TechStuff to Major Tom

your podcast. I am looking at satellite communications and I find it hard to understand how are they used for Internet access, why they use mega hurts instead of megabits per second, and in general, how they communicate to Earth perhaps a continuation episode. Well that's a great topic, and I get how it can be confusing when a technology uses different but similar sounding terms. So today we're going

to break down satellite communications and how they work. Now, the simple and there to the question is that satellites communicate using radio waves, and in fact that's where the mega hurts stuff comes in. But that doesn't really create an understanding of what's going on. To do that, we need to jump into some history. And you might think I would start with nineteen fifty seven with the first

satellite to achieve orbit, but you're wrong. We're going back a bit further I'm going to start all the way back in nineteen o three, which sounds crazy, right, but that's when a Russian scientist named Konstantine Selkovsky worked out the mass that suggested that, yeah, it would be possible to build a rocket that we could launch from Earth and lift a payload into space, so that that payload,

that object would be in an orbit around Earth. Now, see gravity pulls downward, or if you prefer it, pulls towards a center of mass, because you know, once we get out into space, concepts like up and down don't have so much meaning. Inertia of a moving body tends to make it move in a in a straight line. So think of it as we have a perfectly leveled table. Now we've got a ball on the table, and you give a push on the ball, it will tend to travel in a straight line in the same direction as

your push. So if there is a balance between gravity and inertia, an object will continue in a straight line while being pulled toward a center of mass. So, if the object is moving fast enough, the ground of the Earth will curve away from its path as it falls towards the Earth. So it's kind of in a constant state of falling. This, by the way, is one of many proofs that the Earth is round, because if it weren't,

orbits would not work. But we know they work because we built stuff, we put it in orbit, We depend on that stuff on a day to day basis, So that alone is proof that the Earth is round. Now, Silkovski proved that an orbiting satellite was possible from a mathematical point of view, but there was no real, you know, rush to prove him right. For one thing, what the heck would the ding dang durn thing do once it was up there? I mean, would we just be throwing

resources at something just to say we did it? I mean, this would be the equivalent of answering the question why do you want to climb Mount Everest with because it's there? That might not be the best answer for all situations. Besides, Silkowsky's work wasn't widely known for many years. In fact, two decades later, a Romanian scientist named herman O Birth essentially worked out the same stuff completely independently of Solkovsky's work.

He wasn't aware of Silkovsky. But again, even ober It's work was confined to a relatively small circle of physicists, or as the British would say, Boffin's he. Even well read physicists in the United States had never heard of either of these two people, and while they were all thinking about space, none of them had actually proposed an artificial satellite as of yet. Robert Goddard, an American, made another important contribution to our space efforts. While pursuing post

graduate studies at Princeton University. He demonstrated that rocket propulsion would work even in the airless environment of space, and this was around nineteen sixteen or so, and he built a solid fuel rocket in nineteen eighteen. But his funding dried up around the time that World War One ended, and this is going to be an ongoing theme in the space industry. Scientists seem to get way more funds when there are possible military applications to the technology they're developing,

you know, beyond just putting stuff up into space. Goddard would continue his work through various colleges up until World War Two, when a again he would receive funding to work on rocketry with applications for the military, in this case largely in the world of jet assisted takeoff or j to j A. T O. Germany also famously pursued rocketry in World War Two, using it to great effect with devastating weapons like the V two rocket. One of the scientists chiefly responsible for that V two rocket was

Werner von Braun, sort of Germany's equivalent of Goddard. Von Braun was interested in spaceflight, but like Goddard, he put his mind to work for a military in an effort to fund his research. Germany used von Braun's rockets to fire upon cities like London, killing thousands and devastating entire

sections of the city. Von Braun wasn't necessarily the most ardent supporter of the Nazi regime during World War Two, but he joined the Nazi Party and became a member of the s S and while he didn't seem to share any real political views with the Nazis, he did see the allegiance to the party as a necessity for him to get the resources he wanted to pursue the goal of space flight, so to him, the ends justified

the means. In nineteen forty three, scientists working for the U. S. Navy began to look into the possibility that the Nazis were developing rockets capable of putting an artificial satellite into orbit. Their worry was that a device like that might be used for reconnaissance or spy technology, or maybe even as a weapon, whether a weapon capable of actually creating physical destruction or a more psychological weapon to terrorize people into

thinking they'd be subjected to death rays or something. The scientists concluded that it could be possible to launch a satellite into orbit. Essentially, they were retreading the ground that Siolkovsky and o Berth had already walked, and there was some early interest in exploring that as an actual option.

