How do you navigate in deep space?

Daniel and Jorge talk about a potential new GPS: the Galactic Positioning System.

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, do you remember the days before we had smartphones?
I try not to think about it too much. Well,
you can't live with that, Wikipedia do your fingertips? How
else would I seem like an expert on anything? But no,
mostly I couldn't live without the direction right. Yeah. Are
you the kind of driver that needs to check them
out every ten seconds? Oh? Yeah, that is me. I

(00:29):
like to know exactly where I am on the surface
of the air at all times. At all times, I
need constant updates to make sure I've not gone off. Well,
what are you gonna do when humans get out into space?
Are you gonna get around there? I'm just gonna wait
until there are enough cell towers or at least WiFi. Yeah,
basic human survival needs in space, air, food, and WiFi. Hi.

(01:07):
I'm Jorge. I'm a cartoonist and the creator of PhD comments. Hi.
I'm Daniel. I'm a particle physicist, and I plan to
be the one million person in space. One million there.
You know there are seven billion of those, so you
know you let's put it pretty far ahead in line. Yeah. Well,
I don't want to be the first person, or the
second person or the hundredth person, but I also don't

(01:29):
want to be the last person. You don't want to
go when it's still kind of new and fresh but
not dangerous. I'm not a test pilot kind of a person.
A million sounds about right. A million sounds about right,
but hey, I'm flexible two million, million and a half.
You know I'm not going to elbow my way in
that line. Well, welcome to our podcast where you are
first in line to hear this. It's called Daniel and
Jorge Explain the Universe, a production of I Heart Radio

(01:51):
where normally we take you on a mental trip around
the cosmos, zooming out from the tiniest little particles that
define the basic building blocks of the universe all the
way out to the grandest structures that shape the nature
of the cosmos itself. Yeah. I just think it was
as your guide, as your personal GPS to all of
the amazing and wonderful things that are in the universe

(02:12):
and also all of the unknown things that are out
there for us to discover. Do you think we're a
good mental GPS. Sometimes we get lost, We get on
a discussion about neutrinos and we end up talking about
snack foods. Well, you know, I think detours are part
of the fun of a trip. Right. I wish that
my navigation like Siri would tell me, like, hey, pull
over and get some chips. There's a good snack shop

(02:33):
right here. Why not? Yeah, that should be a setting, right,
suggests snacks. I like that suggests yeah, AI engineers, get
on it. Not in a hurry. Should be maybe an
option open to wonderful discovery. That's right. And on this
podcast we try to open your mind to all the
future wonderful discoveries that science will bring us. And we
do that by talking about the cutting edge of science,

(02:55):
all the questions that science has not answered, all the
things scientists are trying to think ground, and all the
technical problems they're trying to solve on their journey to
give us the answers. Yeah, because I think sometimes to
think about a journey of discovery is the journey itself,
you know, and the friends you make along the way. Yeah,
you know, not just where you go and what do

(03:16):
you find when you get there? For also how do
you get there and how do you how do you
even know where to go when you're going? Yeah, I
think people imagine that it's hard to get to Jupiter
or Pluto because it's so far out there. It's just
like you gotta throw a rock really far into space,
but it's not just really far away. It's like very
hard to find. You know. Pluto is a small rock

(03:38):
in the vast, vast reaches of space. If you're gonna
throw something in that direction, you have to be really precise.
You have to really know how to aim it and
have to be able to course correct along the way.
And that turns out to be not so easy. It's
much harder than stopping for snacks. Yeah, you know, they
have good snacks and jubiter. You know, it makes a
little gassy at the end, but you know it's all

(03:59):
totally worth it, right right the Red Storm chips. I
love this. Yeah. So today we're gonna be asking a
question that I personally have had a lot of curiosity
about over the years. I've always wondered about this question,
and even more so now recently I've been rewatching all
the Star Wars movies and so this is a question
that's really present in my mind that I've been asking
myself recently, And why is that? Are you imagining how

(04:21):
you're going to navigate to your in law's house on
the Jovian moons from your vacation place in Saturn or
what inspires you to think about this? Well, my wife
and I are immigrants, but we're not that that kind
of alien. But no, I just kind of wondered, you know, Um,
in Star Wars they always get lost or they pop
up in all kinds of places, and so how do
you know where you are? And how do you know

(04:43):
where to go? Or you know, they talk about like
a map of the galaxy, what does that even look like?
Or how would that even be useful? Yeah, it's it's
very rare that they're like, make a wrong turn. They're like,
we're we supposed to turn left at that pulsar or right.
I don't even really remember. It feels like that's all
just sort of been integrated into the electron next they
have in front of them. But those are hard problems, right,
it's not necessarily trivial to figure out. Yeah, and if

(05:05):
you think about it, in popular culture, there's only been
like one TV show about getting lost in space. You mean,
it was called space and you know at least you
know what it's about. Yeah, So today on the program,
we'll be asking the question, how do you navigate in
space space, and this is a problem that's relevant to

(05:29):
future navigation. Like imagine you are flying a spaceship with
lots of people on board and trying to get everybody
safely to Alpha Centauri. And it's also a question today
as NASA and the E s A launched satellites to
explore our Solar system. How do they make sure they
get to the right spot? How do they course correct
if they are off? Who does those calculations? Is that
on board the satellite or back here on Earth? Are

