How does a plasma thruster work?

Will a plasma-based spaceship engine let humanity zoom between planets?

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, have you guys made any progress on the
new spaceship engine that can cross the vast distances between stars?
Nothing to report yet? Sorry? Oh man, I feel kind
of cheated that I made that a rush order. Well,
no problem. You know, once we finished building it, delivery
is going to be a snap. Yeah. Are you going
to deliver my spaceship on a spaceship now? It's sort

(00:30):
of like when you buy a new car, it comes
on a huge truck. Oh nice, So I can expect
a huge giant space truck pulling up next to my
house soon. Absolutely. The kids are gonna love it. It's
gonna come with a nice big bowl tied around it.
For an extra twenty million dollars, I'll put a bowl
on it. Hi am more handmade cartoonists and the creator

(01:02):
of PhD comics. Hi. I'm Daniel. I'm a particle physicist,
and I've never actually bought a new car. You've never
bought a new car, Never bought a new car, always
a used car. Wow. I guess they are cheaper, right,
because as soon as you buy a car and they
start depreciating. That's right. But I've never had that amazing
experience of seeing your brand new, shiny zero miles car,
pull up on the fancy truck. What's new to you?

(01:25):
So it is technically a new car, that's right. And
we like to drive our cards into the ground until
they're falling apart around us, like the podcast is that
what we're doing here now? Is this a used podcast? Technically?
It is right because we record this a few weeks
in the van, so by the time people listen to it,
it's got some mileach on it, but it's new to them.
That's right. Let's maybe spray some of that new car

(01:46):
smell around. That's right, new podcast smell yeah. Whip an
end people, But anyways, welcome to our podcast. Daniel and
Jorge explain the university production of I Heart Radio, in
which we take you around this very very old universe
that been around longer than we have and trying to
answer some questions about it and what questions do we ask?
We ask all the questions we asked, the biggest questions,

(02:08):
the hardest questions, the silliest questions, and the deepest questions,
and we try to find answers, and when we don't
find them, we are happy to admit what science doesn't know.
We take all that, we mix it around, we throw
in some bananas, and we serve it to you as
a podcast smoothie. That's right, because the universe might be
old and it might be used. In fact, it's actually
a several billions of years old, but it's still full

(02:30):
of amazing and new things to discover for us puny humans.
That's right. Do you think we have to pay full
price for this universe? I mean it's like really pretty
old by time we got it, we should have gotten
some kind of discount. Really, did you think we have
an option? Do we have like other newer universe we
could have bought. I guess you've got to have another
option if your negotiation is gonna be credible, Right, you're
gonna be able to walk out of the universe dealership

(02:50):
and say, I'm just gonna go down the street and
get a universe somewhere else. We have no leverage. We
have no leverage. We're stuck with this universe, and we
love it. It's the only car and a lot, that's right,
And let's not protect we don't love it. It's a wonderful, amazing,
crazy place filled with all sorts of mysteries. I just
sometimes wish we could see more of it. Well, we

(03:11):
can see a lot of it, right, We can see
up to billions and billions and billions of light years away.
But the hard part is getting to those places and
seeing them up close. Yes, exactly. That's why I mean
that we could visit more than that, we could go there,
that we could walk on the surface of Pluto, or
we could see what the atmosphere of Venus is like.
It feels like there are so many amazing mysteries of
science and physics that are right in our neighborhood, and

(03:33):
yet it's still so strangely hard to get there. Yeah,
or not just even our Solar system. It'd be cool
to travel to other galaxies and see if things are
quite the same as they are here in the Milky Way.
That's right. I'd like to be home before dinner, though,
so I'm not sure I'm gonna join you on that
intergalactic voyage. But somebody should go, and somebody should report back.
What if you make the spaceship your home, Daniel, and
then you'll always be home like a space RV. That

(03:55):
sounds great. It's just a couch and a rocket and
rocket field. That's all. Well, if my family is going along,
then my kids definitely need their own rooms, because there's
no way they're getting along if they're sharing a room
in the space RV. Al right, we can at an addition,
but yeah, getting around space is difficult because space is
so big. It's gigantic, it's ginormous, it's a pretty spacious.

(04:18):
It's hard to really wrap your mind around how big
space is. We have this image of the Solar System
is sort of this cozy place where all the planets
are zooming around the Sun and kind of near each other,
but there are vast distances. You know, even just from
the Earth to the Moon is a much bigger distance
than most people imagine. Did you know that if you
took all the planets in the Solar System you could
fit them in the distance between the Earth and the Moon. Wow?

(04:41):
I take it that's a bad idea that you're not
actually planning on doing that. You know what, I'd love
to see it. So if you have somehow the power
to do that, go ahead from your underground layer. Well,
if you just want to see it, then you know,
I can do that in photoshop easily. But the idea
I think is that space is big right, like between
here and the Moon, it's several hundred thousand miles even
right absolute, it's really really far. And you know, the

(05:01):
outer planets are really really far away, Like we are
much much closer to the Sun than we are to Jupiter,
for example. Yeah, I think we're used to maybe thinking
of our Solar System is this cozy, little like collection
of planets, but really it's quite sparse. It's quite empty,
like if you took a picture of it, you would
always see little tiny thoughts as the planets. Yeah, that's
why Jupiter seems like almost a star because it's so big,