In nineteen four be four, while at a party, Von Brown got inebriated and he let it slip that he thought the war wouldn't end well for Germany, which was pretty much a foregone conclusion, but it was essentially a treasonous act. To actually suggest that Germany would lose the war was an act of treason. So he was arrested. However, he was never incarcerated. It did send a message to him, you know, Von Brown said, Wow, my place here is not as secure as I would like it to be.

So he and several other rockets scientists went into hiding. Upon hearing that Hitler had committed suicide, these scientists surrendered to American soldiers and they were part of a negotiation to come to America and essentially pursue the same sort of work they had been doing for Germany, but in the United States. Now. This was known in classified circles as Operation paper Clip, and it involved bringing more than

fifteen hundred scientists from Germany to the United States. Von Braun would continue developing rockets in the US under various military projects and research facilities, still with the dream of

achieving space flight. Now to say that he's a controversial historical figure is really putting it mildly, but he's definitely an inspiration for science fiction authors who like to create sort of those amoral scientists who pursue their obsession with no regard for the consequences, you know, following in that old Jurassic Park line of you spent so much time thinking if you could, you never thought if you should.

That kind of thing. Anyway, German and American scientists would work together in numerous laboratories run by several universities as well as the military branches, and they created rockets that carried payloads holding scientific equipment designed to measure phenomena in the upper atmosphere. So these were rockets that wouldn't escape into orbit, but they would go very, very very high up.

As early as nineteen forty six, these different facilities were looking at the possibility of launching a satellite into orbit, but they largely concluded that these technologies weren't sophisticated enough to make that a reality just yet. It was, however, a long term goal. Now this brings us up to the nineteen fifties. That's when the United States and the

then Soviet Union were deep in the Cold War. The two nations had become more antagonistic to one another since the end of World War Two, and each nation was attempting to keep the other in check while expanding its own power. They were also both racing to develop technologies that can demonstrate superiority over the other. This is part

of what fueled the space race. Now, I don't want to take anything away from the thousands of scientists, engineers, pilots, and everyone else who worked on those early days in the space industry. Though at this point it wasn't yet an industry, there were lots of people who genuinely wanted to use technology to explore beyond what humans had previously been capable of and to push back our boundaries of ignorance. There were a lot of brilliant people who worked on

projects with the motivation to further our scientific knowledge. But the reason they really got the chance to do this was because governments were willing to pour a lot of resources into the endeavor in an effort to try and get ahead of the opposition. So that's the backdrop, but

let's get to some details. In nineteen fifty two, the International Council of Scientific Unions established that the period of July one, nineteen fifty seven to December thirty one, nineteen fifty eight, would be the international geophysical year to coincide with a cycle of increased solar activity. And in case you didn't know, the Sun goes through these cycles in which there's more solar events like solar flares that happen

in that cycle. Then that's followed by a period of decreased solar act ativity, not no solar activity, but less of it. And these are regular and predictable, though the individual activities the individual flares are not as predictable. Then in nineteen fifty four, this same council said, Hey, you know what would be really needo if we figured out how to launch a scientific device up so that could

enter Earth's orbit. Such a thing had never been done before, and the proposed goal was a device that would be capable of mapping the surface of the Earth, giving us the most accurate vision of the Earth's surface to date. Several organizations had been looking at the logistics of getting a payload up into orbit, though not necessarily as part of the Council's proposal. The dream back in nineteen six had never really gone away. It just was on the

back burner because it wasn't really possible. And then something happened to spur the American government to put more support behind this endeavor. A nineteen fifty four broadcast on Moscow our radio revealed that the Soviets were seriously gearing up to push for space flight. Now, that bit of information didn't reach the general American public, but you can bet that the federal government was very much aware of it.

