2026 NASA's Innovative Advanced Concepts Symposium: Part 1 — Nuclear sensors and cave explorers

Sarah Al-Ahmed: We're going to the 2026 NIAC Symposium this week on Planetary Radio.

I'm Sarah Al-Ahmed of The Planetary Society with more of the human adventure across our solar system and beyond. This week, I'm sharing the first of two episodes from the 2026 NASA Innovative Advanced Concepts Symposium, which was held in Wichita, Kansas. Some of the most exciting science in our solar system is hidden in places that we've never been able to reach. This episode is about the researchers developing bold early stage concepts that could one day take us there with nuclear-powered sensors designed to survive the darkest, coldest places on the moon, silent flying robots for exploring karst on Titan, and a laser-powered drone tethered by fiber optic cable that could be the first mission to enter a lava tube on the moon.

Next week in part two, we'll tackle the propulsion and life support technologies that could get us to the outer solar system and beyond. Plus, our chief scientist, Bruce Betts, will join me to look forward to October 4th when Saturn is going to be at opposition. It's also the first day of World Space Week, so we have a lot to celebrate.

If you love Planetary Radio and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you'll never miss an episode filled with new and awe-inspiring ways to know the cosmos and our place within it.

The NASA Innovative Advanced Concepts Program funds researchers to study ideas that could one day change what's possible in aerospace. These aren't incremental improvements. These are the far-out, early stage concepts that could fundamentally reshape how we explore space. Things that mostly sound like science fiction today but could become science fact in the decades to come.

NIAC Awards come in three phases. Phase one is a nine-month study to explore overall viability. Phase two develops that concept further over two years, and phase three is designed to strategically transition the most promising ideas toward NASA missions, other government agencies, and commercial partners. Every year, NIAC holds a symposium where the fellows present their work, and I've had the privilege of hosting that webcast and interviewing fellows at the symposium for the past four years. This year's event was held at Wichita State University in Wichita, Kansas, and I spoke with some truly remarkable people.

First up is a team that I spoke with last year at the symposium whose project has made it into phase two. Dr. Peter Cabauy is the CEO and co-founder of City Labs, Incorporated, and Dr. Mason Peck is a former NASA chief technologist and collaborator on the project. Their phase two concept called autonomous tritium micropowered sensors would scatter tiny nuclear-powered probes across the lunar surface. It would help us explore the places on the moon where solar power can't reach.

It's wonderful to see you guys again this year.

Mason Peck: It's great to see you too.

Peter Cabauy: It's great to have a phase two. We're excited.

Sarah Al-Ahmed: It is wonderful to get to see you guys as you've advanced over the last years. For people who are not familiar with your project, Peter, can you tell us a little bit about what this project is?

Peter Cabauy: It's about putting nuclear micropower on the surface of the moon and to be able to explore lunar permanent shadowed craters and just be able to take sensing in a way that's not done with rovers, be able to spread many sensors across the lunar surface, and be able to get that data reliably.

Sarah Al-Ahmed: And just because I forgot to do this, this is Peter Cabauy. He is the CEO and co-founder of City Labs, Incorporated. And Mason Peck, who is a collaborator on the project, also former chief NASA technologist. So, they have a lot to say about this project.

So, you're going to try to put these sensors on the moon. But in the last year, there's been a lot of advancement in the things that you guys have been doing, including the launch of BOHR, which is the first commercial nuclear satellite.

Can you tell us a little bit about what's happened in the last year?

Mason Peck: Sure. I will say that the BOHR launch has been super exciting. That represents, as you said, the first commercial nuclear spacecraft. And by commercial, we mean with a license that could allow these very small nuclear power sources to be available very democratically and to inform how we do space science. But, the nuclear part of it really is City Labs and Peter's domain.

Sarah Al-Ahmed: How has this informed what you're doing with this NIAC project?

Peter Cabauy: It informs it a lot. I mean, if you're looking at the demonstration of putting commercial nuclear power in space, it's the fundamental basis for what we want to do under this NIAC work. We need to be able to get it on the moon and be able to spread many of these sensors powered by nuclear micropower.

Sarah Al-Ahmed: So, one of the things that came out of your phase one investigation is that this tritium metal hydride that you're using in order to actually power this thing can not only do that, but potentially keep these sensors warm in really extreme environments.

How does that dual functionality change the way you think about building these sensors?

Mason Peck: It's really key. So, in a place like a permanently shadowed region on the moon, or maybe in the shadow of an asteroid or some other place, a lava tube, let's say, whether it's on the moon or Mars, there is no other source of energy. So, you're not going to use solar power. You could use a battery but only temporarily. These provide power for decades, and that means persistent, continuous measurements. And we can think very differently about how a mission is architected around this kind of power system rather than thinking about we have a brief amount of time we've got to run in to get those measurements and hurry up before the batteries die. Now, you sort of take your time, and you can much more slowly meet energy or kind of spread energy into these devices, and they're small devices, so not much power, and extract data slowly.

So, power and energy, two different things. Power is energy over some time. If you have low power, which is true for these nanotritium power sources, you have to spend it slowly. And then you build up the energy, take the measurements, and send them back to Earth or to an orbiter. So, it's a very different kind of architecture from typical mission as well as the other architectural differences of having hundreds, thousands, maybe more of these individual sensors. And again, that's what's enabled by the very small-scale power is distributing that power over the lunar surface rather than all in one place in one rover. And a rover is a great solution for a lot of things, but this actually fills a niche where you can't use a rover. You can't really use remote sensing. It's in situ, in-place, sensing but with the spread and the duration that you associate with remote sensing.

Sarah Al-Ahmed: But, how do you actually spread these across the lunar surface?

Peter Cabauy: That's a Mason question.

Mason Peck: Well, the best version of this we've come up with is the extreme version where you launch these things from an orbiter toward the lunar surface. Something orbiting the moon is traveling very fast, about 1,700 meters per second. Superfast. So, when these things land, it's destructive. It's violent. It's terrible. But remember we're landing lots of them. So, the goal of the design for this phase is, can we come up with the statistics of survival and design a mission around statistical survival rates? Even if it's, let's say, 1%, you want 10 sensors at a 1% survival rate? Launch 1,000. And since they only weigh a few grams each, that's not such a big ask.

