Short Wave - What Science Fiction Gets Wrong About Space Travel

Episode Date: July 14, 2021

Contrary to sci-fi depictions in shows like Iron Man and Star Wars, getting from point A to point B in space is a tough engineering problem. NPR Science Correspondent Geoff Brumfiel explains how space propulsion actually works, and why some new technologies might be needed to get humans to Mars and beyond.Follow Geoff Brumfiel and Short Wave co-host Emily Kwong on Twitter. Email the show at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Well, well, well, NPR science correspondent Jeff Brumfield. Guess you decided to poke your little head up again for another shortwave episode. Emily, it's been too long. And today, I'm pleased to tell you I've got something fun to talk about, kind of some summer fun. Oh, thank goodness. Okay, let's go. So to get things going, just start by telling me your favorite sci-fi shows or movies.

Well, you know my family loves Star Trek, diehard Trekkies. I like The Avengers, Black Panther, Captain Marvel, all those movies are really good. All fantastic choices. I'm a Trek guy myself. But I will say one thing. These shows and movies, they've all skipped over the big problem with space travel. And that is actually getting around. Oh, like flying from one place to another. Yeah, and I'm not really talking about like Trek tech, like a warp drive that lets you

jump huge distances across the galaxy. We all know that's the full realm of sci-fi. I'm talking about the basic business of getting from point A to point B in space. It is a really tough engineering problem, Emily. Jeff, you said this would be fun. You're taking space flying and turning it into an engineering problem. Are you going to ruin my favorite shows? No, I'm going to enrich your understanding of your favorite shows, Emily, by bringing some facts into the conversation. And I'm also going to tell you about some exciting new technologies that may actually allow future space travelers to get a little further out into the Great Unknown. So in a way, I'm making it more real. Uh-huh, uh-huh. So today on the show, we're talking rocket science, how space propulsion actually

works. And why some new technologies might be needed to get humans to go to Mars and be out. You're listening to Shortwave, the Daily Science podcast from NPR. So Jeff, you are on the show today to talk about how rockets get people around space in sci-fi versus how they work in real life. Where do you want to start? Well, let's start by talking about the basics. And to do that, I want to bring in an actual rocket scientist. Her name is Naya Butler Craig. And I'm an aerospace engineering PhD student at Georgia Tech and also a pretty massive fan of the Marvel film franchise.

I love the technology that they employ, specifically Iron Man. and I'm really excited for Rui Williams to get her story out. That's like my hero. Yeah, definitely excited for Iron Heart. An Iron Man, I mean, that's classic. Tony Stark flying around in his suit. Right, and Naya loved it. But as a young budding space propulsion engineer,

she was a little perplexed by those engines on Iron Man's hands and feet. I always kind of thought about, you know, for such a small area, how he was generating so much thrust. I would always think that way, and it's only gotten worse. I can't watch a movie without analyzing it technically. Even though Iron Man doesn't always go into space, I think he's a great place to start, because his suit really illustrates the fundamental problem with all the sort of rocketry we're going to be looking at, and that is generating thrust.

And thrust, that's like the force that pushes a spaceship or Iron Man around. Right. Thrust is one of those words that sounds really cool and maybe a little, fancy, but it's actually super duper simple. Basically, if you want to go one direction, you have to throw something in the opposite direction of where you want to go. Jeff, isn't this one of Newton's laws? Like, for every action, there is an equal and opposite reaction? That's absolutely right. It's actually Newton's third law. And at some level, all rockets work this way. All engines are doing something with mass and basically throwing it in a certain direction to create thrust. In this mass, the stuff is called fuel or propellant in the rocket world.

And that's really all there is to it. A rocket pushes mass out one way to make a mass go the other way. In this case, Iron Man goes in the opposite direction from wherever he points his thrusters. Okay. So Iron Man's suit in real life would actually need a giant fuel tank to get around. That's right. That's right. You need something to push out.

And that's why jet packs haven't ever gotten off the ground because it takes a lot of fuel to make it fly for any length of time, like way more than a person could safely carry on their back. And this problem, Emily, is the bane of rocket designers all over the world. If you want to go anywhere in space, you need a lot of fuel to generate that thrust to move your spaceship. It's a nuisance. I think if a space designer or a spacecraft designer could have it their way, you know, we would, we would, we would, would make fuel out of nothing and just have our thruster. Because when you have fuel, you have a fuel tank. And the more space that propellant or fuel tank takes up, the less space for your actual science instruments or your spacecraft volume.

This is what Tony Stark gets to do. He gets to have all the thrust with none of that overhead of fuel. And the fuel actually creates this bigger problem because the bigger and heavier a rocket is, the more fuel it needs to move. But the fuel makes it bigger still, so it keeps growing. So you're saying spaceships in these shows would technically be giant gas tanks with a teeny tiny little space for the crew. Right. And in fact, that's exactly what we see with real world rockets, right? Like the chemical rockets we use to get off Earth deliver a lot of thrusts. They're great at doing it.