A year later, in nineteen fifty the US government announced a plan to launch a satellite, and that timing is definitely not a coincidence. The government began to request proposals from various laboratories to assist in getting this done, essentially saying, give us your plan so we can figure out where

we're going to put our money. The Naval Research Laboratory responded to this request for proposals with a project called Vanguard, while other groups had alternative proposals and lacking a real sense of urgency, the White House kind of waffled on this. They delayed on selecting an option. They were kind of weighing all of the choices, and this was somewhat understandable as any path was going to require millions of taxpayer dollars, so if the project was a success, it would be

a high point in science history. But if it failed, taxpayers would get mighty miffed at what had been seen as a huge waste of money, Like you took millions of our dollars and you put it towards something that didn't even work. That would be disastrous. Ultimately, the White House chose Project Vanguard, and the hope was to be the first nation to launch a man made satellite into orbit.

But that's not how things turned out. While Project Vanguard was underway, the Soviets had been busy, and on October fourth, nineteen fifty seven, the USSR shocked the world by launching a nearly four pound or eighty three point six kilogram satellite into orbit. That satellite's name was Sputnik. It was about the size of a beach ball, and it would orbit the Earth every hour and a half or so, and it also essentially went beep. It sent out a radio ping signal that could be picked up by radio

stations as the satellite passed overhead. That included radio sets that were operated by amateurs, so ham radio operators could hear as the satellite passed over and this launch shocked the American public. Americans were under the belief that the Soviet Union was far behind the United States from a scientific and technological standpoint. Spot Nik flew in the face

of that, and it also raised a terrifying possibility. If the USSR could launch a payload into space, could it also create a weapon that could be fired from across the world and still hit the United States. Spot Nik launch spurred the U s Government into emergency mode. Vanguard was still on the books, but the White House would turn to the Army Redstone Arsenal Team led by one Werner von Braun for an alternative, and it would be called the Explorer one, and it would become the first

satellite launched by the United Dates. We have a bit more history to go through when we come back, but after that we'll go into how we get these satellites into orbit, and then how they communicate with each other and with stations here on Earth. But first let's take a quick break. The first Spotnik satellite orbited the Earth in October nineteen fifty seven, and it was never intended

to be a permanent fixture. It's orbit gradually decayed until in January nineteen fifty eight, it burned up while re entering the Earth's atmosphere. The Soviets launched spot Nick two in November of nineteen fifty seven, and that's all I'm going to say about that story. I've covered it before, and that story makes me super sad and I hate

to talk about it. So the United States would launch Explorer one on January thirty one, nineteen fifty eight, So several months after both spot Nik and spot Nick two, it did more than beep. Explore one did not just beep. It also didn't kill a dog, So that's two things that made it more advanced than either of the Sputnik satellites. It carried scientific equipment designed to detect cosmic rays, and the fact that it sent data with lower cosmic raid

counts than was anticipated. Let a scientist named James Van Allen to hypothesize about the existence of a belt of charged particles that were trapped by Earth's magnetic field. A second satellite confirmed this hypothesis a couple of months later, and the scientific community would name the charged particles the Van Allen Belts. It took Explore one just under one fifteen minutes to complete an orbit around the Earth, so it would go around the planet about twelve and a

half times per day. It stayed in orbit a little longer than Sputnik did. While the Soviet satellite burned up on reentry just a few months after being launched, the Explorer one remained in orbit from ninety eight until eighteen seventy. It completed fifty eight thousand trips around Earth. The era

of the satellite was just beginning. While a lot of media attention would shift towards space flights with humans and spacecraft, the scientific community around the world continued to develop new satellites for all sorts of purposes, from scientific research to

military reconnaissance to eventually global communications. One other thing I want to mention before getting into the communications tech is how a science fiction author proposed a type of satellite that would be capable of communicating with a ground station every hour of the day. See, if you have a satellite in orbit like Explorer one, there's going to be times when that satellite cannot send communications back to a specific ground station because it's going to be out of sight.

Once the satellite passes a certain point overhead, communications will start to drop. Placing ground stations around the world can saw of that problem, but that gets into the issue of establishing listening stations in places that you know aren't yours, and that gets tricky from a political and real estate standpoint.