(05:23):
but it's so so far away, and so the Solar
System is hard to get around because everything is so
far away. And when we launch even robotic probes to
the outer Solar System, it can take ten, fifteen, twenty
years to reach those places. Yeah. I think the trip
to Mars, just to Mars, it takes several months, right, Yeah,
and that's if you're lucky, right Earth end Mars are
near each other sometimes and far apart other times, and

(05:46):
so the shortest trip to Mars is like more than
half a year, and so it'd be awesome to be
able to get to Mars much faster and make it
easier to explore the Solar System, to send people there
if they didn't have to spend like seven months in
a tin can together. Yeah, I think the big question
is like, how can we get to these planets faster?
Like how can we you know, make a new kind
of spaceship or a new kind of propulsion technology to

(06:09):
basically pushes there faster, because traveling through space is really hard.
It's all about the speed. You know. A hundred years ago,
the Earth seemed much bigger because it was a bigger
deal to get to the other side of it. To
go to China two or three hundred years ago was
a days, weeks, months long endeavor. Now you can do
it in just you know, eighteen hours or so on
an airplane. It's not that big a deal. And that

(06:30):
transformation came because we had new technology, new engines that
could take us there faster. And so we hope we
fantasize about the technology that could take us around the
Solar system faster, that could effectively compress the Solar system
so it doesn't seem so big to shrink the Solar system.
In a sort of metaphorical way of speaking, right, maybe
when day you could buy a ticket to Jupiter and

(06:51):
all you have to worry about is like, how many
movies am I going to watch? Have they made enough
Avengers movies so I could just watch them all between
here and Jupiter. Well, by then they will make five
months worth of Avenger movies. Yeah, and maybe by then
the Avengers movies will each be forty hours long. So right, yeah,
they seem to be getting longer and longer. That's right.
It's the opposite of time dilation. It's movie dilation, which

(07:12):
works in the opposite direction. It's marvel dilation. Marvel, it's
like the quantum realm. Yeah, well, what if I watched
the Avengers movies while moving at high speed? Maybe they'll
shrink it back down to two hours long. Maybe you
actually like them? I like those movies. Come on. But anyways,
there are people out there working on new technologies that

(07:33):
might get us to other planets and other stars faster
and faster. And in particular, there's kind of a new
exciting technology with a pretty cool name. That's right. People
are working on this, People trying to develop ideas. People
have all sorts of different plans for how to develop
new engines for spaceships. So today on the program, we'll
be asking the question how do plasma thrusters work? Now, Daniel,

(07:59):
I'd just like to say the word plasma thrusters. I
feel like that's so you know, science fiction. I feel like,
you know, some some something out of a movie. I know,
it sounds a lot like plasma blaster, right, it sounds
like a weapon you could use against something with like
lots of limbs and gooey insides. Yeah, some sort of
glowing technology that you know, kind of like what you
see behind the starship Enterprise. Yes, but that's the exciting

(08:22):
thing about science fiction is that it gives people ideas
and then we try to make it real. Scientists watch
science fiction and go, man, why can't we actually do that.
We've got an idea, maybe we could actually do that,
And then they go off into their laboratories and they
tinker until boom, it's a reality. And the funny thing
is that those science fiction writers probably got these names
and these ideas from science itself, like plasma is a

(08:45):
real thing and thrusters are a real thing. They just
but hey, why don't we put the two together and
sell more books? Is that the process of science fiction.
You're like, take two things sticking together. Can we get
a banana thruster or a plasma banana? Yeah, it's like
taking two words like science and fiction and then sticking
them together and see what happens. Boom, new genre invented. Yeah,

(09:06):
I think that's the whole process. So plasma thrusters sounds cool,
but what is it? So we were wondering what people
out there knew about these two words stuck together and
whether or not they can actually be real. As usual,
Daniel went out there into the internet to ask people
if they knew how a plasma thruster works. And so
my eternal gratitude to those of you who volunteered to

(09:27):
answer random physics questions for the podcast and enjoy hearing
your voice speculating on the podcast. If you'd like to
contribute your voice as well, please write to me two
questions at Daniel and Jorge dot com. So think about
it for a second. Do you know how a plasma
thruster works? Here's what people had to say. I have
absolutely no idea what a plasma thruster is or how

(09:49):
it works, but it sounds pretty naughty. Well, I don't
know exactly, but it's way better than a chemical like
we have now would luck to us. I'm guessing the
plasma thrusters would work by igniting this ionized gas in
one direction that causes a force that pushes whatever rocket

(10:13):
or object it's in in the other direction. I'm a
hundred cent sure that the plasma thrust is a dance
move that particle physicists do at parties. Well, this is
a guess on my part based on the words, but
I assume that it excites an atom to the point

(10:35):
where the electron is stripped off, and it throws the
nucleus through some sort of magnetic or field at rather
high velocity out the back, which gives you thrust the
same way any normal rocket motor would work, except instead
of using chemical energy, you're using magnetic or electric energy

(10:58):
to throw out plasma. Uh nuclear, All right, pretty cool answers.
I like the one that says it's a dance move
that particle physicists do at parties. You like that? Do
you really want to imagine a bunch of particle physicists dancing?
I mean, does that a mental image you want in
your mind? I've seen it, and trust me, you don't
the particle physicists have party coal parties. There are particularly