So, the idea is they get flung off the orbiter, spinning kind of like, I don't know, throwing a Frisbee but sideways. They land on edge. You can't see it on this example, but there's sort of a titanium ring around it or maybe tungsten carbide ring that ablates or grinds away, and that process moves a lot of the energy out of the actual electronics to the point where now it's traveling relatively slowly, and it will probably survive a certain path through the sandy regolith of the lunar surface.

So, there's a lot going on there, a lot of complicated simulations that help us understand whether or not it'll even work, but what we're leaning on, once again, is statistical survivability, not a guarantee of survivable of any one object. And that's a real different philosophy, a different kind of paradigm.

Sarah Al-Ahmed: That is really interesting because you're not banking on them necessarily surviving. But beyond simulations, how can you try to actually test how survivable these things are? I don't know if you'd like to answer that one, Peter.

Peter Cabauy: I could, but I like the mode where we actually can go ... Instead of deploying from orbit, as the lander is coming, we can deploy it, let's say, at one kilometer and increase the chances of survival. So, with all these CLPS missions that have been assigned, there's [inaudible 00:08:42] 20 CLPS missions, we could potentially ... Right as the lander is coming, it can drop, and it's much more gentle. And we could have more of them survive. So, we are working towards not just having this be an exercise of a NIAC project but to actually get this on the lunar surface as soon as possible. So, working together with Mason, we are already looking, talking to companies that want to do this.

Sarah Al-Ahmed: And of course the CLPS program is the commercial lunar services program from NASA. They coordinate with commercial entities in order to actually land on the moon, and we have actually seen successful commercial landings on the moon in the last year. So, there are a lot of other missions to look forward to.

Are you guys talking with any of the other CLPS missions in order to see whether or not you can get this technology on the lunar surface?

Peter Cabauy: Actively speaking to all the CLPS companies.

Sarah Al-Ahmed: Awesome. All of them.

Peter Cabauy: All of them. All of them. They all need nuclear micropower without ... I mean, we are working on another device. We just launched the nuclear betavoltaic power sources, and they're working just fine, but next year we plan to launch a heat source. It'll look like a postage stamp, and these can provide 30 watts per kilogram of heat. It's important, not just for NIAC, the work that we're doing, but we need heat. It's very, very important. Without heat, you're not going to get through the lunar night.

Sarah Al-Ahmed: What kind of things can you actually determine on the lunar surface using these, considering that they're so small?

Mason Peck: There's a couple answers to that. One of them is that anything in which you're in close contact with. So, because they are in situ sensors, you can be so close as to be able to take maybe chemical samples, which would be really interesting. So, detecting volatiles. Could be water or other materials that normally evaporate in the sunlight, but they don't because they're actually in the frozen cold of the permanently shadowed region or something as simple as temperature, magnetic field. Temperature, for example, you think certainly in the shadow is going to stay pretty much constant forever, but there is a little bit of seasonality to that. As the Earth gets closer and farther from the sun, there's a little bit of a diurnal or daily kind of variation. So, there's subtle changes. Understanding those dynamics informs what we know about the lunar surface and probably the prospects for humans surviving and thriving in those permanently shadowed regions.

Sarah Al-Ahmed: What could that understanding of the volatiles on the lunar surface actually enable us to do in the future, especially as we're seeing humanity finally return to the moon with the Artemis program?

Mason Peck: Well, I mean, a quick answer is water. We kind of sort of know where the water is, roughly, but knowing very precisely through something like this gives you much better, again, statistical perspectives on where that water might be, how hard it might be to extract, so we can design a lunar habitat or lunar outpost with a lot more confidence, a lot more safety, lower risk, saving costs, saving lives. It's a good move.

Sarah Al-Ahmed: We're talking about what this can do for the moon, but there are so many other applications that we could be using this for. So, I'm curious to hear where else in the solar system or even on Earth you might want to apply this technology.

Peter Cabauy: Mars. I mean, we could easily apply this on the Mars surface and spread them all over the surface. And instead of having one rover that only goes one or two kilometers from where it originates, we could have it go thousands of kilometers by just having many, many of these devices working together.

Sarah Al-Ahmed: What about you, Mason?

Mason Peck: I think one of the coolest parts about these is that they'll work underground and underwater in principle. So, any of the gas giant moons, those would be interesting locations. So, Enceladus, for instance, maybe on the surface makes sense or maybe Titan sort of inside one of the strangely constituted lakes or oceans there. Mars is an interesting case because, if you land these with a certain amount of violence, they end up under the regolith. So, an underground sensor is not normally considered to be viable. Think about when we had the Spirit and Opportunity rovers. The thought was they'll eventually just get covered with sand, and we just won't be able to get power from that. Didn't quite work that way, but it is happening.

It's fine if these things get covered with a regolith. We're not impeding the solar power, so it's not a problem. So, long-duration measurements, even if they're covered with sand, makes a lot of sense in a Mars environment. Around Earth, there's so many applications to something that is small and durable and maybe even lightweight enough that it could enter the atmosphere without fully burning up. So, you may be able to get measurements through the mesosphere of phenomena we currently can't measure. Plasma density, for example. So, I think the enabling technology of nanotritium opens up the solar system in a way that maybe solar power did 70 years ago.

Sarah Al-Ahmed: Well, congratulations on making it through phase one. And now into phase two, what are you guys going to be doing with this next phase to advance this technology?

Peter Cabauy: We're now taking it to TRL4, and we're looking and possibly even to five, and we're testing out the betavoltaics. We're actually looking at the layering of the devices and a lot of simulations. Being a NIAC at TRL4, maybe five is great, but the goal is TRL7, to get it all the way up to the lunar surface. May not look exactly the same. But to be able to get on one of these CLPS, lunar landers, and be able to deploy them, there's nothing else that'll bring a smile to our face and, I imagine, to the NIAC community.

Sarah Al-Ahmed: From nuclear-powered sensors on the moon, we're headed to the outer solar system. Dr. Daniel Drew is a roboticist at the University of Hawaii at Manoa in Honolulu. His phase one concept called SPARK, Solid-state Propulsion for Autonomous Reconaissance of Karst, would send silent flying robots with no moving parts into caves on Saturn's moon, Titan.

I'm here with Daniel Drew from the University of Hawaii Honolulu with a project called SPARK. So, it's a Solid-state Propulsion for Autonomous Reconnaissance of Karst.

Daniel Drew: Nice.

