Planetary Radio • Aug 06, 2021

Space Policy Edition: Mars via the Nuclear Option

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On This Episode

Bhavya lal

Bhavya Lal

NASA Senior Adviser for Budget and Finance

Casey dreier tps mars

Casey Dreier

Chief Advocate & Senior Space Policy Adviser for The Planetary Society

Kaplan mat headshot 0114a print

Mat Kaplan

Planetary Radio Host and Producer for The Planetary Society

Can nuclear propulsion fundamentally transform our ability to send humans to Mars? Bhavya Lal, a policy and nuclear engineering expert now working at NASA, helped write a new report on the topic for the National Academies of Sciences. She joins the show to talk about the advantages of various types of nuclear propulsion, the engineering and policy challenges that face them, and the role of government versus the private sector in developing and deploying transformational technologies.

Nuclear thermal propulsion spacecraft concept
Nuclear thermal propulsion spacecraft concept An artist's concept of a spaceship powered by nuclear thermal propulsion.Image: NASA

Transcript

Mat Kaplan: Welcome back, everybody to the Space Policy Edition of Planetary Radio. I'm Mat Kaplan, the host of the weekly show at Planetary Radio. Joined as always for this monthly installment of SPE by the senior space policy advisor for The Planetary Society, he is also our chief advocate, welcome, Casey Dreier.

Casey Dreier: Hey, Mat. Glad to be back.

Mat Kaplan: Good to have you. We have a number of things to get to before we get to a terrific second appearance by the great, Bhavya Lal on the Space Policy Edition. You're going to talk with her today just to tease here about nuclear propulsion or other forms of nuclear energy and how handy those would be out there beyond Earth.

Casey Dreier: The nuclear option at Mars, just not the one that's been... Not at the polls, but to get there faster and more efficiently. Really interesting discussion, really interesting stuff happening behind the scenes for a lot of us. Something that The Planetary Society is getting very interested in and how that could be used, not just for frankly getting humans to Mars, but where else in the solar system can we benefit from that type of power and propulsion. So really fascinating stuff happening and very exciting potential future related to that. So we will go into the details with that with Bhavya.

Mat Kaplan: Atoms for peace. This time for real. I couldn't resist. I used to watch those old videos they showed us in elementary school about too cheap to meet her. We do have some other things to talk about. Casey, something that we have not regularly talked about, we both have newsletters. Yours is out and so it's appropriate to mention that during the Space Policy Edition. How do people read it? How do they find out more about it?

Casey Dreier: Yeah. I realized we haven't been plugging this enough in my own show, our own show, the Space Advocate Newsletter. It's a monthly newsletter where I write a little bit about what's going on. I highlight some important pieces of space policy or politics and it's got a great readership already. I'd love for people to sign up, and it kind of comes paired with this podcast. It comes about the second week of every month. And that's at planetary.org/space-policy. There's a link there to sign up or we will put a link in the show notes of this very podcast.

Casey Dreier: So I hope you sign up it's free. So it's a fun newsletter to do. It's always great interacting. One of my favorite parts is when people write back and interact with me on the topic of the time, that's always great to be pushed and challenged and really explore some of these issues.

Mat Kaplan: So if you can't get enough space policy, have it show up in your email inbox and I can tell you, it's terrific. I'll save talking about my newsletter, which is also monthly. It usually comes out a week after Casey's. We'll, tell you how to subscribe to that as well. How about hopping over to planetary.org/join as well and consider becoming a member of The Planetary Society to enable newsletters and radio shows and social media. Oh my. All of the great stuff that the society is up to including the terrific policy work that Casey and Brendan, our man in Washington do. It all happens because of our members.

Mat Kaplan: Now, yeah, we do have some other sources of funding, but just like they say on public radio stations, it really comes down to our members. We could not exist. We could not do what we do without those tens of thousands of members. And just think how much more we'll be able to do if you and other policy geeks like you join up as well at planetary.org/join.

Casey Dreier: Think of it as Patreon but direct to The Planetary Society it really does enable us to do this.

Mat Kaplan: Speaking of bucks, the kind that they print out of the Department of the Treasury I think, isn't it, Casey? There is more budget news for NASA out of the house.

Casey Dreier: Yeah. So we got the first step from congress this year for NASA's upcoming fiscal year 2022 budget. The president's budget request came out a few months ago. It had proposed a roughly seven or so percent increase for NASA. Overall pretty solid budget. A few tweaks to be made I think. The House of Representatives, one chamber of congress made its first appropriations legislation released. It passed it through committee. It's awaiting a vote by the full house.

Casey Dreier: It seems relatively uncontroversial on the NASA side and we got to see what congress is thinking, at least part of congress. We saw an even bigger boost, a modest one, but about an extra quarter billion dollars on top of what the Biden administration requested. So it's about a $25 billion budget for NASA adjusted for inflation that puts... If that passed as is, it would put NASA back at about mid 1990s levels in terms of buying power.

Casey Dreier: It's a really nice step in the right direction in line with what we've been recommending. These slow and steady increases of budget, every single year. What they do with that extra money, they move some things around. They put more money into the SOS program as usual. They restore funding for the SOFIA flying observatory, which the administration had proposed to cancel. And they add some money for Nuclear Thermal Propulsion, something that Bhavya and I are about to talk about.

Casey Dreier: That's an ongoing area of somewhat division between NASA and the congress right now about how to allocate some of those research funds. Otherwise it's a pretty solid, but we even give a few extra tens of millions to Mars sample return which would make a record level of funding for the Planetary Science Division. So again, overall a very solid budget. I would like to see a few tweaks as I always do. Maybe throwing some extra money towards actual fundamental scientific research in planetary science to enable more scientists to work and more students to work.

Casey Dreier: Those are things we'll keep pushing on the senate side. But very promising overall, pathway to getting a budget this year for NASA. So I have updated all of these numbers. You can read all the gory details of this on our fiscal year 2022 tracking page including links to the original source documents that's on planetary.org. We'll put a link to it in the show notes here, or you can just Google you know NASA FY-2022 Planetary Society and it'll show up right there.

Mat Kaplan: That's nice to know. That's a big kudos to Google for putting you up near the top when people search for something like that. I have a message for you Casey. Amy Meinzer says hello. We talked about NEO Surveyor and planetary defense. Your name came up because we were talking about how you have documented the very impressive and very welcome growth in funding of Planetary Defense activity within the NASA budget. She of course is delighted to see all of that.

Casey Dreier: Oh, I couldn't be more excited for her and for the team and for frankly all of humanity that we're starting to actually build this deep space telescope dedicated to looking for near-earth objects. That's one of the key really positive aspects of this Biden budget that came forward this year. We're really excited about that. We do have a petition online that you can help encourage congress to fund it. In the house, they did. Very happy. They seem to be happy to do so.

