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Mark Kushner: Alright.

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Mark Kushner: Uh Dr. Falls in has a story career in the field of advance and electric propulsion. He receives the Bs from the Ohio State University. He got his Phd. From Princeton University mechanic on Aerospace Engineering.

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Mark Kushner: That's dynamic. Or do you watch propulsion file?

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Mark Kushner: He's been working at Nasa Marshall since two thousand and four, where he first had an advanced concept study team since subsequently transmitted to the chief engineering team,

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Mark Kushner: associate and senior member of the I triple, and then make a plug for his most reason.

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Mark Kushner: And um also you get a nerve on these topics is one of the we'd like to give you this commemorative mug from Nipsey. So let's give that round of applause for that,

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Mark Kushner: you know. Normally you have to. Uh, you have to do the work before you get the mug,

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so I guess i'll leave now.

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Mark Kushner: Oh, thanks, everybody for coming. I really appreciate it. Thank you, Ben, for that introduction. I don't know about story career, but I've I've had a very interesting path getting here. Um, thank you. Everybody here in the room that that showed up today uh those of you that I met earlier today. Uh, in your offices, and and and what not. It's been a great day up, and have really enjoyed my time here.

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Mark Kushner: Um, and I just. I enjoy coming to college campuses and talking about this um,

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Mark Kushner: and that was been said. I am the chief engineer for the space nuclear propulsion project at Nasa Marshall.

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Mark Kushner: Uh, within our portfolio. Uh, we manage both the development of nuclear thermal and nuclear electric propulsion, because this is a plasma seminar. I'm going to focus mainly on the nuclear electric propulsion side of things. Um, This is the first time I actually given this talk kind of kind of tailored for this audience. So uh, so we're going to see how this goes. But I think we're going to have a lot of fun,

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Mark Kushner: and we're gonna talk about kind of the critical development challenges for that. We've been looking at. Uh, you know. Ben's mentioned the National Academy study uh about six or eight months prior to that. Then Nasa, Engineering and Safety Center had a study looking at readiness levels for technologies for nuclear propulsion.

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Mark Kushner: Both it and the National Academies came out to basically the same conclusion.

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Mark Kushner: Um, The technologies are still at low readiness level, and you need to make concerted advancement efforts to get those technologies to the level needed to consider doing a Mars mission in the two thousand and thirtys timeframe. And why Mars Mission, so you can use Um,

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Mark Kushner: somebody's

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Mark Kushner: okay.

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Mark Kushner: So you can

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Mark Kushner: Sorry. A little feedback here in the room. Uh: you can use the uh uh um. It's very distracting.

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Um.

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Mark Kushner: You can use nuclear power to do a variety of missions. You can use it to go to cylinder space. You can use it to do deep space science missions. It turns out that the human Mars mission is one of the most propulsively challenging we can think of. So to develop the technologies for that mission, you necessarily will in the intermediate steps, be developing technologies you would need for those other types of missions. So that's part of why we like to focus on the Human Mars Mission. It's also very cool mission in general. So you know, there there is that going forward.

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Mark Kushner: So that is a nuclear electric propulsion system. It doesn't look like much right now. So this is a a schematic

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Mark Kushner: uh configuration of what such a system may look like. You've got the reactor down here one end power generation. You've got the thrusters kind of out on these booms in this configuration.

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Mark Kushner: Um! A chemical stage back here, which would give it additional high thrust, right? Because electric.

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Mark Kushner: Uh, most people. Okay. So you guys kind of know It's low thrust high isp uh. So you get high specific impulse, high exhaust velocity and be able to go do certain missions. The um.

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Mark Kushner: The problem is when you're leaving uh and arriving at gravity Wells right. You need to either spiral in and out, which takes a lot of time, or you need an an alternative propulsion system to be able to do a high thrust burn. So we've really been looking at doing a Neptem setup where you use a chemical propulsion system to uh leave uh Earth and do an or entry at Mars, and then leave Mars and come back to Earth and you burn the electric propulsion system to pick up additional momentum

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Mark Kushner: between Earth and Mars, and then coming back,

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Mark Kushner: and then these uh gray panels here, which I'm pointing to uh, those are the radiators, and you could see they're very large. And so it turns out that that they're one of the larger systems, the components of the entire system, and we'll talk more about why, that's

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Mark Kushner: uh critical. And why that can be uh a challenge uh for the uh, these types of systems here in a little bit. But you see here, you've got the drawing of it. And then uh over here we've got the schematic uh of what this system looks like just as a block diagram looking at the flow of

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Mark Kushner: a fluids and powers and and uh electricity. So your reactor sitting down here in this Ct critical technology element uh or subsystem

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Mark Kushner: one. So the reactor generates heat. It's really just a heat source. It's a hot rock, just like any kind of terrestrial uh power generation station that has nuclear power. Um and generous the heat. You've got to pull it out,

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Mark Kushner: and somehow get it to a a a power conversion system that takes thermal energy, and in this case dynamically converts it to a motion. Uh Now, you can think about converting heat directly into electricity with thermodynamics or therm electrics. Uh, those are pretty much our lower efficiency uh lower technology readiness level than the dynamic power conversion.