But obviously, if a satellite is on the opposite side of the Earth from a listening station, the radio signals can't get to the listening station, so you really only have a window where you can have useful communications with that particular type of satellite. For an effective communication satellite, you need something in orbit that will remain over the same fixed point here on Earth or in a pattern that keeps it over the same general area of the Earth.

The satellite would need to travel around an orbital path that keeps pace with the rotation of the Earth itself, and this is called a geosynchronous orbit. The satellite will travel over the same general region of the Earth because it will orbit at the rate of once per day,

the same as the Earth's rotation. Now, science fiction author Arthur See Clark, known for writing stuff like two thousand one a Space Odyssey, made a sort of observation and prediction back in nine It was published in a magazine called Wireless World, and it proposed the idea of a

geo stationary satellite. Clark stated that a satellite at sufficient altitude, and he was talking about a an altitude of forty two thousand, one sixty four kilometers or around thirty five thousand, seven eighty seven miles above the Earth's surface and placed over the equator would have an orbital period equal to the Earth's rotation, and so would remain above the same

fixed point on the equator. Now, forty two thousand, sixty four kilometers altitude is obviously a lot, but without any context, it's hard to say that's not so bad or wow, that's way the heck out there. So just for comparison's sake, it's good to remember that the International Space Station, which isn't in geo sin grannous orbit, is a mirror four hundred kilometers in altitude typically four hundred versus forty two thousand, one d sixty four. Wow. Still as far out as

geosynchronous orbital areas are. That's not even halfway to the Moon. The Moon is three four thousand, four hundred kilometers from Earth, So a geostationary orbit is a specific subset of orbits that fall into the geosynchronous orbit category. A satellite in geosynchronous orbit will remain over a general region of Earth, but if the satellite isn't directly above the equator, that

region varies a bit due to the Earth's tilt. In fact, from the Earth's standpoint, it looks like the satellite is moving in a figure eight pattern across the Earth's surface. That's because the path of the satellite crosses above and below the equator during the orbit and the Earth's rotation throughout the day. A geo stationary orbit has to be above the equator, and a satellite along that orbital path will remain over its fixed point on Earth. Uh with

some caveats that I'll get to. Such a satellite could remain in constant contact with the exact same ground stations, and those ground stations would never need to move their antenna to maintain contact, right they would just point their antenna where the satellite is, and that's where the satellite is going to stay. So it really makes it simplified

to communicate with that particular satellite. A network of those types of satellites could communicate with one another as well as their respective ground stations, and boom, you've got your framework for a global communications infrastructure using radio signals beamed out into space and then beamed back down to the Earth. Now, Clark's idea was sound, but there wasn't really any practical

way to achieve it. Back in it would take twenty years before the world would see the first commercial geo stationary communications satellite, and that was called the Intel SAT one. I think it would be handy for us to look at what makes putting satellites into geo stationary orbits so tricky, because it gives us an appreciation for the amount of science and technology required to make stuff like communication networks actually work. So let's start with just putting something into orbit. First,

you gotta put your satellite on a launch vehicle. Now, essentially what we're talking about is a rocket. Now, back in the old days, it was the Space Shuttle. We often use the Space Shuttle to put satellites up into orbit, and the Space Shuttle had rocket boosters attached to it as well as its own rocket engine. But these days we don't have a space Shuttle. We're talking about a rocket here. Usually from our perspective, we launch those rockets

straight up from the Earth's surface. And there's a good reason for this when you think about it. If you're looking anywhere from above the horizon in one direction across the entire arc of the sky to the horizon, and the other direction. So let's say you're doing it from east to west. Well, the whole time you do that, you're technically looking out towards space. So why would you launch straight up if every direction in that arc is

out towards space. What's because the shortest distance between two points is a straight line, and launching straight up means you're taking the shortest path to push through the thickest part of the atmosphere. You're doing it in the most efficient way, and that's really important because that means you're

consuming less fuel. Since fuel is one of the expensive factors in space launches, and since adding more fuel adds more weight to your launch vehicle, which means you then have to factor that weight into your calculations, being frugal

with stuff is generally a really good idea. Once the rocket reaches a certain altitude, the flight plan will call for the rocket to adjust its direction so that the payload our satellite in other words, gets to where it's supposed to be, and a system called the inertial guidance system will calculate the specific adjustments needed to put the

rocket on the correct path. That system uses accelerometers to measure the various stresses it's experiencing in order to interpret that as how the rocket is oriented with respect to the Earth and what altitude it's at. Those accelerometers are in gimbals so that they remain in the same orientation with respect to the Earth. Typically, the rocket will head

toward the east once it reaches that altitude. So why does it go toward the east was because the Earth rotates to the east, and by going in that direction, the rocket gets a bit of a boost, and you'd get the best boost in speed if you happen to be traveling along the path of the equator and going east.