(05:51):
there people with protractors and pencils scribbling things furiously? How
does that actually work? Yeah, because you know, space is
pretty big, and it's three dementi all, you know, at
least three dimensions at least, yeah that we know of
that we think about right now. But it's a multi
dimensional and you're out there and you know, there's no

(06:11):
mountain to reference, no street signs. How do you get around?
How do you know where to go? Do you think
that third dimension is going to lead to like a
lot more marital arguments in the future, Like I told
you to turn up at that move man, why did
you turn down? This is just like so many more
ways to call new dimension to divorces. Probably no, but

(06:32):
it is really hard and it's also vital because you're
so much further away from your resources. Like these spaceships
they leave Earth, they're never getting a refill, like they
run out of gas because they got lost. They're just lost.
So you have like a very limited window to make
the moves you need to make to enter that orbit
or to fly by the moon. There's no reduce, like

(06:53):
you have a one tank and that's it. So it's
absolutely critical that you don't get lost and that you
figure out how to get where you need to go. Yeah, So,
as usually, we were wondering how many people out there
have thought about this question or even have an idea
about how to navigate in space. So as usual, Daniel
went out there and ask the internet to try to
answer this question, how do you navigate in space? That's right,

(07:15):
and if you'd like to participate in our virtual person
on the street interviews, just shoot us an email two
questions at Daniel and Jorge dot com. We would love
to put your uninformed speculation on the podcast. And so
think about it for a second. If you were out
in space in the middle of the galaxy or in
between galaxies? How would you know which way to make
your way home? Here's what people had to say. Because

(07:36):
gravity distill space and time and everything. Maybe you'd have
to go. Maybe you'd have to shoot a little bit
off it because as you as you go close to
and an object, you'd kind of be taken into its
gravitational swing. Other than that, I don't know how do
you navigate through deep space to just keep a set

(07:56):
of stars to your left and hopefully you're going the
same direct action. I have no idea. Maybe like by
distracting energy from the Sun, or if we're very patient,
maybe with solar sales, we could navigate deep space, maybe
through a pulse of a star, or like I don't know,
pole stars or something. I think the only way you

(08:18):
can navigating these spaces the way we do it now
by using stars and galaxies, things that are consistent, not
necessarily constellations, because that could you know, in three D
space they have depth and they have angles that they
are relative each other. You know, constellations do. But if
you use stuff like pulsars and quasars and you know
the Andromeda gag, see those things, we can coordinate ourselves

(08:40):
using a couple of those angles, we can coordinate ourselves
in deep space. I think navere taking in a deep
space or americum woulds to need the bicycles of navigation.
You're do either use inertial navigation, sitting time, speed, and
directions from someone In a short stuff you will have
to pick something like the sun and navigating reference to

(09:03):
the sun. Let's see, if you're heading to a prime centuri,
we should at least have an inbuilt special I had
invisible telescopes, I mean lens and meadows and special lists
and optimal path correction systems and some kind of special clocks.

(09:23):
Navigating in deep space, I would have to assume is
much like seiling the ocean. You look at the stars
and see whe're at relative to the stars. After your
statement that space is expanding faster than um the speed
of light, or faster than light can travel through it,

(09:43):
I really have no idea. Now I think you could
go anywhere you you go. Yeah, well, hopefully you can
do that, but how you do it? My idea would
be to mount a big giant telescope on the top
of your spacecraft, on the front and the back, so
you can see where you're going and where you're where

(10:05):
you came from. Maybe a telescope as big as hubble,
because your spacecraft is going to have to be that big.
After we leave the planet and learn about the like
further stars that we don't see on Earth, we can
pick three stars, and by keeping track of the distance
between us and the stars, we can know our position.

(10:25):
And when the stars are too far away, we can
always peak three new stars that we found out about
along the way in our journey. So there are a
lot of ideas there. What do you think of that?
Pretty good? Pretty good? I feel like people were sort
of thinking about triangulation and using the stars somehow to
tell where you are. I feel like that's a pretty

(10:47):
common idea in science fiction movies and boots. It's like, oh,
you just look at the stars around you, and do
you know where you are and you know where to go?
Or like if you look at the stars and you
don't recognize things, then you're kind of in trouble. I
like the I said, let's put a huge telescope on
the front and on the back of your spaceship, because
I want that anyway, Like, if I'm flying through space,
I want a big telescope because I want to see

(11:08):
with what stuffed around me. You know, I want to
do some sight seeing when I'm out there. But what
do you need one in the bag though, just to
see the fit is of people that you leave behind. Well,
because I mean, I guess you could turn your telescope.
Maybe you're saying you'll need one telescope plus like a
mount or something, but hey, more telescopes are better. Well,
I feel like that is a sort of a common thing,

(11:29):
is to look at the stars around you, and somehow
you use that to orient yourself, you know, kind of
like we use the North Star for a long time
to kind of tell which way was north when you're
out in the middle of the ocean. Is that kind
of an idea that we can use at all? It
is an idea that we can use. And the rest
on this notion that if you have an accurate map
of the stars, you can compare that to what you're
seeing and look for landmarks and try to measure angles

(11:51):
between the stars to give you a sense for where
you are. For example, if two stars are almost lined
up in your vision, then that tells you that you're
along a line drawn between those two stars. And if
you can find other examples measuring angles between stars, you
can give you sort of a point in three D
space for where you are at that moment. Well, I