Sarah Al-Ahmed: I got that one. But before we can even talk about what this project is, we need to understand what is a karst. And specifically, what is a karst on Saturn's moon, Titan?

Daniel Drew: Sure. Thank you. And really good job remembering the name. I think SPARK is much catchier than that whole title. Karst and the labyrinth terrain we find on Titan is this geometrically complicated series of canyons, valleys, cliffs that are driven by fluid and mechanical erosion processes. So, on Earth, those turn into slot canyons or caves that we can go explore. But on Titan, this has been driven by methane, as the liquid, eroding frozen ice, so frozen water. So, we expect to see caves under the surface of Titan that have been bored into by that liquid methane driving erosion. So, karst terrain is a broad term. Caves are kind of a piece of that, and we are specifically targeting investigating inside of subsurface caves.

Sarah Al-Ahmed: It was really interesting when the Cassini mission was operating around Saturn. And when the Huygens probe landed on Titan, I was really amazed to hear that there was anything like karst on this world. The fact that there's a whole hydrological or, if you will, methanological cycle going on is one thing, but the detection of karst, that is a whole other level on top of it.

Daniel Drew: I'm not a planetary scientist, so I can't speak to how surprising this was to that community. To me, I found the video footage quite striking. You look, and it's clearly the same processes that drive that form of terrain formation on Earth are happening on Titan. So, it looks very familiar as that probe is descending. It looks like a dry desert environment you might find in Arizona or something, but it's on Titan which is in the outer solar system. It's incredible.

Sarah Al-Ahmed: See, it's interesting because a lot of the people here, their backgrounds are all in space science, but you come at this from the angle of robotics. How did you find yourself working on a mission for Titan?

Daniel Drew: I've been working on these solid-state propelled robots using electrohydrodynamic or electroaerodynamic propulsors for about a decade. So, these are tiny ion thrusters that can go on flying robots on Earth, and these work on Earth. But, for about a decade, I've been confronting the fact that they're not very efficient on Earth. I've been walking around with this hammer, which is this really cool ion thruster, and I've just been trying to make robots, and it turns out that it's just not competitive with propeller-driven craft here.

But a friend, actually, from grad school, who's now at JPL, emailed me randomly and said, "Hey, Dan, wouldn't your propulsors work really well on Titan?" I thought, "What's Titan?" And then I figured it out, and the back of the envelope math is quite striking. Just from data we know from Cassini, these will work spectacularly on Titan. So, it's almost a dream. It's the perfect atmosphere in terms of pressure density and ion mobility driven by the low temperatures for these ion thrusters to really perform exceptionally.

And they also solve some other problems with cave exploration specifically. So, I don't know. I lucked into it is how I got into it.

Sarah Al-Ahmed: What do you think we might be able to find out from exploring these types of caves?

Daniel Drew: So, caves are interesting. I mean, if you've been inside a cave, you can see defined stratification that the layering process gives you a very clear way to visually observe history. You can see geological history, which is climate and chemically driven, so we can understand about the history of the moon. Inside of caves, you have an undisturbed environment where these deposition provinces have been happening over long periods of time, and you have just kind of the perfect area for steady, controlled visual observation of the unique climate on Titan. And we can do a lot of that with the same imaging techniques that have been pioneered for Earth-based research. So, multispectral imaging will tell you a lot about that chemical composition.

Sarah Al-Ahmed: You said a lot about tangentially what all of these things do, but if we fit it all together, what is SPARK?

Daniel Drew: SPARK is a meter or submeter scale aerobot, so it's a lighter-than-air vehicle platform, with distributed propulsion across its surface, and the propulsors are not typical propellers. They are these atmospheric ion thrusters. So, they generate a plasma which is ionized air. In this case, it would be the ambient Titan air, and then they accelerate ions out of that plasma. They collide with neutral molecules and entrain an airflow. So, you can imagine that we're using the great atmosphere of Titan to our benefit in that it's very dense and heavy, so the ions are hitting a lot of molecules as they're getting dragged in that thruster, and we're getting very efficient airflow entrainment.

So, SPARK is using the high thrust-to-weight ratio of those actuators using their solid-state nature to overcome the fact that it's only 94 Kelvin on the surface. So, your propellers will get stuck immediately. The metal will weld to itself. And we're using the distributed propulsion concept to overcome the challenge with exploring a cave. I mean, caves are complicated navigational environments. And on Titan, we expect them to be larger than on Earth but not necessarily that much larger, not like the lunar caves we heard about earlier.

We need the ability to move quickly and nimbly out of the way of obstacles. A traditional airship can't do that. You can imagine a blimp that they've investigated for Titan atmospheric investigations. So, we need to add actuators to produce a fully actuated or holonomic control system so it can float in any direction and redirect in place so we can point our camera where it needs to be without bumping into a stalactite or something.

Sarah Al-Ahmed: Right now, I'm just going off of the concept imagery. This looks really interesting. So, can you describe visually what this looks like, at least now in concept? I understand it probably could morph over time.

Daniel Drew: Sure. So, imagine about a large beach ball, spherical, floating object with, terrestrially, we would hear nothing because these are silent, solid-state actuators, and you don't see anything moving. So, it's very striking when you see these on Earth. They float around, and there's no visible mechanism. They look a lot like UFOs. I mean, you look at it, it strikes the science-fiction-loving heart of most science people and space people, as you see, and it's like, "Oh, yeah, that's the future robot we were promised, these little orbs that float around." While we don't necessarily get a benefit from the silence on Titan, unless there's anything listening in the caves, there are translation paths for Earthbound robotics that matter still.

I said that the efficiency's low on Earth, but with a lighter-than-air platform, it starts to become more possible to do something. You can imagine one of these floating in the corner of this room. You would not see why it's moving, and you wouldn't hear it. Whereas if a drone was flying around this room, we would all hear it.

Sarah Al-Ahmed: I don't know who out there is watching this. As a Dr. Who fan, I immediately went to the Toclafane which are literally floating orb creatures. Terrifying. The fact that we could possibly make anything like that is so sci-fi. I love it.

Daniel Drew: And I've heard Jedi lightsaber training tools. The Prometheus orbs. So, this is striking imagery that we see in popular culture. I think there's just something alluring about a mysterious floating sphere.

Sarah Al-Ahmed: What kind of applications have you been trying to cram this into here on Earth, since you've been trying for so long?

