence of measurements, and you're taking the Doppler effect into account, and you have all this information available to you, you can then use that info to reckon where you are on Earth. You have to keep receiving signals as the satellite is moving through its orbit and then use the series of data pulses to track where you are on Earth. If a satellite isn't within range, then you have to wait until one is close enough to you for you to start picking up the signals. That could be up to an hour, depending upon when the last one passed overhead, but it would work. So this would become a very early satellite based navigation system for the US Navy. So back to our history lesson. Following Sputnik's incredible impact both figuratively and then semi literally, because it would burn up upon descending through the Earth's atmosphere about three months and more than fourteen hundred orbits after initial launch, the US Advanced Research Projects Agency, or ARPA got to work on funding research for a satellite navigation system that would be called TRANSIT. Today we call ARPA DARPA, and it's a branch of the US Department of Defense that offers contracts to various organizations and companies to advance technologies that would be potentially useful in national defense. It's the agency that's responsible for bringing together the folks who actually built the infrastructure for the Internet. It's also largely responsible for the initial boom in autonomous vehicle research. Anyway, Transit would be handy for the United States Navy. The boffins over at Johns Hopkins University APL designed the satellites, which were intend to provide location information on Earth and in the Earth's socians, to an accuracy of within tens of meters, which thay sounds pretty loosey goosey, right, Like, if you were tens of meters away from your location based upon the app you would think, wow, this is not very useful. But at the time it was significantly more accurate than what we had been used to, So we were able to use this for mapping purposes and it was really handy. It would allow for far more precision, and it proved beyond a shadow of a doubt that England is not a conspiracy among cartographers and shout out to me if you actually recognize that reference. The first attempt to get a Transit satellite into orbit was a failure. As Monty Python might put it, it sank into the swamp, but it did not take four tries to get it right. Transit one B successfully achieved orbit on April thirteenth, nineteen sixty. It passed test with orbiting colors, but it would take more satellites. To create a system that would be useful and reliable, you needed a group of them, or a constellation of satellites in other words, and that's what we call a collection of satellites that collectively provide some specific information or service. It's a constellation anyway. By the mid nineteen sixties, the US launched several satellites into orbit, and this orbital path took the satellites past the Earth's poles, and once there were six satellites making up a very small constellation. The Navy would use those satellites and the Doppler effect to keep track of US subs that happen to be carrying big old boom booms on them, like the nuclear kind of boom booms. When you're on a submersible that happens to be outfitted with nuclear weaponry, you want to keep an accurate account of where you are and where you're going, and more importantly, the country that's in charge of you wants to know where you are, because if you suddenly disappear, that's a huge problem. Using transit, the subs could gain accurate location reading from satellite in just a few minutes, which again was a huge improvement over simply using map making and plotting. I mean, there are people who are phenomenal at figuring out where a submarine is based upon knowing the heading and how long a sub was traveling in that direction. I marvel at it when I see films of navigators doing those kind of calculations. But the nice thing is this would allow for relatively quick and accurate results, assuming that you were within range of receiving a satellite signal. The US Navy took over the operation of these satellites from ARPA by the mid nineteen sixties, and by nineteen sixty eight the system had a total of thirty six satellites in orbit. While the primary function of the system was to keep tabs on nuclear armed submarines, researchers also used it to map out locations, including using it to get a more accurate measurement of Mount Everest's elevation, which I thought was pretty neat. Now. That was in the nineteen sixties and nineteen seventies, and transit would remain in operation until nineteen ninety six, at which point it was retired for navigational purposes anyway, in favor of GPS, which had come online not long before that, actually, but we've still got some steps in between that we're going to need to talk about. So while Transit was taking shape with occasional launches to build out its constellation, another team over at the Aerospace Corporation was developing a more advanced navigational satellite system. Among the scientists and engineers was Ivan getting Hideyoshi Nakamura, James Woodford, and Philip Diamond, and they figured out that with a large enough constellation of satellites, with each satellite carrying an incredibly accurate clock on board, you could provide even more accurate positional information to a receiver on Earth. What's more, the receiver itself wouldn't need to be a super accurate clock. The clocks would just be on the satellites, and this would dramatically reduce the cost of building out receivers on land. Like before, if the receiver on land needed to have an incredibly accurate clock as well as the satellite, then the cost would have been prohibitive for the average person. But this brought all the onus of time keeping onto the satellite site, not the receiver side, and it made it much much more affordable. So you still need those clocks in the satellites themselves, but the receivers on Earth could be drastically simplified and manageurized and again accurate reading on position. A receiver would need to connect with four satellites, so the constellation of navigational spacecraft would need to be fairly large in order to be able to receive signals from four satellites simultaneously. But those four satellites would give enough information to really hone in on the receiver's location here on Earth. So what we're going to do now is we're going to take a quick break to thank our sponsor, and then when we come back, I'll talk more about how this works, like how state lights are able to send information that a receiver on Earth can take and interpret as positional information on the surface of the planet. But first let's take this quick break, all right. I think it's best we now take time to talk about how all this works, and that's what we've been building towards. So remember when I said my parents live like twenty miles away from me, and that just tells you that they're somewhere within a twenty mile radius of my location. That's that's all it tells you. But if I gave you another data point. Let's say that I said, oh, they happen to live seventy miles from Athens, Georgia. Well, now you can take a map and draw two circles, assuming you know where I live. So one circle would be centered on my location with a twenty mile