But basically, they're these giant cylindrical gas cans with teeny tiny capsules way up at the top. So is there a way to make it a little more like the movies, even though Hollywood clearly has, unrealistic proportions everywhere. Yeah. I mean, there is actually, and that's part of what Naya is working on. So it turns out thrust is one way to measure how powerful a rocket is, but there's another important thing to consider, and that's how efficient a rocket is at creating thrust.

And that efficiency is known as something called specific impulse. Okay, so if thrust is like the time it takes to go from zero to 60, specific impulse sounds more like the gas mileage, like the measure of efficiency for that engine. Perfect. You're absolutely got it. And NIA is working on engines that provide fantastic mileage. So these kinds of thrusters take a gas, usually xenon or argon. They charge individual atoms in the gas, and then they use an electric field to push the atoms out of the back of the spaceship.

And so these electric fields are set at a certain strength in order to throw them at a certain speed. and that is how we create that thrust. By pushing individual atoms like these, these engines can be many, many, many times more efficient than the chemical rockets we use to get off Earth. And the other cool thing is, Emily, that these engines, they look totally sci-fi. They have this sort of eerie blue or purple glow to them,

and so you'll often see them in sci-fi movies. Star Wars specifically, because they actually have Thai fighters, which were the twin ion engines, that's pretty much exactly, you know, what an ion engine looks like. I love Thai fighters. Are you saying the tie in Thai fighters stood for twin ion engine? Yeah, yeah. I mean, that's what these engines in real life are called.

They're called ion engines. But again, sci-fi has kind of taken some liberties here because real-world ion engines are super-duper efficient, but they're also super-duper slow because it turns out pushing out individual atoms of a gas. just doesn't give you that much thrust. In Star Wars, they go from like zero to 100 really, really fast, whereas in real life you would go to zero to 100 after maybe like a few days. Can you imagine a Star Wars battle with realistic ion engines? But back in the real world, I mean, the cool thing is that these ion engines are actually used today,

and they're used for deep space exploration missions to places like, like asteroids. Okay, Jeff, so we've learned that regular old rockets are fast, but they use too much fuel. Iron thrusters are efficient, but too slow. Is there a Goldilocks technology that might actually be both fast and efficient? Yeah, that brings us to the final stop in our little journey of rocket technologies today, and that one is nuclear-powered rockets. Oh, is the nuclear with you, isn't it, Jeff? Well, you know what? It's pretty cool, it delivers a lot of energy, and I'm not the only one who thinks so. The National Academy of Sciences did a report earlier this year in which they said future Mars missions should seriously

consider using nuclear rocketry. All right. So how would this all work? Well, basically, here's the simplest version of how it works. You take a light element like hydrogen and you pass it through the core of a nuclear reactor. The reactor will make the hydrogen super hot and then push it out a nozzle, and that creates thrust. Now, this is more efficient than a chemical rocket, so you don't need as much propellant, as much hydrogen to push. And it's more powerful than an ion engine, so you can actually get around reasonably fast. Vichal Patel is an engineer at a company designing nuclear rockets, and they have a name, which is a good name for a company designing nuclear rockets, ultra-safe nuclear. He says that these. These are the same. He says that these,

These rockets are really the way to go. You could take more stuff with you. You can get to where you're going faster, which is always good for like the human psyche and just in general reliability of things. Okay, but still, launching a nuclear rocket into space sounds kind of dangerous to me. I don't know. That's just a lot of chemicals being flung up into space. Yeah, I mean, you know, you can brand it ultra safe, but it does have some risks.

That's true. I will say it's not quite as dangerous as it sounds, though. I mean, it would be sent into orbit using a regular chemical rocket, so they wouldn't turn the nuclear rocket on until they probably left Earth orbit, actually. And as long as the reactor isn't activated, it's not that radioactive. Since we're launching what we call a cold nuclear reactor that hasn't really ever been turned on, it has practically no radiation coming out of it. It certainly has a little bit, but it's such that you could stand in

to it without really being worried. In fact, NASA launches other kinds of nuclear power into space pretty regularly. The two rovers on Mars are run using a kind of nuclear battery. Now, these aren't rocket engines, but NASA has tested nuclear rocket engines in the 1960s. They actually built several full-scale engines that worked. Oh, so this nuclear rocket idea has been kicking around for a while. Oh, yeah, yeah. I mean, they took it pretty seriously back in the 60s.

And now that the idea of going to Mars seems maybe a little nearer, the National Academy says that nuclear propulsion could really make the difference. I mean, it could cut the duration of a mission to Mars from as much as 900 days to as little as 400. Well, this is all good to know. I mean, Jeff, you said you wouldn't ruin sci-fi, but I feel like maybe you did, just a little. And you need to sit with that now. Look, look, look. Vishal and I have both enjoyed their sci-fi. But they do it with an appreciation of how hard the real problems actually are.

And now you can too. Well, I did learn something about real space travel. And for the most part, I appreciate you for it, Jeff from field. Thanks for coming on the show. Thanks, Emily. I hope we can talk again and see you. This episode was produced by Britt Hansen and fact-checked by Indy Kara. The audio engineer for this episode was Gilly Moon.

Dizel Grayson was the editor. I'm Emily Kwong. Thanks for listening to Shortwave from NPR. Thank you.