Daniel Drew: I mean, a lot of my research into these solid-state propulsion mechanisms was motivated of the fact that I hate drones. I hate to listen to them. I do research using drones indoors in my lab at the University of Hawaii, and I hate it.

The noise of a drone is uniquely stressful for a person, and that's been studied by NASA, actually. The stress that a flying drone induces is measurable and is comparable to a jet flying over your head. You can't help but, "Oh, whoa." So, it's obvious we need a solution for things like urban air mobility and package delivery terrestrially.

Whether this is truly competitive will rely on breakthroughs and efficiency because we're already lifetime limited with the drone. But, I think that it's worth pursuing because I view this psychological stress induced by the sound and also the fear of a propeller gouging out your eye is high enough where we need a new technology.

Sarah Al-Ahmed: Well, there's nothing, that we know of, alive on Titan who could be terrified of a drone just yet, but you have pointed out something interesting which is that if you have a drone or a rotorcraft or something like that, necessarily they're going to disturb the air around it.

How would that impact our ability to study these karst?

Daniel Drew: One piece of this project is this idea that distributed propulsion can reduce the downwash in a cave. When we go into a cave on Titan, or even many caves on Earth, you find a fine layer of undisturbed dust, and we want to see the layering pattern of that dust because that deposition process is driven by what happened over time. As soon as you go in there, and you start blowing it everywhere, one, you can't see anything because there's dust everywhere, and two, you've disturbed the layering pattern. So, if I distribute the actuation across multiple outlets, then I can decrease the distance from each outlet that the downwash has felt. So, you imagine if I'm pointing one large jet right at the ground, like a space shuttle taking off, and all the dust flies everywhere. But if I distribute that across the perimeter, I might lose efficiency because I'm getting off-axis force vectors, but I'm distributing the disturbance ,and that's dissipating in the air faster.

And this is very clear from first principles, and luckily the efficiency of these actuators is so high on Titan, 140 times less power for hover on Titan than on Earth, so we will have efficiency or power to burn on that distributed propulsion.

Sarah Al-Ahmed: Titan is such a wonderful place to fly. I know all of us are looking forward to Dragonfly. I mean, honestly, you could strap some wings to a human, have them flap around, and just take right off. So, you could do some amazing things with this.

How large of a spherical object could you fly on Titan with this?

Daniel Drew: I guess the question is how small is maybe ... And that's driven by the science. I don't think that thrust and the power for the thrust will be the limiting factor. It'll be more, what do we need to carry to do the job we want to do in a cave? So, if that's a UV, the hyperspectral imager, the illumination you need, that drives the mass budget.

But, we wanted to make it as small as possible because we don't know how narrow the cave access points will be. We don't know what's going to be inside the interior. If you've ever been caving, sometimes you have to contort yourself into weird spots, so maybe you're not a person who likes that, but that's challenging when you're a large robot, especially if you have exposed moving parts. Ours should be nice and compact and have no moving parts that could potentially strike the wall. Potentially, we could bounce right off, if forbid we do that, because it should be a pressurized, lighter-than-air platform.

Sarah Al-Ahmed: I've definitely had that nightmare, stuck in a lunar lava cave or something.

But, a part of the title of SPARK is autonomous, right? And we're dealing with a communication lag, but also in this case, we're dealing with trying to communicate with a craft that might be deep inside something underground.

So, what kind of autonomy are you building in to SPARK?

Daniel Drew: Right. Autonomy in comms-denied environments and caves or one of those is very challenging. We know that on Earth, robotics has struggled to break into these subterranean environments, especially for long-term complicated autonomous tests.

We are studying the right way to do this. I mean, there are different mechanisms, different ways, we could handle comms to a more high-compute vehicle. The navigation itself is relatively well understood. We can fly a drone in a cave here. We do that all the time. With onboard visual odometry, lidar, we can do that. The problem is, if we want to communicate data out, or if we need external control, even with the time lag to Titan, we need something that can hover in place, which is helped by the fact we're a lighter-than-air platform. So, we only expend power to station keep. Imagine that balloon. It only needs to pulse its thrusters to stay in place.

And maybe we're waiting for the next mission parameter from an Earthbound controller. How do we get that signal back and forth? We could string fiber optic cable. We can have a relay system with multiple robots. We can physically go in and go leave whenever we want to send a message. I mean, we can conceive of lots of different concepts of operations here, but we need to study those as part of the phase one process.

Sarah Al-Ahmed: It might be one of those situations where it goes inside the cave, learns a little bit, comes out, humans communicate with it. Do you have any idea kind of how deep into these karst that you could actually go with this technology? And that's mostly, I think, based on the communications issue.

Daniel Drew: Well, maybe it'll be based on just the power. And if we do onboard power, we might be limited by that, depending on how much it draws for the full-autonomy package. I don't view the thrusters as being the limiting factor for power. It depends how much maneuvering we need to do inside the cave because, like I said, this is a lighter-than-air platform, so it should be low-duty cycle and that we don't need to continuously expend thrust power to stay aloft, but we might need to use them relatively often to get out of the way of obstacles. So, there's just too many unknowns to answer that.

The dream is that we find a vast subsurface network of caves that go deep into Titan where it starts getting warmer, and we start seeing those ingredients for life and maybe liquid water super far down. That's beyond the wildest dreams, but it's theoretically possible, especially with the hyperefficient platform that can work for a long duration.

Sarah Al-Ahmed: I think a lot of people might be familiar with the fact that on the surface, there's methane and ethane and lakes and rivers and rain, but underneath all of that, underneath the organic dunes, underneath the water ice might be this subsurface layer of liquid water. And the fact that there are organics mixing with this on a world that's had a thick atmosphere for ages is just so exciting.

What was it like learning and experiencing Titan from your perspective for the first time when your friend contacted you?

Daniel Drew: Well, it's honestly shocking. You see a video like the Huygens probe, and you almost don't believe it really happened. You're like, "What?" And it's the only landing we've made on a moon besides Earth, and it's the only landing of a spacecraft in the outer solar system. And you look at it. Just incredible that there was video taken or pictures taken that you can stitch together. I don't know. It's remarkable. It's inspiring that that happened, and then you can potentially follow in those footsteps and do more exploration that can change the way we think about the universe. It's awesome.

Sarah Al-Ahmed: We definitely need to go explore more moons, although I am super excited for the upcoming Martian Moon Explorer that's going to the moon Phobos soon. Look for that launch later this year. But, we're not just talking about Titan, potentially, with this technology. There aren't that many worlds in our solar system that have a thick atmosphere, but there is one super notable exception: Venus.