radius around it. The second circle would be around Athens, Georgia at the center. It would extend out seventy miles. So these two circles would overlap slightly. They kind of cross one another at two points, kind of like a ven diagram. And now you've narrowed down my parents' house to one of two possible points. Because where they live needs to be within twenty miles of me and seventy miles of Athens. That only leaves two locations on the map. Now, unless one of those points happens to be somewhere where a house could not possibly be located, like in the middle of a lake or something, they're still ambiguity. You don't know if they're in location one or location two. Ah. But what if I also said my parents live within or ten miles away from the amusement park six lags over Georgia. Well, you could draw a third circle with a radius of ten miles around that park, and you should see that this circle intersects with the other two already drawn at a single point. They three circles meet only in one location, and that is where my parents would live, or it would be if I weren't giving total made up answers to these different distances. For one thing, I don't think you could have circles that overlap seventy miles out from Athens and ten miles out from six Legs. They're too far apart. But you get the idea. GPS satellites work in a similar way, except we need to think about spheres rather than circles. We have to go into three dimensions, right, So a GPS satellite essentially sends out a pulse of data and it indicates a time stamp and the satellite's location. A receiver on Earth receives this message and by doing a little math, figures out how far away it is from the satellite by knowing how long it took the message to travel from the satellite to the receiver. These pulses are traveling at the speed of light, so we actually do know the velocity or the speed rather of those signals. So we've got time and we've got speed. We need to figure out the distance to know how far the receiver is from the specific satellite, and we can eliminate all the positions that aren't on Earth. Right once we figure out, oh, it took x amount of time to get here, that means where why number of miles away from the satellite we happen to know where the satellite is located, you could create a sphere representing all the points around the satellite that are the proper distance away. A lot of those points are going to be out in space. We can disregard those because obviously we're not in outer space. But for the ones that are on Earth, there's going to be a lot, right, Some are going to actually extend into the Earth. We can probably dismiss those as well. So we're just looking at the ones that actually intersect with the surface of the Earth. But there's still a lot, so we have to narrow it down. We do that by receiving multiple signals from multiple satellites, preferably for satellites to really get rid of any ambiguity. If the receiver does this with at least three but typically four satellites. Then it can pinpoint where on the surface of the Earth the receiver happens to be. It's a clever way to figure out locations because once we do figure out all, right, where why number of miles from satellite A, where Z number of miles from satellite B, where AA number of miles or satellite three and BB from satellite four, you create the spheres around all four of those satellites. You know where they are, they've told you where they are. You know what time stamps you're looking at. The time stamps also need to be in sync with the receiver's clock, but the receiver's clock can be modified here on Earth. We don't have to worry about the satellites doing that, and collectively that will end up giving you a single location where it's the only place on the surface of the Earth where all of those points of data converge. And that's how GPS works. So the scientists work fed nicely into work that was already being done at the US Naval Center for Space Technology, where other brilliant people were hard at work developing atomic clocks. So let's talk about that for a second too, because this timekeeping element is absolutely vital for navigation purposes. Remember, all of our navigation calculations are based upon how far we are from these satellites. But if the timekeeping is off, then our distance is going to be off, which means we're going to think we're somewhere else on the surface of the Earth and where we actually are. So let's take quartz based risk watches as sort of a starting point. Quarts will vibrate physically when subjected to a voltage. This relates to piezo electricity, which is the ability for certain materials like quartz to store an electric charge in response to mechanical force that's been applied to that substance. In other words, like if you'll whack quartz, it'll build up an electric charge. But the other effect can also be true. Certain materials, when exposed to an electric field, will produce physical vibrations, and quartz is one of those materials. What's more, it will always produce the same frequency of vibrations in response to specific applied voltage. So if you apply the same voltage over and over, is going to vibrate at the same frequency over and over. It does not vary, at least not for the purposes of wristwatches. As it turns out, for the purposes of space navigation, it's not nearly precise enough. But if you apply specific voltage to a quartz crystal, the crystal will produce a vibration of a specific frequency, which you can then use as if it were the swinging pendulum of an old timey grandfather clock, and you can calculate the passage of time by the frequency of vibrations. If you know that it takes twenty thousand vibrations per second, then once you hit twenty thousand, you know a second has passed. That's essentially how it works. Now, atomic clocks are not that different, but there are many orders of magnitude far more precise. So quartz crystals are consistent enough for our earthly needs, but when it comes to space operations, we need much more stability and much more accuracy. A quartz space clock will gradually start to drift and start to lose accuracy over time. Now, it typically takes a while. It might be more than a month before the clock is off by so much as a millisecond, but that would still be enough to provide extremely wrong navigational information. So imagine you're looking at your GPS app and you are flabbric acid because according to the app, you are like two hundred miles away from you where you actually are. And it's all because the receiver would be depending upon the wrong information, that time code would be wrong, and that would mean that it would be calculating the wrong distance. So yeah, a small error in space translates into an enormous error when you get to navigation systems on Earth. So atomic clocks rely upon oscillations of atomic energy states. Like think of electron energy states. You probably know atoms are made up of a nucleus around which are orbiting electrons. These electrons in habit various energy states. If you pour energy into an atom, you can make an electron go move out to a higher energy state, and then once you stop pouring energy in, the electron will naturally move back down to its normal energy state. So this can be an oscillation. Now to go into this further, to really dive into it, would get far too