(12:12):
guess the problem that I have always should have thought
about is like, what if you find yourself on the
other side of the galaxy, how would you even recognize
any of the stars because the stars are gonna look
totally different from the other side of the galaxy. Yeah,
if you just look at like teleported to a random
place in the universe where you have no reference points,
there's literally no way to know where you are because
there's no absolute reference there's no like point in space

(12:35):
that's defined in zero and you can measure your location
relative to that. If you get teleported to an arbitrary
point in space, special relativity says it's impossible to know
where you are. You can only measure your distance relative
to other stuff. So if you have no familiar references,
you're totally screwed. Wow, and things are like changing in time. Also,
everything's moving, so you're sort of totally lost in You're

(12:56):
totally lost. You have. The only way to orient yourself
in space is relative to known things. So if you
get teleported to some part of space that's totally unfamiliar.
Then you literally have no way to find your way
back except for randomly exploring until you do find a landmark.
And when I try that the next time I get
lost and my spouse is complaining, I'm like, it's special relativity.

(13:18):
It's it's law of the universe. It's not my fault.
Daniel said, this should work. Don't you feel like smartphones
must have solved this marital complaint? Right, houses don't have
to argue about how to navigating anymore, and they just
listened to the phone. That's right. The phone has saved
a lot of marriages. Probably maybe, or maybe people are like, no,
listen to my phone. Well, my phone says it's faster

(13:38):
take the expressway using Google Maps. No way, we aren't
using ways. People who argue are going to argue anyway.
I guess, So I guess the phones can't fix that. Yeah,
And you know, navigators in throughout history have used the stars.
Like if you have sailed the oceans, then to figure
out where you are in this vast sea where you

(13:59):
can see no land marks is just to look up
and look for star marks. Right, to look for the
positions of stars in the sky that gives you a
sense for where you might be. All right, well, let's
get into the sort of the nitty gritty of this problem.
And because I know you, you've told me that there
are sort of several ways in which we can right
now sort of calculate where we are in space, you know,
barring kind of like a complete map of the entire galaxy. Um,

(14:22):
so step us through. What's the what's the sort of
the basic way that we get around in space. So
the simplest way, in the dumbest way, and the worst
way is basically dead reckoning. And that says you know
where you started, and you started on Earth, and if
you have a record of all the moves you took,
you went in this direction at this velocity, you should
be able to calculate where you went. Because you know,

(14:43):
spacecraft follow the laws of physics, and we know what
those laws are. We have a whole model of the
Solar System, so we should be able to predict if
you leave in this direction at this time, and you
fire your rockets here and there, we should be able
to predict where you end up. That's kind of like
closing your eyes and like knowing where you are right now,
closing your eyes and just by like counting your steps

(15:06):
and how you think you turn, sort of like making
it to your fridge or something like that. It's like
following one of those treasure maps, like fifteen paces forward
then turn left step four paces, then dig right right.
And that's a little terrifying. Like if you remember the
days before smartphones where people had to like actually write
down directions and there were things like drive for fifteen
miles then take a left right, and you had no

(15:28):
idea is this the correct left or not? You know, yeah, yeah,
and we all know how well that works. In the
middle of the night when you have to go to
the bathroom in total darkness, you know, you better put
your hands in front of you, just in cakes. Yeah,
and so sailors used to call this dead reckoning, and
you know it's not terrible, like it works. Okay, we
have a pretty good model of the solar system, and

(15:49):
we have rockets, and we can even measure we don't
even have to just guess. And like the effect of thrust,
you can measure how much you've accelerated using accelerometers, you
can measure your the direction that you ended up in
using gyroscopes, So we've tried to be really careful about this,
and some spacecraft in the history of you know, American
exploration have used dead reckoning. But I guess it's tricky too,

(16:11):
because you know, in space you can't count your steps,
like there's nothing to hold onto to tell you how
far you move. You have to you have to measure
your exploration and then integrate DAD to convert to velocity,
and then integrate DAT to convert it to distance. So
it's like a lot of room there to get error. Yes,
and you mentioned a very critical step there, which is integration,

(16:33):
and that requires knowing the time. You can't count your steps.
What you need is a very accurate clock. And the
more accurate your clock, the more you accurately you can
calculate how far you've gone. Right, you said I shot
off in this direction of the speed, Well did you
go for two point seven seconds or two point eight seconds?
When you're traveling at ten thousand kilometers per second, that

(16:53):
makes a big difference. Yeah, And when distances are so huge, right,
and the stakes are so high, like you can't if
you miss Jupiter by a few miles, it could be
bad us. Yeah, as you're gonna do a Jupiter drive by, right,
then you only get one shot at it, literally, and
so it's pretty tricky. And the problem here is that
errors build up, Like you make a little mistake because

(17:13):
you turned a little too far, then you're off, and
the next time you can't correct it, and so the
errors just build up in the integrate and eventually you
can be pretty far from where you thought you right.
It literally is like walking around with your eyes closed. Yeah, exactly.
So that's the most basic strategy, and you can make
that more sophisticated by doing corrections. You can say, well,
I'm gonna use dead reckoning. Plus I'm going to look