Casey Dreier: So this is just a great step forward. And this is just such an important mission. Actually, I'll be having an op-ed publishing in scientific American on the 25th talking about this. A very important investment that we can make. In light, of what we have learned in our pandemic year coming out of COVID. Right? Another type of low probability, high impact, natural disaster. That is at some level preventable or at least you can mitigate the consequences of it. If you pay attention early, if you act early and you're ready.

Casey Dreier: If you even put the proper investments in protecting humanity. I think there's quite a bit we can learn good and bad from our experience with COVID into how we plan and prepare and invest in preventing near-Earth object collisions with the Earth.

Mat Kaplan: After all we're just trying to save the world as the boss says. Get us into this conversation with Bhavya. We've given people a little bit of a preview.

Casey Dreier: Yeah. So the big motivation for this discussion with Bhavya. And Bhavya Lal by the way, she just introduced... She has held a number of hats over the last few years, but right now she's a senior advisor for budget and finance at NASA. Now, she's briefly served as the interim chief of staff before the administrator nelson came in. And prior to that, she was at Space Policy Institute, Science and Technology Policy Institute, STPI and had done a number of very interesting reports and analysis on various aspects of human space flight, scientific space flight, nuclear propulsion and others. In April, there was a release of the National Academies of Sciences Engineering and Medicine focused on the role of using nuclear propulsion to enable human missions to Mars.

Casey Dreier: Of course, that gets us excited at The Planetary Society. Getting humans to Mars ultimately is one of our big goals. What is this kind of enabling technology used for? How close is it to being real? How important is it that we invest in that technology first before going to Mars or is it something that can come after and what else can it be used for? Now, can it be used for things at the moon? Can it be used for scientific missions? Can it be used to create power in addition to thrust? These are non-trivial questions.

Casey Dreier: Space nuclear power has been investigated in the past. It was programmed during at NASA in the 1960s, early '70s before it was canceled. Russia has flown fission power systems in space a number of times in the 20th century and it on paper solves a couple of problems theoretically. It could get you to Mars really fast. It can give you a ton of propulsion, a ton of thrust. It can also generate a lot of electricity. Electricity is one of those very limiting aspects of space hardware design that we have to grapple with.

Casey Dreier: And if you have lots of electricity. You can do lots of stuff with it including power electric propulsion engines like the ones we've seen on smaller scale ones we've seen on Deep Space 1 or Dawn. Medium scale ones, we'll see on the gateway. So that can be very enabling and important stuff. So we talked through this report, which tried to analyze the differences of Nuclear Electric Propulsion and Nuclear Thermal Propulsion, why those are important.And then also really try to address some of the fundamental engineering challenges.

Casey Dreier: What are we actually asking for if we want to pursue a serious development effort for one of these? So it's one of those things. We're at this kind of, I think key point in history. You already said this is a very interesting times we live in. How do we make sure that 10, 15 years from now, we're also living in interesting times? And that means that we have to be investing in fundamental technology now that pay off in a decade or two. And if we don't, we're faced with the same set of physical constraints that we face now that prevent us from doing certain types of missions that we might like to do.

Casey Dreier: So this is again when and how do we make these decisions. This report is a big aspect of that. Bhavya is an expert. Her background is not just in policy, but in nuclear engineering. Very helpful in this field and we really get into the details of it. I think it's a fascinating discussion.

Mat Kaplan: Well, let's listen to it now. It is the return of Bhavya Lal of NASA to the Space Policy Edition. Here is her recent conversation with Casey Dreier.

Casey Dreier: Bhavya, welcome back to the show.

Bhavya Lal: I am so excited to be here Casey. I love your your podcast. I eagerly await it every week. So thank you for doing these. They are so wonderful for the community.

Casey Dreier: Well, thank you. I appreciate that. This is an area that you are, I'd say relatively intimately familiar with. Your background is in nuclear engineering. Is that correct?

Bhavya Lal: That's right. My bachelor's and master's degrees are in nuclear engineering. However, having said that, space nuclear is a totally different kettle of fish. So there's a lot of learning that's happening on that front.

Casey Dreier: Well, let's dive right into it then So you were on the national academies committee that released in a report earlier this year called Space Nuclear Propulsion for Human Mars Exploration. Nuclear propulsion is something that just organizationally here at The Planetary Society we've been growing really interested in. I personally have been growing really curious and interested in it.

Casey Dreier: But as you point out, nuclear engineering is not an easy thing to wrap your head around. So I'm really excited just to ask you some... Most of these questions, to be honest, things I do not understand. I'm very curious to hear your input and perspective on. So let's just kind of talk maybe big picture for a second to help define some of the terms of what we mean by nuclear propulsion and in space nuclear.

Casey Dreier: In this report, you're talking about fission nuclear as opposed to the use of plutonium 238. What's the difference between what NASA's already been doing with nuclear power in space and what this report is talking about?

Bhavya Lal: Great question. For the last 60 years or so, NASA has been using what are called radioisotope thermoelectric generators or RTGs to produce power and heat. Never any propulsion. So that's sort of the first distinction. Both RTG and fission reactors use nuclear reactions to generate heat. However, the two reactions are very different. Nuclear reactors such as the ones we would use for propulsion involve, or even power generation involve what's called controlled nuclear fission.

Bhavya Lal: We use slow or fast moving neutrons to split a nucleus. And because this is done in a active deliberate way, the rate of the reaction can be controlled with neutron absorbing control drugs for example. So power can be varied, and you can even shut it off. RTG works entirely differently. Heat is produced through spontaneous radioactive decay. So plutonium 238 is artificially created, but it decays with the half-life of about 87 years and releases alpha particles.

Bhavya Lal: So the heat produced during this decay process can be converted into electricity using a device called the thermocouple. There are some other more advanced approaches as well. In an RTG and that's a pretty key difference, heat generation cannot be varied with demand or shut off when not needed. It is not possible for example to save more energy for later by reducing the power consumption.

Bhavya Lal: It's like a hot rock. You got it hot and it's going to get cool at the rate it wants to be. So we've been using this plutonium 238 fuel devices since the 60s. The first RTG was launched aboard a navy satellite, 1961. And since then, we have had a an RTG in almost every NASA mission including several Apollo flights, Viking 1 and 2, Mars landers, the voyager one and two probes that went to the outer planets of the solar system, the new horizons mission to Pluto, and most recently the Mars perseverance rover.

Bhavya Lal: In fact, the upcoming dragonfly mission to explore Titan will also include an RTG. Moving to use of nuclear reactors, the United States has only ever launched one nuclear reactor called the SNAP-10A in 1965. Russians have launched lots of fission power systems. To the best of my knowledge, we have never launched a propulsion system though the SNAP-10A did include an experimental thruster that could be useful for a Nuclear Electric Propulsion system.

