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How far can we go with chemical rockets? · Daniel and Kelly’s Extraordinary Universe

• 0:07
  Speaker 1: How long are we going to be stuck on this
• 0:10
  Speaker 1: tiny little rock? And by we I mean humanity, not
• 0:14
  Speaker 1: me or Kelly or even you. I'm plenty happy to
• 0:18
  Speaker 1: live out my life here on Earth, but humanity should
• 0:21
  Speaker 1: push beyond, should find other places to live, should walk
• 0:25
  Speaker 1: on alien planets, should see sunrises from different distance stars.
• 0:31
  Speaker 1: But what's gonna make that happen? For a long time,
• 0:34
  Speaker 1: humans have relied on chemistry. Blow stuff up, funnel the
• 0:38
  Speaker 1: output out the back of your ship, ship goes forward. Cool,
• 0:42
  Speaker 1: that works, But is that steampunk kind of plan going
• 0:45
  Speaker 1: to power our future? Can use that chemical technology to
• 0:50
  Speaker 1: explore the outer reaches of the Solar System and to
• 0:53
  Speaker 1: reach other stars. And if chemistry lets us down, what's
• 0:57
  Speaker 1: gonna come to the rescue? We know it's not. By today,
• 1:01
  Speaker 1: we'll dig into the issues with chemical rockets and show
• 1:04
  Speaker 1: you how physics is going to save the day. Welcome
• 1:08
  Speaker 1: to Daniel and Kelly's Extraordinary Propelle Universe.
• 1:25
  Speaker 2: Hello. I'm Kelly Waitersmith. I study parasites and space, and
• 1:28
  Speaker 2: it doesn't matter what method you use. I'm not going
• 1:31
  Speaker 2: to space.
• 1:35
  Speaker 1: I am Daniel. I'm a particle physicist who loves thinking
• 1:37
  Speaker 1: about aliens and I've never been on a rocket powered anything.
• 1:43
  Speaker 2: Yeah, I guess I haven't either.
• 1:47
  Speaker 1: But you have to think about it for a minute.
• 1:49
  Speaker 1: What were you considering where you're like, ooh with that
• 1:51
  Speaker 1: bicycle and I strapped a huge engine to rocket.
• 1:55
  Speaker 2: Powered or not? Well, I will embarrassingly admit that I
• 1:59
  Speaker 2: was thinking like, all right, how do planes go? How
• 2:03
  Speaker 2: do ships go? How do trains go? And then the
• 2:06
  Speaker 2: answer to all of them was not by rocket? So
• 2:11
  Speaker 2: you know, I just had to make sure I was
• 2:13
  Speaker 2: telling the truth.
• 2:14
  Speaker 1: All right, Well, let's close the gap in your answer.
• 2:16
  Speaker 1: You said you wouldn't go to space, but would you
• 2:18
  Speaker 1: get in a rocket powered something here on Earth?
• 2:21
  Speaker 2: Uh? No, I doubt It's hard for me to imagine
• 2:25
  Speaker 2: that I would do that.
• 2:26
  Speaker 1: What about you, Well, let's check it again after you
• 2:29
  Speaker 1: hear about ion thrusters, because maybe a gentle ion thrustered
• 2:34
  Speaker 1: powered bicycle is something you would ride, but.
• 2:36
  Speaker 2: That wouldn't be a rocket. Then right now we're in
• 2:38
  Speaker 2: a whole different zone. I do travel on vehicles, I'm
• 2:42
  Speaker 2: not anti getting around, but by rocket makes me a
• 2:47
  Speaker 2: little nervous. I think.
• 2:48
  Speaker 1: All right, Well, I hope on today's episode we're going
• 2:50
  Speaker 1: to expand your mental conception of what is and what
• 2:54
  Speaker 1: isn't a rocket. Oh, it's not all flames and exclusions.
• 2:58
  Speaker 2: Well, then, how do I know that I haven't been
• 3:00
  Speaker 2: on a rocket? If I clearly don't have a good
• 3:03
  Speaker 2: conception of what a rocket is and what it isn't.
• 3:05
  Speaker 2: All right, it's time to teach me. Let's jump in.
• 3:09
  Speaker 1: All right. Well, on today's episode, we're gonna be talking
• 3:11
  Speaker 1: about how it's possible to explore the rest of the
• 3:14
  Speaker 1: Solar System. Our current technology are ugly, nasty, dirty, expensive,
• 3:20
  Speaker 1: heavy chemical rockets. Can they take us to the edges
• 3:24
  Speaker 1: of the Solar system and beyond? That's the question we
• 3:28
  Speaker 1: put to our group of listeners who love to speculate
• 3:31
  Speaker 1: without a chance to google or do any research. If
• 3:35
  Speaker 1: that sounds fun to you, we'd love to hear your
• 3:37
  Speaker 1: thoughts on the topic of the day. Write to us
• 3:39
  Speaker 1: to questions at Daniel and Kelly dot org. In the meantime,
• 3:43
  Speaker 1: think about it for yourself for a moment. How far
• 3:46
  Speaker 1: do you think we can get with chemical rockets that
• 3:49
  Speaker 1: Kelly hates?
• 3:50
  Speaker 2: All right, hold on, hold on, hold on. Before we
• 3:52
  Speaker 2: hear from the extraordinaries, I want to a stick up
• 3:56
  Speaker 2: for myself and be stick up for rockets. You used
• 3:58
  Speaker 2: a bunch of really negative words to describe rockets. But
• 4:01
  Speaker 2: I watched a rocket launch to space once and I
• 4:04
  Speaker 2: thought it was very moving and beautiful. And I do
• 4:09
  Speaker 2: think it's amazing that we can use rockets to send
• 4:12
  Speaker 2: stuff to space. And though I don't want to be
• 4:13
  Speaker 2: absolutely i'd like to change the negative tone a little bit.
• 4:17
  Speaker 2: It's not perfect, they're not perfect, but they're pretty amazing.
• 4:21
  Speaker 1: They are pretty amazing, and I think it's awesome what
• 4:24
  Speaker 1: humans have built. Every time I see a project like
• 4:26
  Speaker 1: that literally get off the ground, I think, Wow, look
• 4:30
  Speaker 1: what we can do, and I'm odd the same way
• 4:32
  Speaker 1: I feel like when I see the Golden Gate Bridge
• 4:34
  Speaker 1: or any huge engineering project, like something that's so far
• 4:38
  Speaker 1: beyond the scope of an individual person, yet we can
• 4:40
  Speaker 1: do it collectively. It gives me hope for the future.
• 4:43
  Speaker 2: Yeah, i'd say it gives me goosebumps. I get very
• 4:45
  Speaker 2: excited seeing big projects. But so okay, But chemical rockets
• 4:48
  Speaker 2: have their limitations. They take something like six to nine
• 4:51
  Speaker 2: months if you're going to Mars. If we want to
• 4:53
  Speaker 2: explore the rest of the universe, it would be nice
• 4:55
  Speaker 2: if we could go faster.
• 4:56
  Speaker 1: For example, it would be nice if we could go further,
• 4:59
  Speaker 1: for sure. Yes, So we asked the extraordinaries how far
• 5:03
  Speaker 1: we can go with just chemical rockets. Here's what folks
• 5:07
  Speaker 1: had to say. The Moon and Mars, and even Mars
• 5:11
  Speaker 1: will be a stretch. We're going to need some new
• 5:13
  Speaker 1: form of propulsion to get further. We would need a
• 5:18
  Speaker 1: tank the size of Jupiter to get anywhere. Well, you
• 5:22
  Speaker 1: can get pretty far if you have patients, not too far.
• 5:25
  Speaker 1: I think our space pubes to date have got most
• 5:29
  Speaker 1: of their speed from gravitational slingshots, not chemical rockets. You
• 5:34
  Speaker 1: can explore as far as you want, as long as
• 5:36
  Speaker 1: you can keep finding chemicals. I imagine we could probably
• 5:39
  Speaker 1: go pretty far with chemical rockets if we could make
• 5:42
  Speaker 1: them big enough to carry a lot of chemical fuel.
• 5:46
  Speaker 2: We need nuclear fuel to go anywhere far away like Mars.
• 5:50
  Speaker 2: With our current chemical rocket technology, we're not able to
• 5:54
  Speaker 2: get even close to the speed of light.
• 5:56
  Speaker 1: I can imagine it would be very far. It's difficult
• 5:59
  Speaker 1: to even explore Mars.
• 6:01
  Speaker 2: That's kind of a hard question because I actually don't
• 6:03
  Speaker 2: know what a chemical rocket is to.
• 6:05
  Speaker 1: The asteroid belt. I think we need to switch to
• 6:09
  Speaker 1: solar sales or perhaps some kind of experimental ion drive.
• 6:14
  Speaker 2: I think we have a pretty space savvy audience.
• 6:17
  Speaker 1: Yeah, yeah, I think so. They've all read your book,
• 6:20
  Speaker 1: they thought about space.
• 6:21
  Speaker 2: They've been listening to you for years talk about this
• 6:24
  Speaker 2: kind of stuff, and they're paying attention. They know what's up.
• 6:27
  Speaker 1: They didn't know until now, though, that you are anti rocket.
• 6:30
  Speaker 2: I di've clorified. I'm not anti rocket.