The circumference of the Earth is approximately forty thousand kilometers, and we know the Earth rotates once every twenty four hours, not exactly twenty four hours, but close enough, so that means a point on the equator must travel at a speed of one thousand, six hundred sixty nine kilometers per hour. If you are further north or south of the equator and you are traveling east, you don't get quite that

same speed boost. For example, at Cape Canaveral, which is in Florida in the United States, you start off at a latitude that is twenty eight degrees thirty six minutes twenty nine point seven seconds north of the equator, and at this latitude the rotational speed of the Earth is one thousand, four hundred forty kilometers per hour, so a little bit less than the equatorial speed of one thousand,

six hundred sixty nine kilometers per hour. It might not seem like a huge difference, but again that speed boost means that you consume less fuel, So a flight path that moves closer to the equator also means you need less juice to get to your final orbit, as long as that orbit is also near the equator. To escape Earth's gravity, a rocket would have to accelerate to at least forty thousand, three hundred twenty kilometers per hour. That

is Earth's escape velocity. If you move slower than that, gravity claims the rocket, it will go into an orbit, it won't escape Earth's gravitational pull, and eventually it'll fall back to Earth if it's uh. If it's inertia, isn't enough to keep it in space. But to put a satellite into orbit, you don't need escape velocity, right, You're not trying to escape Earth's gravity because an orbit is a kind of controlled fall. It depends upon a gravitational pull.

So instead you have to reach orbital velocity. That's that balance between a satellite's inertia and moving in a generally straight line and the force of gravity that's pulling it downward. That speed is dependent upon altitude. The closer the satellite is to Earth, the greater the orbital velocity is required

in order to balance out the force of gravity. If the satellite we're at two kilometers over the Earth, it would have to travel at twenty seven thousand, four hundred kilometers per hour to maintain orbit and not come falling back down. But in a geo stationary orbit much much much further out from Earth, it can travel at a comparatively sluggish eleven thousand, three hundred kilometers per hour to

keep pace. Now remember that's to stay in a fixed position above a point on the Earth that's traveling at one thousand, six hundred sixty nine kilometers per hour. So the satellite has to cover more distance because it's further out in the same amount of time as the fixed point on Earth, which is why it has to travel faster than that relative position. And this is also why we need to remember that those satellites that are closer to us, they're actually going around the Earth more than

once per day. They might not be a whole lot more than once per day, depending on how far out it is, but they are not maintaining a fixed position above a point on the Earth, so they actually do have to travel faster. Not around in altitude, the rocket will fire smaller thrusters to change that rocket's altitude and orientation, so it enters into a more horizontal position relative to the Earth, and at that orientation, the rocket releases its payload.

The satellite will part ways with the rocket and the rocket will then fire some other thrusters that will help create separation between the rocket and the satellite. Okay, so we've boosted a satellite with a rocket so that it can move into its orbital path. Upon separation, the satellite is at the parage. Now, this is the lowest point of its orbit, the closest it will be to the Earth. Now, the satellite may cross the equator a couple of times and it will reach its apogee, or its highest point

at at this section. And you can think of this orbit is looking like it's spiraling out from the Earth, like it starts off close and then as the satellite goes around the planet, it starts to get further away before it starts to come back in. So when we talk about lowest and highest points, there's really quite a range.