(17:37):
at the stars and I'm gonna try to figure out
if I'm off. And this is what like a lot
of astronauts did, like Apollo eleven and follow their team.
They flew to the Moon by dead reckoning, but occasionally
they would check in and they would look at the
stars and try to get a more precise measurement for
where they were, and they would use that to correct
their flight path. Really, so I guess two questions. One

(17:57):
is why didn't they just use the moon as reference
because they were flying towards it, and they could tell
her they were going away from it or towards it.
And the size of it too, wouldn't it tell you
said of the distance? But and then my second question was,
you know, can you actually use the stars to tell
where you are? You can? So, yes, they were pointed
at the moon. But that's pretty rough, right, And what

(18:18):
you want to do was get to the Moon and
then enter into orbit around the Moon. And that was
a very precise maneuver. And just like with the spacecraft,
they had a limited amount of fuel, so if they
burnt their fuel the wrong time, they might not be
able to make it home. I said. The fuel is
very expensive to lift off the surface of the Earth,
and so everything was a very tight budget, so they
had to be really precise. There are no exactly you

(18:41):
can't just pull a eui in space. That costs a
lot of energy to pull ui. Like you missed the
snack shop. You missed the snack shop, man, you are
not going back. And yes, they did stellar navigation. They
looked by I to find stars, and they measured the
declination using gyroscopes and they use that to correct their calculations.
A huge fraction of the time they actually spent in
that module was typing data into that computer. You know,

(19:05):
it's a complicated system. And remember the whole program was
loaded into the computer before it launched, Like you didn't
have guys up there, like you know, tip tapping editing
the program being like I think we must change the
flight path or something. They had it all built in
with the opportunity for small corrections based on looking at
those stars. So what do you mean declination like where
the constellation was relative to the Earth or something like that. No,

(19:27):
relative to them, Right, they had an idea for where
they were, and they had an idea for if we
are here, the stars should appear at this angle relative
to the spaceship, and then they would measure where is
the star relative to where the spaceship is pointing because
I had careful gyroscopes and and those angles helped them
figure out exactly where they are. All right, Well that

(19:48):
sounds like, um it worked because they got to the
a few times, So I can't argue with that. All right, Well,
let's get into some of the other ways that we
can navigate in space and whether or not they could
help us explore the furthest switches of the Cosmos but first,
let's take a quick break, all right, Dina. We're talking

(20:19):
about navigating in space. Space, space, space, And I just
wonder why there's always an echo when people talk about space,
because there's no echoes in space. It's because it's cool, man,
It's so cool cool. It makes it sound mysterious. It
gives you a sense of literally space, right, echoes give
you a sense a big emptiness. But you know that's

(20:40):
just the um audio version of the artistic impression, which
you know, I'm not a fan. You not a fan
of the echoes in space. No, I'm a fan of
realistic science fiction. It should give us a cent or
what it's actually like to be out there. Though maybe
you know, if you're in a kind of little metal box,
maybe there are actually a lot of echoes, but inside
I see. Well, we're talking about how to navigating space,

(21:03):
which is a big question, you know. I feel like,
you know, whenever you watch a movie like Star Wars,
it's like how are they getting around? How do they
know where to go? And so we talked about it
one way, which is dead reckoning, Like if you know
you're an Earth and you leave Earth, you can sort
of track your progress, but then you also have to
kind of correct your errors as you go. That's right,
and a better way to do that is not just
be based on your initial calculation from Earth, but it

(21:25):
takes inspiration from how your smartphone gets you to your
friend's house, which is that it gets messages from satellites.
Here on Earth, we have the GPS system, which is
constantly broadcasting messages. That's giving your phone an idea for
where it is, and your phone figures out where it
is by hearing these messages and knowing how long it

(21:45):
took the message to get here from the satellite, and
it uses that to figure out where the phone is
right and it also uses like a map, like your
phone knows where all the satellites should be at any time,
so once it gets a signal, it sort of knows
where it is, yeah, precisely in knows where the satellites are.
And then it gets these messages. And the messages have
a little time stamp on them. They say I sent
this message at exactly this time, and if you get

(22:08):
this message, you know, seventeen milliseconds later, then you know
how far the message flew because you knew it flew
at the speed of light. And you get enough of
these things and you can figure out where you are.
And there's an analogous system. There's GPS for deep space.
There is there's a space GPS. Yeah, there's a space GPS,
and it's called the Deep Space Network and NASA runs

(22:30):
it and it basically sends messages out in deep space
from three locations on the Earth, and satellites get those messages,
send them back and then we can use that to
figure out where the satellite is. It's like a reverse
Why are you seriously, it's like a reverse GPS. It's
like a reverse GPS. Yeah. What happens is you send
a message to a satellite and then it comes back

(22:51):
and you count, well, how long did it take for
the message to go there and come back, And that
gives you a sense for the distance. And then when
the message comes it's a little bit Doppler shifted based
on the speed of the satellite, and that tells you
how fast this satellite is moving away from you. So
it gives you a measure of the current position and
the velocity of the satellite. But I guess that only

(23:13):
works for satellites, right, like it doesn't work if from
in Jupiter or does it. Well, it works for anybody
that can receive these deep space messages and send them back.
So it doesn't give you your position relative to Jupiter. Note,
only gives you your position and velocity relative to Earth. Right,
But like if you know where Earth is, what this
signal help you know where you are in this solar system? No,