Could you fly this on our sister world?

Daniel Drew: Flying anything on Venus is a pain. In theory, the atmosphere is still conducive to it. But in practice, I think it would require a fundamentally different design than we might target for Titan. I would have to do more digging into the exact kind of atmospheric composition, ionization processes, we expect to see, but we'd be really fighting advanced dielectric breakdown, and high-voltage components would struggle. It makes me nervous to think about the conditions on Venus, so I'll leave that to some of the Dave Bugby people who are more accustomed to working at extreme temperatures. But maybe as a maneuvering system onboard one of the higher-altitude airships, that makes sense. And that's one of the things we pitched, where it's a little more friendly to technology we have now.

Sarah Al-Ahmed: The surface of Venus, absolutely terrifying. Only the Venera probes managed to make it down there and last to take photos. But, there is this dream that perhaps humanity could live in the cloud tops of Venus someday in those places where it's just the right temperature. And interesting to think that maybe we could apply this kind of electrohydrodynamic propulsion in order to accomplish that.

Daniel Drew: So, you have nightmares about getting stuck in lunar caves and dreams of your Venutian cities. Exactly. So, I mean, it's always exciting to explore something that's fundamental. Propulsion is fundamental to how we can enable new missions. So, if this proves to be truly useful on Titan, and it should be ... There's a lot of science left to do on Titan. There's a lot left to do on Venus. So, it will translate. I mean, the things we do to make this space ready do translate, even if cryogenically compatible is quite different than what we do to make it Venus compatible.

I feel like I have hit on a new frontier of research, which is space applications of atmospheric high-end thrusters, so I'm excited to do more and learn more.

Sarah Al-Ahmed: Well, you're just starting out with phase one on this project. What are you guys going to be doing during this phase in order to see whether or not this is viable for a place like Titan?

Daniel Drew: So, I have the ill-advised idea of doing hardware experiments with Titan analog conditions. I've been in this game long enough with these electrohydrodynamic propulsors to not trust first-order models or simple numerical models at all. And maybe I could convince one of the reviewers, but I feel like I need to convince myself, that what we expect to happen at really low temperatures and high gas pressures will actually happen.

So, we will put these in an environmental test chamber. We will fill it with nitrogen, elevate the pressure, lower the temperature, and we'll just run these actuators. And I have expertise in building them, so it shouldn't be that hard. The platform design, it will be accomplished with my collaborators at JPL. So, I have Ethan Schaler, Jacob Israelovitz at JPL, and familiar names to a NIAC audience, probably, and then Michael Melaska at Blue Marble Space, who's the Titan cave expert. So, he's driving the science mission. JPL is driving largely the mission design, larger platform trade study, and I'll be handling the experimental characterization of actuators and Titan analog conditions and the downwash disturbance and maneuverability benefits of distributed propulsion. So, I'll have a lot of balloons in my lab with ion thrusters strapped to them.

Sarah Al-Ahmed: Have you considered collaborating with Johns Hopkins Applied Physics Lab who built a Titan chamber, essentially, for the Dragonfly mission that's upcoming?

Daniel Drew: Yeah, I think that was in use and expensive with the NIAC phase one budgets, but that's something that we would pitch. I mean, phase two, we're not going to be able to reach 94 Kelvin for the test chamber in phase one. So, in phase two, we'd probably accelerate to true Titan-like conditions and more maybe platform scale instead of a really small test chamber. And that's when we needed the expertise of collaborators like that. And that's 2028, so the timing might line up well.

Sarah Al-Ahmed: That would be really exciting. I mean, it wasn't even in my brain that you could potentially try to work with the Dragonfly team on this. It would be so cool to have a pairing of something like that with Dragonfly, the way that we had Ingenuity with Perseverance, but we'll see where this goes. Maybe phase two, we can explore what that might look like.

Daniel Drew: Thanks.

Sarah Al-Ahmed: We'll be right back with the rest of our coverage of NASA's Innovative Advanced Concepts Symposium after this short break.

Bruce Betts: What if a salty frozen lake in British Columbia holds the key to searching for life in other worlds? That's just one of the questions Dr. Jacob Buffo and his team have been working to answer, thanks to generous supporters like you. Dr. Buffo is a recipient of The Planetary Society's STEP Grants. That's our Science and Technology Empowered by the Public program which funds groundbreaking research driven by your support. They've been studying salty lakes with chemistry like ancient Mars, chemistry that may still exist in the hidden oceans of distant icy moons.

Now, it's time for the next phase. With your help, the team will build artificial intelligence tools that let future spacecraft help find the most promising places to look for signs of past or present life and be able to do it all on their own as needed, even without waiting for instructions from Earth. They'll test it right here on Earth at Mono Lake in California and the Great Salt Lake in Utah.

Since 1980, The Planetary Society's members and donors have supported science and technology projects crucial to future space exploration. Visit planetary.org/step, that's S-T-E-P, today. Your support will help fund the next phase of Dr. Buffo and his team's work. Thank you.

Sarah Al-Ahmed: Our final conversation takes us once more underground. Dr. Gilly Elor is a physics lead at Stone Aerospace and the principal investigator for LUX, the Lunar Underground eXplorer. She's joined by Stone Aerospace's founder, Dr. Bill Stone. He's spent more time working from deep subterranean camps on Earth than anyone else. Together, they've designed a phase one concept for a laser-powered drone tethered by fiber optic cables. It could be the very first technology to enter and explore lunar lava tubes.

So, you're Gilly Elor, right? And Bill Stone from Stone Aerospace Incorporated with a project called LUX, which is a Lunar Underground eXplorer but enabled by fiber. Before we even get into how this works, I want to talk a little bit about lunar lava tubes and why you are interested in exploring these in the first place.

Gilly Elor: So, lava tubes are incredibly interesting. Scientifically, we can learn a lot about lunar vulcanism, the history of the moon and the Earth. They're also really interesting as future bases for humans or scientific outposts. The Moon is a really harsh place. We don't think about this, but it's bombarded by galactocosmic radiation, micrometeorites, things that would kill humans in hours. The lava tube is shielded from all that. So, it's an ideal place for a base. It's an ideal place to do science in the future. Well, we like caves. We're terrestrial cave explorers, so we're excited about caves.