• 6:33
  Speaker 1: If you liked rockets, you would have written on one. Kelly, Look,
• 6:35
  Speaker 1: put your money where your mouth is.
• 6:36
  Speaker 2: Okay, have you written on a rocket? I've jumped out
• 6:38
  Speaker 2: of a plane.
• 6:39
  Speaker 1: But I'm not pro rocket.
• 6:42
  Speaker 2: I don't How many people have opportunities to ride rockets.
• 6:45
  Speaker 1: That's a good question, that's fair. Yeah, you're you're saying
• 6:48
  Speaker 1: you haven't said no to a rocket ride.
• 6:49
  Speaker 2: That's right, that's right.
• 6:50
  Speaker 1: But you would say no?
• 6:51
  Speaker 2: Yeah I would, Yeah, I would. But that doesn't mean
• 6:55
  Speaker 2: I'm not, you know, happy they exist.
• 6:57
  Speaker 1: Yes, me too. I'm happy people go and explore space,
• 6:59
  Speaker 1: even though I never want to do so myself.
• 7:01
  Speaker 2: Amen. All right, tell me about rockets, Daniel. How do
• 7:04
  Speaker 2: they work?
• 7:06
  Speaker 1: Right? So, rockets are a way to increase your momentum.
• 7:09
  Speaker 1: What you need is energy and mass and basically the
• 7:13
  Speaker 1: way a rocket works is it uses energy to push
• 7:16
  Speaker 1: mass out the back, and when you do so, you
• 7:19
  Speaker 1: send momentum in one direction, and because of conservation of momentum,
• 7:23
  Speaker 1: you go the other way. A basic example of a
• 7:26
  Speaker 1: rocket is sitting in a rowboat throwing rocks out the
• 7:29
  Speaker 1: back of the rowboat. You're using energy to throw those rocks.
• 7:33
  Speaker 1: The rocks have mass, and because they carry mass, they
• 7:36
  Speaker 1: carry momentum, and so the rocks go one way and
• 7:39
  Speaker 1: the boat goes the other way.
• 7:41
  Speaker 2: And the more mass, the more momentum. Right, so if
• 7:44
  Speaker 2: you throw a rock or a comparably sized chunk of styrofoam,
• 7:47
  Speaker 2: the rock would get you farther.
• 7:49
  Speaker 1: That's right. Momentum and non relativistically is mass times velocity,
• 7:54
  Speaker 1: and that's going to be absolutely crucial in today's conversation.
• 7:57
  Speaker 1: So equivalent momentum. By throwing a really mass thing very
• 8:00
  Speaker 1: slowly or by throwing a very low mass thing very
• 8:04
  Speaker 1: very fast, you get the same momentum. So those two options, okay,
• 8:08
  Speaker 1: So what you got to do is transfer momentum out
• 8:10
  Speaker 1: the back. Anything that does that basically is a rocket.
• 8:13
  Speaker 1: So you need energy and you need mass, and if
• 8:16
  Speaker 1: anybody out there happens to be a space is not
• 8:18
  Speaker 1: real denialist. Yes, rockets can work in space. You don't
• 8:23
  Speaker 1: need air for rockets, all right. The same principle throwing
• 8:27
  Speaker 1: mass out the back works just fine in an atmosphere
• 8:31
  Speaker 1: or not. In an atmosphere. These things are not climbing
• 8:34
  Speaker 1: up the atmosphere and they're not pushing against the air.
• 8:37
  Speaker 1: You're just throwing momentum at the back. So the rocket
• 8:40
  Speaker 1: moves forward to balance the momentum and to maintain conservation
• 8:44
  Speaker 1: of momentum.
• 8:45
  Speaker 2: So if you were on like an old fashioned paddle
• 8:48
  Speaker 2: boat sort of thing, and the energy is your legs
• 8:52
  Speaker 2: and you are spinning like a little paddle thing behind
• 8:56
  Speaker 2: and it's pushing water out the back, is that a rocket?
• 9:02
  Speaker 2: Why is it not a rocket?
• 9:04
  Speaker 1: I see you want to like re engineer the definition
• 9:07
  Speaker 1: of rockets so that you have been on a rocket.
• 9:09
  Speaker 2: So you have told me that the definition of rocket
• 9:12
  Speaker 2: is broader than what I thought it was, and so
• 9:14
  Speaker 2: now I'm trying to figure out what the bounds are.
• 9:17
  Speaker 1: So unfortunately, I don't think a paddle boat qualifies as
• 9:21
  Speaker 1: a rocket because a rocket needs to bring that mass
• 9:24
  Speaker 1: with it, right, And on the paddle boat you are
• 9:26
  Speaker 1: pushing against the water. You're not like carrying water that
• 9:30
  Speaker 1: you're then pushing out the back of the paddle boat. Right,
• 9:33
  Speaker 1: So a rocket carries with it mass and throws that
• 9:35
  Speaker 1: mass out the back. A paddle boat is not doing that.
• 9:38
  Speaker 1: It's pushing against the water. So, for example, a paddle
• 9:41
  Speaker 1: boat would not operate in a vacuum, right, whereas a
• 9:44
  Speaker 1: rocket can.
• 9:45
  Speaker 2: I feel like you're moving the target. You didn't mention
• 9:47
  Speaker 2: ahead of time that the mass has to go with you.
• 9:49
  Speaker 2: But all right.
• 9:50
  Speaker 1: We're clarifying here. That's why we're having a conversation. Okay,
• 9:55
  Speaker 1: And in the future, every conversation I have, I will
• 9:57
  Speaker 1: give complete exhaustive definitions of everything to future proof myself
• 10:01
  Speaker 1: against any questions.
• 10:02
  Speaker 2: This is our last episode, folks. No one's gonna want
• 10:05
  Speaker 2: to listen after this. All right, let's move forward. We're
• 10:08
  Speaker 2: carrying the mass.
• 10:09
  Speaker 1: With us, that's right. Okay, So you need energy and
• 10:12
  Speaker 1: you need mass, and you got to carry the mass
• 10:14
  Speaker 1: with you to throw it out the back. Cool. That's
• 10:16
  Speaker 1: the basic principles of rockets, and the rockets we're familiar
• 10:19
  Speaker 1: with them are mostly what we call chemical rockets, and
• 10:21
  Speaker 1: they solve this energy and mass problem by bringing fuel.
• 10:25
  Speaker 1: Fuel stores energy, it's chemical process releases it, and it
• 10:30
  Speaker 1: provides mass that you can expel out the back. So
• 10:33
  Speaker 1: it's like an all in one solution to the rocket problem.
• 10:35
  Speaker 1: It's very cool. Right, you burn the fuel and that
• 10:38
  Speaker 1: gives you energy and it produces stuff that you can
• 10:40
  Speaker 1: throw out the back. So that combustion reaction does everything
• 10:44
  Speaker 1: you need.
• 10:45
  Speaker 2: Okay. And the difference between fuel and propellant, because the
• 10:52
  Speaker 2: engineers when we first wrote soonish and we made the
• 10:55
  Speaker 2: mistake of saying fuel or whatever, we're very upset, and
• 10:59
  Speaker 2: so the difference twin fuel and propellant is that propellant
• 11:03
  Speaker 2: something gets thrown out the back. What is the difference.
• 11:06
  Speaker 1: Yeah, so propellant can be totally inert. It's just something
• 11:09
  Speaker 1: you throw out the back. So in the example of
• 11:11
  Speaker 1: the rowboat, you're throwing rocks at the back, right, that's
• 11:14
  Speaker 1: your propellant. You're using it to propel yourself. But you
• 11:17
  Speaker 1: wouldn't call rocks fuel. They don't storing the energy. Fuel
• 11:20
  Speaker 1: is something which stores energy and has propellant. Okay, So
• 11:25
  Speaker 1: it solves the whole rocket problem all in.
• 11:27
  Speaker 2: One, awesome. So one of the problems with this is
• 11:31
  Speaker 2: that the stuff that you create with that you throw
• 11:34
  Speaker 2: out the back is not necessarily great for the environment.
• 11:37
  Speaker 2: Have we found a propellant that is less bad for
• 11:41
  Speaker 2: the environment.
• 11:42
  Speaker 1: Well, the basic process here is a chemical reaction combustion
• 11:45
  Speaker 1: right where you're turning, for example, like methane plus oxygen
• 11:49
  Speaker 1: into CO two and water and energy. So the core
• 11:53
  Speaker 1: reaction is bad only in that it produces CO two right,
• 11:56
  Speaker 1: which is not good for the environment, but it can
• 11:59
  Speaker 1: be fairly clean otherwise. But some of the fuels do
• 12:02
  Speaker 1: produce other nasty stuff. There's a whole range of various
• 12:05
  Speaker 1: chemical processes used here, and ranges of kinds of fuel
• 12:09
  Speaker 1: that humans have used to make their glorious launches into space,
• 12:14
  Speaker 1: ranging from like solid fuels, so the Space Shuttle boosters
• 12:17
  Speaker 1: had aluminum powder and ammonium perchlorate in them, which you
• 12:21
  Speaker 1: can use as fuel, which is very cool. The SLS
• 12:24
  Speaker 1: core has liquid hydrogen and liquid oxygen, so very basic,
• 12:29
  Speaker 1: very simple stuff. But again this is fuel because it
• 12:33
  Speaker 1: can combust so it releases energy and it produces propellant
• 12:37
  Speaker 1: that you throw at the back. SpaceX Falcon rockets use
• 12:41
  Speaker 1: something called rp one or caralox, which is basically kerosene
• 12:46
  Speaker 1: plus liquid oxygen, so all the components you need for combustion.