(23:35):
because you can't actually do the calculation yourself. And that's
one problem with this deep space network is that only
Earth gets to figure it out. Earth gets your message,
and then the second link gives Earth the information about
where you are, and then the folks on Earth have
to calculate Okay, turns out you were in this position
and send it to you. So it's kind of a
lot of back and forth. It's not that you can
just get this message from the deep space network and

(23:57):
figured it out yourself. The way your phone can from
s GPS is one directional, right, because it comes with
these time stamps. Right, So why why couldn't this work
the same way? The reason is the clock. The clock
on the satellite is not very good because really accurate
clocks are necessary to do these calculations. Is because it's
much more important to be super accurate more important than
your phone's GPS, and the clocks that are on the

(24:19):
satellites are not good enough to do this, so they
have to do the calculation back on Earth and then
send it to the satellite because on Earth to have
these super precise atomic clocks that keep everything in lockstep.
Interesting alright, So we we can't rely on the Earth
to tell us where we are, like if I'm out
in space, or can we can we rely on Earth

(24:41):
to tell me where I am. Earth can figure out
where you are, how far you are from the Earth,
and how fast you're going, but you know, it's kind
of limited. Like they can get really precise measurements of
where you are up to about one meter, which is
really pretty amazing, like you're out you know Jupiter distance,
and Earth can measure how far away you are to
within one meter based on the balance of the echo,

(25:03):
like the signal coming back and going there and back. Yeah,
just timing the echo because they have really precise atomic clocks.
But what they can't do is figure out like where
you are laterally, like your angle because there they don't
have an echo measurement, right, and so they're the uncertainties
more like four kilometers for every a U the distance
between the Earth and the Sun. I see, because you know,

(25:28):
if we're out by Jupiter, we don't shine like a star,
that's right, right, Like we're not visible to the Earth,
So they have no idea where we are. They just
know kind of how far we are. They know how
far you are, and they figure out where you are
laterally basically using dead reckoning and then correcting using these
radio measurements. But you know, that's a pretty big uncertainty.
If you get out to like the distance of Pluto,
then they're uncertainties two hundred kilometers, which is really big

(25:52):
if you're trying to enter into the orbit of Pluto. Yeah. Yeah,
that sounds like a pretty big error. Viewer off by
two meters in your phone GPS, you be in a
whole different state. Yeah. And so practically, what these folks
do is they use landmarks in the Solar system too
correct So if you're getting near Jupiter, it sund I

(26:12):
can be like, okay, I see where Jupiter is. It
can compare it to where thought Jupiter should be, and
you can use that to correct. So you're like you're
getting landmarks. You're like, oh, you're driving your friend's house
is supposed to be a hill there. Hoops, I must
be in the wrong spot passing to McDonald. I know
I'm halfway there kind of thing. Yeah, And so cameras
on board can give accurate measurements of nearby objects, not

(26:33):
very far away, only very nearby. You see a big,
well known asteroid, you pass the Moon or a planet,
then you can correct You're no longer reliant on the
messages from earthly interesting, but the satellite does that calculation
or like it has to send the picture bag and
then here on Earth were like, oh, it just pass Jupiter.
This is where you are. Yeah, that's all done on
Earth currently sends the data back and then we can

(26:54):
get corrections. And that's one of the problems is that
a lot of this stuff relies on calculations done on
Earth and then these back and forth communications with the
deep space network, which tie up the deep space network.
You know, you're only talking to one satellite. All the
other ones are waiting, so you can only talk to like,
you know, a few of them at a time. And
that's pretty serious because like GPS doesn't work that way.

(27:15):
GPS just sends out its messages and all the phones
in the world just kind of listen. It doesn't have
to be bothered by the fact that I'm using it
and somebody else is using it at the same time.
But deep space network gets tied up every time a
satellite needs to figure out its position. So they have
a new idea for how to improve this so that
it can be more like GPS. Well, how does that work?

(27:35):
Just put more clocks in it, or yes, build a
really precise clock and put it on the satellite. The
most precise clocks we have are atomic clocks. These are
clocks that measure little atoms doing very precise wiggles that
like vibrated very specific frequency. One of the most precise
things in the universe because it just happens over and
over and over again exactly the same time step. But

(27:58):
these atomic clocks are expensive and they're big, and so
the reason that we don't have good clocks on satellites
is because nobody's ever miniaturized them. So NASA spent a
lot of time building a deep space atomic clock, basically
a miniaturized version of atomic clock you can put on
the satellite. And is it a lot smaller or yeah,

(28:18):
it's a lot smaller, and it's a lot cheaper, and
it's about the size of a toaster. Wow. So you
wouldn't want to wear this atomic clock. It's not it's
not ready for wristwatch use. If you want to be
super untime to meetings and podcast recordings, I could wear
an atomic clock, but it might be a little inconvenient. No,
And these atomic clocks cost you know, enough fifty to

(28:39):
a hundred thousand dollars, which amazingly is actually cheaper than
some wristwatches you can buy for wearing. I never understood that.
But some people spend a ridiculous amount the gold plated iPhones, right, Yeah, Well,
I spent a few years in Switzerland where they have
these ridiculous watch shops. You can go in and spend
two hundred thousand dollars on a fancy watch. But it's
like hand built with all these little levers and gears thereby,