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Mark Kushner: So this is drawn out as a break in the system. So you got a turbine, a compressor, um, you know, and you reject heat down here to uh the Ct. Five, which is the radiator Panels

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Mark Kushner: determined, turns. Your power. Generation makes electricity, uh which you, then pump to the spacecraft, but then to your thruster, uh which then, uh, you know, Accept that power and generates thrust

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Mark Kushner: uh You've got this box here kind of between the thruster and your power generation and pmad, not a ppu or D to you this. So that's the power processing unit, or may maybe a direct drive unit where you're accepting the uh current voltage from the spacecraft,

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Mark Kushner: and you're converting it to the flavor uh the type of current voltage that the thruster wants to see um. The thruster itself is not so difficult in terms of costs. That Ppu is one of the higher uh cost items on the thruster system. Uh, because power electronics, you know,

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Mark Kushner: uh, this is driving the electronics industry, right? Power electronics for electric thrusters to fly megawatts of electric power

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Mark Kushner: is not the thing driving the industry right now. So it's very specialized and very hard to get the components that. Oh, by the way, are sitting there in a soup of radiation, both from the reactor

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Mark Kushner: uh and from deep space kind of imparting uh galactic cosmic rays to it.

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Mark Kushner: So you have these five critical technology elements, and you really need to advance all of those to a level where uh, you know where you're confident that they'll uh produce the output you want at the scale and the power levels you want, but also

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Mark Kushner: that they'll properly interface with each other Right? They don't all exist in in isolation. You actually have to make sure that at the end of the day they will fit together. And so these are some of the challenges you have

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Mark Kushner: for uh nuclear electric propulsion as we go on here. I'm going to talk a little bit more about some of the challenges of of several of these subsystems. And please, if you have questions, feel free to ask them as I go. I kind of prefer that. Actually.

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Mark Kushner: So. I don't want to spend too much time on this chart. Um, but what we have here on this first one We've got the the transit Transit Times for human Mars Mission uh and total Mission Delta. V. Now, who's poor propulsion people in here?

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Mark Kushner: Some, so you kind of understand Delta v. So Delta V is the energetic cost of doing a given mission.

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Mark Kushner: Uh. So it's. It's basically the momentum increment you have to impart. And so to go faster to a planet. Say, Mars. Uh, I need to impart more momentum overall to my spacecraft.

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Mark Kushner: And so you see that you need more momentum to get that tel to V, and then, and this is that curve that closes that mission so higher. Delta V. You go there faster. Why is that important? So nuclear electric propulsion?

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Mark Kushner: Uh, is a high, specific impulse system. So the only thing about the rocket equation which tells you the delivered mass fraction to a destination. You know that you know you're

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Mark Kushner: uh your delivered mass. Fraction is a function of both the Delta V

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Mark Kushner: and the specific impulse or the exhaust philosophy of the rocket. Electric thrusters are thousands of seconds of specific impulse or tens of thousands of meters per second of exhaust velocity by way of comparison. The rs twenty-five

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Mark Kushner: is about four hundred and fifty seconds of vacuum is about four thousand five hundred meters per second.

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Mark Kushner: So

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Mark Kushner: uh, the ratio of Delta V to that exhaust velocity

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Mark Kushner: to an exponential gives you your uh delivered mass. What that means is this is this other church we have round trip

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Mark Kushner: uh uh duration, and we have initial mass in Leo. So I want to do a mission faster. Uh, I want to, you know it takes more delta V

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Mark Kushner: to do more Delta V. I need more specific impulse to have less mass. I need more specific impulse, And that's why nuclear thermal and nuclear electric

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Mark Kushner: kind of have these nice lower curves on this scale. So it says I could do a mission faster, and I can do it for less mass, using nuclear propulsion than I can with chemical uh, or that I can with solar electric propulsion. It's not to say you can't do it. It's just to say that

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Mark Kushner: I need to launch less

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Mark Kushner: mass from the ground to do that mission. So I've hired Delta v capacity, but that can also do the more robustness, because if something goes wrong, I've got enough propulsive utility to change course. Possibly turn around, get come back early, so it gives me a lot more uh of uh leeway and latitude in how I fly my mission.