Casey Dreier: Basically, what we're talking about here for nuclear fission, it's kind of like the same conceptually power generating source that's used in nuclear power plants. Is that correct?

Bhavya Lal: So for Nuclear Electric Propulsion that is correct. An EP system, basically, yes, you produce heat in the reactor, which is converted into electricity, which then propels ions, electric thrusters that get shut out the back of the system. And TP, or Nuclear Thermal Propulsion system, it's a different process. NTP is actually pretty similar to how chemical rockets work. So for example, in a chemical rocket, a combustion chamber creates a hot gases that are then expanded in a nozzle to produce thrust that pushes the spacecraft forward.

Bhavya Lal: In an NTP system, the energy source is not that combustion, but rather the heat created when the atom fissions. So this heats a propellant, which is most often hydrogen, which then goes out the back as a traditional system. So very different approaches to NTP and NAP.

Casey Dreier: I want to emphasize those two things because those are really key particularly for this report in evaluating different types of nuclear propulsion, these two main types NTP and EP. And maybe we should just like call them nuclear thermal, nuclear electric just so we don't do these soup of acronyms for the rest of the discussion. For sending people to Mars, and that's kind of something I want to emphasize here too that this report that you worked on that was tasked to evaluate a very specific set of requirements specifically for sending people to Mars in a NASA type mission, right?

Casey Dreier: That really drove the requirements in terms of how you evaluated the nuclear thermal option, which was, again, let's just emphasize that kind of this classic rocket where you're using nuclear energy to heat up basically a hydrogen to expel it out, some nozzle propulsive pushing you forward versus nuclear electric, which is an upscale version of what we've seen already on some small NASA missions that use otherwise solar power.

Casey Dreier: So basically, you're using nuclear energy to create electricity that then expels ions out the back. They're two very different types of propulsion even though they both use nuclear fission at their core to create that energy.

Bhavya Lal: That is accurate. In fact, one of the biggest challenges we had as as part of our committee deliberations is to better understand the different challenges in both systems. Nuclear thermal systems, it's almost a single system and it's a kind of system we have a lot of experience with since we know how to operate chemical rockets. It's what I call complicated. It's hard. We have to heat a propellant to very high temperatures, 3,000 kelvin, 2,700 kelvin for example.

Bhavya Lal: But it's doable. It's just a matter of investing in it. We need to solve some materials challenges, but we can do that. NEP is actually a combination of a lot of subsystems. There is the generation subsystem and the conversion subsystem and the electric thruster subsystem. It's what I call a more complex system. Complicated and complex is kind of the the distinction I'm trying to make here. Complicated, it's hard but we know how to do it. Complex, we don't even fully understand.

Bhavya Lal: So one of the findings of the academy's report was that... Our assignment was to kind of assess if we could get to Mars with one of these systems by 2039. And our assessment was that with nuclear thermal systems there is... With aggressive investment in R&D and we don't have it right now, you can make it to Mars by 2039. However, the committee assessed that even with aggressive investment, 2039 is what I would call a sporty date to Mars.

Casey Dreier: Let's step back for just a second before we start really comparing thermal nuclear electric because I want to get to the core of why you were even asked to investigate this. Assuming either one. What's the pitch for using nuclear propulsion and doing all this work to figure out these complicated and complex systems to begin with? What advantage do they give over the technology we have now?

Bhavya Lal: Okay. So now, you're testing my fundamentals, Casey and I'm going to give it a shot. I'm going to already apologize to my mentor, Mark Lewis. He will say I'm over simplifying things, but let's get to it.

Casey Dreier: Let's start with the simple, yeah.

Bhavya Lal: Yes. So to answer the question, we actually first need to understand the concept of specific impulse. Speaking plainly, ISP is a specific impulse or ISP is a rough measure of efficiency sort of like a car's gas mileage. So a propulsion system with higher ISP produces more thrust for the same amount of propellant. Put another way, the higher the ISP system, the less propellant you will need for the same level of thrust.

Bhavya Lal: So you can see where I'm going with this. With nuclear propulsion systems, we get high ISP. Nuclear thermal systems have twice ISP of chemical systems and nuclear electric systems have 10 times the the the ISP of chemical systems. Therefore, to get to Mars you will need less propellant if you use nuclear systems. And since all the propellant we need today is launch from Earth, this translates into less cost.

Bhavya Lal: SLS launch may be a billion dollars launch. So if you're doing 20 launches versus 40 launches for chemical systems. So now you will ask me why is the ISP high for a nuclear system. That's a harder question. So if you remember the rocket equation and maybe you can put that on the episode webpage, you will see that the ISP is roughly proportional to the exhaust velocity of the rocket. In a thermal system because the molecular weight of hydrogen, which is a propellant and the coolant for the reactor, because the molecular weight is lower than that of water vapor, which is essentially what comes out of the chemical rockets, for a given temperature, the hydrogen is moving faster because of its low low weight and therefore giving a higher ISP.

Bhavya Lal: In an nuclear electric propulsion system, the charged particles can be sped up to even higher velocities. So the ISP is even higher, five to 10 times higher than chemical systems. So basically the problem nuclear is solving is that it reduces amount of propellant needed for a distant journey. And because it uses propellant more efficiently, for the same amount, nuclear can provide much higher acceleration which means we can reach the destination faster.

Bhavya Lal: So now I'm coming to your core question. It's a really long way of saying that all else being equal, nuclear reduces the length of time it will take to make a round trip to Mars compared to chemical systems. And given how far away Mars is and how much galactic cosmic radiation astronauts might get exposed to, that's desirable.

Casey Dreier: I think that really is what resonates with me is thinking about the time question. We've talked about this and many people have talked about this over time, but the difficulty in sending humans to Mars when you just think about the requirements for perfect functionality of all of these thousands of systems for using chemical propulsion, talking about two to three years or so for a round trip. And you look at something like the ISS which constantly needs repairs, constantly needs to be resupplied. Constantly things are breaking and is in constant communication with the ground.

Casey Dreier: And to then say we're going to go from that to basically an autonomous human capable supporting life spacecraft, that will be on its own with almost no supply improvements like no ability to provide new materials. For years at a time, that starts becoming just very hard. If you can reduce the length of time things have to function perfectly by reducing your trip time, it could actually simplify to some degree a lot of different problems, life support, psychological issues, health from radiation exposure as you mentioned. And that seems to me to be this really compelling fundamental motivation for humans to Mars.

Casey Dreier: And just to emphasize here, I'll try restating something and you can tell me if this is the correct way to think about it, but nuclear in a sense offers this huge advantage in energy density that then you can use for propulsion because chemical rockets, you're limited to how much energy can be stored per unit volume in hydrogen combustion, at some level of combustion.