(29:02):
you know, dwarves underground or something I don't know, And
it's not even as accurate as a toaster exactly exactly.
I'll take a toaster's eye atomic watch from my wrist
any day. But the idea there is if you have
this atomic clock on the satellite, then it can get
messages from the Deep Space Network that have time stamps
on them to say we sent this message at whatever time,

(29:24):
and you can just compare that too. It's atomic clock
and they say, oh, it took x seconds to get here.
I can figure out where I am myself. And that's
a big step forward in what they call autonomous satellite navigation,
with the satellites are just sort of driving themselves, right then,
it's more like the GPS we have on our phones. Yeah, exactly,
and you can just be sort of passive. The folks

(29:44):
at home don't have to do these calculations themselves and
updated to the satellite. So there are fewer links because
the Deep space network is kind of sort of overburdened
right now. It's got like too many things to do,
is I mean time slice between too many projects. So
this would really free it up, all right. Well, it
sounds like things are looking good for navigating within the
Solar System. So we're getting better clocks on these satellites

(30:06):
and spacecraft, and we're also we can also use familiar
landmarks like Jupiter or other planets or the Sun to
sort of orient where we are within the Solar System.
That's right, but then it sort of gets trickier one
once we get out into space. Right, Yeah, all these
things still rely on being able to contact Earth. You're
getting these messages from the Deep Space Network, which is

(30:27):
on Earth, and if you want to navigate to like
Alpha Centauri or halfway across the galaxy, you don't want
to be getting messages from Earth. They're gonna be way
too faint. You're not gonna be able to pick remain.
So you need a broader system. You need a galaxy
spanning system. In order to get you out of the
Solar System and still make it to McDonald's. We need
like a like a capital GPS galactic positioning system. All right, Well,

(30:51):
let's get into how you would actually navigate if you
wanted to venture out from the Solar System or even
go to another galaxy. But first let's take a quick break.
All right. There we're talking about how did not get

(31:13):
lost in space? Although that's such a fun show, is it?
You like that show that, the new one or the
old one. I like the old one, but the new
one's fun watching with the whole family because you know,
it's a bit of a family adventure, some family tension there,
you know, you leave somebody behind. If you were frozen
underwater on some alien moon, would your family stop and
save you or not? Oh? Man, To me, it was

(31:34):
almost too much family drama. I'm like, where is the
space and they're getting lost in space they're like melting ice. Yeah, exactly.
I thought it was good anyway, A lot of fun anyway. So, yeah,
it's a problem if you go out into space, especially
you can like in another part of the galaxy where
the stars are in a totally different arrangement. How do
you get around, how do you know where you are,
and how do you know where to go? So what

(31:56):
can we do then, Daniel? Yeah, well, what you need
is some other source of signals. Either have a very
accurate galactive map of where all the stars are, but
as you say, these things are changing in time and
we have only measurements from Earth and those positions are
not that accurate. Which you really need is some sort
of network of signals from all over the galaxy sending
you time stamped messages. I mean, if you could design

(32:18):
it yourself, you would have a bunch of sources around
the galaxy sending you messages saying time equals one time
equals two time equals three, right, and from those like
the like the GPS satellites we have just now on Earth,
you just have If you could just have GPS satellites
all the way through the galaxy super powerful, that would
be enough because you could use the nearest satellites to

(32:39):
figure out how far you are from each one, and
you need three of them to triangulate your position in
three D space and then you be golden. But you
know that's a trillion dollar program, right, could could you
use like galaxies to orienter cell? Like you know, like
if I'm in somewhere in the Milky Way, I could
tell where the center of the Milky Way was maybe,
and I could look for other galaxy ease out there,

(33:01):
and so can I use that to orient myself? Yeah,
And you can get a rough orientation that way, right,
you can tell you know where Andrameda is relative to
the Milky Way, So you can spin yourself around and
tell where and Drameda is. But it's very rough, I mean,
and Drameda is really far away, and so measuring its
location precisely is not that helpful. We need much more
precision than you can get from just like fixing the

(33:23):
positions of other galaxies, like, yeah, that will tell you roughly.
But if you want to navigate and you want to
save fuel and you want to make it with your
thousand frozen human bodies to Alpha Centauri or whatever, then
you've got to be more precise than that. You don't
want to miss by a few million kilometers, You got it,
You do not, And then they start to warm up
and there, you know, expecting the land in Alpha Centauri

(33:45):
and have breakfast, and you didn't bring any months and
so and so you're saying that one idea could could be,
like to make these GPS satellites and put them all
over the galaxy. But that's really expensive. Yeah, that's ridiculous,
Like we didn't even know how to get them there, right,
that's the whole problem. You're right, How would the satellites
know where to go or where they are? How would

(34:06):
we know where they are? We'd have to bootstrap them somehow.
If you don't know where the satellites are, then they're
not very useful right there, Like here's a signal from
someplace we don't know, thank you very much. That's useless.
So what you need to do is find some naturally
occurring equivalent something in the galaxy that operates similar to
GPS that lets you figure out where you are. And

(34:27):
it turns out the galaxy provides is it alien satellites? Daniel,
are you going for the alien button? I didn't even
think about the alien button, but now I am. Now
I'm wondering if aliens are using our GPS system to
navigate our solar system right to us. Yes, well, if
you enter the solar system that already had alien civilization

(34:49):
and have GPS signals, then yeah, you could use it
without them even noticing, because it's a passive system, right right,
then maybe they're using us as a GPS exactly exactly,
that's the concerned. But even without aliens, there are naturally occurring,
very regular clocks in our galaxy interesting and they are
called pulsars. You don't have to build them, they're already there.