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Mark Kushner: It was really useful, because I may not just want to fly this one mission there may be there are. There are different curves like this for different mission opportunities depending on where the plants are relative to each other when I depart when I arrive. Um! And so i'm looking to build the capability to be able to hit

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Mark Kushner: a lot of those opportunities, not just one single one. I thought I saw a question in here. Yeah. I was wondering why the those curves on the right hand plot are disjointed there. Seven hundred and twenty things

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Mark Kushner: there is multiple,

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Mark Kushner: Yeah. And so so I believe, and I don't know the answer to that question off the top of it. It's. I think that's an orbital thing, because you've got to make sure that your orbits right. If I leave verse. I better hit Mars, and if I leave Mars I better hit earth again. Um. Otherwise astronauts are not very happy

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Mark Kushner: if they go speeding by, and there's no earth or by they get really upset about that.

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Mark Kushner: So yes, please. What's the difference between conjunction and opposition classes? Is youified here? So uh, so conjunction and opposition classes. Uh are two different types of missions. You can fly to Mars. Essentially you fly to Mars the same way. You'll leave while Mars is kind of passing the earth and catch up to it.

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Mark Kushner: Um! But on a conjunction class you wait until Mars is uh in conjunction with her. So we're both on the same side of the sun again before you depart. So conjunction class is a long stay opportunity at Mars opposition class. I get there.

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Mark Kushner: Uh, but then I leave again very soon after, when Mars is in opposition, or on the opposite side of the sun from the earth. Um! So it's a short stay opportunity. They're both, you know. They both take a a while to do um. The opposition class is actually a higher Delta v

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Mark Kushner: um opportunity than the conjunction. So again, that's another thing. We're looking at looking at things that are more propulsively intense. Uh, so that if I wanted to do something that was easier, you know. It would be more straightforward to do

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Mark Kushner: all right. So

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Mark Kushner: basically, there is, you know, current capabilities will be like chemical, right? So there's a huge growth potential in what I can do if I can do this the nuclear way.

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Mark Kushner: So what do I mean by nuclear? So let's talk about nuclear physics. This is uh a chart from a colleague of mine at Marshall, uh which I've I've uh shamelessly stolen.

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Mark Kushner: Uh, but these are two ways to do nuclear power generation. The first is radioisotope. Radio is to It takes plutonium. Uh, you have radioactive decay. So it has a half life. It releases some amount of energy per decay Um!

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Mark Kushner: And and that there's the level. And so it's It's just you know, releasing energy all the time at a certain level slowly going down, but over a very long period of time,

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Mark Kushner: a fission reaction. You've got uranium. You bring in a neutron that neutron splits a nucleus uh into a fission fragments and releases energy. You can see that it's a lot more energy released per fission event, but it's also not just a random decay process either. It's controllable, so I can adjust how fast that process is occurring, and I can just the power being released, which is why fission is so much more attractive,

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Mark Kushner: because not only am I releasing more power per event, but I can have make it a much higher power density source. Um! That's why we have nuclear reactors for power plants and not radioisotope sources for nuclear power plants. Uh, also, I notice here it launches hot um

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Mark Kushner: plutonium is uh, not natural right? We create plutonium at the minute plutonium is born. It starts to radioactive decay. So it is radioactive hot from the moment it's more uh. Now, you see, we've actually launched a whole bunch of plutonium uh two of our Mars Rovers have it.

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Mark Kushner: A voyager, has it, Pioneer? Has it, Cassini? Had it. So you know,

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Mark Kushner: we've launched a lot of radio I stuff, but it is hot. It is radioactive, dangerous from the moment it's produced.

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Mark Kushner: That's what's different about a fission reactor fission reactors. I can build one. I configure their uranium in the right configuration. Um, but they don't turn it on. So it's not radioactive hot until I actually reach space and activate it. So it's very safe in terms of of building it

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Mark Kushner: and launching it. Uh, now, I've got to be careful to make sure. I don't inadvertently turn it on, because if it's in the right configuration and I mess up, it will go.