Sarah Al-Ahmed: We'll get into your exploration of caves in a little bit because, oh, my gosh, you guys have been through some amazing experiences. But, I think so many people that think about going to the Moon envision this future where we're all living in lunar lava tubes, potentially, but I don't know if they understand the scale of this kind of thing.

So, for example, could you talk a little bit about Mare Tranquillitatis which is near the Apollo 11 landing site? I say near. It's maybe about 250 kilometers or something. But, what is the scale of that kind of structure on the Moon?

Gilly Elor: It's huge. So, the Moon has less gravity than on Earth and no atmosphere. So, that allows for really large cave formation from ancient lava flows. So, what we know from remote sensing and also modeling of structural stability is that we are talking about pancake-size passages where the width is a kilometer or more wide, and the height is maybe 100 to 200 meters, and they can go on for tens or hundreds of kilometers.

Sarah Al-Ahmed: That's kind of terrifying, if you think about it, but maybe you guys don't think that's so terrifying because you've experienced deep caves. But, in order to explore these places, we're going to have to be able to drop down in there, send information out.

How are you guys proposing to do that with LUX?

Bill Stone: Well, as you said, we've had a lot of experience with terrestrial cave exploration and both on the human side and on the robotic side. And what we've concluded after looking at the topography and the morphology of these things, the only way you can really effectively do this is the way that we do underwater cave exploration on Earth, which is a flying vehicle. So, basically a six-degree-of-freedom drone, if you will. And you can't have a drone on the Moon because there's no air, so you have to have a propulsively stabilized system to do that. But, within that context, we know most of the things that we can do. The trick is trying to increase the range. So, we're targeting kilometer-plus penetrations into these things so you can really see what's there.

Sarah Al-Ahmed: Man, I can't even imagine how cool that would be. We heard a story yesterday, and I believe the presentation was actually on Tuesday, about exploring these karst on Titan. So, there are all these underground passages on so many worlds, but the Moon proposes a really serious challenge because it has no atmosphere in order to do this.

In order to send power and send data and make sure you can have propulsion in this area, you're proposing using fiber that runs to the actual LUX unit. How does that work?

Gilly Elor: So, it does three things. So, the first thing is it allows us to talk to the vehicle and to send data out from the vehicle to outside the cave and back to Earth. So, this means that it's a one-way mission. The vehicle goes in, and it constantly sends out data. And if anything happens, we have the data.

The other thing we do is we send power over, so that can be used on the back end. So, this is optical energy that's converted into electricity to power LUX's systems. And this is stuff that Stone Aerospace has been doing, and Bill can talk a lot more about that. But the trick is, the NIAC hard thing is, we're going to also use that thermal energy from the laser to boost the propulsion. Think of it as a way to get more mileage in your gas tank by just taking energy from the laser which stays outside the cave and sending it to the vehicle.

Sarah Al-Ahmed: Where is the laser originating from?

Gilly Elor: So, the laser is going to be on the surface outside the cave. It's either going to be on a lander or rover or possibly on a base, if this is a far futuristic mission. We're thinking of all kinds of different mission scenarios, and we're doing a full mission ConOps to look at maximizing our science and exploration objectives.

Sarah Al-Ahmed: Well, she just mentioned it a second ago that Stone Aerospace has been applying these kinds of technologies to other things. What have you been using it for?

Bill Stone: Mainly, we use it for subsurface aquatic environments. So, we've spun off a commercial company called SUNFISH, Inc. that does aqueduct inspection, harbor port pier inspections, karst aquifer inspections. There's a project going on to survey 100 kilometers of karst aquifers near Tallahassee, Florida right now.

To talk to that vehicle, RF doesn't propagate through water. So, we have a self-deploying fiber system on the vehicle that can go out as far as eight kilometers from the base and send back two-gigabit-per-second data link. So, we get full 4K video coming back, even though it's as much as eight kilometers underground.

Sarah Al-Ahmed: See, I'm glad you mentioned that it's that long because one of my first questions is that these lunar lava tubes, if you compare them to the volcanic caves we see on Earth, they can be up to 1,000 times larger than what we see here, which means that you're going to be trying to evaluate a subterranean area that is just so much larger.

Does that pose problems?

Gilly Elor: Yeah, absolutely. For one thing, we need a lidar that has a very long range. And these things exist. They can get an off-the-shelf lidar that has a 600-meter range. If anything, it's kind of nice because it means that we hope that we're not going to have to wiggle through tight passages like we do on Earth. The bigger danger might be getting lost. And for that, we're going to think very carefully about the autonomy and the routines and all the different instruments. One of the things that we're talking about is also equipping LUX with a radar. So, if you stir up some dust, which we do expect to see in the entrance pit, you can use the radar to still figure out where you are and avoid obstacles.

Sarah Al-Ahmed: Living in caves is one thing, but there's also what we can learn scientifically from the caves themselves. Do you worry that the propulsion systems disturbing the area might have any impact on the scientific value of that region?

Gilly Elor: So, that's why we have a NIAC project about this in the first place. So, we want to make sure that we don't damage the cave. And because we have a propulsive vehicle, we want to be very, very careful that the fuel or the propelled byproducts don't contaminate the cave and don't stir anything up. So, we first thought of doing this with a cold gas nitrogen thruster, and that just doesn't have enough energy to get us into the cave. So, what the whole project is about is how to have a green propellant that's not going to muck up science objectives or put anything toxic in the cave that can still allow the vehicle to explore up to a kilometer or more into the lava tube. So, yes, we absolutely care about that.

Sarah Al-Ahmed: I mean, conceivably, you might be the first people exploring an area that humans might call home on another world. What does that feel like to you guys?

Bill Stone: Well, we do that, as a matter of fact, on expeditionary work here on Earth. Going where nobody has ever gone before is something we do regularly. But for this, the real thing that exists right now is this is a total unknown. You can't image this stuff from orbit. And you can't really easily do it even in an EVA suit because of the fact that there's 160-meter drop, for example, into the Mare Tranquillitatis bit. So, getting this geometric information is what allows us to do civil engineering thoughts about, how would you turn that into a base? So, do you need an elevator and a bridge to get down to the entrance? What kind of structures would you be able to put in there? Is the floor flat enough to put structures, or is it entirely jumbled until you get some distance inside? So, the paradigm with this kind of stuff for cave exploration in general is you explore first, you map, and then you figure out what the science is behind that.