(35:11):
They are already there. We talked on the podcast before
about what happens when really massive stars collapse that they
blow up, there's a supernova, and then if there's enough
stuff in the center of it, in the core, but
not enough to make a black hole, they can form
this thing called a neutron star, which is a ridiculously
dense ball of matter. It's called like the mass of

(35:31):
the Sun, but it's the size of a city. Right,
It's it's like almost a black hole. It's almost a
black hole. Yeah, if your star was like eighty two
thirty masses of the Sun, then you're probably going to
turn into a neutron star. If it was heavier than
you probably get into a black hole. But some of
these neutron stars are amazing because they have a magnetic
field which is really intense, and the magnetic field means

(35:55):
that there's a huge column of radiation that's spewed out
from the north magnetic field and the south magnetic field.
So they're like shining a really bright light of radiation
in two directions in space. Right, Because the stars themselves
don't shine that much, but like the chaos they cause
around them with the magnetic field and all the stuff
around them, then that is what glows and points in

(36:17):
a particular direction. Exactly. There's no fusion happening inside a
neutron star, but there's still an intense amount of other
radiation produced, and the magnetic field funnels it into these
type beams. And then if the magnetic north pole is
not aligned with the spinning of the star, right, it's
not perfectly aligned like on Earth. Then what you get
is this neutron star that's sweeping around. It's rotating, but

(36:40):
the direction in which its signal is beaming keeps scanning
through the galg like a galactic lighthouse, you know, like
a spotlight that just miss just like that, yeah, Or
like just like on the top of a police car,
you have this rotating red light and it never turns
on or off, but it looks to you like it's flashing.
So from Earth, if you look at a pulsar, it

(37:02):
goes on off, on off, on off, on off very regularly,
just like a lighthouse would or a police light, and
it's not actually turning on off, it's just sort of
sweeping past you. Right. So if we can use these
to kind of tell where we are, like as as
literally like lighthouses in space, sort of like lighthouses in space,
And the reason is that they're incredibly accurate. They have

(37:24):
about as much regularity as an atomic clock. Really, like
these little particles in very special conditions and cold climates
and special laboratories are very regular. But these enormous, massive
spinning hunks of neutrons are also regular, and so they're
basically like a very powerful galactic clock that's constantly descending

(37:45):
out a pulse like tick tick tick. Suddenly that makes
a nice guy a little more stressful. It's full of
ticking clocks. But it's it's like crazy periods to right,
it's not like tick tack tick. Take. It's like every
twenty millis like and they're shining. There's a big variety
of them, from radio pulsars down to X ray pulsars.

(38:05):
It depends, as you say, on their period. And these
ones that are very fast and like twenty milliseconds, these
are the best ones to use for timing. And it's
hard to imagine, like an enormous, super dense star boiled
down into a tiny object that spins every twenty milliseconds. Right,
It's like, hey, thousands and thousands of times a second,

(38:25):
this huge thing is spinning. It's it's an incredible amount
of energy. It's mind blowing. So we can use these
because we know from Earth where they are, and so
if you're out there in space, you could maybe find
them by looking out, and then you can tell kind
of where you are because you could recognize them. Buy
what their period. Each one has its own fingerprint because

(38:45):
of its period, and you already know where they are,
so you find them, you identified and you're like, okay,
this is pulsar x J seventeen or whatever. And then
you listen to the pulses, you know, tick tick tick,
and based on the pulses that you hear, you can
tell where in the wave form you are. Now, the
problem is they don't send messages like the GPS satellites.

(39:06):
The GPS satellite say okay, it's time equals seven, it's
time equals eight, and then when it gets to you,
you can compare against your own clock they have. You
have like synchronized clocks on each side, so you can
measure how long it takes the signal to get there.
That's from the GPS. Pulsars aren't as convenient. They don't
have a clock built in that labels each pulse separately,
so it's harder to tell exactly how long it took

(39:29):
the pulse to get there. Right, But why do you
need to know that? Couldn't you just kind of look
where they are and you know the angle to you,
and then use like three or four of them to
kind of triangulate where you are. What you really want
to know is your distance to an individual pulsar, because
that defines your position on the surface of a sphere
that surrounds that pulsar. And you do it for another pulsar,
and then your distance is defined by where those spheres intersect,

(39:52):
and we do it for three pulsars. Then you can
figure out where your distance is exactly in three D space.
You're right there. You can tell roughly where you are
by the angles, but that's not precise enough. Which you
really want to know is the distance to these things? Really?
Why is the angle not precise enough? Because these things
are really really far away, right, and so a pretty
big change in the location of the pulse are relative
to you corresponds to a really small change in the angle.