Casey Dreier: Nuclear by definition, you're very, very dense. Huge amounts of energy in small spaces that allow you to use just way more energy in general than you could possibly bring with you in a chemical system.

Bhavya Lal: That's exactly right. You could get the same kind of performance with chemical, but you just need so much more chemical propellant. Again, I don't have the exact numbers with me and I don't think SpaceX has released them, but you would need hundreds of launches of a starship to be able to do Mars with chemical systems. So yes, you can do it, but you are going to be taking so much more mass.

Bhavya Lal: There are actually a lot of challenges with aggregating these tanks and again, like you said, all of this maybe may need to be done autonomously. So you're arranging around a spacecraft. These tens of tanks of or hundreds of tanks and then you are pre-positioning these propellant tanks throughout the way. So you cut a lot of risk by having nuclear. Having said that, Casey, I mean there are other long poles in the tent as well.

Bhavya Lal: So we don't really understand the effect of galactic cosmic radiation, extended exposure. I mean, the Apollo trips were a few days max. The ISS is in low Earth orbit and it is not the radiation environment of deep space. So we need to figure out what is the effect of being in deep space for long periods of time. And actually that's one reason a moon is a good testing ground, right? Moon is in deep space.

Bhavya Lal: There's other long poles. You mentioned an environmental control and life support system. All the oxygen we need. All the water we need. All the food we need. Everything we have to take. If you have a car ride, it's a 30-year car ride and you have to take everything, there's no gas stations. There's no convenience stores, grocery stores. Everything you need in your 30-year journey. Well, I guess two to three years from Mars if you're coming back. You have to take everything with you and that's a whole lot of logistics we need to understand and worry about.

Casey Dreier: Yeah. It seems like there'd be like a lot of predictive statistical analysis to say what things are most likely to be needed for repairs, what are most likely to break and how you would have this proper balance of mass to useful repairs prioritizing things that will keep you alive. I always think about Kelly's year-long stay on the space station in the book he wrote about it.

Casey Dreier: He talks about half his time I spent fixing the CO2 scrubber and how he'd get these terrible headaches and NASA would be walking through on the ground like these intricate repairs of these machines that keep them alive. They have to send new materials to repair these machines with. Something your CO2 scrubber or whatever machine broke on the way to Mars, you would hope you would have the right tools to fix it, otherwise you're done for.

Casey Dreier: I think that just emphasizes again the complexity... And also, again, this is where I come down to if you can reduce that trip time, your requirements for assuring performance, I imagine scales at some non-linear way, right? If you want to assure performance for three years, it seems like it would be much harder than assuring performance for a year and a half. That's intuitive. An engineer may correct me on that, but that seems to be the types of improvements you would get from reducing trip time.

Bhavya Lal: That's exactly right. So even though the trip time only goes down, let's say 40%, it is an extraordinary accomplishment to be able to do that. So every month we reduce is that exponential effort. So actually nuclear offers a couple other reasons, so it's not just reduced trip time. But also, we have a broader set of windows to launch. So we are not stuck with a particular time frame, and for which you might cut corners for example. I mean, not that NASA would ever do that, but it's allowed. We have just more windows to launch which is important.

Bhavya Lal: This leads up to the point you were making just right now, nuclear also gives us more abort capabilities than chemical. With the chemical system, once you're on your way, you're going. There is no coming back. There is no changing course. With nuclear, you can abort for a little bit longer than chemicals. Those are important points. Actually, I mean across the board Mars is really hard. Folks who say you know why don't we just go to Mars, obviously we do, and it's a horizon goal but there's so much that needs to be done and so much that can be done in the vicinity and on the surface of the moon. The sorts of things that you brought up.

Bhavya Lal: What is the data that would go in those statistical models to figure out how things break? I mean, we just need to be in deep space for us to be able to answer some of those questions. And again, folks outside NASA have been working on this for a while. Well, I understand one brand wrote the first plans from Mars the day Apollo 11 landed back. We've been thinking 60 years. More than 50 years for how to get to Mars. So there's a lot of information. We have a lot more we need and we just need to get going.

Casey Dreier: I want to just hit on one point that you made, which is it opens up more opportunities to launch to Mars if you have nuclear propulsion. Specifically for this report, you were actually tasked with looking at what was called opposition class launches. Do you want to just briefly mention what those are as compared to what we're usually used to in our 26-month cycle of conjunction class launches?

Bhavya Lal: Yes. Opposition class missions are missions which reduce the amount of time we have to be in space. Conjunction class missions force us to stay on the surface of Mars for a year or longer so we are back in a specific alignment between Earth and Mars. With the opposition class missions, you're not forced. So you can be on the surface of Mars for 30 to 50 days for example. And again, there's advantages especially for the first trip or the first few trips for us not to be on the surface. This is controversial. There's folks like Robert Zubrin who say that when we go to Mars, we want to stay. There's so much to do. And there's others who say, "Well, maybe the first trip, we can focus more of the trip rather than the surface day." Because in order for you to be on the surface of Mars you need to pre-position a lot of cargo power for example.

Bhavya Lal: I mean, you absolutely need to have power on Mars before the first humans arrive. So with opposition class missions, you can spend less time on Mars especially for the first time, which is important. The trip time, like the amount of time you're in space is longer especially for the return journey. Often, you have to fly by Venus, but I guess those are things we just need to figure out better. The one downside of opposition class missions and that's why [inaudible 00:32:16] nuclear really comes in handy is that it has a very high delta C requirement. And you cannot get that as easily with chemical or even NTP systems as easily. But it is feasible and that's where the trades start to get very complicated.

Casey Dreier: And delta V just to remind people is that the change of velocity required, which takes more energy, which takes more propulsion and depends on the type of system you're using. And again, just to really make sure I understand this we talk about opposition and conjunction. Conjunction is basically when Mars is close to Earth when you launch and that's what we do when we send spacecraft to Mars for perseverance. When Mars was coming close to Earth, we launched and it hits Mars on the other side of the solar system. Opposition is when we launch, when Mars is on the other side of the solar system and catch up with it. I love the idea of like let's just do a swing by Venus on the way and wave.

Casey Dreier: I would love to do that mission, I think from an experiential thing. You open up a lot of opportunities. And one question I actually didn't see mention in the report is these broader uses of in space nuclear, which in addition to propulsion, would they be able to provide energy for the spacecraft as well? Power for the spacecraft is also such a precious utility and a limiting factor in so many ways. Does this open up other options for that or can it serve a dual purpose for getting to Mars?

Bhavya Lal: So I think the systems we are currently thinking about do not have the power piece attached to it. But there is this thing called bimodal operation for nuclear thermal reactors where you can generate power and obviously for any P systems, you are generating power already. So, yeah. So that would be very helpful. In fact, we are talking about human missions to Mars, but let's say we talked about science missions. Science missions don't have as strong a need for high delta VR or fast propulsion systems.

