NASA's Electric Thruster That Could Take Us to Mars

In this episode, we explore NASA’s successful test of a powerful new lithium-fed electric thruster that could one day power human missions to Mars. Learn how electric propulsion differs from traditional chemical rockets and why this breakthrough could make deep space travel faster, more efficient, and capable of carrying the massive payloads needed for astronauts. 

Farbod: Friends, welcome back to the Next Byte podcast. In the last week, SpaceX did IPO, but that's not even the coolest thing that's happened in space news in the past week because NASA just cracked a code on electric propulsion, which means that we're gonna be able to get to space faster, cheaper, and more practically than ever before. And yes, we can finally get to Mars. So if you've been waiting on buying your tickets, now's the time. Let's get into it.

All right, friends, as you heard, today we're talking about propulsion. But before we get into today's propulsion topic, my god, tongue twisters already. It's gonna be a long one, we're gonna be talking about VTOLs. And this is actually a technical resource from today's sponsor, Mouser Electronics. So if you've been rocking with us for a while, you know we love Mauser. They kind of have the same mentality as us, that there's a lot of interesting things going on in the world. Especially given that they're at this intersection with like academia and industry, being one of the world's biggest electronic suppliers, they take whatever they're seeing, whatever they're learning, and deliver it to audiences like you. So one of those is about vertical takeoff and landing vehicles, VTOLs, right? And if you ever played Call of Duty in the two thousands like Daniel and I did, the Osprey was one of the more common military aircrafts that did the vertical takeoff and landing, and it was super cool. But as we think about the world today, VTOLs are becoming more and more common. How so? Drones, right? Like drone delivery is the big thing. Amazon wants to do it, Walmart wants to do it. And for the drones to be able to take off vertically instead of needing a runway, that's that's absolutely huge. However, there's this big elephant in the room being how do we like actually feel these things, right? The combustion engines that are used for the military aircraft obviously don't really make sense here.

The world has changed, regulations have changed. We probably don't want more gas coming out of drones that are gonna be flying everywhere, dropping off packages. So electric power makes sense. Cool. What are we gonna do? Are we gonna use batteries? Well, technically we are today, right? But that has its own drawbacks, like the fact that after 20 to 30 minutes of operation, it kind of needs to spend the rest of the time on the ground being charged up again. So this article is all about what does this landscape look like? What alternatives are there? And this is gonna be a hot one already. It suggests that hydrogen fuel could be a great alternative because it has great power density, meaning that from the amount, you know, size, weight, whatever you put in, you can get a lot of power out of it.  Sorry, that's energy density. And then you have power density, which means that you can charge and discharge very quickly. The reason I'm saying it's a hot topic is because I think Elon Musk famously said hydrogen is for stupid people, something something along those lines. Am I paraphrasing here? It's like it's never gonna take off. But they're talking about how a hydrogen fuel cell approach will have less moving parts, it's quick for refills, and it has the energy density and the power density that we're looking for. So they're painting this future, this picture of what the future can actually look like. If you're interested about propulsion technology, aerospace, hydrogen fuel cells, and controversy, then you should definitely check out the article. It's gonna be in our show notes.

Daniel: And if you want the verbatim Elon Musk quote, it's Tesla CEO Elon Musk calls hydrogen the most dumb thing I could possibly imagine for energy storage. So take that with a grain of salt and then go read this article and let us know what you think.

Farbod: All right. Today's article. NASA, specifically NASA JPL, NASA Glen, and Princeton University. And I feel like we haven't talked about NASA in a while. And it's easy to forget about NASA given that there's so many interesting companies. I mean, SpaceX just went public. Blue Origin and SpaceX have been doing incredible work, and there's all these other rocket startups that are happening, which have kind of, I think, stolen the spotlight for young engineers.

Are we young anymore? I don't know.  But all that to say, we haven't talked about NASA for a while. Regardless of us talking about them, they've been doing cool stuff in the background all this time. One of the big ones that they've been focusing on is electric propulsion. Before we get into that, I think it's worth giving some context about what chemical propulsion is, what electric propulsion is, and what does the landscape look like today? Is that fair?