So for example, the g Sat fourteen communications satellite, which had a geostationary orbit, had a parody of KOs that's where it's separated from its launch vehicle and its APOGE was thirty six thousand kilometers now an appo G. The satellite will conduct a series of controlled burns with onboard

thrusters on the satellite itself. This helps reshape the orbit from being an elliptical path where it's further out from the Earth on one side and closer to the Earth on the other side, into a more circular path where the Earth is at the center. This typically takes a few different controlled burns. You could technically do it in one, but it would probably require a lot more fuel, so it's more frequently done in short bursts to gently reshape

that orbit. Ultimately re each in orbit where the satellite remains in a fixed position above a specific point somewhere along the equator. However, the satellite won't stay there forever if you just leave things the way they are, because stuff like the Moon and even the Earth itself will

affect the satellite's path through gravitational pull. Earth's gravitational field is not uniform and these forces will slowly but surely pull the satellite out of position, so once in a while the satellite has to use those thrusters to correct for that. It's another reason why it's really important to

conserve fuel. It conserves the lifespan of that satellite. The more fuel you use, the less time that satellite is going to be able to maintain that position, and it will ultimately have an orbital decay and eventually it will fall back to the Earth and break apart upon re entry. Now, when we come back, we'll talk about how these satellites actually communicate. But first let's take another quick break. Okay, we've covered the early history of satellites and the challenges

of getting one into geo stationary orbit. Let's tackle how they communicate. Now. I mentioned that a geostationary satellite is ideal for communications because it will always maintain its relative position above the Earth. So once you know where the satellite is, you point your antenna in that direction and

you can pick up signals from that satellite. So let's say you are a satellite TV subscriber and the company providing your signal beams information up to a communication satellite that's up in orbit, which then can broadcast that same signal back down toward a region on Earth. If your satellite dish is pointed toward that satellite, you should be able to pick up on that signal. But what do

I mean when I say signals. So we're talking about the electro magnetic spectrum, and specifically we're talking about radio waves. So remember that the electro magnetic spectrum is huge. On one end, you have the long are electromagnetic waves that carry less energy. We have radio waves in that section. On the opposite side, you have very short waves that

carry more energy. Gamma rays are on that side. So within this spectrum, if we go longest to shortest in wavelength of the types of electromagnetic radiation we have discovered, keeping in mind, there can be others out there on either end of the spectrum, we just have no way of really detecting them. We have radio waves on alongside, than microwaves, then infrared radiation, than visible light, than ultra

violet radiation, then X rays, and finally gamma raise. All of these forms of energy travel at the speed of light, which makes sense right. I mean, light is one of the forms of electromagnetic energy. But they all have different frequencies and that can get a little confusing. And this

is where an audio podcast really hits the challenge. So let's imagine first second, that you've got a sheet of graph paper in front of you, and you draw a center line in the middle of that sheet, so there's a solid center line, and you start on the left side of the sheet at that center line, and you start drawing a curve that moves upward from the center line and has a peak that's at five squares above the center line. Then you curve it back down so

it crosses that center line. You keep going past it, and you draw essentially the mirror image of that curve, but you're going down now to you hit five squares below center. Then you slowly go back up to the center again. That's sort of a representation of a sign wave. You've drawn one full wavelength. So electromagnetic energy travels in waves like this, but radio waves have much longer wavelengths than gamma waves. That's, by the way, a heck of

an understatement. Radio waves carry less energy than gamma rays as well, But there are a couple of reasons that we you radio waves for communication. One is that they require way less energy to generate than stuff like light. But another very practical reason is that light waves and shorter wavelengths of electromagnetic radiation get absorbed and scattered by

the Earth's atmosphere. In fact, gamma rays can even penetrate the air, which is really good news for us, because otherwise life as we know it would not have formed on this planet. Gamma radiation would have wiped out anything remotely resembling life as we know it. Radio waves, though lower energy, can pass through the atmosphere without distortion, so they are ideal for communication. And because the radio waves are longer, fewer full wave lengths will pass a given

fixed point within a second than with gamma waves. Now, I always use the analogy of a road to understand this concept. So let's say you're standing by a road and there's going to be a line of smart cars that are travel bumper to bumper, and they're all going to pass by you. The cars are all going fifty kilometers per hour, and your job is to count the number of smart cars that go past you in thirty seconds.