complicated for this episode. But the important thing to remember is that atomic clocks are both more stable and more accurate than quartz crystal based time pieces. Depending on the type of atom being used, the clock might count billions of oscillations per second, like more than nine billion, So you're really dividing a second down into unfathomably small units of time by looking at the frequency of these oscillations. This is an incredible level of accuracy, which is a necessary component when we're talking about navigation. But I also promise y' all some relativity up here in this podcast. So what does that have to do with anything, Well, Einstein's theories of relativity. Both of these special relativity and general relativity varieties have something to say about the passage of time. It's all relative, you see. And some factors that determine the speed at which time passes for a subject relative to an outside observer includes stuff like gravity and speed. Now, let's get one thing out of the way first, because this gets whibbly wobbly timey. Whymy, Like, you wouldn't believe the passage of time to an observer like their own sense, their own sensation of the passage of time, that doesn't change. To them. Time continues on as it would in any other condition. It's only as they observe outside points of reference that the sense of time changes. So like, for example, one thing is that the faster you go, the slower time moves for you relative to an outside observer. So if you're in a ship and you're going super super super fast, it would feel like time is passing as normal. To someone outside of the spaceship here on Earth, it would look like you were moving in slow motion. If they could magically see you inside this ship, even though the ship is moving super fast, you would appear to be moving at a crawl. And that's why at the end of your journey, when you would get off your spaceship, your friends and family who had stayed behind on Earth would have all aged much more than you did, because relative to them, time passed more slowly. For you. Your experience, however, was that time just continued on as it always has, very very mind binding kind of stuff. Right, But what does this have to do with satellites. Well, let's talk about general relativity first. It explains that gravity can alter time such that a satellite that's in orbit around Earth will have clocks that are running a little bit faster than they would if they were just on Earth. And by a little bit faster, I'm talking about like forty five microseconds per day drifting right, like they're getting ahead by about forty five microseconds per day. However, we also have special relativity. This says that because the satellites are whizzing through space pretty darn fast, the clocks run a little more slowly relative to the ones on Earth, and they end up losing about seven microseconds per day. So you've got to factor both of these in. Right, you're gaining forty five microseconds on one side and losing seven microseconds on the other side. But this means that we have to send up clock modifications corrections to the satellite's clocks in order to adjust them and make sure they don't drift too much over time, because the longer they do so without a correction, the more inaccurate the results are going to be here on Earth when we're depending upon them for navigation. All right, let's get back to our history. So in the late nineteen seventies, a US military GPS constellation was slowly taking shape, and initially it was called Navstar. And this project took the work that was being done independently in the Army, the Navy, and the Air Force and kind of brought all that learning together and became a really massive nationwide effort and eventually it would evolve into what we just referred to as GPS these days. The first fully operational satellite in the GPS constellation would finally launch in nineteen eighty nine. So yeah, this was a system that was in development for like two decades pretty much, and then finally in nineteen eighty nine, the first satellite goes up. And that's just one. You can't navigate just on one satellite, at least not using this trilateration approach. But meanwhile, manufacturers here on Terra Firma were busy building the navigation devices that would be reliant upon these satellites once there were more up in orbit, and this would include handheld navigation units. The constellation of GPS satellites wouldn't reach what old Emperor Palpatine would consider fully operational until nineteen ninety five. The military would end up receiving clear signals for the purposes of navigation. So if you were using GPS and you were in the military and you were using it officially, you would get really accurate results. However, the same was not true for everybody else. The rest of us got something that was called selective availability. I mentioned that at the top of this episode. So essentially for civilian use, the satellites were fudging the timecode just a tiny, tiny amount in those data pulses. Now, it wasn't fudging the timecode enough to put you well outside where you actually were and make it totally useless, but it was enough to muddle the accuracy to within maybe one hundred meters of your actual location. So you could still use GPS for general navigation, but it wouldn't be suitable for stuff like turn by turn directions because the muddled data would not be accurate to your real location. So why was this Well, it was to protect stuff like military bases and that sort of thing. The thought was that the information was potentially too dangerous to be made public. This would hold true until two thousand, when former President Bill Clinton rescinded select availability. At that point, GPS receivers could display accurate information to within a couple of meters of a person's actual location on the Earth, and this would improve over time, and this is when turn by turn directions will become a possibility for civilian use. Now today there are more than thirty satellites that are part of the GPS constellation. They are frequently updated where you know, a newer generation of tech satellite will go up and replace ones that are no longer in service or have stopped working, and our capabilities improve with each generation. The United States is also not the only nation to operate a global satellite based navigation system. Russia has an alternative to GPS. It's called Glonas GLO NASS. Receivers that can work with both GPS and clonos are typically more reliable because they can more easily receive signals from, at least for satellites, like even if you're a place that has lots of tall buildings that might block signals, you have a lot more satellites up there that you could potentially pull from and thus get a better reading on where you are, so you can get devices that are compliant with both GPS and GLONAS. Glonas initially completed its constellation in nineteen ninety five, the same year that the GPS constellation went fully operational, but budget cuts in Russia led to degradation of the constellation. It lost some of its capability, and eventually Russia was able to reinvest and in twenty eleven they were able to bring a full constellation back online. It's been pretty much that way ever since. Again, like the United States, Russia has also upgraded individual satellites in