Sarah Al-Ahmed: Well, of all the people on this planet, you're probably the person who would know the most about this because you spent more time in subterranean camps than any other human on Earth. Is that right?

Bill Stone: Yeah, closing in on 1,200 days below 1,000 meters.

Sarah Al-Ahmed: What is that like? And why are you so passionate about this kind of exploration?

Bill Stone: It's the next best thing to being on the Moon.

Sarah Al-Ahmed: I could see that. But it's not just you, right? I haven't seen the documentary myself, but my understanding is that you both went to Sistema Cheve in Oaxaca, Mexico, and there's a National Geographic documentary called Explorers: The Deepest Cave about your adventures. What was that like?

Gilly Elor: We do it because we are excited about exploration and being the first people to be where no one has gone before. So, that's why we do it, and caves are really the only place on Earth where you can go do that without knowing anything in advance.

Sarah Al-Ahmed: After the experience of doing that, what do you think humanity is going to need to accomplish in order to actually live in these lunar lava tubes if we do it someday?

Bill Stone: Well, the beauty of these things is that they are, for lack of a better word, benign compared to the surface of the Moon in particular. Now, these exist on Mars as well, and the same logic applies to those, as Gilly was mentioning before.

The thing that most people don't think much about, and if you look at even the standard artistic renderings of the future lunar bases that are being given to the public, if you look at that, the first thing you have to think about is these are not designed for radiation shielding. And aside from solar events, constant galactic cosmic radiation is going to be a health hazard for anybody that doesn't have shielding. That shielding has to be more than four meters of regolith. Well, that's a lot of civil engineering.

The alternative is, if you can find a mass effective way of getting into these caves, now you have shielding not only from the radiation but also from micrometeorites, and you have thermal neutrality. You're looking at a range of probably minus 20 to minus 10 C because caves are the average of the ambient temperature outside. So, once you get into these things, you're basically home free. In fact, the other thing is, because the radiation is shielded, we're looking at not having to use as much rad-hard gear on the LUX vehicle itself. Once you've transitioned from the lander into the cave, you're basically in a nice, safe environment. And so, once it finally sets down, it's actually set up to be a scientific experiment base for long duration until the lander runs out of power.

Sarah Al-Ahmed: I love this idea. I mean, we've seen some wonderful proposals over the years of ways that you can live on the surface of the Moon. Last year, we even had a proposal to blow giant bubbles made out of lunar regolith in order to live on the surface. But the radiation issue plus meteorites coming in, there's so much that you have to deal with in order to survive there. So, it might just be me, but I do think most likely, if we're going to survive in those spaces, other than building small lunar bases, it's probably going to be these caves. Do you agree?

Gilly Elor: Yeah, absolutely. And I'll also add that a lot of the technology that would be tested with the LUX mission would go towards enabling things that you would need for a base like power, communications, which are out of line of sight. That's all things that you would need for the base itself as well. So, we're kind of getting ready for that with the LUX mission. A little bit of a demonstrator of that technology, if you will.

Sarah Al-Ahmed: Well, I know Stone Aerospace hasn't just worked on this, right? You've also worked on other things with NASA, Antarctica, even Europa concepts. What has that been like?

Bill Stone: We've done a lot of work on Europa missions, not so much on the lander but what happens after a lander. And so, it's split into two pieces. One is, how do you get through the ice? Those are called cryobots or ice-melting robots. And then the other part is, if you get below the ice camp into the subsurface ocean, how do you expand your exploration radius to see if you can, for example, find a hydrothermal vent on the floor of the ocean, which is what a lot of people think might be the second origin of life in the solar system. A lot of people think Mars may have had this, but Europa has liquid water. So does Enceladus. But if you want to get to those places, you have to do these two things. And getting through 24,000 meters of ice is no hat trick.

So, you're into power sources that are nuclear of one type or the other, whether it's radiothermal or whether it's microfission. And once you get through, you have to have a vehicle that is also going to be radioisotopically powered, an AUV, if you will, and solving that navigation problem below the ice where there's no GTS, there's no radio signals, there's no communication from Earth to tell you what to do, that's where we've hung our hat for the last 23 years. We've built five generations of completely autonomous AUVs. We've built at least that many generations of different cryobots, and we're waiting for the opportunity to actually make that a flight mission.

Sarah Al-Ahmed: Well, hopefully someday, right? But we're still a long ways from getting below the ice on Europa, unfortunately. I'm hoping I get to see it in my lifetime.

What are you guys going to be doing in this phase in order to test that this is viable? Are you going to be going all the way up to building a practice version of LUX?

Gilly Elor: Building it would be phase two or what we hope would be pre-phase a funding for a mission. Right now, we're looking at the feasibility. We've really shown preliminary feasibility. It's just a question now of what fuel do we use, what is our mission ConOps, what exactly are our first-priority objectives? And right now, we're designing prototypes for power-over-fiber laser-enhanced thrusters, and we're hoping that the next phase is when we start building and testing the actual LUX vehicle.

Bill Stone: The core of the whole concept here for NIAC is whether you can increase the effectiveness of the fuel that you carry. So, as Gilly was saying, double or triple the gas mileage. And so, we have a very high-power industrial laser at our lab, and the trick is to see if we could show at scale, subscale, from what we're coming up with in the LUX scenario to show that we can actually increase the ISP in various types of propellants. And then if it works at that, you can assume that it's going to linearly scale up to your 100 or 200-kilowatt power source.

Sarah Al-Ahmed: Well, I hope this works out and we get to see you next year for phase two because I would love to see what this thing looks like when it's finally built. And I really appreciate you guys joining us. I don't know. I have been so enamored with this new phase of where we're at in space exploration, and maybe it's just because I didn't get to see the Moon landings when I was a kid, but all of this thought about the fact that we get to return there and potentially live there someday and that this could be the starting point of a whole new age of human exploration across the solar system is just so exciting.

Gilly Elor: I mean, I'm super excited too. Everything I've done in my life has been geared towards some form of exploration. I'm sure that's even more true for Bill. So, obviously going into space, into the Moon and beyond, is what I think humanity should be doing and prioritizing.

Sarah Al-Ahmed: Thank you to all of the researchers who shared their work at this year's NIAC Symposium. Be sure to join us next week for part two. We'll hear more from researchers working on solar sails, nuclear rocket engines, and oxygen production for Mars.