• 12:50
  Speaker 1: And then there's methylox which is basically methane and liquid oxygen.
• 12:54
  Speaker 1: Methane is just H four, so that's pretty clean.
• 12:57
  Speaker 2: Yeah, okay, great.
• 12:59
  Speaker 1: So the good news about come rockets is they produce
• 13:01
  Speaker 1: high velocity and they use a lot of volume very
• 13:04
  Speaker 1: very quickly, so you can burn through a huge amount
• 13:07
  Speaker 1: of fuel very quickly and produce a huge thrust. So
• 13:10
  Speaker 1: you can get like exhaust velocity of like three kilometers
• 13:13
  Speaker 1: per second. Remember we were talking about throwing propellant out
• 13:17
  Speaker 1: the back, and what you need is high velocity at
• 13:20
  Speaker 1: high mass to get high momentum. And so this is
• 13:22
  Speaker 1: pretty high velocity three kilometers per second. But most importantly,
• 13:26
  Speaker 1: it is a large volume here. So for example, each
• 13:29
  Speaker 1: one of the Falcon nine's Merlin rocket engines burn two
• 13:33
  Speaker 1: hundred and fifty kilograms of fuel per second. Wow. Wow, exactly,
• 13:40
  Speaker 1: And so this provides a huge momentum change, right because
• 13:44
  Speaker 1: it's an enormous amount of mass moving with high velocity.
• 13:47
  Speaker 1: And so each engine has a gigawat of power and
• 13:51
  Speaker 1: the Falcon nine has nine of these things. Wow. So
• 13:54
  Speaker 1: the basic principle for chemical rockets is a short, hard
• 13:58
  Speaker 1: burn with a huge amount of thrust. Right, you're burning
• 14:02
  Speaker 1: a lot of fuel, You're getting a lot of velocity.
• 14:05
  Speaker 1: It's not just one push as an extended burn as
• 14:07
  Speaker 1: you're watching this thing lift off. But chemical rockets don't
• 14:10
  Speaker 1: tend to burn for very very long times for the
• 14:12
  Speaker 1: reason we'll talk about in a minute. It's mostly like
• 14:15
  Speaker 1: a big hard push at the beginning.
• 14:17
  Speaker 2: Well, all of that sounds amazing, So what's the problem, Daniel.
• 14:20
  Speaker 1: The problem is that consuming a lot of mass means
• 14:23
  Speaker 1: having a lot of mass, right, so you're burning all
• 14:26
  Speaker 1: of this fuel. You got to have a lot of fuel,
• 14:28
  Speaker 1: and the burning is not very efficient because I'm gonna
• 14:31
  Speaker 1: poop on chemistry. It's a chemical reaction, right.
• 14:34
  Speaker 2: And so oh, that wasn't the bad part.
• 14:38
  Speaker 1: Sorry, Well, the bad part is that you know, you're
• 14:40
  Speaker 1: changing the configurations of these atoms, so you're releasing some energy,
• 14:45
  Speaker 1: but the energy was stored in chemical bonds, and chemical
• 14:48
  Speaker 1: bonds can store energy, but it's like a tiny fraction
• 14:50
  Speaker 1: of all of the energy stored in that fuel. If you,
• 14:53
  Speaker 1: for example, combine that fuel with an antimatter equivalent of
• 14:56
  Speaker 1: that fuel, you could convert all of that matter into energy,
• 15:00
  Speaker 1: enormous amount of energy produced. But instead you're just like
• 15:03
  Speaker 1: moving the atoms around and clicking them into slightly lower
• 15:06
  Speaker 1: energy configurations. So for a lot of mass, you're getting
• 15:10
  Speaker 1: a fairly small amount of energy out. So there's a
• 15:13
  Speaker 1: small amount of energy carry for every pound of fuel
• 15:17
  Speaker 1: or every kilogram of fuel that you're bringing along.
• 15:19
  Speaker 2: So is your argument that the problem is that it's
• 15:21
  Speaker 2: chemistry not physics because you want things to be happening
• 15:24
  Speaker 2: on an antimatter physics.
• 15:26
  Speaker 1: Level, Well, physics can access the power of the atom,
• 15:30
  Speaker 1: right it can annihilate these things and convert all of
• 15:33
  Speaker 1: that store energy if you could do that. I'm not
• 15:35
  Speaker 1: saying that you know, I know how to design an
• 15:37
  Speaker 1: antimatter engine or anything, but that's one of the problems
• 15:41
  Speaker 1: with chemical rockets is that you're releasing a small amount
• 15:44
  Speaker 1: of energy per mass. So you need a lot of
• 15:47
  Speaker 1: mass right now. If you need a lot of mass,
• 15:49
  Speaker 1: you're going to need a bigger push to get you
• 15:51
  Speaker 1: up to some velocity. And to get that bigger push,
• 15:53
  Speaker 1: what do you need more mass? That mass means you
• 15:56
  Speaker 1: now need a bigger push and so very quickly to
• 15:59
  Speaker 1: get anywhere or to get a big thrust you need fuel,
• 16:02
  Speaker 1: and then you need fuel to carry that fuel, and
• 16:04
  Speaker 1: you need fuel to push that fuel, and you need
• 16:05
  Speaker 1: fuel to carry that fuel, and so eventually you're mostly fuel.
• 16:10
  Speaker 2: I think it's like a mortgage, But how about you
• 16:12
  Speaker 2: explain it, Daniel.
• 16:15
  Speaker 1: Well, in a mortgage, what you're doing is you're borrowing
• 16:17
  Speaker 1: money to buy your house, and then you're paying it back,
• 16:20
  Speaker 1: but the interest is compounded, right, and so for the
• 16:23
  Speaker 1: first long time, you're just basically paying off the interest
• 16:26
  Speaker 1: before you're ever paying off the principle, So you're not
• 16:29
  Speaker 1: actually making progress on your loan. And by the time
• 16:31
  Speaker 1: you pay off your house, you've ended up paying like
• 16:34
  Speaker 1: three or five times as much as you borrowed. Right,
• 16:37
  Speaker 1: you borrow a million dollars to my house, you end
• 16:39
  Speaker 1: up paying the bank five million dollars overall that time.
• 16:42
  Speaker 1: And so in the same way, when we launch a rocket,
• 16:44
  Speaker 1: most of the mass of that rocket is the fuel.
• 16:47
  Speaker 1: We're mostly launching fuel. Right. We have like a little
• 16:50
  Speaker 1: capsule on top where we get to put something we want,
• 16:52
  Speaker 1: but mostly we're launching fuel because we need to burn
• 16:55
  Speaker 1: that fuel when we're halfway up.
• 16:57
  Speaker 2: I think the payloads that get sent up on rocket,
• 16:59
  Speaker 2: it's like one percent or less. When you look at
• 17:01
  Speaker 2: a rocket is stuff that you're actually sending the space,
• 17:04
  Speaker 2: and the rest of that skyscraper shaped thing is just
• 17:08
  Speaker 2: fuel that's gonna get you there.
• 17:09
  Speaker 1: Yeah. So most of a Mars bound rocket's mass is propellant.
• 17:13
  Speaker 1: So it takes like, for example, one thousand tons of
• 17:16
  Speaker 1: metalocks fuel to get two Mars from Earth orbit. Wow.
• 17:20
  Speaker 1: So if you're already in Earth orbit, right, and we're gonna
• 17:23
  Speaker 1: talk about how together in a minute, then it takes
• 17:25
  Speaker 1: still one thousand tons and you're gonna burn that fuel
• 17:28
  Speaker 1: in space. It's gonna give you a big push, and
• 17:30
  Speaker 1: then you're mostly gonna coast the rest of the way
• 17:32
  Speaker 1: to Mars. That's the way a chemical rocket works. But
• 17:35
  Speaker 1: then if you want to get a thousand tons of
• 17:38
  Speaker 1: metalocks fuel into Earth orbit, you got to spend twenty
• 17:41
  Speaker 1: five thousand tons just to get that fuel up there.
• 17:44
  Speaker 2: Wow.
• 17:45
  Speaker 1: Right, So that's a factor of twenty five just to
• 17:48
  Speaker 1: get the fuel you need into orbit so you can
• 17:50
  Speaker 1: burn it to get to Mars, and a thousand tons
• 17:53
  Speaker 1: of metholocks is what it costs at the cheapest transfer moment. Right.
• 17:57
  Speaker 1: Remember Earth and Mars don't go around the Sun at
• 17:59
  Speaker 1: the same speed. So sometimes on the opposite side of
• 18:02
  Speaker 1: the Sun really hard to get to Mars. Sometimes they're
• 18:04
  Speaker 1: on the same side of the Sun, and once every
• 18:07
  Speaker 1: twenty six months they're at their closest approach and it's
• 18:10
  Speaker 1: the best time to go to Mars. So this is
• 18:13
  Speaker 1: the cheapest it could ever cost to go to Mars
• 18:16
  Speaker 1: using methalocks fuel.
• 18:18
  Speaker 2: And even then it's not You've gone through all of that,
• 18:20
  Speaker 2: you've paid all of that, you've burned all of that
• 18:22
  Speaker 2: into the atmosphere, and it still takes you six to
• 18:24
  Speaker 2: nine months to get there.
