TechStuff to Major Tom

How do satellite communications work? What's the difference between megahertz and megabits? We learn about the tech of communication satellites.

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Episode Transcript

Speaker 1 (00:04):
Welcome to Text Stuff, a production from my Heart Radio.
Hey there, and welcome to tech Stuff. I'm your host,
Jonathan Strickland. I'm an executive producer with I Heart Radio
and I love all things tech and today's episode is
in response to a request Carlos wrote to me and

(00:27):
asked me this. He said, Hey, Jonathan, great work on
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

(00:47):
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

(01:08):
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

(01:30):
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

(01:54):
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

(02:16):
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

(02:37):
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,

(03:00):
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,

(03:22):
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

(03:43):
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

(04:04):
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

(04:26):
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

(04:48):
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

(05:08):
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

(05:29):
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

(05:51):
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

(06:13):
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

(06:36):
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.

(06:59):
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,

(07:21):
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

(07:44):
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

(08:06):
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

(08:27):
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

(08:48):
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

(09:11):
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

(09:33):
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

(09:55):
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

(10:16):
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

(10:39):
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

(11:02):
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,

(11:25):
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

(11:48):
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

(12:10):
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

(12:32):
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

(12:54):
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

(13:14):
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

(13:38):
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

(14:01):
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

(14:21):
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

(14:44):
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

(15:05):
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

(15:26):
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

(15:46):
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.

(16:08):
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,

(16:32):
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

(16:53):
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,

(17:15):
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

(17:38):
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

(17:59):
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

(18:19):
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

(18:42):
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

(19:03):
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,

(19:26):
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,

(19:48):
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

(20:12):
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,

(20:35):
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

(20:57):
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

(21:18):
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

(21:41):
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

(22:02):
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

(22:25):
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

(22:45):
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

(23:08):
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

(23:29):
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

(23:52):
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

(24:14):
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

(24:37):
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

(24:58):
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

(25:19):
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

(25:42):
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

(26:03):
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

(26:26):
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

(26:50):
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

(27:12):
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

(27:33):
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

(27:56):
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.

(28:18):
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

(28:38):
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

(28:58):
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

(29:20):
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

(29:41):
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

(30:01):
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

(30:24):
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

(30:46):
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

(31:08):
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

(31:30):
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.

(31:54):
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

(32:16):
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

(32:40):
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

(33:01):
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

(33:22):
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

(33:46):
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.

(34:08):
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

(34:29):
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,

(34:49):
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.

(35:12):
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

(35:35):
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

(35:56):
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

(36:18):
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

(36:40):
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

(37:02):
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

(37:26):
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,

(37:48):
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

(38:09):
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

(38:30):
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,

(38:51):
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

(39:13):
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

(39:33):
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

(39:54):
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

(40:18):
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.

(40:40):
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.

(41:04):
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,

(41:26):
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

(41:47):
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

(42:11):
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

(42:33):
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

(42:54):
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

(43:15):
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

(43:37):
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

(43:57):
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.

(44:18):
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

(44:41):
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

(45:02):
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

(45:26):
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

(45:46):
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,

(46:09):
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.

(46:29):
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

(46:50):
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

(47:12):
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.