If you want to see the full presentations for any of these fellows, I'm going to leave a link to the complete symposium webcast in the show notes. And if anything you've heard here today has sparked an idea of your own, we'll also leave information on how to apply to NIAC.

Now, let's check in with Dr. Bruce Betts, our chief scientist of The Planetary Society for What's Up. Hey, Bruce.

Bruce Betts: Hey, Sarah.

Sarah Al-Ahmed: Man, every time I go to NIAC, I come back with so many cool stories, but I will not tell all those stories now. People have already heard several of them over the course of the show.

Bruce Betts: Well, then, thanks for that tease.

Sarah Al-Ahmed: But, I mean, we had this event. That was super fun. Another thing I want to remind people of, which we spoke about on the show a few weeks ago, is that this upcoming week starting on Sunday, October 4th is actually World Space Week, which is themed for rocketry. It's Rocket Revolution. So, encourage people to do fun things for that.

But also, the first day of World Space Week is the day of Saturn at Opposition, which, for anyone who has a telescope who loves seeing Saturn, this is one of those days that I think people look forward to. So, I thought we'd take a little moment. Let's talk about Saturn.

Bruce Betts: Saturn's cool. It has rings. You can see them in a telescope. And you know when a good time to do that is? Around opposition or, as I like to call it, opposition. But I don't know why. So, basically opposition is when, in this case, Saturn is on the opposite side of Earth from the sun. And so, it is in their mutual orbits, approximately the closest it gets during that time period, and is basically the closest. So, therefore it's also the largest. Therefore, it's also easier to see. And it has the wonderful side benefit of the fact that when it's at opposition, it is rising around sunset and setting around sunrise. And so, it is up all night.

Sarah Al-Ahmed: That's so cool.

Bruce Betts: So, if you check it out in the evening or in the middle of the night or in the predawn, you'll do better. You'll be looking through less atmospheric crud if you do it later in the evening. But in any case, you can see it. It'll be the best view in terms of distance. Now, it's not like Saturn is going to change from one night to the next. Sorry, that was an incorrect statement. It changes from one night to the next, but it doesn't change a lot in terms of what you're going to see. So, if you're cloudy on the 4th, you look on the 5th, you look on the 10th, you're still going to have a good shot at it.

And the fun thing about Saturn, and most of you have probably experienced it, but if you haven't, even a small telescope with decent quality, Saturn will look tiny, but you will see the rings, and there's just something magical about seeing the rings from a billion-and-a-half kilometers away, a billion miles away, through your little telescope or your big telescope.

So, check it out. It's yellowish, and it is bright but not super bright, but it is one of the brightest objects in that area of the sky, and you'll see it rising in the east and then moving across the sky and setting in the west as things tend to do.

Sarah Al-Ahmed: I'm also really glad that we're not in one of those years where we're completely edge on with the rings. Over the last few years, I mean, Saturn is always spectacular no matter what year you look at it, but whenever you're looking at an edge on, you don't get that nice, the beautiful view of the rings, and you don't get the view of the Cassini Divide either. So, I think this is going to be a good year to actually see this.

Bruce Betts: So, Saturn goes through periods where, just like Earth, Saturn is tilted compared to its orbit. And so, there are times when the rings are completely edge on, in which case you are not going to see them at all, but then they start to open up, and this happens over many years. And so, they're in the process of opening now, but they're open enough that you should be able to see it.

If you have a larger telescope, you might see the Cassini Division which is perceived, from Earth anyway, a gap in the rings. A lot less stuff in there that appears and was named after that Cassini guy who did space astronomy stuff back in the space astronomy stuff early days.

I agree with you. Although, it's kind of wild to watch the rings disappear.

Sarah Al-Ahmed: It is so true. Although, not as much fun to show people at star parties and things.

Bruce Betts: Look, it's Saturn. It looks just like every other planet now.

Sarah Al-Ahmed: Right. I mean, whenever people see the rings through the telescope, it's always like, "How did you do that? Is there a picture at the end of the telescope?" People freak out. But when the rings aren't visible, that's a whole other level of freak-out.

Bruce Betts: Who stole them?

Sarah Al-Ahmed: Who stole the rings? The Grinch stole the rings.

Bruce Betts: It's a magic trick, but it takes a few years to really pull off nicely.

Sarah Al-Ahmed: But, good opportunity to go outside and look up at the sky and have a good thing to celebrate on the first day of World Space Week, which I will remind people is the largest space event in the world. So, it's a wonderful time to connect with people, think about this moment in space history, and, who knows, maybe build some fake rockets or real rockets.

Bruce Betts: Well, let's be careful out there.

Sarah Al-Ahmed: Always.

Bruce Betts: We move on to random space vac rewind. So, Saturn, we talked about it. Saturn and its rings would just about fit ... And I've mentioned this before, but it's really cool. It would just about fit in between the Earth and the Moon. Plunk that baby in there with the rings, and it's about-

Sarah Al-Ahmed: That's insane.

Bruce Betts: Well, fairly approximately the same distance. The main rings.

Sarah Al-Ahmed: I don't know if that says more about the rings or about the distance to the Moon or all things at once. That's a lot of rings.

Bruce Betts: There you have it, the official quote. "That's a lot of rings."

Sarah Al-Ahmed: You heard it here.

Bruce Betts: Everybody go out there, look up the night sky, and think about the rings you own and how many it would take to fit between Earth and the Moon. Thank you. Goodnight.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week with more space science and exploration. If you love the show, you can get Planetary Radio T-shirts at planetary.org/shop, along with lots of other cool spacey merchandise. Help others discover the passion, beauty, and joy of space science and exploration by leaving a review or rating on platforms like Apple Podcasts and Spotify. Your feedback not only brightens our day but helps other curious minds find their place in space through Planetary Radio.

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Planetary Radio is produced by The Planetary Society in Pasadena, California and is made possible by our members from all over this planet. You can join us as we continue to dream of the technologies that'll carry us to other worlds at planetary.org/join.

Rae Paoletta is our producer. Kate Howells and Mark Hilverda are our associate producers. Casey Dreier is the host of our monthly Space Policy Edition, and Mat Kaplan hosts our monthly Book Club Edition. Andrew Lucas is our audio producer. Josh Doyle composed our theme which is arranged and performed by Pieter Schlosser. My name is Sarah Al-Ahmed, the host and executive producer of Planetary Radio. And until next week, ad astra.