• 18:26
  Speaker 1: Yeah, well, we're not going to solve that problem with
• 18:29
  Speaker 1: ion thrusters today that we are going to make it
• 18:31
  Speaker 1: more flexible to get to Mars. Okay, but you know
• 18:34
  Speaker 1: that's how we can get to Mars, and that kind
• 18:36
  Speaker 1: of works. But say you wanted to go further, right,
• 18:39
  Speaker 1: you wanted to go to Jupiter. Now you need two
• 18:42
  Speaker 1: thousand tons of metalocks fuel, and then you've got to
• 18:44
  Speaker 1: get all that into orbit, So it becomes very expensive
• 18:48
  Speaker 1: very quickly. In the prospect of like going to Alpha
• 18:50
  Speaker 1: Centauri using chemical rockets, you know, you end up needing
• 18:54
  Speaker 1: fuel tanks. Like the size of the moon.
• 18:56
  Speaker 2: Holy cow. All right, but don't despair, because we are
• 18:58
  Speaker 2: going to take a break, and when we get Daniel
• 19:00
  Speaker 2: is going to tell us about other solutions that are
• 19:03
  Speaker 2: going to get us to Alpha Centauri.
• 19:05
  Speaker 1: That are still not paddle boats that are.
• 19:07
  Speaker 2: Still not which aren't rockets because you're not taking the
• 19:10
  Speaker 2: water with you.
• 19:32
  Speaker 1: Hey, Kelly, let's design a rocket powered version of a
• 19:34
  Speaker 1: paddle boat. What would that look like?
• 19:36
  Speaker 2: That would I would bring the water with me and
• 19:39
  Speaker 2: then I would throw it out the back.
• 19:41
  Speaker 1: Yeah. So if you had like a fire hose on
• 19:43
  Speaker 1: the back of your boat, and you had a huge
• 19:45
  Speaker 1: tank of water, and you had some way to have
• 19:48
  Speaker 1: energy so you could pump that water out the back
• 19:51
  Speaker 1: of your boat, then yes, that would be a rocket
• 19:53
  Speaker 1: powered boat. It wouldn't be paddled anymore unless Kelly is
• 19:56
  Speaker 1: a source of energy. There we go, we have a
• 19:58
  Speaker 1: huge tank of water, we have Kelly on on a
• 20:00
  Speaker 1: little exercycle, and she's pumping, pumping, pumping, pumping, pumping, pumping.
• 20:03
  Speaker 1: There you go, and it's pushing water out the back
• 20:06
  Speaker 1: out of the tank. That's a rocket powered paddle boat
• 20:09
  Speaker 1: that we could legitimately build. And then you could say, yes,
• 20:12
  Speaker 1: I've been on a rocket.
• 20:13
  Speaker 2: Okay, but this is like the least exciting rocket history
• 20:16
  Speaker 2: has ever created. Like boo boo to this rocket. Right.
• 20:22
  Speaker 1: Well, that's the principle though, behind the other technology we're
• 20:25
  Speaker 1: going to talk about today. Instead of chemical rockets, where
• 20:29
  Speaker 1: you have the fuel that gives you the energy, though
• 20:31
  Speaker 1: very inefficiently, and the propellant which requires huge, massive tanks
• 20:36
  Speaker 1: to go anywhere, we're going to talk about ion thrusters,
• 20:39
  Speaker 1: which separate this question of propellant, the mass you're throwing
• 20:42
  Speaker 1: out the back, and the energy source in the same
• 20:45
  Speaker 1: way that like Kelly pumping the water out the back
• 20:48
  Speaker 1: of the boat separates the energy source from the water.
• 20:50
  Speaker 1: You're not getting the energy from the water. The water's
• 20:53
  Speaker 1: totally inert, right, sure. So ion thruster is the approach
• 20:56
  Speaker 1: we're going to talk about today, and it solves the
• 20:58
  Speaker 1: energy and mass problems separately. First we're gonna talk about
• 21:01
  Speaker 1: the mass and then we'll talk about the energy. And
• 21:04
  Speaker 1: they're called ion thrusters because they use ions. An ion
• 21:08
  Speaker 1: is just an atom that's not neutral. So if you
• 21:10
  Speaker 1: take for example, xenon, it's got a bunch of electrons
• 21:13
  Speaker 1: in it which balance out the protons in the nucleus
• 21:15
  Speaker 1: and then you if you strip some of those electrons away,
• 21:18
  Speaker 1: then you have an ion. So now it has a
• 21:20
  Speaker 1: positive charge, and that's useful because you can then accelerate
• 21:25
  Speaker 1: it in electromagnetic fields. Right, So if you have a
• 21:28
  Speaker 1: bunch of xenon and you strip away some of the electrons,
• 21:31
  Speaker 1: now they have a charge in them. If you can
• 21:33
  Speaker 1: build an electromagnetic field, it will accelerate those ions. Shoot
• 21:38
  Speaker 1: those ions out the back of your ship, and it's
• 21:41
  Speaker 1: the ionic equivalent of Kelly's water rocket. Right, Just shoot
• 21:46
  Speaker 1: them at the back. They carry momentum with them because
• 21:49
  Speaker 1: you have high velocity. Now and that's a rocket.
• 21:52
  Speaker 2: Okay, that sounds cooler. You're bringing ionized gas. Does this
• 21:57
  Speaker 2: help you cut down on weight because gas weighs less
• 22:02
  Speaker 2: than propellant? Or not really because once you can press
• 22:04
  Speaker 2: the gas, it gets heavy.
• 22:06
  Speaker 1: What's the deal here, No, it really does help you
• 22:08
  Speaker 1: cut down on weight because you're can be more efficient
• 22:11
  Speaker 1: about the energy. One of the things about chemical rockets
• 22:14
  Speaker 1: is that they're trying to solve both problems at the
• 22:15
  Speaker 1: same time, energy and mass, and the energy extracted via
• 22:19
  Speaker 1: combustion is very inefficient. And so here if we can
• 22:22
  Speaker 1: let's ignore the energy question for now, and imagine we
• 22:25
  Speaker 1: have some energy source to fund our electromagnetic fields. Now,
• 22:29
  Speaker 1: if we have some energy source, we can very efficiently
• 22:31
  Speaker 1: use that to accelerate our ions to very very high speeds,
• 22:36
  Speaker 1: and so we can get much more push per unit
• 22:40
  Speaker 1: of propellant, right, because the mask can go to higher velocities.
• 22:44
  Speaker 1: So it sounded impressive earlier when we said like three
• 22:47
  Speaker 1: kilometers per second for the propellant from a chemical rocket.
• 22:50
  Speaker 1: That's cool, But ion thrusters can get much higher velocities,
• 22:54
  Speaker 1: and so for every pound of propellant that we bring along,
• 22:57
  Speaker 1: we can now get much more push. And this is
• 23:01
  Speaker 1: what rocket folks talk about as specific impulse. If you
• 23:04
  Speaker 1: start reading about rockets, get into all these weird terms,
• 23:06
  Speaker 1: but it's just a bunch of fancy terms to cloud
• 23:09
  Speaker 1: some basic physics, which is you want as much momentum
• 23:12
  Speaker 1: change per mass. So remember momentum is mass times velocity.
• 23:17
  Speaker 1: If you're bringing rocks or water or xenon or whatever
• 23:20
  Speaker 1: to throw at the back, you want as much velocity
• 23:24
  Speaker 1: in every kilogram we throw out the back, because momentum
• 23:26
  Speaker 1: is mass times velocity, and so for a fixed mass,
• 23:29
  Speaker 1: you want the most velocity to get the most momentum.
• 23:32
  Speaker 1: And so if you can get these things to higher speeds,
• 23:34
  Speaker 1: which ion thrusters can do better than chemical rockets can do,
• 23:38
  Speaker 1: then you can get more momentum per unit mass that
• 23:41
  Speaker 1: you're bringing.
• 23:42
  Speaker 2: My gut would not have guessed that pushing an eyeon
• 23:46
  Speaker 2: would get things out the back faster than exploding propellants.
• 23:50
  Speaker 1: Cool Well, physics is more powerful than chemistry, Kelly. And
• 23:54
  Speaker 1: we're using electromagnetic fields here, right, And so if you
• 23:58
  Speaker 1: have enough energy, and this whole thing hinges on having
• 24:00
  Speaker 1: enough energy, which we haven't talked about at all yet,
• 24:03
  Speaker 1: but if you have an energy source, right, then you
• 24:06
  Speaker 1: can accelerate these ions to very high speeds. Here on Earth,
• 24:09
  Speaker 1: we accelerate protons, which are just hydrogen ions, to nearly
• 24:12
  Speaker 1: the speed of light, right, enormous amounts of momentum in
• 24:15
  Speaker 1: the collisions at the Large Hadron Collider, for example. So
• 24:18
  Speaker 1: this all sounds great so far. We're talking about a
• 24:20
  Speaker 1: lot of momentum created for every ion, right. The issue
• 24:24
  Speaker 1: is that it's hard to scale up. So we have
• 24:26
  Speaker 1: a small amount of mass in general, which means a
• 24:29
  Speaker 1: small momentum change. So while for each ion we can
• 24:33
  Speaker 1: get each one to high velocity, which means that per
• 24:36
  Speaker 1: pound of xenon we're bringing, we're getting a lot more
• 24:39
  Speaker 1: momentum change than per pound of methyl locks or hydro
• 24:43
  Speaker 1: lockx or whatever fuel chemical rocket is burning. It's a
• 24:47
  Speaker 1: real challenge to get a lot of kilograms out the
• 24:50
  Speaker 1: back to get a huge thrust. And so instead of
• 24:54
  Speaker 1: like a big hot burn that gives you a lot
• 24:55
  Speaker 1: of thrust all at once, an ion rocket tends to
• 24:59
  Speaker 1: have a slow, gentle, long thrust. So, for example, it
• 25:03
  Speaker 1: might take like two days for an ion rocket to
• 25:05
  Speaker 1: get you up to even like highway speeds, whereas a
• 25:09
  Speaker 1: chemical rocket's going to be like kaboom, we're going pretty fast,
• 25:12
  Speaker 1: but then it's all spent.