Daniel: Pretty much all of propulsion is, goes back to like Newton's laws of physics, right? To propel a mass forward and this mass forward being a spacecraft. If I'm sending something forward, I need to send an equal amount of energy backward to be able to force that thing to go forward. So all the basic principles of chemical rocket, electric propulsion, this new MPD thruster, all of those are, let me throw as much mass out the back as fast as I can to force my spacecraft to go forward. And they all have different methods of what the masses that's being thrown out of the back, what the propellant is, the thing that's speeding up that mass to throw it out the back, and then a different speed at which those things are exhausted out of the back. All of that adds up to how much energy can you emit out of the back of your spacecraft to force the rest of the spacecraft to fly forward. And the best example I can think of when it comes to propulsion is like, if you imagine you're sitting on a big giant sheet of ice and you're on skates and I've got a bunch of rocks in my pocket, I can throw a really hard, I can throw a boulder, I can push it really hard away from me and it will send the boulder flying backwards, but it will also send me flying forward. And that's the best example I can think of of like how this analogy works.

All of these propulsion systems, chemical, electric, MPD, they're all different versions of that. Can I throw mass out the back to force my spacecraft to go forward? The only difference is where's that energy coming from and how fast and how much mass can you throw out the back? That changes how fast you can go forward.

Farbod: Yep. And like traditionally, I think even to this day, the most common approach is the chemical format, right? I think it was the Saturn V rockets that use two tons of fuel, maybe solid state, maybe liquid, I don't remember, but I think the Raptor engines for SpaceX use liquid fuel, right? They're also b burning something to go up into space. The issue with that has always been that it's it's fine for getting out of Earth's orbit, but it's actually a lot of mass. Like that fuel is again two tons that you're sitting on to take with you. So, you know, if we're leaving Earth to just go do a quick tour around the moon and come back, it's like whatever. But if you have longer space missions, that starts to become a massive constraint of how far you can go, right? Just the principle of taking weight with you. So electric propulsion was kind of promising and the i idea started floating in the nineteen sixties. So it's not even that new, like this has been over sixty years in development. That, like you're saying, can we spit stuff out using electricity instead of requiring that chemical reaction? The answer has been yes, but it's just generally low amounts of thrust generated. Funny enough, the best stab at this that NASA or any lab I think in the world has been able to accomplish was NASA's Psyche mission. This was a drone that they sent out,  I think to Saturn? We we d we actually talked about it in episode fourteen, which is crazy.

Farbod: Yeah, it was going to an asteroid Psyche 16. Yes, you're right. You're right. It was going to an asteroid. And even though the thrust is very small, over the course of however long it's been in flight, it ramped up to a hundred and twenty-five thousand miles per hour or kilometers an hour. So it's pretty impressive. Like the the acceleration is slow, but it can still reach the velocity that it needs to. Now, again, NASA has not stopped working on this. They've been tackling it in the background and they even say it in this article, you know, Mars has been in the back of their mind. And what they're talking about in this article is how they've been able to achieve a thruster that's 25 times the power of the one that went to Psyche 16. So the principle is still the same, you have a hot gas and basically an electromagnet that is pushing it out of the thruster. What is changing here is that this time around they're using vaporized lithium metal lithium vapor. There we go. Yeah, metalized lithium lithium vapor. Is that it? Yeah, that's it. So that burns hot enough, which allows them to I think five thousand degrees Celsius was the number they used to generate higher and higher levels of thrust that they've been able to before. The number they were able to achieve was an operation at 120 kilowatts, but they want to ramp it up to five hundred to five five hundred kilowatts to one megawatt is the goal that they're going for. And a spaceship that is actually able to make it to Mars would need two to four megawatts. So like they're slowly, slowly stabbing at the problem. And I think episode 14 was what four years ago at this point that we recorded? Twenty-five to

Daniel:  No, I think this is exciting. One thing that I still like, I think I want to recap because it took me when we researching for this a couple of times to wrap my head around.  Just the walk from chemical to electric to MPD thruster. Chemical is pretty simple. It's like the most, I don't know, like the most stereotypical, yeah.