Bhavya Lal: We actually don't mind if it takes a few years to get to Jupiter. Although, it would be nice to get there faster. I don't know if you remember the Galileo mission. It had to use multiple gravity assists around Venus, around Earth, and even then it took 10 years With Nuclear Electric Propulsion, you may not need any gravity assists and you have the power which science missions need for instrumentation for communication and other things.

Bhavya Lal: And of course the advantage that gives you is you can conduct extended investigations rather than brief flybys of bodies of interest. You can visit multiple bodies much more easily. And actually, if you find something interesting, you can alter a spacecraft trajectory in response to whatever a particular thing you want to make a change about in a particular mission. So certainly, having both power and propulsion would be a good thing to have both for human missions, but especially for science missions. And that is something that folks like John Cassini and others have written about the value of NEP for science missions.

Casey Dreier: I was interested to say like why is nuclear thermal not generally associated with science? Is it merely because nuclear electric is theoretically better or would science still not benefit from a Nuclear Thermal Propulsion system? Or is there something fundamental?

Bhavya Lal: No. I don't think there's anything fundamental. I think a nuclear thermal is just... It's associated with high thrust emissions. When you have a need for speed, with science missions that is not the most important criterion. And also science missions don't need megawatts of power. They would be perfectly right now. An RTG that, for example, was on the Mars, the Perseverance Rover is 110 watts. I think the New Horizon was, I think, 300-ish watts. Cassini was 500 watts. A kilowatt of power for example on a science mission is good enough.

Bhavya Lal: An NTP reactor tends to generate 500 megawatts of thermal power, not electric. I want to make a distinction. And an NEP that we are thinking about for human missions, we are looking at one to two megawatts. So the NEP system for science missions is a smaller system generating a few kilowatts of power, which is a lot more doable than some of the bigger systems we need for Mars.

Mat Kaplan: Don't leave us. Casey and Bhavya Lal of NASA headquarters have a lot more to share about nuclear propulsion to get around quickly and efficiently in space. You're listening to the Space Policy Edition.

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Casey Dreier: Let's dive in and talk about each of these systems a little more detail so we can emphasize the challenges, the technical challenges that would require to pursue them and just emphasize their distinction a little more. So let's start with nuclear thermal, and this is what you just said that a nuclear thermal creates thermal energy and I think that's really the key word here, that it's not generating electricity. It's just generating the heat that heats up, generally uses a hydrogen feedstock to expel hydrogen atoms out its propulsion system and that creates the thrust.

Casey Dreier: Nuclear thermal tends to be, he said associated with high thrust. So I saw it in the report. This is generally more similar in concept to an existing chemical rocket. Does this make it a more straightforward system overall or is there some inherent advantage of nuclear thermal and just how it works that it seems familiar?

Bhavya Lal: Yeah. There's nothing you said that I disagree with. I'll just reinforce. So conceptually, they're identical to chemical systems. However, they do have to operate at high operating temperatures. The reactor system must heat the propellant to 2,700 kelvin. We don't currently have materials that can handle that kind of temperature especially in the environment, the corrosive environment. But there's other challenges as well. Even though we need less propellant than chemical, we do need a lot of propellant and it needs to be stored in space.

Bhavya Lal: Hydrogen is notoriously difficult to store because it is such a small atom or such a small molecule that it just leaks through. A lot of R&D needs to be done to be able to store liquid hydrogen in space. Also testing. In the '60s, when we tested nuclear thermal systems and we have tried to develop them in the past, we didn't really worry so much about releasing radioactive gases. Remember, this gas is flowing over a reactor, right? So it is in some ways activated. And there's some radioactive particles there. So we need better ground-based test facilities that currently don't exist.

Bhavya Lal: They may cost hundreds if not billions of dollars to make. So there is a cost to that. But going back to your original question, yes, NTP is... And the report said so too that by 2039 with aggressive R&D investment, we can have an operational NTP system. Obviously, we would want to test it by maybe using it for cargo for a while. We don't want the very first system to have humans on it, but it's doable. On NEP, the challenges are quite different. The complexity of the interaction between the various subsystems, the parallel development of all of these different pieces and then putting them together is something that we don't know how to do. While NTP, in Nuclear Thermal Propulsion, we have data from the '60s for example or some experience. I don't know how useful the data would be. But for an EP, we have not done anything.

Casey Dreier: For nuclear thermal, let's just key on this for a little more. I want to follow up on a few of these challenges you mentioned. You said one of the first challenges for nuclear thermal is how do you deal with something that is heating up hydrogen to 2,700 degrees kelvin, which is something around. It's over 4,000 degrees fahrenheit, extremely hot. Something that I was noticing and I don't know, perhaps I was reading between the lines too much on the report, which was that heat, that temperature is actually a byproduct of the requirement of what you went back away at the beginning, the specific impulse.

Casey Dreier: So if you want a specific impulse of about 900 seconds or something, I think was the threshold, you do your calculations backwards, okay, that means we need to heat up hydrogen to about 2,700 degrees kelvin. Is that locked in stone? Is that a fundamental problem? What drives that 900 second ISP requirement? Is there any way to get around that without having to develop completely new materials that will withstand this incredible amounts of heat?

Bhavya Lal: Yeah. So that's a really great question, Casey. For the academy's report, this was given to us. So these are very complicated trajectory calculations that folks with deep expertise. They work on it backwards from high level goals. And the ones that we were talking about earlier for example, how long are we willing to have astronauts being deep space versus the surface of a planet. How much mass do we want them to be carrying with them? How big the habitats. Basically, how can we adjust the mass that the system needs to carry.

Bhavya Lal: So they're kind of work backwards from that. My understanding is that even switching to a conjunction class mission reduces the ISP to about 850 from 900. So it is not a huge reduction. I guess as we start to do these developments, and if it looks like it is really not possible to get 2,700 nozzle exit temperature, then yes, so there would be these trades that would continue to get made and maybe we would need to back away. But for the moment just based on the models and other computations, 900 seconds is the ISP that is kind of our target.

Casey Dreier: Okay. So basically, if you want to have this range of options, opposition and conjunction classes, you need to have performance that then requires this exit temperature, this extremely high exit temperature. We're talking about materials science here, materials engineering, just the really extreme environment that we shouldn't diminish that was actually called out by the report as one of the fundamental technology challenges is like how do you build something to withstand temperatures to this degree. Something that fascinates me about this type of discussion now is how our desires translate into the fundamental challenges that we face when engineering these types of things.