• 25:13
  Speaker 2: Okay, So does that mean ion thrusters can't get you
• 25:16
  Speaker 2: out of Earth's gravity?
• 25:17
  Speaker 1: Well, that's exactly right. Ion thrusters as currently designed can't
• 25:21
  Speaker 1: get you off of Earth because they're very very gentle thrust.
• 25:25
  Speaker 1: But they can burn for a very very long time,
• 25:28
  Speaker 1: and they're very efficient, and they can travel with a
• 25:30
  Speaker 1: small amount of mass. The amount of mass you need
• 25:33
  Speaker 1: to get to Mars, for example, is like thousands of
• 25:36
  Speaker 1: kilograms of xenon, which compares to like a thousand tons
• 25:40
  Speaker 1: wow of chemical fuel. So it's a huge difference. Your
• 25:43
  Speaker 1: whole ship is much lighter, and then that's not as
• 25:46
  Speaker 1: hard to get into orbit. Right, even if it's a
• 25:48
  Speaker 1: factor twenty five to get something into orbit from Earth,
• 25:53
  Speaker 1: you need to use chemical fuel to do that. Now
• 25:55
  Speaker 1: it's a factor of twenty five times a thousand kilograms
• 25:58
  Speaker 1: instead of a thousand tons, So it takes much less
• 26:01
  Speaker 1: chemical fuel to get an ion rocket into space with
• 26:05
  Speaker 1: the fuel it needs to get to Mars. Then chemical
• 26:08
  Speaker 1: fuel to get a chemical rocket into space.
• 26:11
  Speaker 2: Okay, so but we'd still have to use a chemical
• 26:14
  Speaker 2: rocket to get the ion rocket to space, and then
• 26:16
  Speaker 2: you use the ion rocket to get to where you're going.
• 26:19
  Speaker 1: Yeah, exactly, unless you can build these things in space
• 26:22
  Speaker 1: with Jeff Bezos's future space based economy from asteroids or whatever. Right,
• 26:27
  Speaker 1: So this isn't a complete solution. It's not like, you know,
• 26:30
  Speaker 1: we're building warp drives or teleportition portals to get to
• 26:33
  Speaker 1: Alpha Centauri you know, in your living room or something.
• 26:36
  Speaker 1: But this will allow us to get further out into
• 26:39
  Speaker 1: the Solar System and even past the Solar System once
• 26:42
  Speaker 1: we can get out of Earth's orbit.
• 26:44
  Speaker 2: Well, so you mentioned it takes two days to reach
• 26:46
  Speaker 2: highway speed. Do you eventually reach high enough speeds that
• 26:49
  Speaker 2: a trip to Mars wouldn't take like five billion years?
• 26:53
  Speaker 1: Yes? Absolutely, And NASA is building exactly this kind of rocket.
• 26:56
  Speaker 1: We're able to use it to go to Mars in
• 26:58
  Speaker 1: twenty twenty eight. It's called s Are Freedom. And I'll
• 27:01
  Speaker 1: tell you all about that trajectory once we're done talking
• 27:04
  Speaker 1: about the energy source of these things, which is really.
• 27:06
  Speaker 2: Important, all right, where do we get the energy?
• 27:08
  Speaker 1: So there's a long history actually of ion thrusters, which
• 27:11
  Speaker 1: I think is interesting and it traces sort of the
• 27:13
  Speaker 1: different sources of energy. People start talking about these things
• 27:16
  Speaker 1: back in like nineteen eleven, and there's a few different
• 27:19
  Speaker 1: approaches for how to build it and then how to
• 27:21
  Speaker 1: power it. The approach is for how to build it
• 27:24
  Speaker 1: are things like a gridded ion thruster. Basically you just
• 27:27
  Speaker 1: have like an anode and a cathode. You know, you
• 27:29
  Speaker 1: have one thing with a positive charge, one thing with
• 27:31
  Speaker 1: a negative charge. You put your charged particles in it.
• 27:34
  Speaker 1: They get attracted to the opposite side. They going fast,
• 27:38
  Speaker 1: they sum out the side. So it's a grid because
• 27:40
  Speaker 1: they're holes in it for the particles to go through.
• 27:42
  Speaker 1: So imagine like two chaining fences, one is positive, one
• 27:45
  Speaker 1: is negative. You drop a positive particle into their acceleer
• 27:48
  Speaker 1: sorts a negative one and then shoots through the gaps
• 27:51
  Speaker 1: and out the back. That's the basic principle, okay.
• 27:54
  Speaker 2: But so to make the anode in the cathode, do
• 27:56
  Speaker 2: you just like stick magnets on there or do you
• 27:58
  Speaker 2: need like a battery to make that happen.
• 28:01
  Speaker 1: You need energy, Yeah, you need electricity. Magnets can't do
• 28:04
  Speaker 1: that for you.
• 28:04
  Speaker 2: Okay.
• 28:05
  Speaker 1: Also, that design isn't great because it corrodes. You're shooting
• 28:09
  Speaker 1: particles at the chaining fence, which tends to eventually destroy
• 28:12
  Speaker 1: the chaining fence or it gets jammed up or something.
• 28:15
  Speaker 1: So these days to have even fancier ones to something
• 28:17
  Speaker 1: called a Hall effect thruster, which doesn't have the actual cathode.
• 28:22
  Speaker 1: As a virtual cathode, you have a magnetic field there
• 28:25
  Speaker 1: which traps electrons, so they move in circles and they
• 28:29
  Speaker 1: ionize the gas which they collide into. So there's sort
• 28:31
  Speaker 1: of like an electric mixing spoon that breaks up the
• 28:34
  Speaker 1: gas into ions, and then you don't actually have a
• 28:38
  Speaker 1: cathode there. The electrons there act as the cathode and
• 28:41
  Speaker 1: so there's nothing to get corroded or broken down. So
• 28:45
  Speaker 1: that's the technology. But in every case, the limit is
• 28:47
  Speaker 1: the energy source. If you want to crank up ion
• 28:50
  Speaker 1: thrusters to give you a real amount of thrust, then
• 28:53
  Speaker 1: you need a lot of energy. And so the first
• 28:55
  Speaker 1: example of an ion thruster I want to talk about
• 28:57
  Speaker 1: is called the sert Ones. This is back in ninth
• 29:00
  Speaker 1: teen sixty four. This was a test by NASA and
• 29:03
  Speaker 1: it was basically like, hey, does this work at all?
• 29:06
  Speaker 1: And it was up in space for thirty minutes and
• 29:09
  Speaker 1: it worked, and it was powered by chemical batteries, so
• 29:12
  Speaker 1: these were like zinc silver oxide batteries, and it wasn't
• 29:16
  Speaker 1: a whole lot of energy. It was like one point
• 29:18
  Speaker 1: seven kilowatts of energy, but you know, it didn't go
• 29:22
  Speaker 1: for very long, so they didn't even like try solar panels,
• 29:25
  Speaker 1: though a later version of it, SIR two, did have
• 29:27
  Speaker 1: solar panels. But this was like, hey, all the equations match,
• 29:31
  Speaker 1: does it actually work in practice? And it did, so
• 29:34
  Speaker 1: that's cool.
• 29:35
  Speaker 2: Very cool. Well i've never heard of it, which is
• 29:37
  Speaker 2: a bummer.
• 29:38
  Speaker 1: Oh yeah, it's pretty cute. It's just like a little ball,
• 29:42
  Speaker 1: and then people said, all right, well, let's try to
• 29:44
  Speaker 1: go for longer periods, and let's avoid using batteries and
• 29:48
  Speaker 1: let's use solar power. And this is really exciting because
• 29:51
  Speaker 1: now you're not carrying the energy with you at all.
• 29:54
  Speaker 2: And it's not a rocket.
• 29:56
  Speaker 1: No, it's a rocket if you're carrying the propellant, so
• 29:58
  Speaker 1: you still have to carry the mass you're throwing at
• 30:00
  Speaker 1: the back, but it's not a requirement that you bring
• 30:02
  Speaker 1: the energy with you, right, So if you can just
• 30:06
  Speaker 1: beam the energy to the rocket and you can use that,
• 30:10
  Speaker 1: then that's awesome. So they tried this. The first one
• 30:13
  Speaker 1: is called en Star, which has two point three kilowatts
• 30:17
  Speaker 1: of solar power. So these solar arrays generate the electrical
• 30:21
  Speaker 1: power which then you use to build electric fields to
• 30:24
  Speaker 1: shoot ionized xenon out the back at really high speeds.