You've got a bunch of fuel and you actually need an oxidizer there as well to help you burn the fuel. You basically create in a controlled explosion and the controlled explosion, the hot gas expanding from that explosion is the mass that's being ejected backwards to exit the nozzle and that creates thrust. That's great. But like you're saying, it typically requires up to 100 % of the weight of the spacecraft in fuel just to get out of the Earth's atmosphere and into space. If you want to then continue to use that for thrust in space, you need to carry a proportionally increased amount of fuel to be able to lift it off. You end up when you're trying to go to Mars, as an example, you end up in a situation where there literally is not enough fuel or there's not a strong enough booster to be able to carry all that fuel with us into space and drive us to Mars. The complete other end of the spectrum are these electric thrusters like the ones in that Psyche spacecraft. They use solar panels that generates electricity, they magnetically repel ions out of the back. That's great. Really, really mass efficient. Awesome continuous thrust can run for years and years and years with only a small amount of mass. The problem is the amount of thrust coming out of the back of that is about this comparable to the weight of a few sheets of paper. So it's like, great, the Psyche 16 spacecraft has sped up to this incredible speed due to this continuous thrust. But when it first started, it was probably crawling very, very, very slow. And that's because the thrust that's coming out of this very, very efficient electric thruster is very, very small. And so this NPD thruster is kind of like a best of both worlds scenario where you're not just emitting ions using electricity. You're actually heating them up with this massive electric current and the lithium, the metalized lithium actually becomes plasma.

And then there's a magnetic field that accelerates that plasma and ejects it. It's much higher thrust because it enables them to accelerate a small amount of propellant very, very fast. So it's much faster than the propellant coming out of the back of the electric thrusters. That's where they're getting the extra force from. That's where they're getting the extra thrust. That's why engineers get excited about there being a lot more potential speed to these spacecraft. And this potentially being somewhere that's a happy medium between: let me blow up a bunch of rocket fuel or let me slowly emit ions like a drip out of the back of my spacecraft. This is like, can I control blow up using electricity, a medium amount of fuel and use it as a way of getting me a lot further, a lot faster in space.

Farbod: And then instead of having, you know, solid state fuel or liquid fuel. And you know, you were talking about the example of going to Mars, that's not even considering coming back, right? So so you need to like, double the math there anyway. You can now have a nuclear reactor and like you said, a small mass of whatever your propellant is. In this case, it was solid lithium metal that's being vaporized and used as the propellant, to then take you there and bring you back. And it's totally feasible. And it's kind of not to get too nerdy, but Project Hail Mary, they were talking about the astrophage. It's kinda like making me think about the astrophage.

Daniel: Well, no, I was going to say astrophage thruster would be like the actual solution to this. It doesn't exist in real life, but the astrophage, like they had, I think the thrusters on the back of the spacecraft wielded as much energy as like a small star. So, so we're not there yet, but the principle is actually very similar in Project Hail Mary, right? Can I use an energy source to accelerate mass and eject it out of the back of my spacecraft? And just so happened that the energy source they had in the fictional project, Homer, is like the highest energy density of any material they had ever discovered ever. Yeah.

Farbod: Material known to man. Yeah. but yeah, I I think we actually kind of touched on the so what in our discussion of like what they were doing, but technologies like this make it a lot more feasible for us to think about you know, the the the human missions to Mars that have been in conversation since I was in high school, which apparently was a long time ago because I'm not a young man anymore. Okay. But it's demonstrating that like, you're saying, we don't we might not have to think about solid state chemical reactions as like one end of the spectrum and these like super low powered electric propulsion on the other side, but that there is actually a happy medium where we can have the best of both worlds as Hannah Montana one side. So pretty exciting if you're into aerospace or propulsion technology or you know, living on Mars, you've been waiting for that. Seems to be just around the corner.

Farbod: You good for me to wrap it up? Alright. Folks, for decades we've been relying on these chemical rockets because they're really powerful, but they're also really fuel hungry. Up to two tons of fuel for the Saturn V. These electric propulsion technologies have been able to provide us some goodies when it comes to propulsion, but the trade off is actually different for them. They give you very little thrust, but they have very little mass. So do we really want that for long term? Probably not. Well, here comes NASA saving the day. They just took this massive leap towards an electric propulsion technology that can absolutely change that. They've increased the amount of propulsion generated by 25 times the next best option that they came out with four years ago. And these thrusters are only the starting point. It looks like in the next couple of years, they want to eight times the output of that, and they do have a clear roadmap to doing so. What they've been able to accomplish here has been great thanks to this liquid, sorry, solid lithium metal as the propellant, and still using the same technology that turns this lithium into plasma and ejects it out with electromagnetic technology. So, all that to say, this sustainable way to go into space and come back, like a Mars mission, is becoming more and more possible. And space technology and space travel in general will become faster and cheaper and a lot more practical with technologies like this.

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