Casey Dreier: I just find out fascinating to say, "Okay, because we want to launch an opposition, because we want to have these set of options, because these are basic physics, therefore it would be in NASA's best interest to figure out how to develop materials that can withstand beyond hellish levels of temperature. That seems like fundamentally just a useful thing for a variety of broader applications, but it's driving it all because we want to send humans to Mars within these certain constraints." I just find that very interesting conceptually that that's how we end up with these specific engineering challenges to decide whether to tackle or not.

Bhavya Lal: That's a great point and actually that also kind of shows one of the differences between how governments think and how commercial entities think. Governments start with the requirements. And if the requirements push the technology to its absolute frontier, then that's what we do, right? In this particular case, the department of energy has a lot of... They're really long-standing world-class labs that do materials research not just for nuclear, but other reasons as well. In principle between industry and these DOE labs and in academia, some of these challenges will get addressed and then maybe you dial down requirements.

Bhavya Lal: I mean, I think commercial folks think about it differently. They think about what can we do and then go from there to developing systems. So it's just a different approach. I just think we need to actually take the time and start to think through these things. I don't think that as much of it has been done as I would like to see. Unfortunately, as you know well, NASA has a 10-pound mission and a 5 pound bag. There's a ton of stuff we are trying to do and this is just one more thing we need to get. Just make those trade-offs differently.

Casey Dreier: That's such a good point and I think really important for anyone listening to remember, yeah, that fundamental philosophical difference of approach between a commercial or private sector and the public sector. I mean, and this is kind of why we have both in the ideal case that they're complementary, but the public sector is saying, "Okay, this is what we want to do therefore this drives all of our investments. It's such an interesting shift when you flip it the other way and say, "Okay, what can we do that becomes useful to some degree that then we can maybe build on, which is kind of you said the more commercial private approach to it?"

Casey Dreier: So, Bhavya, I just want to touch on two more challenges you mentioned offhand just to emphasize again on nuclear thermal and then we'll move a little bit more to nuclear electric. The amount of liquid hydrogen is not a small problem. I think if I remember from the report, you're talking something around 20 megatons of liquid hydrogen propellant.

Bhavya Lal: That sounds about right, yes. And that's a lot of launches.

Casey Dreier: Yeah. I mean, I think there was a replot, I think it was in the report. I've been reading a lot of these lately is the International Space Station is around 400 megatons.

Bhavya Lal: Yeah. 400 metric tons, that is correct.

Casey Dreier: Metric tons. Sorry, not megatons, metric tons. So we're talking about a similar, like a half of that being in propellant. This is efficient. This is nuclear thermal. This is a straightforward one. So we're talking about launching huge amounts of liquid hydrogen that then have to be encapsulated in this hyper efficient manner in these giant amounts to last years because, again, if this boils off, you don't have a ride home from Mars.

Casey Dreier: Again, this is like how do we make really efficient reliable storage for this volatile material. Again, I found that as one of these fascinating challenges and there's one more aspect you said, which is ground testing. I'll rephrase it back to you. You can tell if I understand this correctly. Because you're effectively running through hydrogen basically right through the core of a nuclear reactor that uses uranium, you can get some nuclear material coming or a radioactive material coming out with the hydrogen on the other side. To test it on the ground, you don't want to spew all that stuff into the air, you need to capture it and control it. And that's where these facilities just do not exist anywhere on Earth.

Bhavya Lal: That's correct. As I said, in the '60s, we didn't mind as much. It was a different environment.

Casey Dreier: Literally, yeah.

Bhavya Lal: Now, we absolutely do not want to be having any radioactive material beyond obviously their safety limits going into our biosphere. These facilities would be very expensive to construct. There are some proposals I have read, which are really interesting that instead of testing on the ground, why don't we test in space? Space already has a very... It's a very, very high radiation corrosive environment. Our capabilities in autonomous operations are getting better. So it's actually an intriguing idea. I don't have strong views one way or the other. The academy's report did have strong views. I don't think they wanted to see just space test bypassing a ground test. I mean, it's something we need to continue to think about.

Casey Dreier: So let's move on to nuclear electric just a little bit to emphasize against some of these challenges. And you've given a few previews of this basically, which is... So nuclear electric again, it's using conceptually technologies we know how to use in pieces. We've done electric propulsion, for I think Deep Space 1. Dawn spacecraft uses xenon thruster. We're developing kilowatt scale electric propulsion for the Gateway. We're talking here about megawatts. So we're just scaling that up to a huge degree. And then using a nuclear fission generator to create... Basically, there's a ton of electricity to drive this type of thing. So what are the fundamental challenges from just doing that, that you said we don't know how to even start doing these. What are the key things that we don't know how to start doing?

Bhavya Lal: So I'll tell you one really key one. On Earth, just from college physics, you may remember that when you generate electricity, only about a third of it actually gets converted into power. Remaining two thirds just is heat and it's waste heat, right? On power plants on Earth, we have cooling towers. We have all sorts of kind of ways to conduct away that waste heat. In space, there's no atmosphere. So conducting away waste heat is an enormous challenge.

Bhavya Lal: If you remember 2001: A Space Odyssey, the big spacecraft. There's an NEP one. And even actually in The Martian, you see these big things that look like solar panels. They're actually fins to radiate away that heat. If there's just such an enormous amount of heat we need to get rid of, that's a third the size of the solar panels on the ISS. So we do not know how to get such large amounts of heat in a quick way. Then you already mentioned the electric thrusters we are currently working on or the ones that were used for Dawn and other space missions were in the single kilowatts or 10 of kilowatts. So now we need to be having megawatts of power at that thruster end.

Bhavya Lal: Again, the scale up is a huge challenge. It's a scaling not just those piece, but for each sub-system, there is a scale-up challenge. Then you need to combine it with a compatible chemical system because NEP by itself, Nuclear Electric Propulsion by itself, it will not have the thrust we need to get to Mars especially for human missions. So the proposal for NEP is always combining it with the chemical system. So now you need to make that marriage happen.

Bhavya Lal: We need to do a lot of cryogenic fluid management, research modeling and simulation, research testing, safety and other sorts of regulatory research. A lot of these work can happen in parallel, but there is just an extraordinary amount of work that needs to be done to make nuclear electric repulsion systems come to fruition.

Casey Dreier: There's something you said there that I was trying to wrap my head around in the report. I didn't feel it was discussed as much. So nuclear electric that we're talking about here, and you kind of mentioned this earlier, it's incredibly efficient, but it's very low thrust, right? It's asked to fire for very long periods of time to change your velocity. So in order to get humans to Mars within the time scales that were these upper bounds provided by NASA to consider this report, the committee said you basically have to also augment that as you just said by additional chemical propulsion. So in order to get you moving out of the initial gravity wells... Is that right? For Earth and Mars initially and then you can use nuclear electric in between?

Bhavya Lal: Yes.