• 30:28
  Speaker 2: Wow.
• 30:28
  Speaker 1: And this thing ran for sixteen thousand hours and used
• 30:32
  Speaker 1: only eighty kilograms of xenon propellant to get pretty good
• 30:37
  Speaker 1: delta ve it's like four point three kilometers per second.
• 30:40
  Speaker 1: So it was a good demonstration of these things running
• 30:43
  Speaker 1: for a long time, which is what we need to, like,
• 30:45
  Speaker 1: you know, get to alvia Centauri or get even to
• 30:48
  Speaker 1: the edges of the Solar System. The next step up
• 30:51
  Speaker 1: is the Dart mission. I don't know if people remember this.
• 30:54
  Speaker 1: This is the one that went and visited an asteroid,
• 30:56
  Speaker 1: and I think it dropped like a washing machine sized
• 30:59
  Speaker 1: block of metal on the asteroid, just like see, like
• 31:02
  Speaker 1: what happens. Yeah, Well, and.
• 31:05
  Speaker 2: It wasn't it also to see I mean, it was
• 31:06
  Speaker 2: to see what happens, but it was to see what
• 31:08
  Speaker 2: happens in the hopes that if there's ever an asteroid
• 31:10
  Speaker 2: coming towards us, we would have some information about how
• 31:13
  Speaker 2: hard you'd have to like hit it to try to
• 31:14
  Speaker 2: deflect it from the Earth or something. Right, it was
• 31:16
  Speaker 2: more than just see what happens.
• 31:19
  Speaker 1: Oh no, you're right. I'm actually thinking of the Hyabusa
• 31:22
  Speaker 1: mission that dropped a huge metallic paylude as an impactor
• 31:26
  Speaker 1: onto the asteroid. You go, But Dart is different, You're right.
• 31:30
  Speaker 1: Dart was there to like, let practice deflecting an asteroid,
• 31:34
  Speaker 1: so it does something else. So Dart's main propulsion was
• 31:37
  Speaker 1: a chemical rocket, but it also had an ion thruster
• 31:39
  Speaker 1: for testing, which is very cool.
• 31:41
  Speaker 2: Well, and didn't Hyabusa bring back a sample from the asteroid,
• 31:45
  Speaker 2: didn't it like it made an explosion to collect something.
• 31:48
  Speaker 2: I feel like you're being uncharacteristically negative, and I'm being
• 31:51
  Speaker 2: uncharacteristically positive this time.
• 31:53
  Speaker 1: No, No, that's totally positive. I love the idea of
• 31:56
  Speaker 1: dropping a washing machine sized piece of metal on an
• 31:59
  Speaker 1: asteroid just to see what happens. Like, that's fantastic. I'm
• 32:02
  Speaker 1: super curious, Like I love when that mission went up.
• 32:05
  Speaker 1: Total supporter. My tax dollars should definitely be spent on
• 32:08
  Speaker 1: missions like that.
• 32:09
  Speaker 2: Okay, yes, might as well. Okay, so we have gotten
• 32:12
  Speaker 2: to the asteroids with ion thrusters.
• 32:15
  Speaker 1: Yeah, exactly, And so this one also used sunlight electricity
• 32:18
  Speaker 1: from solar panels was used to accelerate zine on atoms.
• 32:21
  Speaker 1: The ion engine was not the primary propulsion system for
• 32:24
  Speaker 1: the impact. It was mainly a flight demonstration of this
• 32:27
  Speaker 1: next technology for future deep space missions. And ion thrusters
• 32:32
  Speaker 1: are all over the place, Like China's space station has
• 32:34
  Speaker 1: ion thrusters which it uses to adjust and maintain orbit.
• 32:39
  Speaker 1: Starlink uses ion thrusters that have Krypton or orgon in them.
• 32:42
  Speaker 1: They're good for like very gentle little pushes to like
• 32:46
  Speaker 1: maintain where you are, not like a quick like ooh,
• 32:48
  Speaker 1: I'm going to hit something. I really got to get
• 32:50
  Speaker 1: out of here. You know. Also stuff out in space
• 32:53
  Speaker 1: tries to avoid using thrusters whenever possible because it uses
• 32:56
  Speaker 1: up propellant. You know, for example, like Hubble or the
• 32:59
  Speaker 1: space telescopes, they try to do all of their adjustments
• 33:02
  Speaker 1: using reaction wheels. Like you want to turn the thing,
• 33:05
  Speaker 1: you have internal reaction wheels that store angular momentum, so
• 33:08
  Speaker 1: you can turn without any thrusters. We can talk about
• 33:11
  Speaker 1: that on another episode. Because every time you're using a thruster,
• 33:14
  Speaker 1: it's a rocket. You have propellent, you're using it up
• 33:17
  Speaker 1: and so eventually it will run out. But the real
• 33:20
  Speaker 1: question is like what is the best way to get energy.
• 33:23
  Speaker 1: We've talked about chemical batteries. That was always just going
• 33:26
  Speaker 1: to be a test. Solar power is cool, right because
• 33:29
  Speaker 1: it's up, it's free, it's out there. You don't even
• 33:32
  Speaker 1: need to bring the energy with you. That's very cool.
• 33:34
  Speaker 1: The problem is with solar power is that it drops
• 33:37
  Speaker 1: off really hard with distance. The intensity of sunlight goes
• 33:40
  Speaker 1: like one over the distance squared, So if you're twice
• 33:44
  Speaker 1: as far from the sun, you get one fourth the energy,
• 33:47
  Speaker 1: and space is big, and so by the time you're
• 33:49
  Speaker 1: like out by Jupiter, there's almost no usable solar power,
• 33:54
  Speaker 1: especially to power a rocket. So we need something else.
• 33:57
  Speaker 1: We need a low mass source of energy.
• 34:01
  Speaker 2: Physics is what we need. And when we get back,
• 34:03
  Speaker 2: we're going to hear about how physics is going to
• 34:06
  Speaker 2: get us out to Jupiter. Yeah, all right, Daniel, how
• 34:29
  Speaker 2: is physics going to get us to Jupiter?
• 34:32
  Speaker 1: Yeah, physics is absolutely the solution here. And so of
• 34:36
  Speaker 1: course the better way to make energy is not by
• 34:39
  Speaker 1: burning coal or burning methane, or even by solar power,
• 34:43
  Speaker 1: because that's not available out in the outer reaches of
• 34:45
  Speaker 1: the Solar system. It's nuclear power. Right, We already know
• 34:49
  Speaker 1: that the amount of energy stored in like a kilogram
• 34:51
  Speaker 1: of uranium is huge compared to what you could get
• 34:55
  Speaker 1: from a kilogram of methane. Right, Random Monroe has this
• 34:59
  Speaker 1: amazing He's in comic where he shows like the energy
• 35:01
  Speaker 1: density of like uranium versus coal, versus wood or whatever,
• 35:05
  Speaker 1: and it's just off the charts, you know, It's like
• 35:08
  Speaker 1: even on a log scale, it's just insane. And so
• 35:12
  Speaker 1: if you want a bunch of energy and you don't
• 35:13
  Speaker 1: want to carry a bunch of mass, around. This is
• 35:16
  Speaker 1: the way to go. Have a fission reactor. So bring
• 35:19
  Speaker 1: a small amount of uranium, use that to power your
• 35:23
  Speaker 1: nuclear reactor. Your nuclear reactor produces electricity. You feed that
• 35:27
  Speaker 1: into your ion thruster, and now you have propellent, which
• 35:30
  Speaker 1: is very effective because you're pushing it up to very
• 35:32
  Speaker 1: high velocities, and you have fuel uranium, which is very
• 35:36
  Speaker 1: low mass. You're gettin a lot of energy out of
• 35:38
  Speaker 1: it per kilogram.
• 35:40
  Speaker 2: I'm gonna look past the fact that you mentioned the
• 35:42
  Speaker 2: competition on this show. You know, I'm just kidding. We
• 35:46
  Speaker 2: love XKCD.
• 35:47
  Speaker 1: It's not a competition. It's good for everybody. And anyway,
• 35:51
  Speaker 1: nobody's in competition with Randall because he wins.
• 35:54
  Speaker 2: He does win, he does, and he's and he's a
• 35:57
  Speaker 2: lovely human being.
• 35:58
  Speaker 1: Also, yeah, he really is genuinely in that.
• 36:00
  Speaker 2: Yeah. Okay, all right, so we've decided that nuclear powered
• 36:04
  Speaker 2: ion thrusters are the way to go. Have we had
• 36:07
  Speaker 2: any nuclear powered ion thrusters in space? I know we've
• 36:10
  Speaker 2: had little nuclear reactors in space to power satellites.
• 36:15
  Speaker 1: So it depends on what you mean by we. The
• 36:17
  Speaker 1: United States hasn't.
• 36:18
  Speaker 2: By we, I mean humanity.
• 36:21
  Speaker 1: Well, then the Soviets have done that. The Soviets in
• 36:24
  Speaker 1: nineteen eighty seven had a nuclear powered plasma thruster in orbit,
• 36:29
  Speaker 1: so this has definitely happened. It's worked before, and the
• 36:32
  Speaker 1: US says, I'm sure, you know has operated nuclear fission
• 36:35
  Speaker 1: reactors in space. So all the pieces are there. We
• 36:38
  Speaker 1: know ion thrusters work in space when they have an
• 36:40
  Speaker 1: electrical energy source. We've powered nuclear fission reactors in space,
• 36:45
  Speaker 1: and the Soviets even put them together in eighty seven
• 36:48
  Speaker 1: to use nuclear powered ion thrusters.