Then you've got to do the exact same thing, except this time, instead of using smart cars, we're using double length buses. Those double length busses are also going by bumper to bumper. They're also traveling at fifty kilometers per hour. Now, the smart cars and the buses are all traveling at the same speed. Right, they're all traveling at fifty kilometers per hour, but you're going to count way more smart cars in those thirty seconds because they're shorter, more can

fit in that space within that time. Well, the same thing is true with electromagnetic radiation. The speed limit is set right the speed of light. It's the length of the vehicles that changes. Now we measure of frequencies in hurts h E R t Z. This refers to the number of cycles or wavelengths that pass a fixed point within a second. So one hurts would mean one wavelength would pass in one second. The U. S. Navy initiated a project that would transmit radio signals at frequencies as

low as thirty hurts, so that's thirty wavelengths in a second. Now, keep in mind this is energy that's traveling at the speed of light. The speed of light is two hundred thousand, seven kilometers per second, so if we divide that number by thirty cycles per second, we would see that the wave length for thirty hurts is somewhere around nine thousand, nine hundred nine three kilometers per cycle. So that means a thirty hurts radio signal has a wavelength that is

nearly ten thousand kilometers long. Using that to communicate is tricky because typically we need antenna to be some regular fraction of the length of the wavelength that we're transmitting and receiving, and a very common one is to have an antenna that is one half or one quarter the length of the wavelength of radio wave. But at ten thousand kilometers, even half or one quarter is still way too long, right, So practically we use much shorter wavelength

radio communications. Uh, it just doesn't make sense to build antenna for the longer ones, and different countries chop up the radio spectrum and designate bands of frequencies for specific uses.

For example, in the United States, AM radio uses a frequency range between five dred twenty five killer hurts that means five twenty five thousand cycles per second, so five five thousand wavelengths will pass a fixed point in a second at that frequency all the way up to one thousand, seven hundred five killer hurts, which would be one million, seven hundred five thousand cycles per second or one point seven oh five mega hurts if you want to think of it that way. And here we get too part

of that original question. The hurts here refers to the radio frequency we're using as a carrier signal. It's all about the frequency used to transmit and to receive information. It has nothing to do with the amount of information in that signal. It's specifically the frequency we're using to transmit that signal. It's not directly related to the amount of information being sent or processed. This is the medium

through which we're sending data. So you can think of it as serving the exact same purpose as a physical wire or cable, except instead of sending a signal down a physical piece of hardware, we're sending it through the air and through space as radio waves. Now, you could try and communicate with a basic unaltered radio wave, but you would really be limited by just doing pulses. Right, the wave is either on or it's off, and this

would be kind of like sending Morse code. And maybe do you leave it on for a short amount, like a very short pulse as a dot, and maybe you leave it on a little bit longer as a dash. And when you don't have it on, there's a gap, right, You know that that's a gap between individual pulses, But that's not terribly useful. It's also really easy to have errors introduced in that kind of signal, so we don't

typically use it that way. Instead, radio communications take a basic frequency as a carrier signal, like I mentioned a minute ago, and this is sort of the baseline. You've got a basic signal at a specific frequency. By altering that signal or modulating it, we can encode information with it, and the deviations from the carrier signal all have meaning. As long as we define what those deviations from the carrier signal represent, we can encode and decode information sent

along that carrier wave. I mentioned a M radio a couple of moments ago, and that stands for amplitude modulation. Amplitude describes the measure of change in a single period or cycle. But what does that actually mean in practical terms. Well, in our drawing of a sign wave, when we drew that that curve that went up and down, that amplitude would describe how tall the peak and how deep the trough is. And in our example we said it was five squares, So that would be the amplitude of that

sign wave. If we were describing amplitude in terms of squares with sound waves, amplitude corresponds with volume. The greater the amplitude of a sound wave, the louder it is. This does not affect the frequency, which with sound waves we would experience as pitch. Right, a higher frequency would be a higher pitch sound, So amplitude and pitch are

not connected. There are two different things. By making precise changes in the amplitude of a radio wave as a carrier wave, you can encode information on that radio wave. A receiver tuned to the proper frequency will pick up this incoming signal. It will detect those changes in amplitude and it will decode that into useful information. So all you really need to do to make this work is to come up with a set of rules that corresponds to the changes you're going to make in that signal.