Casey Dreier: These are big chemical propulsive things. Did I read this correctly? Because do you not then get any time advantage with a Nuclear Electric Propulsion system if you're worried about getting there fast enough that you need to augment it with chemical propulsion? Do you save any time on the transit compared to nuclear thermal or is this just because it's efficient, it's useful?

Bhavya Lal: In the study, we kept the time as a constant. So we were looking at, I think a 650 or 750-day roundtrip. We didn't change that for NTP or NEP and we worked backwards from that to figure out some of those details. So looking for a time advantage, it wasn't our goal. Our goal was to understand more. If this is the ISP requirement, there's a round trip requirement. What is the NEP system that's needed? What mega wattage would we need the reactor to be? What would be the level of the chemical propulsion system? Then of course we work from that into developing a road map. How would you actually get from here to having a working system by the end of the 2030s? So to answer your question, we weren't looking for a time saving out of NEP.

Casey Dreier: Is that the correct interpretation though from my end that if you are required to add a chemical propulsion system to keep that same amount of time, that NEP is generally going to be slower than nuclear thermal? Is that fair to say?

Bhavya Lal: So you could have a 200-megawatt NEP in space.

Casey Dreier: Sure.

Bhavya Lal: Then you can match up. But our current capabilities, we don't even think anything more than one to two megawatts is feasible. So the answer, you would be correct if we were only looking at those small levels. But eventually, at some point NEP would be capable of doing everything. NTP level speeds. Science level power. But for the moment, for the next 20, 30, 50 years, I think if we need high thrust, we need to combine NEP systems with chemical systems, which is why actually NEP is great for science missions because over long periods of time, tens of years you can get very high levels of acceleration. So over time, you can get that velocity you want, but Mars in the grand scheme of things isn't as far away as Pluto or the Kuiper belt.

Casey Dreier: Right. So let's start talking about some of the policy implications of all of this in our last few minutes here because people hear nuclear and I imagine there's a good segment of people who might be worried about safety. There's going to be a lot of, I imagine regulatory issues that you've already mentioned in terms of environmental control and safety for analyzing nuclear materials. We're talking about here uranium, right? We're not talking about plutonium naturally decaying creating heat, we're talking about fissionable materials. So what are some of the big policy challenges that you see that are going to be slowing down or potentially complicating this process either side of whether it's nuclear electric or nuclear thermal that we have to begin to tackle?

Bhavya Lal: So if you'd asked me this question a couple years ago, I would have had a different answer. In 2019, there was a presidential memorandum on how nuclear systems could approve launch, or how the government could approve the launch of nuclear systems. And there was a policy in place before, but it was very high level. It was very vague. We didn't even know if it really could apply as well to nuclear fission systems. So in 2019, the policy was updated. It really laid out very specific ways on how you would approve for example an RTG work system or a nuclear system with highly enriched uranium versus low enriched uranium.

Bhavya Lal: It's a very step wise detailed process. It will take many, many years to get through. First, you have a NEPA, National Environmental Policy Act statement that says what the environmental effects would be. Then there is a detailed safety analysis called SAR, Safety Analysis Report, which report is then reviewed by this Interagency Nuclear Safety Review Board, which includes all federal government agencies. This board issues a report called the SER, the Safety Evaluation Report, which depending on the level of risk of a launch would either go to the president or stay with NASA.

Bhavya Lal: So there is a process in place which would help regulate a nuclear launch system. So that is no longer as much of a challenge. I mean, obviously there's a public perception challenge, which we just need to work through. We just need to explain that nuclear reactors when they're launched. They are not launched active. It's a cold reactor and it's basically just a metal that gets launched. And the reactor isn't turned on until it's in deep space.

Bhavya Lal: Actually, this is a really interesting thing. At launch, 3.5 kilograms of plutonium 238, which is what's in an RTG has about 60,000 curies of radioactivity, whereas 30 kilograms of uranium has about single digit units curies of activity. So a fission system is actually a lot safer for launch than a RTG system. And the other sorts of things we need to communicate with the public. We are a democracy and what the public says matters. It behooves us to do our job to explain.

Casey Dreier: I kind of wonder about this policy again of just this the environmental review, the safety review. Are those types of things... I have to say this carefully without being blithe about it, but I mean they're coming out of hard lessons learned in terms of dismissive approaches to safety and environment in the past. But at a certain point, are they limiting the amount of technology that we can develop even if they were created for good intentions? I mean, it sounds like to some degree launch is being revised, but I was thinking a lot of this work is going to have to be done through the Department of Energy.

Casey Dreier: Just in my very limited experience with the Department of Energy working through plutonium, which is again, non-weaponizable level of plutonium, they're quite secretive and there's all this environmental additional cost to launching missions with plutonium because of all these environmental reviews. Are those things worth reconsidering for these specific situations or is this kind of an inevitable outcome of working in this nuclear arena that we have to just accept a heavy regulatory burden that's going to add cost and add time?

Bhavya Lal: I think one reason DOE had a lot of bureaucracy around plutonium is because it is weapons grade. So they actually had to put that heavy bureaucracy on top of the plutonium in generating infrastructure. If you've seen some of those diagrams, you produce plutonium by irradiating neptunium-237 targets. At Oak Ridge, instead of one DOE lab and then it gets transported to another DOE lab and then it goes to Los Alamos to get separated. There's a lot of process and a lot of transportation, which needs to be protected.

Bhavya Lal: My sense is that for fission systems, it may not be as onerous, mostly because we plan to use low enriched uranium, which we have a lot of experience and expertise. I mean, the united states has had nuclear reactors for many, many decades and as the Nuclear Regulatory commission has figured out how to make transport, et cetera in safe ways.

Bhavya Lal: My hope is that for fission systems, the bureaucracy would be less onerous. The other part, and we've been touching on it throughout, I mean I think there's a lot more private sector interest in space nuclear systems and I think they have put pressure on the government to make some of these rules easier to understand, easier to follow. And some of that is underway as well. I think as more commercial entities enter the fray, the easier things may become.

Bhavya Lal: [inaudible 01:00:39] a good example. Right now, we have this one plutonium 238 driven RTG. These commercial companies that I know about, they are producing RTGs from other materials that are not weapons grade. An RTG is 110 watts. But what if you only need a few milliwatts for keeping an instrument warm on the moon? But you're stuck with this super expensive, because the government only has... It's like four set as long as... You can have any color you want as long as it's black. So these new companies are coming up with ideas with much smaller RTGs which will have a totally different regulatory regime, and that's a good thing.

Casey Dreier: Is there any fundamental... When people hear commercial companies doing nuclear work, is there any reason we should worry beyond what government... I mean, they're bound obviously by safety standards and so forth. But at what level can private companies work with nuclear material? Again, this distinction between what's weaponizable or versus not, is that going to be the fundamental difference between the two regimes?