• 36:51
  Speaker 2: Wow. Yeah, and all the pieces are still there because
• 36:53
  Speaker 2: I think our attempt is still in orbit somewhere because
• 36:57
  Speaker 2: it didn't quite go according to plan exactly.
• 36:59
  Speaker 1: And so Naslam was already building fission reactors to operate
• 37:04
  Speaker 1: in space. It's part of the Lunar Gateway space station,
• 37:07
  Speaker 1: which was then canceled. But they had a power and
• 37:10
  Speaker 1: propulsion element being built by Lentis Space Systems, and they
• 37:14
  Speaker 1: were already building those, and so we're going to take
• 37:16
  Speaker 1: those and put them at the end of a very
• 37:19
  Speaker 1: very long trust to keep the radiation away from like
• 37:22
  Speaker 1: the electronics of the rest of the ship. And that's
• 37:25
  Speaker 1: going to provide power for the new SR one freedom,
• 37:28
  Speaker 1: which is going to power a mission to Mars in
• 37:31
  Speaker 1: twenty twenty eight, nuclear powered ion thrusters to Mars.
• 37:36
  Speaker 2: WHOA, okay, right, I feel like you're still going to
• 37:38
  Speaker 2: need the chemical rocket to leave Earth, but now you're
• 37:42
  Speaker 2: carrying with you a nuclear reactor. Yes, what is our
• 37:46
  Speaker 2: plan for making sure that everything stays safe?
• 37:51
  Speaker 1: Cross our fingers? Rely on engineers. There's not a great plan,
• 37:56
  Speaker 1: Like this is an issue. It's always going to be
• 37:58
  Speaker 1: an issue. Things go boom when you launch them, and
• 38:02
  Speaker 1: so if you're launching radioactive fuel into space, it's always
• 38:05
  Speaker 1: a danger.
• 38:06
  Speaker 2: There's not some way that you can like keep it
• 38:08
  Speaker 2: clad in something that's less likely to go boom and
• 38:10
  Speaker 2: then open it up and let the reactions start happening
• 38:13
  Speaker 2: once you're in space and away from Earth. There's no way.
• 38:17
  Speaker 2: I feel like there's got to be ways to make
• 38:18
  Speaker 2: this less scary.
• 38:22
  Speaker 1: So there are smart folks working on this, and of
• 38:24
  Speaker 1: course they're taking whatever precaution they can. One thing you
• 38:26
  Speaker 1: can do is don't turn on the reactor until you
• 38:30
  Speaker 1: get to space, for example, So there's still a risk
• 38:33
  Speaker 1: because you have uranium fuel in there, which is radioactive,
• 38:36
  Speaker 1: but you don't have like dangerous nuclear byproducts being produced
• 38:40
  Speaker 1: or already present on the rocket, so that if it
• 38:42
  Speaker 1: does go boom, you're spreading some uranium fuel, which is
• 38:46
  Speaker 1: not good, right, but it's not as bad as spreading
• 38:49
  Speaker 1: like really toxic radioactive nuclear byproducts.
• 38:52
  Speaker 2: Okay.
• 38:53
  Speaker 1: In addition, like you know, they're putting this thing inside
• 38:56
  Speaker 1: highly durable, heat resistant containment materials designed survive extreme launch
• 39:01
  Speaker 1: vehicle explosions, and it's supposed to be like subcritical no
• 39:05
  Speaker 1: matter what, even if the launch fails. So they're doing
• 39:08
  Speaker 1: what they can. And I have not dug into the
• 39:09
  Speaker 1: details here, but I trust the engineers are doing their
• 39:12
  Speaker 1: best to solve this problem. And I totally acknowledge that
• 39:14
  Speaker 1: it's very dangerous to be launching nasty, toxic stuff into
• 39:18
  Speaker 1: space because it might not get there.
• 39:19
  Speaker 2: All right, thank you for giving me my daily dose
• 39:21
  Speaker 2: of Kelly being able to like worry and be a
• 39:23
  Speaker 2: wet blanket. And all right, what do we need to
• 39:26
  Speaker 2: think about next?
• 39:27
  Speaker 1: So, the way this thing works is it's a fission reactor,
• 39:30
  Speaker 1: which means you're taking uranium and you're splitting it, and
• 39:34
  Speaker 1: that causes a chain reaction because it produces neutrons, and
• 39:37
  Speaker 1: those neutrons split other uranium atoms, and along the way
• 39:40
  Speaker 1: it produces heat, and then how do you turn that
• 39:42
  Speaker 1: heat into electricity? While on Earth we often do something
• 39:45
  Speaker 1: like boil water, right and use the steam to spin
• 39:48
  Speaker 1: a turbine, and so up in space we're doing something
• 39:51
  Speaker 1: only a little bit more sophisticated. Instead of water, we're
• 39:55
  Speaker 1: using a helium neon mixture, which still spins a turbine
• 39:59
  Speaker 1: and creates electricity. So the basic process is the same,
• 40:03
  Speaker 1: and then we can use that electricity to accelerate the ions.
• 40:07
  Speaker 1: The cool thing is the fuel is very very low mass.
• 40:11
  Speaker 1: Remember the propellant it's like thousands of kilograms of xenon,
• 40:13
  Speaker 1: which is still really low mass compared to the thousands
• 40:16
  Speaker 1: of tons you need for chemical rockets. But the uranium
• 40:20
  Speaker 1: fuel to give you the energy to push that out
• 40:22
  Speaker 1: the back is just like ten kilograms. It's like a
• 40:25
  Speaker 1: rounding error. That's how powerful uranium is. It's really amazing.
• 40:30
  Speaker 1: So it's almost as free as sunlight. But you can
• 40:34
  Speaker 1: keep using it when you get past Jupiter.
• 40:36
  Speaker 2: Why haven't we done this already? Then? This seems pretty
• 40:40
  Speaker 2: obviously better, is it? Because of concerns about like where
• 40:43
  Speaker 2: you're going to get the uranium. Yeah, why haven't we
• 40:45
  Speaker 2: done this already?
• 40:46
  Speaker 1: Well, you know, the Soviets have been doing it since
• 40:49
  Speaker 1: the eighties. But chemical rockets are easier, right, there's no
• 40:52
  Speaker 1: nuclear power issues and they can get off of Earth.
• 40:55
  Speaker 1: So this is really only useful for exploring in places
• 40:58
  Speaker 1: where you're not fighting a big gravity Well, okay, got it.
• 41:02
  Speaker 1: And it gives a pretty different signature for your mission.
• 41:05
  Speaker 1: Like for a chemical rocket, you want to get to Mars,
• 41:08
  Speaker 1: you burn for like ten minutes, and then you travel
• 41:10
  Speaker 1: to Mars for six to nine months, and you're going
• 41:13
  Speaker 1: to like peak velocity almost all the time, like thirty
• 41:16
  Speaker 1: three kilometers per second. An ion rocket is going to
• 41:19
  Speaker 1: give you like a year of continuous burn, and it's
• 41:22
  Speaker 1: going to start very very slow. It's going to eventually
• 41:24
  Speaker 1: get up to the same peak velocity thirty thirty five
• 41:27
  Speaker 1: kilometers per second. But it's not in freefall, right, It's
• 41:30
  Speaker 1: a continuous thrust and it can be adjusted in flight,
• 41:34
  Speaker 1: and so it's a very different kind of trajectory and
• 41:37
  Speaker 1: that makes it less sensitive to the timing. So you
• 41:41
  Speaker 1: can't get to Mars when it's on the other side
• 41:43
  Speaker 1: of the Sun. But because you're not just in freefall,
• 41:46
  Speaker 1: you can do all sorts of different kinds of trajectories,
• 41:49
  Speaker 1: so you don't have as narrow a window, so it
• 41:52
  Speaker 1: takes a little longer to get there, like a year
• 41:54
  Speaker 1: instead of six to nine months, but you have more
• 41:57
  Speaker 1: flexibility about when you go.
• 41:59
  Speaker 2: I don't think I understand the you're not in freefall thing.
• 42:03
  Speaker 2: Why would a chemical rocket versus an ion thing? If
• 42:07
  Speaker 2: you had enough chemicals for your chemical rocket, couldn't you
• 42:11
  Speaker 2: have the same flexibility.
• 42:13
  Speaker 1: In principle if you brought enough fuel along that you're
• 42:16
  Speaker 1: burning it during the flight, then yes, you could do
• 42:19
  Speaker 1: the same thing with the chemical rocket, but then you
• 42:21
  Speaker 1: need even more fuel. Member. Chemical rockets are very very inefficient, Okay,
• 42:25
  Speaker 1: that's why they like to burn it all the very
• 42:26
  Speaker 1: very beginning. And it's basically it's almost like a cannonball launch. Right.
• 42:30
  Speaker 1: A cannon ball, you give it one push and then
• 42:32
  Speaker 1: it just flies. Okay, chemical rocket, it's like ten minutes
• 42:35
  Speaker 1: of pushing and then it's just a free fall trajectory.