If you say, if I change the amplitude in this way, it means X, and if I change it in that way, it means why. And then you have a decoder that follows those same rules, but just reverses the process. You can encode and decode information. It's a really elegant way of being able to send data. But what about FM radio Then, well, that that still involves modulation. But now

we're talking about frequency modulation. So you take that carrier signal of a very specific radio frequency, and then you make small changes to that frequency, not not big ones, just small one. You're actually changing the wavelength of the wave that you're sending out, making it slightly shorter or slightly longer, and you can encode information onto the carrier signal in a way similar to you could with amplitude modulation.

Now you can't change the wavelength too much or else you'll push the signal outside of the effectiveness of your transmitting and receiving antenna. But you actually have a good deal of leeway there. With communication satellites, the modulation is a little more complicated than changing amplitude or frequency. Satellites use what is called phase modulation. So for this, let's imagine you've got two radio waves, and let's say that

they are absolutely identical radio waves. They both have the same frequency, and they have it where the crest of one wave is lined up with the crest of another wave. So wave one's crest and wave two's crest are perfectly in alignment, and because they're the same frequency, they match up all the way down the line. So they're in box step with each other, or they're in phase with

one another. However, if you offset those two waves even just a little bit, they are out of phase with each other, and we can measure that bit by degrees, if it's a lot or a little. If you have two waves that are one degrees out of phase with each other, it would mean that the crest of wave one would match up with the lowest point of the trough of wave two. They would be as out of phase as they possibly could be. So phase modulation first

establishes a baseline wavelength of the signal. Then you begin to alter the phase of that signal by moving that wave out of phase in predetermined ways to represent a zero or a one communicating in binary data. And you can do this at incredibly fast speeds. And this is where we get to data throughput, which we measure in bits per second. Remember a bit is a basic unit of digital information. It's a zero or a one. A high throughput satellite can communicate at really high data throughput rates.

We're talking about on the order of a hundred gigabits per second or more, and a gigabit is one billion bits, so one billion basic units of digital information every second. One billion bits per second. That's a lot of information. So now we see what the mega hurts versus megabits thing really comes down to. Mega hurts refers to the frequency of the radio wave signal that we're using as

a medium. It's really just telling us the type of connection being used, the signal that's being sent out by a transmitter and the signal that's being picked up by a receiver. The receiver is ignoring all other signals except for the one that it's tuned into. Otherwise you would just be getting tons of noise and you wouldn't be able to tell what was the signal you were looking

for versus everything else. There are a few other factors that allow a receiver to lock into a specific transmission, but that gets a lot more technical and uh, mega hurts does not directly correlate to data throughput. Uh. The frequency does have an effect, but I'll have to go into more detail in the future episode because it requires a more involved discussion about the nature of frequencies versus

data throughput. Megabits or gigabits or kill a bits or whatever just tells us how much information can be transmitted per unit of time per second, for example. Now, I hope all of this gives you, guys a deeper understanding of what's going on with satellites, including how amazing it is the humans figured out how to get stuff out into space in the first place, let alone use it

to communicate information back to Earth. It's a phenomenal achievement and really a remarkable display of how a deep understanding of science leads to us being able to leverage that

understanding through technology. It's also why I argue that exploratory science is a great thing in gen a role where you set out to understand more about the universe, not for a specific application, but more just to get that understanding, because you never know what kind of applications could come from that as we learn more about how the universe works. That's why I think funding for sciences is so important.

You never know what we'll learn and then how we'll put that learning to use to benefit people in the future. So um fund science, I guess, is what I'm saying. All right, guys, that wraps up this discussion about communications satellites, very very high overview pun intended of communication satellites. We can get into a lot more detail if you guys want to um, but it does get pretty tricky. Also, it gets tricky for me because I have to get a deeper understanding myself in order to be able to

communicate it properly. And also just figuring out how to explain stuff without visual aids is always a challenge. If you have any other suggestions, maybe there's some other topic totally unrelated to satellite communications that you would like me to talk about. Reach out to me on Twitter. The handle is text stuff h s W and I'll talk to you again really soon y. Text Stuff is an

I Heart Radio production. For more podcasts from my Heart Radio, visit the i Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.