(40:14):
So what you really want to know is the radial distance,
not just the angle. Oh, I see, it works if
you're moving a huge distances, but like you couldn't tell
you like by the meter where you are, yeah, or
if you're really close to something, like if you're really
close to Jupiter, then it's angle relative to you has
a lot of powerful information about your location. But if
Jupiter is really far away, then that information loses value

(40:36):
and all these pulsars are pretty far away. But there's
actually a really cool trick to overcoming this problem of
pulsars not being like GPS statelines just using because great,
because I don't have the time stamp. They just have
a pulse. Yeah, so all you know is where you
are on the pulse. And so say these pulses are like,
you know, a kilometer long, for example, So if you

(40:58):
listen to a specific pulse, are that you could tell
where you are within that one kilometer long pulse. You're like, oh,
I'm at the top of it, or I'm at the
bottom of it, or I mean the quiet part of
it or the loud part of it. That doesn't actually
tell you how far you are from the pulse are.
What you know is how far you are through one
pulse length, but you don't know how many more pulse

(41:19):
lengths there are between you and the pulse are. If
you know you're halfway through its pulse, then you could
be half a pulse length away from the original pulsar,
or you could be one and a half pulse lengths away,
or three hundred forty two and a half pulse lengths away.
There's an infinite number of possibilities. So instead of locating

(41:39):
you onto a single sphere when you know the distance,
it's actually given you an infinite number of spheres, each
one one pulse length away, because all of those are
consistent with what you're seeing. That's not as good as GPS,
but you know it can still work because you can
do the same thing for another pulsar and get another
set of spheres, and then find a third pulsar and

(42:02):
get a third set of spheres, And where those spheares
intersect is the number of places that you could be
places that are consistent with the signals you're seeing. Now
that's not just one place, it's not a unique solution.
There's still a few ambiguities. There's more than one possible
location that's consistent with those signals, and then you have
to figure out which one is yours based on where

(42:23):
you thought you were recently, and you know other clues.
I see, you're sort of converting the time stamp of
these pulses to like using the speed of light to
kind of tell where you are in terms of space. Yeah, exactly,
and you don't know exactly how far your way you
are from the pulsar, you know, like, I'm a certain
number of beats of this pulsar's pulse away plus a

(42:46):
little bit, you know, only that extra little bit. And
so there's lots of different solutions, lots of different possibilities
for how far you might be away from one pulsar.
But if you have two or three or four, then
you can narrow it down. You can say I'm a
certain from this one, a certain distance from that one.
It's a harder problem because these pulsars aren't nicely time stamped,

(43:06):
but people have figured it out, and if you do
all the mathematics, you can figure out where you are
in the Solar system to within five kilometers. Wow, that's
pretty good. That's pretty good. That's better than the two
from before. Yeah, exactly, it's pretty good. And it works
all the way across the galaxy, not just within our
Solar system, so you can be far from even if
Earth in blodes the nuclear war, you can still figure

(43:29):
out where you are from these pulsars. Are the pulsars
distributed all over the galaxy or are we only looking
at the ones around us. They're distributed across the galaxy.
People have done a study and they found like fifty
or sixty good X ray pulsars that are distributed well
enough across the galaxy that you could use them as
reference points. And they've actually tried this. They've done it.

(43:50):
They've built a little one and they fluid on the
International Space Station and they tried it and it worked. Wow.
Pretty cool, all right, So it sounds like we do
have a GPS for the Alexy. We have a galactic
Pulse source system. You should also call it GPS. It's
pretty awesome. It's pretty awesome. I love this idea of like,
you know, astronomers don't get to build what they want.

(44:10):
They just get to look out there and find stuff
and use it to be clever to extract the information
they need. And here's another great example of just like
making do with what you have. Right, it's almost like
a nature and the universe made these lighthouses and put
them all over the galaxy just for us to kind
of used to get around. Yeah, probably not just for us,
but it would be a cool science fiction universe where

(44:32):
we actually visit one of these pulsars and discover, oh,
they're artificial. Maybe they're part of some billion global positions. Oh,
it is a lighthouse. It didn't occur naturally, that would
be pretty awesome. That would be worth some echoes in space.
Space space space space space cool cool cool. All right, Well,
I feel a lot better now about Star Wars and

(44:53):
about other science fiction movies and books. It sounds like
in the future we could be using these pulsars to
kind of know where we are in the galaxy and
to kind of build a map of the entire place. Yeah,
and as we venture out further and further beyond our
solar system and try to explore other solar systems, this
will be a critical way to know where we are

(45:13):
and hopefully how to come home. Yeah, And so future
space explorers flying around with their partners and spouses can
not argue about where they are getting lost, which would
probably make for a messy divorce out in space. Well,
they'll probably still argue, like, let's not use that pulsar.
That one's not reliable. Everybody's using that pulsar. You sound

(45:34):
like you, You sound like your father. All right. Well,
I hope that was interesting and gives you a little
bit more of a sense that we kind of know
where we are in the universe and the galaxy, and
that it would be a little bit hard to get
lost in space. That's right. And this idea of pulsars
took decades to figure out to narrow down to make
it work, and it only gives us five kilometer uncertainty.

(45:55):
Probably somebody out there will have an even better idea
for how to narrow down our edition. So have that
idea today so that it's ready for us to use
in twenty or thirty years. That's right. You don't want
to miss those snacks, you know. If you miss that
snack by five kilometers, that's that's not good eating. If
you learn nothing else today. Remember there are no U
turns in space or echoes, but there probably are snacks,

(46:18):
all right. Thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of I Heart Radio. For
more podcast for my Heart Radio, visit the I Heart
Radio Apple Apple Podcasts, or wherever you listen to your

(46:41):
favorite shows.