Bhavya Lal: Great point, Casey. And in fact, that is one reason NASA chose to... So all of NASA... Not just all of NASA, the whole entire world, every reactor we've ever launched has been highly enriched uranium. The one we launched in 1965, and the dozens of reactors, the Russians have launched, the Soviets launched over the years, all HEU. NASA has made a decision, a conscious decision to switch to low enriched uranium. And one reason for that is it reduces the barriers to collaborate with the private sector, reduces the barriers to collaborate internationally. It grows the number of players that can be involved. It doesn't have to be just DOE labs, we can work with private labs. Other people can get involved. Startups can come into the game as we've seen that happen in recent years.

Casey Dreier: Last question is something that I've been stewing on for a while. I'd be very interested to hear your thoughts on this, which is we're looking at nuclear whether it's thermal or electric, just to put aside. We're looking at this opportunity to say, "We could invest in a fundamental technology advancement that obviously can enable changes and advantages to sending humans to Mars." But a lot of things as you just said commercial interest. There's a scientific interest in having these propulsive systems, but we just mentioned commercial stuff.

Casey Dreier: They're not going to make these scale of propulsion systems. This is a fundamental government R&D thing. It's not going to be cheap to do this. For context, I was looking back to the '60s about what NASA was spending on its nuclear rockets propulsion systems at that point, and it scales out to rough numbers half a billion a year. NASA right now is spending 100 million, so we need to ramp up a lot to really tackle this. Is there so much value in doing this type of fundamental advancement in propulsion for sending humans to mars that it's worth waiting until this is done and then designing missions around this enabling technology, or is this something that can only or should happen in parallel with getting humans to Mars using the technology we have now or should we prioritize getting humans to Mars with the technology we have now instead of using that money to do nuclear propulsion, which won't pay off for 20 years. How do we make that decision given a limited set of resources to work with?

Bhavya Lal: Wow. Really great question, Casey and we'll take a lot of thinking by a lot of people. My initial reaction to that question is nuclear propulsion isn't just about getting to Mars. We want to be a space faring civilization, not just for getting humans out into the solar system, but getting science robotic emissions out into the solar system. This is the technology we need to eventually develop. So there is no reason to not get started. Having said that, I think that if there's alternatives that we are seeing, we should be supporting them.

Bhavya Lal: So again, I'm just thinking aloud here. So if for example, SpaceX is planning to go to Mars with chemical systems, I think we need to see how they're doing, and if there's ways that can be supported. Because if they can focus on that piece, maybe NASA can focus on NEP, which is long-term everything. And the very initial thing, we need to do in terms of thinking what limited resources what do we do, I think nuclear power is a higher priority than propulsion. When humans get to Mars, they will need power. Mars is 1.6 times farther away from the sun, and there's 50 to 60 less solar flux. Solar power is not an option on Mars, and you remember what happened to the Opportunity rover all covered with dust.

Bhavya Lal: Even if we do put solar panels, it'll be this size of a football field. In fact, somebody, I was speaking to was kind of saying five football fields if we account for dust storms. So let's start with power. It's not as expensive as propulsion and it has traceability to propulsion. So for example for NEP, the core is power, right? So if we start with power, we can continue to make it out to go to NEP. Obviously, it will be small NEP as in NEP for science missions, not the human missions.

Bhavya Lal: But that's a start. So that's kind of my recommendation. I think the direction NASA is going in as well although, obviously, we have a lot of constraints. We have congressional direction to invest in NTP and we will. We always follow the law. But I would say that power is something we need to prioritize over propulsion for the moment.

Casey Dreier: And power of course works at the moon too, right to the more immediate needs for your two-week lunar night in addition to Mars, right? Power is like a fundamental constraint in space that you're always working against, right? The more power you have, the more you can do with it. So that's an interesting point. Then again, that's the frustrating contrast to me is that it looks like nuclear thermal seems like a very useful as propulsive in my opinion more than nuclear electric just because of the thrust advantage. But then you don't have that multi-use utility that you get from nuclear electric, where you're just generating all this electrical power.

Casey Dreier: So nature has not done us a favor in this decision, unfortunately. We have to really think through this. But again, that's the point. And what's exciting to me fundamentally, why I enjoy this report and why we're looking into this is that this is being evaluated and committed to in a very serious way, and I think we haven't seen in decades. This could be one of those fundamental enabling technologies that we finally start investing in again that can really change how we get into space and stay in space.

Bhavya Lal: That's exactly right, Casey. I think in the past when we started and then we stopped, and we started and we stopped. It was almost one step forward, two steps back. However, I am very optimistic that this time it is going to stick. Not only do we have this launch approval. We actually have space policy directive six which lays out a national strategy for responsible and effective use of space nuclear power and propulsion. There's an executive order that requires that NASA develop a plan for Rohingya and robotic missions using nuclear systems through the 2040s. The Biden administration is supportive of at least surface power. The constellation is coming together as they say. I'm super excited that we will finally be moving forward.

Casey Dreier: Great place to end it. Bhavya Lal, thank you for joining us on this month's Space Policy Edition. Let's stay in touch and join sometime in the future. There's always so much to talk about.

Bhavya Lal: It was so fantastic to talk to you, Casey. Talking to you is always sort of brain expanding for me. I love everything that Planetary Society does, a proud member and keep doing the good work.

Casey Dreier: Thank you.

Mat Kaplan: Casey Dreier and his guest, Bhavya Lal of NASA, often found at NASA headquarters nowadays advising the new administrator. Great conversation, Casey. This is one that a lot of us who are science fiction writers and believers in a future where we zip around the solar system, we've been looking forward to for a long time. There are all those other concerns that you began to talk about with Bhavya though. Absolutely fascinating. That's all we need to do today except that I will remind you of Casey's newsletter that you can subscribe to, that monthly newsletter we talked about upfront. Do you have that URL in front of you again, Casey?

Casey Dreier: Yeah. It's the Space Advocate Newsletter you can search for or planetary.org/space-policy and we'll link to it also in the show notes for this episode.

Mat Kaplan: Also, planetary.org/join. The most important URL we will give you today. No slide against the newsletter.

Casey Dreier: One enables the other.

Mat Kaplan: Exactly right. And this is the enabling URL. It's the one that will allow you to join us at The Planetary Society. I'm a member, Casey is a member. We would love to welcome you. And we're very happy to have welcomed you once again to the monthly Space Policy Edition. We will be back almost certainly on the first Friday in September of 2021. Until then, we'll have several weekly episodes of Planetary Radio for you that I hope you'll join us for. Some great guests coming up there as well. Casey, keep up the great work and I look forward to talking again soon.

Casey Dreier: Always good to be with you, Mat.