the constellation in order to provide better service. So that's it. That's kind of how GPS works. It's really all about figuring out where you are based on how long it took satellites to send you a little data message. You know, it's pretty cool, I think. I think it's a really intriguing way to figure out your location. It's so clever because it's not relying on things like landmarks or anything like that. Not the way that people like myself typically navigate, right. I navigate through landmarks and street names and that kind of stuff. Occasionally I will reorient myself based upon which where the sun is, because I know enough to know if it's before noon, the sun's in the eastern part of the sky, and if it's afternoon, it's in the western part of the sky. Once you get past that, all bets are off. I was never that good of a boy scout, but yeah, GPS is really truly revolutionized travel beyond what I can even express. Like, it's hard to communicate to people who have never lived without GPS what it was like to try and get around, like to have an atlass in your car and you know, rely on on paper maps or like in the old, the old days of things like map quest, you would find turn by turn directions on your computer and then print them out or write them down because smartphones weren't really a thing yet, so you need to have a way to actually carry the directions with you. It's a different world these days, but still pretty cool. Like I think, it's a neat thing to know that this system works in this way. It's also important, by the way, to learn how to read maps, because you never know. If stuff goes down for whatever reason, you want to be able to still get around, like things like solar flares coronal mass ejections. These big solar events can sometimes wipe out stuff or at least shut things down temporarily, and if in the process of that you still need to get around, knowing how to read a map can be really useful, so it's a skill I recommend developing. That's it for this episode. I hope you are all well. I hope those of you who have fun trips planned in the future can take a moment to appreciate the beauty and utility of GPS, and how amazing it is that we're using things like theory of relativity and space technology just so that you know where you need to turn to go to the next in and out burger. I think that's pretty cool and I will talk to you again really soon. Tech Stuff is an iHeartRadio production. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.

Welcome to Tech Stuff, a production from iHeartRadio. Hey there, and welcome to tech Stuff. I'm your host, Jonathan Strickland. I'm an executive producer with iHeart Podcasts and how the tech are you so, y'all. I love to travel. I love to visit new places or revisit ones after I've been away for a long time. I even don't really mind the journey part of travel, which can often be you know, stressful, in a hassle if things aren't going well. One thing that does give me a huge amount of anxiety if I'm traveling is just getting lost or even the thought of getting lost. I do not do very well with that. There's some part of my brain that mistakenly believes that as long as I know where I am, nothing can go too wrong. And boy I wish that were true, but but yeah, whatever, I just need my brain to let me function properly when I'm out on holidays. So I remember traveling on my honeymoon to London. At that point, I had never been outside the United States before. This was my first trip outside the country, and I was going to a city that I had read about extensively. I knew a lot about London. My major in college was in English literature, but it was with a focus on medieval studies, so things had changed slightly by the time I got there, and reading about a city is very different from actually walking around one. Also, my honeymoon was in the nineteen nineties because I'm old, and that meant I was a decade out from the era of smartphones, so I didn't have a handy mobile device to tell me where I was as I wandered around the city. Even if smartphones had been around back then, I wouldn't have been able to rely on map apps on the smartphone because of something called selective availability. More on that in a bit, but at any rate, I had to rely on physical maps to get around and hope that I didn't mess it up too badly. Yeah, it's like the Stone Age right. Well, these days, as long as I have my smartphone with me and I'm not buried under a mountain or something, I feel fairly confident I'm not going to get lost. If I'm going somewhere that has limited connectivity, like limited view of the sky, then my anxiety starts to creep in again. But usually I'm okay, and that's thanks to the Global Positioning System or GPS. So today we're going to learn about GPS, what makes it work, how the technology has to take into account, Einstein's theories of relativity and more. And a huge thank to JP Morgan, Chase Bank, and the United Explorer Card for sponsoring this episode. We'll hear more about them later too. So GPS, well, that story begins back in the nineteen teen fifties when the United States and the then Soviet Union were locked in a Cold war, and that cold war manifested in many different ways, including an effort to launch vehicles into space. For one thing, if you could launch a rocket into orbit, then you could show your technological superiority over your opponent and say, look how much further advanced we are compared to you. But you could also send the message of hey, if I can send a rocket to space, I could send a rocket to your front door, all the way from across the world, and it could be carrying a heck of a boom boom. Now this gram message underpinned what would become the space race. But the space race also meant that brilliant engineers and scientists would actually get the resources they needed to advance technology by incredible leaps and bounds over the following decades. So you got to take the good with the bad, right. The good part is you suddenly had actual financial support for or incredibly important scientific and engineering work. The bad is, well, it was all done in service of this perceived rivalry with this massive country on the other side of the globe. On October fourth, nineteen fifty seven, at approximately seven thirty pm, the USSR launched the first man made satellite into orbit, Sputnik. Non past episodes, I have referred to the satellite as the ball that went beep. That's not exactly inaccurate. The satellite was spherical in shape. It did have these long antenna extending out the back of it, so it kind of looks like a comet, like a silver comet. But the antenna transmitted short radio pulses, and these pulses could be picked up very easily by ground based audio receivers, including radio sets operated by amateurs, just an amateur radio set. This meant that Sputnik's existence couldn't be kept a secret because if you or someone you knew operated a radio, you could learn about the thing. And in the United States, it prompted no small amount of anxiety. Americans believed their country was well ahead of the Soviet Union, at least on a technological basis. But here they could see that their adversary had launched stuff into space and did it before the US could do it. That really kicked things into gear here in the United States. But I would argue that Sputnik would ultimately plant a