(11:21):
good parties, yes, particularly awkward, as I think, when we
discover a nice particle, then yes, we have a party.
We celebrate, we drink champagne, we shake our booties just
like everybody else. Wow. Sounds exciting, all right, And so
a lot of people don't seem to have a pretty
good idea, although they definitely you know, I have some
ideas of what plasma is, but maybe not what a
plasma thruster is. Yeah, but they're excited about it. They

(11:45):
want this thing to be a reality. That sounds like
a promising step in the direction of getting us around
the Solar System. And so I think everybody is in favor.
All right, Well, Daniel, let's talk about first why we
might need a plasma thruster. You know why this idea
of creating something that can push you in the vacuum space,
why is that so hard? Right? So, one of the
reasons that this is a hard problem is that when

(12:08):
you are in space, you need to push against something. Right,
If you're in space and you want to get speed,
what you have to do is throw something out the
back of your rocket ship. Because of conservation momentum. If
you're going to go in one direction, something else has
to go in the other direction. So this is like
the reaction. You know, you could like fire a bullet,

(12:28):
for example, out the back of your spaceship and the
gun will push you in one direction and the bullet
in the other direction. So the basic elements you need
of any thruster are some energy and then something to
throw out the back, some reaction mass to push the
other direction, right, Because I guess when you're in space,
you're if you're out there floating, it's not like you
can swim your way to Mars or to the moon.

(12:51):
You can't just there's something to like push against, right,
So you need to throw something out the back, and
for that you need energy. So that's what you're saying.
You need energy and then something to throw out the bag.
Using that energy exactly, you have to carry with you
stuff that you can throw away so that you can
move along. As you say, you can't like grab space
and swim through space itself, right, it's not like air

(13:12):
or water that you can pull against, right. You can't
just like blow out the back like or maybe you
can can you Yeah, actually that would work. I mean,
that is a form of a rocket engine, right, you
blow air out the back, and you can even use
a flashlight. Right, if you turn on a flashlight on
a spaceship out the back of your spaceship, then that's
a form of a thruster because you're shooting energy in

(13:32):
one direction and so the spaceship will go the other direction. Right,
that would be a photon thruster. That's a different episode.
That's a different episode. Yeah, exactly. But you know, it
reminds me some listener rode in and asked about their headlights.
Every time you turn on headlights in your car, are
those effectively like photon brakes? And they kind of are,
because you're like throwing energy forwards, sort of like having

(13:53):
tiny little thrusters pointing forward. So every time you turn
on your headlights, your car slowed down the tiny a
little bit. And it just made me think when you
hit the brakes and you turn on the brake lights
in the back, and you're also sort of working against
yourself there because you're breaking, but you're also kind of
propelling yourself using photons. Yeah, brake lights should be in
the front. Oh my god, it's so much better. I

(14:15):
think that would defeat the purpose of brake lights. So
one of the problems with using a rocket is that
you've got to have all this stuff on board. You're
gotta have the fuel, you've got to have the stuff
to throw out the back, and then the further you
want to go, the more fuel you need, and the
more fuel you need, the more fuel you need to
push that fuel, and so pretty quickly this is sort
of like a runaway mass problem. You need to have

(14:37):
a really really big ship to get anywhere at all
because you need fuel to push all the fuel that
you're pushing with all the fuel, right, And that's kind
of how rockets work right now, right like the ones
on current spaceships and spacecraft and rockets, that's how they work.
They use a chemical reaction to explode something and then
that explosion pushes the stuff out the back. That's right.

(14:57):
The fuel itself is the propellant and the source of energy,
right Like, you have something along like diesel fuel or
liquid oxygen or something that has energy stored inside of it,
and then you release that energy and at the same
time creates something at high velocity which can get thrown
out the back. So most chemical rockets work in that way.
They're both the propellant and the source of energy. And

(15:20):
that's how, for example, rockets lift off the Earth, and
that's how the Space Shuttle maneuvers in space. All these
are chemical rockets, right, And what makes it work, I
think is the idea is this kind of this difference
or this ratio between the energy and the mass of
what you're throwing behind you. If your planets to like
throw out you know, your trash or throughout your couch
to propel yourself in space, that wouldn't last very long, right,

(15:42):
because you would run out of couches. Yeah, and you
know maybe r vs and children you want to get
very far. But the idea with the chemical fuel is
that it has a lot of energy stored in it, right,
So like it you release that energy, it throws a
little bit of mass out there back, but with so
much energy it actually pushes you forward, that's right. The
key thing is having high exhaust velocity, so that those

(16:05):
particles you're throwing out, whatever they are, particles of couch
or particles of smoke, or particles of burnt rocket fuel, whatever,
are carrying a lot of momentum. Because any momentum that's
going at the back is equivalent to the momentum gained
by your rocket ship. Right, This is all about conservation
of momentum. And so the higher speed, the higher exhaust
velocity that goes out the back, the more momentum you're

(16:26):
throwing away in your exhaust, and so the more momentum
your rocket ship is going to get. Right, because momentum
is like mass times velocity. So if you want to
conserve on how much stuff you throw out the back
the mass, then you just need a lot of velocity. Yeah, exactly,
that's the way to do it. So those are chemical
kind of rockets, and that's what we used to get
off the Earth, but those are kind of tough for

(16:46):
going across to other planets or stars. Right. Yeah, if
you wanted to travel, for example, to the nearest star
system like Alpha Centauri, and get up to a reasonable speed,
like you know, a few percent of the speed of light,
so that a trip which is just a few light
years would only take you know, fifty or a hundred years,
you would need an enormous amount of chemical fuel to