• 42:39
  Speaker 1: And so you're very limited in how you go from
• 42:40
  Speaker 1: one place to the other if you can't burn along
• 42:42
  Speaker 1: the way. So the ion thruster can do that, it
• 42:45
  Speaker 1: takes longer to get up to high speed, so the
• 42:47
  Speaker 1: whole trip is going to be a year. The plus
• 42:49
  Speaker 1: side is you have a little bit more flexibility, so
• 42:51
  Speaker 1: your window is a bit broader. It's still not like
• 42:54
  Speaker 1: we can go to Mars any time, and you can't
• 42:56
  Speaker 1: get to Mars faster, but there's a little bit more
• 42:59
  Speaker 1: flexibility there.
• 43:00
  Speaker 2: Okay, I mean that that's pretty cool because needing to
• 43:02
  Speaker 2: wait two years, yeah for every launch window, Like yeah,
• 43:07
  Speaker 2: I mean you missed that. Now you're waiting two years.
• 43:09
  Speaker 2: Like that's that's a real pain in the rear ends
• 43:11
  Speaker 2: is how do we how much do ion frusters open
• 43:13
  Speaker 2: this window?
• 43:14
  Speaker 1: So chemical rockets have like a few weeks of a
• 43:17
  Speaker 1: window when they can effectively get to Mars, and ion
• 43:19
  Speaker 1: thrusters have like a few months. Nice, so it's a
• 43:22
  Speaker 1: meaningful change. It's again, it's not like totally solving the problem.
• 43:25
  Speaker 1: It's not like you can go to Mars on a whim,
• 43:28
  Speaker 1: but there is flexibility there.
• 43:29
  Speaker 2: Well, but you could imagine a few weeks of bad
• 43:32
  Speaker 2: weather totally messing up your Mars plans if that bad
• 43:36
  Speaker 2: weather happens during your window, but like probably not gonna
• 43:38
  Speaker 2: have a couple months of bad weather, So like that
• 43:41
  Speaker 2: makes your probability of getting to Mars. I don't know,
• 43:43
  Speaker 2: I think much.
• 43:44
  Speaker 1: Higher, Yeah, exactly, looknd maybe.
• 43:46
  Speaker 2: In a ray of sunshine.
• 43:50
  Speaker 1: And so for example, if your launch is like delayed
• 43:52
  Speaker 1: by ninety days, the spacecraft just like adjusts the thrust
• 43:55
  Speaker 1: profile burns more propellant to catch up to Mars rather
• 43:58
  Speaker 1: than having to scrub the entirely. And adding a little
• 44:01
  Speaker 1: bit more propellant is not disastrous because the propellant is
• 44:05
  Speaker 1: fairly low mass here. We're talking about like a few
• 44:07
  Speaker 1: more kilograms of xenon right, and the energy is very,
• 44:11
  Speaker 1: very dense, So we don't have this rocket equation trap
• 44:14
  Speaker 1: where we fall into where every time we bring a
• 44:16
  Speaker 1: pound more fuel, now we need thousands more pounds of
• 44:19
  Speaker 1: fuel to push that fuel, and we still got to
• 44:21
  Speaker 1: launch this thing up into space. But remember the fact
• 44:23
  Speaker 1: that it's lower mass means it's cheaper to launch it
• 44:26
  Speaker 1: into orbit in the beginning. And we're going to do
• 44:29
  Speaker 1: this in like twenty twenty eight. It's just around the corner.
• 44:32
  Speaker 1: SR one Freedom is going to go to Mars. It's
• 44:34
  Speaker 1: going to drop three helicopters that land themselves on Mars,
• 44:39
  Speaker 1: which is amazing given Mars has a very dilute atmosphere
• 44:43
  Speaker 1: and helicopters have a real challenge to navigate there. And
• 44:46
  Speaker 1: then it's going to keep going. It's just going to
• 44:49
  Speaker 1: keep going and explore. I love that when we just
• 44:51
  Speaker 1: like send something out into space and because it has
• 44:54
  Speaker 1: an ion thruster, it can go for a while.
• 44:57
  Speaker 2: Where's it going next?
• 44:58
  Speaker 1: So the final target is specified, but the idea is
• 45:02
  Speaker 1: explore the outer Solar System, including high powered missions beyond Jupiter.
• 45:06
  Speaker 2: Wow.
• 45:06
  Speaker 1: So they're still figuring it out, but we have flexibility
• 45:10
  Speaker 1: because we're not just limited to narrow launch windows. I
• 45:13
  Speaker 1: also want to give a shout out to the listener
• 45:16
  Speaker 1: who commented on gravitational slingshots, which are another way that
• 45:20
  Speaker 1: NASA has historically used to explore the Outer Solar System
• 45:23
  Speaker 1: without bringing a lot of propellant. You know, how do
• 45:26
  Speaker 1: you change your direction without any fuel? Gravitational slingshots are
• 45:30
  Speaker 1: super duper cool, but they also take forever. You need
• 45:33
  Speaker 1: like everything to be in the oriented and exactly the
• 45:35
  Speaker 1: right place. So sometimes you do like two or three
• 45:38
  Speaker 1: swings around things. It could take like ten years to
• 45:41
  Speaker 1: like gravitationally slingshot your way from one place to another.
• 45:44
  Speaker 1: So ion thrusters are much more direct way to get there.
• 45:48
  Speaker 2: I think Kim Stanley Robinson used gravity slingshots as a
• 45:52
  Speaker 2: really great plot point in Aurora, Like they were running
• 45:54
  Speaker 2: out of fuel, so everybody had to go into like
• 45:56
  Speaker 2: hibernation and they use gravity slingshots to get you there.
• 45:59
  Speaker 2: Like it takes a long time. Yeah, but if you
• 46:02
  Speaker 2: don't have fuel and you can use that that, if
• 46:04
  Speaker 2: you've got the time, it's a good way to go.
• 46:06
  Speaker 1: Yeah. It's also cool because it's physics again, right, which
• 46:09
  Speaker 1: inherently makes it awesome.
• 46:11
  Speaker 2: Yeah, better than chemistry. Notice, good biology, but it's a hierarchy,
• 46:14
  Speaker 2: it's okay.
• 46:16
  Speaker 1: And their other side benefits, like if we can get
• 46:18
  Speaker 1: reactors to work in space, maybe that's going to help
• 46:20
  Speaker 1: us figure out how to get reactors to work in
• 46:23
  Speaker 1: crazy environments like on the Moon, and people who are
• 46:25
  Speaker 1: talking about building moon bases are talking about powering those
• 46:28
  Speaker 1: things with nuclear reactors. Getting to Mars, it's going to
• 46:31
  Speaker 1: help us open up more launch windows. It's a good
• 46:34
  Speaker 1: way to send cargo to Mars, and it opens up
• 46:37
  Speaker 1: the outer Solar system. Remember, solar power is just not
• 46:40
  Speaker 1: useful past Jupiter, which gets like four percent of the
• 46:44
  Speaker 1: Earth's sunlight. So if we're going to explore the outer
• 46:48
  Speaker 1: reaches of the Solar System. It's not going to be
• 46:50
  Speaker 1: with chemical rockets. It's going to be with ion thrusters.
• 46:53
  Speaker 2: So if we want it to get like straight to
• 46:55
  Speaker 2: Jupiter really fast, we'd want ion thrusters powered with nuclear
• 47:00
  Speaker 2: reactors rather than gravity sling shots. Yeah, absolutely, okay cool?
• 47:04
  Speaker 2: And what a voyager you use? Voyager is a gravity
• 47:06
  Speaker 2: slingshot situation?
• 47:08
  Speaker 1: Right, yes, exactly?
• 47:09
  Speaker 2: Okay, Well, this is amazing. I can't wait to see
• 47:11
  Speaker 2: how those helicopters fare in the Martian atmosphere like the
• 47:15
  Speaker 2: helicopter that came before.
• 47:17
  Speaker 1: I can't wait to see if Kelly ever achieved her
• 47:18
  Speaker 1: lifelong dream of sitting on a rocket.
• 47:21
  Speaker 2: Yeah. Well, I hope you're sitting right behind me, Daniel,
• 47:25
  Speaker 2: and I hope it's a safe rocket like our paddle
• 47:27
  Speaker 2: boat rocket and not a chemical rocket.
• 47:30
  Speaker 1: Well, I look forward to sitting on that rocket with you, Kelly.
• 47:33
  Speaker 1: Until then, thank you everybody for taking this journey with
• 47:36
  Speaker 1: us through the history of rocket development and into the
• 47:39
  Speaker 1: future for how humans could explore the Solar System.
• 47:42
  Speaker 2: Yay space exploration. Until next time.
• 47:51
  Speaker 1: Thanks everybody for listening. Please go and do us a favor.
• 47:54
  Speaker 1: And rate the show on whatever podcast app you're using.
• 47:57
  Speaker 1: It really helps people find us.
• 48:00
  Speaker 2: Daniel and Kelly's Extraordinary Universe is edited by the amazing
• 48:03
  Speaker 2: Matt Kesselman.
• 48:04
  Speaker 1: He really is a wizard. You can also find us
• 48:08
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• 48:13
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• 48:14
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• 48:18
  Speaker 2: We really do want to hear from you, and you.
• 48:20
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• 48:24
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• 48:27
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• 48:31
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• 48:35
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