seed that would blossom into GPS further down the line, because here you had a satellite sending regular radio signals to Earth, and those signals were pretty primitive. Essentially, the satellite was signaling that it was within range overhead, along with basic information about stuff like air pressure and temperature indicated by the length of the radio pulses. Like the pulses didn't give data the way Wi Fi does. Literally, you would measure how long the pulse lasted and that would tell you, oh, the temperature is whatever, if you happen to have the chart. Two scientists were able to adfer other information, however, from this signal, such as how the propagation of radio signals interacted in the upper atmosphere like the ionosphere, and it hinted that there could be other uses for as satellite beaming information down to Earth. Also, those signals were subject to what we call the Doppler effect. It's named after Christian Doppler effect. No, I'm sorry, it's just Christian Doppler. He first observed this effect back in eighteen forty two. And this is how the frequency of a wave changes relative to an independent observer if the thing that's emitting the wave is moving toward or away from that observer. Which was a clumsy explanation, Let's just take an example because that makes it way more clear. So let's say you're just walking down the street. You're on a sidewalk, and say one hundred feet or so in front of you, there's an emergency vehicle and it's parked. It's not currently driving anywhere, but it is running its siren. The sound of that siren is going to remain consistent relative to you, right, it may increase and decrease in pitch because the nature of the siren, but it's going to keep doing that pattern over and over again. But now let's say that it's an emergency vehicle that's rushing off away from you. It's driving off. You'll notice the pitch of the siren will start to go lower. The frequency of the sound wave decreases as the vehicle accelerates away from you, or let's say the vehicle is driving towards you, the pitch of the siren will go up as the frequency increases. You can kind of think of it like this. An approaching object emitting a wave is effectively pushing or compressing that wave as it moves closer to you. An object moving away from you is stretching out the wave it's emitting as it moves away from you. That is the Doppler effect. Scientists at the Applied Physics Laboratory or APL, at Johns Hopkins University noticed that the Doppler effect was also applicable to Sputnik's radio waves. The satellite's radio pulses were compressed as Sputnik would approach, and then they would stretch out as the satellite would move away from their point of observation, and this meant that just by listening to the pulses, the scientists could track Sputnik's movements. They didn't need to have eyes on the satellite to track it. They could just follow the pulses and observe the Doppler effect in order to know generally where it was and when it was heading away, but very generally, like they couldn't give you a pinpointed location. However, this was another important seed for what would become GPS, because it would lead to the hypothesis that a satellite could send signals to a receiver on Earth, and if that receiver quote unquote knew how far away the satellite was from the receiver, you could determine the location of that receiver on Earth. You would need to be able to get signals from more than one satellite, however, to do that, otherwise, you would really just know how far away you were from one satellite. But that's not really useful information because it doesn't narrow stuff down enough, or to put it in another way, let's say, let's take this to two dimensions. So let's talk about a map. Let's say you've got a map of North Georgia, Okay, because that's where I live. And I could say, hey, I live twenty miles away from my parents. And let's say you happen to know where I live. Not that I'm gonna dox myself, but let's say you know where I live, so you can take that point on the map you could draw out a line that's twenty miles out and then create a circle with a radius of twenty miles but without more information, that could mean they could be anywhere along that circumference of the circle right in a radius of twenty miles from me. They could be east or west, or north or south, or any point in between, as long as it was twenty miles out from my location. We'll come back to this analogy in a little bit. Let's get back to the Doppler effect. It could all be used to get a more accurate location. If you know where the satellite is as you receive signals, you can use a series of pulses from that satellite to determine your location on Earth. This actually takes a bit, right. So if you know where a satellite is as it's beaming down these radio pulses to you, and you are able to get a sequence of measurements, and you're taking the Doppler effect into account, and you have all this information available to you, you can then use that info to reckon where you are on Earth. You have to keep receiving signals as the satellite is moving through its orbit and then use the series of data pulses to track where you are on Earth. If a satellite isn't within range, then you have to wait until one is close enough to you for you to start picking up the signals. That could be up to an hour, depending upon when the last one passed overhead, but it would work. So this would become a very early satellite based navigation system for the US Navy. So back to our history lesson. Following Sputnik's incredible impact both figuratively and then semi literally, because it would burn up upon descending through the Earth's atmosphere about three months and more than fourteen hundred orbits after initial launch, the US Advanced Research Projects Agency, or ARPA got to work on funding research for a satellite navigation system that would be called TRANSIT. Today we call ARPA DARPA, and it's a branch of the US Department of Defense that offers contracts to various organizations and companies to advance technologies that would be potentially useful in national defense. It's the agency that's responsible for bringing together the folks who actually built the infrastructure for the Internet. It's also largely responsible for the initial boom in autonomous vehicle research. Anyway, Transit would be handy for the United States Navy. The boffins over at Johns Hopkins University APL designed the satellites, which were intend to provide location information on Earth and in the Earth's socians, to an accuracy of within tens of meters, which thay sounds pretty loosey goosey, right, Like, if you were tens of meters away from your location based upon the app you would think, wow, this is not very useful. But at the time it was significantly more accurate than what we had been used to, So we were able to use this for mapping purposes and it was really handy. It would allow for far more precision, and it proved beyond a shadow of a doubt that England is not a conspiracy among cartographers and shout out to me if you actually recognize that reference. The first attempt to get a Transit satellite into orbit was a failure. As Monty Python might put it, it sank into the swamp, but it did not take four tries to get it right. Transit one B successfully achieved orbit on April thirteenth, nineteen