(17:07):
accelerate you up to that speed. And because you need
so much fuel, you need a lot more fuel to
push that fuel, and so you'd end up with like
a toothpick sized chip pushing a Jupiter sized gas tank.
That sounds crazy. I think A good analogy I think
we've read once was that it's sort of like if
you're trying to drive a truck across the country without

(17:29):
stopping for fuel, you sort of need to bring all
your fuel with you. But then the more fuel you bring,
the more fuel you have to use because you're heavier, exactly.
And then pretty quickly you're driving basically like a stadium
size gas tank behind you, and that's pretty inefficient and
takes a lot of fuel, so it really limits how
far you can go, right, And that's kind of why

(17:50):
rockets are so big. Like if you look at a
rocket that goes to space, most of it is just
a giant fuel tank. Right. Yeah, I'm not sure people
really understand how massive these things are. Like the Earned
five rockets, one of the workhorses of the American space program,
is taller than the Statue of Liberty. Like, this thing
is enormous, but most of the actual active part of
it is this tiny little nose cone on the very top. Basically,

(18:13):
it's a huge gas tank with a tiny little cab
on top, because you need to bring a lot of
that fuel with you. And so that's really the hard
part about space travel, is like bring all the fuel
that you will need later because there are no gas
stations in other planets. Right, there are no gas stations
out there in space. It sounds like you're identifying a
business opportunity here, you know, rocket fuel for sale on

(18:34):
Pluto or halfway between here and Alpha Centauri. You could
sell a lot of slim gyms also, you know, yeah,
there you go and and turkey turkey. But then what
do you do with the restroom waste? That's the hard part.
That's just more rocket fuel. Man, you can just mix
it all in there you go, biomass, biomass fuel, biofuels
and solutions solved all at once. All right, Well, so

(18:56):
that's the main problem with thrusters and getting around the
Solar system in space. And so there's this new idea
of using plasma based thrusters. So let's get into that
and whether or not they're real and where they they
can work. But first let's take a quick break. Alright,

(19:24):
we're talking about plasma based thrusters. Now, this sounds really
sci Fi Daniel, Plasma. Anything I think with the word
plasma sounds cool, but it's the opposite. It's not cool, No,
it's not cool. It's very very hot, and it's actually
one of the most common forms of matter in the universe. Right.
People think of plasma is weird and rare and unusual,
but it's really just weird and rare and unusual here

(19:46):
on Earth, where it's sort of weirdly cold, Like the
Sun is basically a huge ball of plasma. And since
the Sun is most of the stuff in the Solar System,
the Solar system is basically all plasma with a few
crumbs like us, we should just call the Sun the
plasma ball, the giant plasma ball in the sky. It
basically is, it's such a big, hot plasma that we

(20:06):
can feel it even ninety three million miles away, and
thank goodness. But maybe step us through what is exactly
a plasma? You said, it's a state of matter. Yeah,
you're familiar with several states of matter right there. Solids
when the atoms are cool and sort of locking into
a crystal structure, so they become solid and then liquid.
If you heat it up, then those atoms get liberated.
From those bonds and squish around. Keep heating something and

(20:28):
it becomes a gas. As those atoms like to whizz
around and aren't even connected to each other. If you
keep heating it, then what happens is that the electrons
that are whizzing around those atoms get so much energy
that they're no longer held on by the nucleus. So
you have a positive nucleus and a negative electron, and
usually the strength of that electromagnetic bond is enough to

(20:50):
keep the electrons bound to the nucleus of the atom.
But if you get them hot enough, then they escape,
and then you have something which has nuclei and electrons
floating around, whizzing around. You have charged particles. So a
plasma is like a gas that's been heated up so
much that it becomes ionized that the electrons are now free. Right,
it's basically like just regular matter, right, that's heated up

(21:13):
so much that it breaks the atoms, like the items
kind of break apart. Yeah, they're broken apart, and it's
sort of like the original state, you know, before things
cooled down the electrons got captured by the nuclei, they
were free. Electrons were born free. They were captured, and
some of them have been in this state for billions
of years, and now if you heat something up, you're
returning them back to their original state of freedom. Oh man,

(21:35):
Now you make me sad for the atoms in my
body and the electrons in my body. You make it
sound like I'm trapping them and I'm keeping them from
being free. No, some atoms very happy to be married forever,
you know, but other ones want to be single, and
so you know, there's good sides of both to each
their own. But a plasma is basically like a singles
bar right now. It can anything be a plasma? Like

(21:55):
can any kind of matter be a plasma if I
heated up enough, Yeah, anything can be a plasma. As
long as you heat it up enough that it starts
to lose its electrons and it is made out of
ions and its components are now charged instead of neutral,
then that's a plasma. So yeah, you can have a
plasma out of hydrogen. That's what most of the universe is.
You can also have a plasma out of like iron.
You eat, have iron enough, you get an iron plasma.

(22:16):
And you know you said it happens in the sun
and it happens when you heat things up a love.
But there are other ways that you can make plasma
that doesn't heat them up that much, right, Like there's
I think you can use radio waves or some sort
of radiation to create a plasma, like in your desktop. Yeah,
we have plasma all around us. Like fluorescent lights have
a plasma in them, right, that's why they glow. You know,
you can talk about the definition of temperature. I found

(22:38):
it's a little fuzzy. You are making those particles move
fast enough. You're giving them enough energy to be released
from their atoms, so they have that high velocity even
if there's not that much actual heat. Right. A plasma
doesn't have to be very very hot, even if it's
high temperature because it doesn't store a lot of heat
because the gas is very diffuse and dilute. Then you
might not like burn yourself from touching a container that

(22:59):
has plasma in it, but it's still would be officially
high temperature because the particles are moving fast. So fluorescent lights,
like the lights we all have in our offices and
in stores and stuff, that's plasma. That's like a canister
of plasma, right, that's a canister of plasma and neon.
For example, neon lights those have plasma inside them. So
those are atoms that are whizzing around. They have so

(23:20):
much energy that they glow and they give off photons
right there, just like shedding energy constantly. I wonder if
they had named those plasma lights, if we would feel
the same way we feel about fluorescence lights right now,
like they would be this name that's associated with something
like unpleasant, boring, an unpleasant Yeah, yeah, a fluorescent blaster.

(23:43):
I'm gonna shoot fluorescent light at you and give you
a headache. There you go. That will make for a
Nokward science fiction marble, the headache gun. All right. So
that's plasma. So how does the plasma thruster work? Like,
how would you use something like fluorescent light to push
yourself through space? A plasma is glowing, it's giving off energy,
it's stuff moving around fast. The problem with the plasma

(24:06):
is that generally glows in every direction, and so it's
sort of throwing momentum off in every direction. Like the
sun isn't an engine, it's not flying in one direction
because it's giving off energy in every direction. So if
you want to take a plasma and turn it into
a thruster or what you need to do is make
it only point it's glow only shoot particles out, only
send momentum away in one direction. And the way you

(24:28):
do that is you just take a plasma and you
put it in basically a magnetic bottle. I mean, the
plasmas are charged particles, and charge particles bend in magnetic fields,
and so it's hard to contain a plasma because has
so much energy. You'll basically eat through anything. It's sort
of like acid. But if you could build a bottle
around it that bends the particles back into the plasma,
but leave a hole in one side, then particles will

(24:51):
shoot out through that hole and effectively push the whole
plasma the other direction. I see. It's like you're heating
a water, kind of like you're making a water a gun,
kind of like you heat up the water, it steams up,
becomes a high pressure gas, and then you shoot it
on on one side, and that's kind of what would
push you in space, but you're doing it with a
plasma material. You take a water balloon, for example, if

(25:14):
you poke a water balloon on one side, then water
is going to squirt out through the hole that you made,
and the rest of the balloon is going to go
the other direction. And so that's basically what a plasma is.
It's hot and high speed, and so it's always shooting
particles off. It's basically trying to expand. But if you
contain it in every direction but one, but only where
the hole is, can particles leave and they will carry momentum.

(25:34):
And that's basically an engine. And so that's kind of
the basic mechanism of a plasma thruster. It's like you're
heating something up and then you're letting it escape out
one end of your space. That's the basic mechanism. And
you remember once we talked on the podcast about using
the Sun as an engine, or building an engine that
could move the whole Sun. It was the same basic idea.
It's to build something around the Sun that reflects its

(25:55):
energy back into the Sun, except in one direction. And
so you can use this idea to move the whole Sun,
or you can build your own little mini plasma, your
mini sun, and reflect most of its energy back into itself,
except in one direction. So that's the basic premise, right.
It's kind of like a flashlight or even your headlights, right,
Like you're heating up an element, it's creating photons, but
then you're focusing those photons to one side. Yeah, because

(26:18):
flashlights usually have like a mirror on one side, so
the photons that are generated that come back towards the
handle get reflected to go the other direction, so it
produces a more calmnated beam. So that's the basic principle.
If you can shoot off momentum in one direction, then
the rest of the engine goes the other way. And
so what you need to do is get some cold stuff,
really almost anything, and heat it up until it becomes

(26:40):
a plasma and confine it in all but one direction.
I guess the tricky thing here that I'm not seeing
is how is this better than a chemical reaction because
it seems like you're just you have to spend a
lot of energy to heat up this plasma as opposed
to like rocket fuel, which explodes because it has that
energy stored inside of it. Yeah, that's true. It's sometimes
times can be an advantage to decouple those things. Like here,

(27:03):
you're right that the source of energy is something else,
and that means that you're sort of free to get
that energy from another source. Like solar power. If you
have huge solar cells, you can collect that energy, turn
it into electricity, and then hook it up to a
plasma rocket and use it for propulsion. So that's one advantage,
sort of like the way you have an electric car.
It's nice that you have an electric car because it
means that you can accept energy from lots of different

(27:24):
kind of sources, not just dirty coal burning power plants,
but also clean solar panels. For example. Oh, I see,
they said, do you want to somehow collect solar energy
while you're out there in space and somehow convert that
to thrust and instead of brain to fuel with you. Yeah,
because it's lower mass, right, So if you can gather
the energy along the way, then you can have this

(27:46):
plasma thruster and you don't need to bring all that
fuel with you. But it can also be a disadvantage, right,
because you need to gather that solar energy and that's complicated,
or you need to have some other source of electricity.
The nice thing about rocket fuels that it's sort of
like all in one, as you say, So there are
pros and cons there. What are some of the other cons. Well,
one of the cons is that plasma is really really