sixty. It passed test with orbiting colors, but it would take more satellites. To create a system that would be useful and reliable, you needed a group of them, or a constellation of satellites in other words, and that's what we call a collection of satellites that collectively provide some specific information or service. It's a constellation anyway. By the mid nineteen sixties, the US launched several satellites into orbit, and this orbital path took the satellites past the Earth's poles, and once there were six satellites making up a very small constellation. The Navy would use those satellites and the Doppler effect to keep track of US subs that happen to be carrying big old boom booms on them, like the nuclear kind of boom booms. When you're on a submersible that happens to be outfitted with nuclear weaponry, you want to keep an accurate account of where you are and where you're going, and more importantly, the country that's in charge of you wants to know where you are, because if you suddenly disappear, that's a huge problem. Using transit, the subs could gain accurate location reading from satellite in just a few minutes, which again was a huge improvement over simply using map making and plotting. I mean, there are people who are phenomenal at figuring out where a submarine is based upon knowing the heading and how long a sub was traveling in that direction. I marvel at it when I see films of navigators doing those kind of calculations. But the nice thing is this would allow for relatively quick and accurate results, assuming that you were within range of receiving a satellite signal. The US Navy took over the operation of these satellites from ARPA by the mid nineteen sixties, and by nineteen sixty eight the system had a total of thirty six satellites in orbit. While the primary function of the system was to keep tabs on nuclear armed submarines, researchers also used it to map out locations, including using it to get a more accurate measurement of Mount Everest's elevation, which I thought was pretty neat. Now. That was in the nineteen sixties and nineteen seventies, and transit would remain in operation until nineteen ninety six, at which point it was retired for navigational purposes anyway, in favor of GPS, which had come online not long before that, actually, but we've still got some steps in between that we're going to need to talk about. So while Transit was taking shape with occasional launches to build out its constellation, another team over at the Aerospace Corporation was developing a more advanced navigational satellite system. Among the scientists and engineers was Ivan getting Hideyoshi Nakamura, James Woodford, and Philip Diamond, and they figured out that with a large enough constellation of satellites, with each satellite carrying an incredibly accurate clock on board, you could provide even more accurate positional information to a receiver on Earth. What's more, the receiver itself wouldn't need to be a super accurate clock. The clocks would just be on the satellites, and this would dramatically reduce the cost of building out receivers on land. Like before, if the receiver on land needed to have an incredibly accurate clock as well as the satellite, then the cost would have been prohibitive for the average person. But this brought all the onus of time keeping onto the satellite site, not the receiver side, and it made it much much more affordable. So you still need those clocks in the satellites themselves, but the receivers on Earth could be drastically simplified and manageurized and again accurate reading on position. A receiver would need to connect with four satellites, so the constellation of navigational spacecraft would need to be fairly large in order to be able to receive signals from four satellites simultaneously. But those four satellites would give enough information to really hone in on the receiver's location here on Earth. So what we're going to do now is we're going to take a quick break to thank our sponsor, and then when we come back, I'll talk more about how this works, like how state lights are able to send information that a receiver on Earth can take and interpret as positional information on the surface of the planet. But first let's take this quick break, all right. I think it's best we now take time to talk about how all this works, and that's what we've been building towards. So remember when I said my parents live like twenty miles away from me, and that just tells you that they're somewhere within a twenty mile radius of my location. That's that's all it tells you. But if I gave you another data point. Let's say that I said, oh, they happen to live seventy miles from Athens, Georgia. Well, now you can take a map and draw two circles, assuming you know where I live. So one circle would be centered on my location with a twenty mile radius around it. The second circle would be around Athens, Georgia at the center. It would extend out seventy miles. So these two circles would overlap slightly. They kind of cross one another at two points, kind of like a ven diagram. And now you've narrowed down my parents' house to one of two possible points. Because where they live needs to be within twenty miles of me and seventy miles of Athens. That only leaves two locations on the map. Now, unless one of those points happens to be somewhere where a house could not possibly be located, like in the middle of a lake or something, they're still ambiguity. You don't know if they're in location one or location two. Ah. But what if I also said my parents live within or ten miles away from the amusement park six lags over Georgia. Well, you could draw a third circle with a radius of ten miles around that park, and you should see that this circle intersects with the other two already drawn at a single point. They three circles meet only in one location, and that is where my parents would live, or it would be if I weren't giving total made up answers to these different distances. For one thing, I don't think you could have circles that overlap seventy miles out from Athens and ten miles out from six Legs. They're too far apart. But you get the idea. GPS satellites work in a similar way, except we need to think about spheres rather than circles. We have to go into three dimensions, right, So a GPS satellite essentially sends out a pulse of data and it indicates a time stamp and the satellite's location. A receiver on Earth receives this message and by doing a little math, figures out how far away it is from the satellite by knowing how long it took the message to travel from the satellite to the receiver. These pulses are traveling at the speed of light, so we actually do know the velocity or the speed rather of those signals. So we've got time and we've got speed. We need to figure out the distance to know how far the receiver is from the specific satellite, and we can eliminate all the positions that aren't on Earth. Right once we figure out, oh, it took x amount of time to get here, that means where why number of miles away from the satellite we happen to know where the satellite is located, you could create a sphere representing all the points around the satellite that are the proper distance away. A lot of those points are going to be out in space. We can disregard those because obviously we're not in