(28:06):
hard to contain. You know, like you have a plasma,
it's going to be eating away at the walls that
you're trying to use to contain it all the time.
One of the big challenges we have with fusion research
here on Earth is that we're trying to make a
plasma and contain it. We can't just like have our
own little sun a little destroy the Earth. So we
need to build these magnetic bottles. But they are hard.
Plasmas are always trying to escape and keeping them stable

(28:29):
and keeping them contained is really tricky. And you don't
want your spaceship engine breaking down or the plasma leak
out and basically destroy your ship. So it's got to
be really really robust, especially if you're talking about like
a year's or decades long journey and there are no
repair stations along the way, right. Yeah, you need like
a cool container to keep that plasma in check. Yeah,

(28:50):
And the plasma gets hot and it generates a lot
of waste heat, and so you need some like large
way to radiate off all of that heat from the
plasma that you're not using, and so that's a huge
waste of energy. It's inefficient and sometimes it requires like
large fins just to cool this thing, which means more mass,
which means that you're not going to be moving as quickly.
So there really are some disadvantages there. I think the

(29:13):
main disadvantage though, is that plasmas don't get particles up
to very very high speeds like a rocket engine or
ion thrusters or other things that have like active acceleration
of these ions can get much higher exhaust velocities. A
plasma is basically just saying, hey, you've got something that's
kind of already hot, The particles are already kind of
moving around, so why don't you just use that. You're

(29:35):
not really getting very high exhaust velocity. Yeah, it doesn't
seem that efficient because you're you're basically just throwing stuff
out the back, right, You're not sort of like releasing
any sort of inherent energy on it. You're literally like
just pushing stuff out the back, like you're throwing your
couches out the back of Yeah. Well, there is some
extra flexibility there, for example, because you can almost use anything,

(29:55):
Like you said, you can turn anything into a plasma,
and so you can use like astro not urine or
astronaut waste and throw it in the engine and it
will turn into fuel. Yes, you really can, or your
couch if you want to take more cleanly. You know,
other things sometimes require very special chemicals, like you got
to use rocket fuel in a chemical engine, or if
you have an ion thruster for example, and needs some

(30:17):
very sort of like inert gas like zenon. You know,
things that like those Starlink satellites have. These are little
ion engines that create a little plasma, but they have
to start from zenon. But if you have a real
plasma engine on your spaceship, you can basically toss anything
in their banana peels, coffee grounds, astronaut urine, whatever. Right,
you can have a poop plasma. That's a crappy idea,

(30:40):
I know, let's flush that down the toilet. All right.
Well then, so what are some of the pros of
using a plasma thruster? Like why convinced me that it's
a good thing? Well, I'm not sure I can give
in too is a great thing. This is sort of
the basic design for a plasma thruster. There are improvements
will talk about in a minute that make it more appealing,
but they do have some advantages over other approaches, like,

(31:01):
for example, the exhaust is naturally uncharged, doesn't have electric
charge because what you have are both positive and negative
particles shooting out the back, and so as they come
out the back, they naturally sort of recombine into neutral particles.
You don't need to do something extra to make sure
their neutral. Like for ion thrusters, you're only shooting positively
charged particles out the back, and you need to add

(31:24):
electrons to them as they come out the back to
recombine them so they don't get like sucked back into
your ship. So there's one positive. Another positive is that
they're sort of simple. You know, they're basically just magnetic
bottles that you're heating up using some sort of electrical energy,
So there's not a whole lot of stuff to break,
except of course, for the plasma eating the bottle. All right, Well,
it sounds like simplicity and flexibility in the kind of

(31:47):
fuel is a good thing. So let's get into how
it to actually make one of these and whether or
not it would be practical to do. First, let's take
another quick break. Or we're talking about plasma thrusters that

(32:12):
may or may not be made out of p and
poop in space. Definitely on the mayn or hopefully not.
You don't want to be like the car behind that
spaceship that's getting all that you know, high energy waste. Yeah,
then again, do you really want to carry all that
waste with you to Alpha Centauri so that when you
show up and you meet the aliens, the first thing

(32:33):
you ask him is like, Hey, do you have a
place I could put all this stuff? Because I have
a huge storage tank filled with it? Right, do you
want to recycle it? All? Right, we'll talk to us
about whether or not people are actually making this and
maybe what kind of specific technology people are focusing on.
So people are definitely working on this. They are developing

(32:53):
these things in the laboratory, and the one that we
just talked about, the most basic sort of plasma thruster.
There's a version of a called Vasa mirror v A
s I m ARE that people are working on, and
it has like a magnetic nozzle at the end of it,
so you can sort of tune how much of the
plasma comes out and at what velocity. That's cool because
it lets you adjust this exhaust velocity and so you

(33:15):
can like ramp it up when you get into outer
space and get more thrust. So that's pretty cool. People
are working on that. But then there are some other
exciting ideas that's sort of more cutting edge that people
are working on to improve plasma thrusters and sort of
next generation devices. Yeah, and these involve another pretty cool
science fiction work, which is fusion. Are we actually considering
like making fusion plossible for space travel, Yeah, we are,

(33:37):
because what we talked about so far is just plasma
right now. Plasma is an important component of fusion in
the sun, but you can have plasma without fusion or
plasma and your fluorescent light is not doing nuclear fusion.
It's not like a bomb. But the way that we
do fusion is through a plasma. You gotta get a gas,
you've gotta heat it up, then you've gotta squeeze it
down so that those very high energy particles smash into

(33:59):
each other and make heavier elements. And so people are
working on taking plasma thrusters to the place where they
actually can fuse some fuel to release additional energy as
a way to avoid having a pump in external energy
like from solar panels or from some sort of electrical source.
So now we're talking about making fusion in space. Fusion
in space like a fusion engine that you put on

(34:21):
a spaceship. Yeah, and it's called a direct fusion drive.
And you might be wondering why you would want to
do that, because the whole idea of a plasma thruster
was that you could take energy from all sorts of
different directions. What the idea here is that, again, like
a chemical rocket, you're now bringing the fuel that has
the energy inside it. Right, it's more like a chemical rocket,
but this fuel is very, very dense. You know, fusion

(34:44):
is much more efficient than chemical burning because you're turning
mass into energy much more effectively. That's why I like,
for example, hydrogen bombs are much more powerful than T
and T because fusion is much more powerful than just
chemical burning, and so you have a much denser source
of fuel, and so it's more efficient transformation of that
fuel into energy. So you just don't have to bring

(35:06):
nearly as much fuel if you can use fusion as
the source of energy. Right, it's like you're bringing all
the energy that's trapped inside of the bonds or that's
trapped in the potential bonds of the fuel that you're
bringing so it's almost like you're being extra clever about it. Yeah,
it's all about getting as much energy as possible out
of the same mass of fuel, because then you need
less fuel mass for that energy. You know, the best

(35:28):
case scenarios to bring like antimatter fuel and to smash
matter and antimatter together because it's total annihilation of mass
into energy. But you know, antimatter is basically impossible to
fabricate in large quantities and very difficult to transport. Fusion
is sort of like at the edge of plausibility, like
it might be possible to build a fusion reactor in

(35:48):
space that transforms the energy stored in the nucleus into
energy you can throw at the back of your rocket. Yeah,
that's the thing, because I feel like, you know, we've
been working on trying to get fusion working here on
Earth for like fifty years, and we still don't have
a pretty good or a working or an efficient fusion generator.
What makes this thing that we can suddenly do it

(36:08):
in space? Well, I talked to some plasma physicists and
they don't They don't think this is possible. They're like, no,
I don't think so. I mean, some people make the
argument that it's simpler. They think it doesn't have to
be such a huge, massive thing, like you could build
basically a minivan sized fusion container rather than like the
fusion reactors were building here on Earth, like either this

(36:30):
new reactor they're building in France is like sixty meters high,
and so they think it could be simpler. It can
be smaller. But frankly, there's a lot of skepticism in
the plasma physics community about whether this is plausible at all.
It's basically relying on an uninvented technology, small scale fusion
that would have to work and be reliable for years.

(36:51):
And so what's the basic idea that we somehow trapped
plasma and then somehow ignited so that it fuses together
and then that energy goes out the back. That's the
basic idea. You start the plasma with some other external
heat source, maybe r F energy or whatever you've captured
from before, and then once you've got it hot, you
put in your fuel and then that fuel releases more

(37:11):
energy and sort of then it's sort of like a
fire because it releases the energy needed to ignite the
next piece of fuel, and so it's self sustaining, So
you're putting in energy, but only in terms of this
like very very dense fuel that releases a huge amount
of energy. So then the particles are now very high
speed and they flow around the field lines of your
magnetic bottle and they shoot out the back. And so

(37:33):
that's pretty cool. It generates very high speed particles, which
are very good for a rocket engine, and at the
same time you can capture some of that energy and
turn it into energy for your spaceship. Right, you also
want to like heat coffee and power your life support systems. Well,
you have a fusion reactor on board now that not
just is generating thrust, but also can generate direct electricity.

(37:54):
I guess when maybe one advantage to is that, unlike
a future generator here on Earth, you're not trying to
like power a whole city, right, Like it doesn't have
to me maybe energy positive for a space engine, like
you actually want to spend some energy to push yourself,
so it doesn't maybe have the same requirements as a
fusion generator here on Earth. Yeah, that's true. Some of

(38:14):
these designs that are even more complicated than the ones
that are working on here on Earth, Like here on Earth,
we try to use simpler fuels like deuterium and tritium.
These are isotopes of hydrogen with extra neutrons on them.
But the ones that people are talking about for space
travel use like advanced fuels like helium three. And these
are cool because you can find like deposits of it
on the Moon. But nobody has made fusion for helium

(38:37):
three work. It's even much more complicated than the kind
of fusion we're talking about on Earth that we also
haven't made work. And so this is definitely in the
category of like the could work, would be awesome, might
never work. It's currently at the science fiction novel stage. Yeah,
it's currently at the Marvel movie name drop stage. No,
they're like, there are prototypes. They are working on it

(38:57):
at Princeton. Princeton has an incredible plasma physics obratory. They're
grade at fusion, and so there are people working on it,
but you know, it's far away from being a proven technology. Well,
there are some pretty new and interesting ideas. I think
you spoke to some of the scientists there at the
Princeton Lab and they have some new concepts for making
this happen. Yeah, there was a new idea just this

(39:17):
year from an Iranian scientist at plasma, Dr Fatima Abrahimi,
And she was actually thinking about the way the Sun
works because the Sun is a huge ball of plasma
and the Sun has these crazy releases of energy, right,
like these huge coronal mass ejections, and these happened when
the magnetic fields on the Sun like reconfigure themselves and