outer space. But for the ones that are on Earth, there's going to be a lot, right, Some are going to actually extend into the Earth. We can probably dismiss those as well. So we're just looking at the ones that actually intersect with the surface of the Earth. But there's still a lot, so we have to narrow it down. We do that by receiving multiple signals from multiple satellites, preferably for satellites to really get rid of any ambiguity. If the receiver does this with at least three but typically four satellites. Then it can pinpoint where on the surface of the Earth the receiver happens to be. It's a clever way to figure out locations because once we do figure out all, right, where why number of miles from satellite A, where Z number of miles from satellite B, where AA number of miles or satellite three and BB from satellite four, you create the spheres around all four of those satellites. You know where they are, they've told you where they are. You know what time stamps you're looking at. The time stamps also need to be in sync with the receiver's clock, but the receiver's clock can be modified here on Earth. We don't have to worry about the satellites doing that, and collectively that will end up giving you a single location where it's the only place on the surface of the Earth where all of those points of data converge. And that's how GPS works. So the scientists work fed nicely into work that was already being done at the US Naval Center for Space Technology, where other brilliant people were hard at work developing atomic clocks. So let's talk about that for a second too, because this timekeeping element is absolutely vital for navigation purposes. Remember, all of our navigation calculations are based upon how far we are from these satellites. But if the timekeeping is off, then our distance is going to be off, which means we're going to think we're somewhere else on the surface of the Earth and where we actually are. So let's take quartz based risk watches as sort of a starting point. Quarts will vibrate physically when subjected to a voltage. This relates to piezo electricity, which is the ability for certain materials like quartz to store an electric charge in response to mechanical force that's been applied to that substance. In other words, like if you'll whack quartz, it'll build up an electric charge. But the other effect can also be true. Certain materials, when exposed to an electric field, will produce physical vibrations, and quartz is one of those materials. What's more, it will always produce the same frequency of vibrations in response to specific applied voltage. So if you apply the same voltage over and over, is going to vibrate at the same frequency over and over. It does not vary, at least not for the purposes of wristwatches. As it turns out, for the purposes of space navigation, it's not nearly precise enough. But if you apply specific voltage to a quartz crystal, the crystal will produce a vibration of a specific frequency, which you can then use as if it were the swinging pendulum of an old timey grandfather clock, and you can calculate the passage of time by the frequency of vibrations. If you know that it takes twenty thousand vibrations per second, then once you hit twenty thousand, you know a second has passed. That's essentially how it works. Now, atomic clocks are not that different, but there are many orders of magnitude far more precise. So quartz crystals are consistent enough for our earthly needs, but when it comes to space operations, we need much more stability and much more accuracy. A quartz space clock will gradually start to drift and start to lose accuracy over time. Now, it typically takes a while. It might be more than a month before the clock is off by so much as a millisecond, but that would still be enough to provide extremely wrong navigational information. So imagine you're looking at your GPS app and you are flabbric acid because according to the app, you are like two hundred miles away from you where you actually are. And it's all because the receiver would be depending upon the wrong information, that time code would be wrong, and that would mean that it would be calculating the wrong distance. So yeah, a small error in space translates into an enormous error when you get to navigation systems on Earth. So atomic clocks rely upon oscillations of atomic energy states. Like think of electron energy states. You probably know atoms are made up of a nucleus around which are orbiting electrons. These electrons in habit various energy states. If you pour energy into an atom, you can make an electron go move out to a higher energy state, and then once you stop pouring energy in, the electron will naturally move back down to its normal energy state. So this can be an oscillation. Now to go into this further, to really dive into it, would get far too complicated for this episode. But the important thing to remember is that atomic clocks are both more stable and more accurate than quartz crystal based time pieces. Depending on the type of atom being used, the clock might count billions of oscillations per second, like more than nine billion, So you're really dividing a second down into unfathomably small units of time by looking at the frequency of these oscillations. This is an incredible level of accuracy, which is a necessary component when we're talking about navigation. But I also promise y' all some relativity up here in this podcast. So what does that have to do with anything, Well, Einstein's theories of relativity. Both of these special relativity and general relativity varieties have something to say about the passage of time. It's all relative, you see. And some factors that determine the speed at which time passes for a subject relative to an outside observer includes stuff like gravity and speed. Now, let's get one thing out of the way first, because this gets whibbly wobbly timey. Whymy, Like, you wouldn't believe the passage of time to an observer like their own sense, their own sensation of the passage of time, that doesn't change. To them. Time continues on as it would in any other condition. It's only as they observe outside points of reference that the sense of time changes. So like, for example, one thing is that the faster you go, the slower time moves for you relative to an outside observer. So if you're in a ship and you're going super super super fast, it would feel like time is passing as normal. To someone outside of the spaceship here on Earth, it would look like you were moving in slow motion. If they could magically see you inside this ship, even though the ship is moving super fast, you would appear to be moving at a crawl. And that's why at the end of your journey, when you would get off your spaceship, your friends and family who had stayed behind on Earth would have all aged much more than you did, because relative to them, time passed more slowly. For you. Your experience, however, was that time just continued on as it always has, very very mind binding kind of stuff. Right, But what does this have to do with satellites. Well, let's talk about general relativity first. It explains that gravity can alter time such that a satellite that's in orbit around Earth will have clocks that are running a little bit faster than they would if they were just on Earth. And by a little bit faster, I'm talking about like forty five microseconds per day drifting right, like they're getting ahead by about forty five microseconds per day. However, we also have special relativity. This says that because the satellites are whizzing through space pretty darn fast, the clocks run a little more slowly relative to the ones on Earth, and they end up losing about seven microseconds per day. So you've got to factor both of these in. Right, you're gaining forty five microseconds on one side and losing seven microseconds on the other side. But this means that we have to send up clock modifications corrections to the satellite's clocks in order to adjust them and make sure they don't drift too much over time, because the longer they do so without a correction, the more inaccurate the results are going to be here on Earth when we're depending upon them for navigation. All right, let's get back to our history. So in the late nineteen seventies, a US military GPS constellation was slowly taking shape, and initially it was called Navstar. And this project took the work that was being done independently in the Army, the Navy, and the Air Force and kind of brought all that learning together and became a really massive nationwide effort and eventually it would evolve into what we just referred to as GPS these days. The first fully operational satellite in the GPS constellation would finally launch in nineteen eighty nine. So yeah, this was a system that was in development for like two decades pretty much, and then finally in nineteen eighty nine, the first satellite goes up. And that's just one. You can't navigate just on one satellite, at least not using this trilateration approach. But meanwhile, manufacturers here on Terra Firma were busy building the navigation devices that would be reliant upon these satellites once there were more up in orbit, and this would include handheld navigation units. The constellation of GPS satellites wouldn't reach what old Emperor Palpatine would consider fully operational until nineteen ninety five. The military would end up receiving clear signals for the purposes of navigation. So if you were using GPS and you were in the military and you were using it officially, you would get really accurate results. However, the same was not true for everybody else. The rest of us got something that was called selective availability. I mentioned that at the top of this episode. So essentially for civilian use, the satellites were fudging the timecode just a tiny, tiny amount in those data pulses. Now, it wasn't fudging the timecode enough to put you well outside where you actually were and make it totally useless, but it was enough to muddle the accuracy to within maybe one hundred meters of your actual location. So you could still use GPS for general navigation, but it wouldn't be suitable for stuff like turn by turn directions because the muddled data would not be accurate to your real location. So why was this Well, it was to protect stuff like military bases and that sort of thing. The thought was that the information was potentially too dangerous to be made public. This would hold true until two thousand, when former President Bill Clinton rescinded select availability. At that point, GPS receivers could display accurate information to within a couple of meters of a person's actual location on the Earth, and this would improve over time, and this is when turn by turn directions will become a possibility for civilian use. Now today there are more than thirty satellites that are part of the GPS constellation. They are frequently updated where you know, a newer generation of tech satellite will go up and replace ones that are no longer in service or have stopped working, and our capabilities improve with each generation. The United States is also not the only nation to operate a global satellite based navigation system. Russia has an alternative to GPS. It's called Glonas GLO NASS. Receivers that can work with both GPS and clonos are typically more reliable because they can more easily receive signals from, at least for satellites, like even if you're a place that has lots of tall buildings that might block signals, you have a lot more satellites up there that you could potentially pull from and thus get a better reading on where you are, so you can get devices that are compliant with both GPS and GLONAS. Glonas initially completed its constellation in nineteen ninety five, the same year that the GPS constellation went fully operational, but budget cuts in Russia led to degradation of the constellation. It lost some of its capability, and eventually Russia was able to reinvest and in twenty eleven they were able to bring a full constellation back online. It's been pretty much that way ever since. Again, like the United States, Russia has also upgraded individual satellites in the constellation in order to provide better service. So that's it. That's kind of how GPS works. It's really all about figuring out where you are based on how long it took satellites to send you a little data message. You know, it's pretty cool, I think. I think it's a really intriguing way to figure out your location. It's so clever because it's not relying on things like landmarks or anything like that. Not the way that people like myself typically navigate, right. I navigate through landmarks and street names and that kind of stuff. Occasionally I will reorient myself based upon which where the sun is, because I know enough to know if it's before noon, the sun's in the eastern part of the sky, and if it's afternoon, it's in the western part of the sky. Once you get past that, all bets are off. I was never that good of a boy scout, but yeah, GPS is really truly revolutionized travel beyond what I can even express. Like, it's hard to communicate to people who have never lived without GPS what it was like to try and get around, like to have an atlass in your car and you know, rely on on paper maps or like in the old, the old days of things like map quest, you would find turn by turn directions on your computer and then print them out or write them down because smartphones weren't really a thing yet, so you need to have a way to actually carry the directions with you. It's a different world these days, but still pretty cool. Like I think, it's a neat thing to know that this system works in this way. It's also important, by the way, to learn how to read maps, because you never know. If stuff goes down for whatever reason, you want to be able to still get around, like things like solar flares coronal mass ejections. These big solar events can sometimes wipe out stuff or at least shut things down temporarily, and if in the process of that you still need to get around, knowing how to read a map can be really useful, so it's a skill I recommend developing. That's it for this episode. I hope you are all well. I hope those of you who have fun trips planned in the future can take a moment to appreciate the beauty and utility of GPS, and how amazing it is that we're using things like theory of relativity and space technology just so that you know where you need to turn to go to the next in and out burger. I think that's pretty cool and I will talk to you again really soon. Tech Stuff is an iHeartRadio production. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.