(39:37):
snap into a new direction in which you get are
these like bubbles of plasma that are trapped in these
little magnetic field ripples and they move really really fast
through the plasma. So she thought, well, I wonder if
you could use that to build an engine, Like what
if you could have a plasma to generate these little
magnetic bubbles and then shot them out the back. That
would be an effective way to take your plasma. You

(40:00):
wouldn't necessarily need it to be fusing and to shoot
really high energy plasmoids out the back. So that's what
these little magnetic bubbles are called plasmoids. This is just
some like phenomenon that happens with all plasmas. And she's saying,
let's capture those bubbles and use them. Yeah, let's capture
those bubbles and direct them and if we can make
our magnetic fields in such a way that they always

(40:21):
shoot in one direction, then we can basically shoot these
magnetic bubbles out the back. And because they move at
very high speeds, like twenty kilometers per second, then you
can get a very high exhaust velocity from your plasma,
much higher than the generic plasma thruster we were talking
about before, which is just like a hot gas with
stuff leaking out. This is like magnetically directed and accelerated

(40:41):
inside the plasma. Yeah, the generic version is always you know,
a little suspect cheaper, but yeah, cheaper, Yeah, but you
never know, right, So this is sort of like using
plasma burbs, right, Like this could be called the plasma
burp engine. Yeah, the plasma burp engine. I'm sure she'd
love to have it called that, better than the other
name you could give it for, you know, shooting gas. Yeah, well,

(41:03):
these are high velocity burps. Right. This is like ten
times faster exhaust speed than a generic plasma engine. And
that's exciting because the exhaust speed is key, right, That's
the thing that gives you that push of momentum. That's
what lets you really get your spaceship going up to
high speeds very quickly. Yeah, these are name brand burps,
not the generic kind. All right, Well, let's be hopeful,

(41:25):
and so let's say they make this work and we
have this exciting technology. Can it takes us around the
source system faster? Like could we get to Mars in
less than a month? Yeah? If you had this kind
of technology and it was reliable and you trusted it,
then you could get to Mars in like thirty nine days.
They've done these calculations and this kind of engine again,
if it works can get you to Mars in a

(41:46):
pretty short amount of time. That's great because it means
you could also get to like Saturn in just a
couple of years. You can get to Pluto in like
less than five years where its currently it takes more
than a decade to get out to those outer parts
of the Solar system Mars and already nine days that
is like a Marvel movie a day. So your dream
might come true. Yeah, and they keep making them so

(42:08):
they can just beam them to you. You You can download them.
There you go. I hope they have free WiFi. You
can you can burp your way through the Marble catalog.
What if you shoot avengers movies out the back of
your ship. That's the potential engine right there. They're pretty massive. Yeah,
definitely takes them. All the money that marble and is
made to make these engines work. So and it's not

(42:28):
just humans that need to get around the Solar System.
They're very real reasons why we want faster ways to
move around the Solar System, and one is to intercept asteroids.
You know that we're always on the lookout for objects
that might hit the Earth, that might come and impact
the Earth and cause an extinction event, and we're pretty
good at watching these things, but sometimes they appear with
very little warning. And the critical thing when you're trying

(42:50):
to avoid getting hit by a rock is just spotted
as early as possible, because that's when you can give it,
like just a little bit of a nudge and push
it off course to spare the Earth. But if you
see this rock, you gotta get to it. You gotta
get out there to give it a nudge. And so
a faster rocket like a plasma based interceptor might literally
save the Earth someday if it means that we can

(43:11):
get it out there and give that asteroid a nudge
before it comes and hits the Earth. Interesting, just gives
you faster first responders in case of an emergency. Yeah,
so you can get to it sooner, which means you
need a smaller push, which means there are a lot
more asteroids that you could deflect. Right, A really really
tiny push two years in advance is the equivalent of
like a massive nuclear thrust five minutes before it hits

(43:34):
the Earth. It's much easier to deflect these things if
you catch them early. All right, Well, then maybe you
should stop watching so many Marvel movies and get to
work on this, Daniel. Come on, would you never know
when that asteroid might come? I would happily do it
if anything I did ever had any practical benefits. But
you know that's not true. Yeah, maybe you're not the
person to put on this project. All right, Well, last question, Daniel.

(43:57):
If somebody did make a spaceship but it is powered
by direct fusion and plasma plasma thruster, would you buy
it if it was used? Well, I guess it depends
on what happened the last people who used it, Right,
if they're still around and they had a good trip,
then yeah, I would trust it better than spending all
that money on a new fusion drive. Geez who space?

(44:21):
All right, Well, I think that answer is the question
what is a plasma thruster and how that might work
and how it could work in the future. And again,
scientists are hard at work trying to get us out
there into space so that we can explore more and
see things up close and learn more about the universe.
That's right. Some of these things are real and working
in the laboratory, and some of these things are still

(44:41):
pipe dreams that scientists are working on. And there's lots
of room for new ideas. So if you have an
awesome idea for a new spaceship engine that let's just
get around the Solar system. Hey, get to work, that's right,
and you could create the next name brand spaceship. All right,
thanks for joining us, see you next time. Thanks for listening,

(45:05):
and remember that Daniel and Jorge explained. The Universe is
a production of I Heart Radio or more podcast from
my Heart Radio. Visit the I Heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. H