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Mark Kushner: Um. But it is radioactive cold until I launch it until I get to what we call a nuclear safe orbit. That's an orbit above which it's basically never coming back, which is where we want it to be. We don't want it ever to come back once it goes up, and so that's one of the main reasons Why,

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Mark Kushner: uh, we like fission. You know It's got high power density, and it's inherently safe until we actually turn it on. Those are great aspects for a power source.

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Mark Kushner: These are these two studies I mentioned uh the Nasa Engineering and Safety Center and the national Academies of Science engineering medicine. Uh, had studies on the current state of nuclear propulsion. They looked at both Ntp. And Np. I've pulled out the Nep. Parts here for our benefit.

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Mark Kushner: Um, I'm not going to read all these to you, you guys, if you want to go back to the the video and you know, stop it and read through, you can uh, but really what they say, uh in in shorthand are a lot of the critical technologies are not ready. Um,

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Mark Kushner: The critical technology levels that advocates of each technology say in the literature are overestimated. Everybody kinda kind of says that they're better than they are.

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Mark Kushner: Um,

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Mark Kushner: and that we need a large level of concerted investment in these technology. There' been a lot of programs and projects over the years lot of investment dollars, but not a lot of progress, because they've been focused on maybe missions and not on actually developing technologies and advancing them. So they kind of get caught in this do loop of Well, we got to do this mission. Okay, we're going to start designing for it. Okay, the mission changes. Okay, we've got to change our design, and they never get to the point where they build

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Mark Kushner: hardware and test it at the right sizes, the right temperatures and the right scales to actually show that these things will actually work when you put them together right.

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Mark Kushner: We're talking about things that are much higher power. Um orders of magnitude larger than anything we've ever flown uh in space. And uh,

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Mark Kushner: it's not clear that it's just straightforward engineering. It's not clear that it's just scaling to a larger size. So we really have to be sure that we test these things thoroughly at scale

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Mark Kushner: to make sure we understand the right problems. Um, because you're going to put things together. You know this is This is one of the examples I like from very recent history who watch Artemis go up,

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Mark Kushner: or video hardness going up, who watch the green run before it,

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Mark Kushner: you guys familiar with the green run. So

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Mark Kushner: Artemis has four rs, twenty-five engines on it. Right? Space shuttle main engines.

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Mark Kushner: These are engines that have existed my entire life, right? We've run a million plus seconds on these engines and ground tests. They've flown on one hundred and thirty, some shuttle missions,

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Mark Kushner: and yet, when they put four of them in a configuration on the course stage, and what to run it At Stennis

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Mark Kushner: something happened that wasn't expected.

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Mark Kushner: That's why you have to run it at scale configuration, putting it together, integrating it actually matters. And those are the kind of problems you need to fer it out before you actually fly something.

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Mark Kushner: So it's about the challenges of doing nuclear electric propulsion. So challenge number one.

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Mark Kushner: I like to all the high essay, low and rich uranium challenge. So, hey, Lou, so uh, most

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Mark Kushner: nuclear work done, and for space reactors in the past has been done using H of you, or highly enriched uranium. Well, what's highly enriching? Well, that's that's weapons. Great uranium right it's very high density of uranium, two hundred and thirty-five so very high enrichment um

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Mark Kushner: of course, the problem with that is that it's got a very high proliferation risk. If you steal that, you can make a weapon with it.

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Mark Kushner: Um, which is bad. So Halu is below twenty percent enrichment so low and returns below twenty percent enrichment.

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Mark Kushner: It's a much lower pro proliferation risk, because you can't just make a weapon with it, and there's a big gulf between having twenty percent enriched and having ninety percent enriched. That's that's a lot of effort to put in. So you know

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Mark Kushner: It's a lot safer from a security and proliferation standpoint, which means it's a lot less costly.

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Mark Kushner: It also means that it's easier to get a license to handle and use it, and that's the second part here. It allows us to have broader engagement with the nuclear expertise in the country

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Mark Kushner: for for for high enrich uranium.

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Mark Kushner: Basically the only people that can handle that are the Department of Energy, and maybe one or two other companies in the country.

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Mark Kushner: That's not a lot.

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Mark Kushner: I get to lower enrichment levels. A lot more of my industrial base can actually start to contribute to this. They can actually start working on this, they can start to bring ideas up uh to the front. That, uh,

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Mark Kushner: you know. Maybe the big guys can thought of or wouldn't have thought of. And so it's really useful, not only from a from a growth of the industrial base, but also from just engaging that that intellectual expertise, that intellectual base of the country.

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Mark Kushner: Uh, to be able to use Halu because all of a sudden they can all start working on this problem and coming at it from different ways.

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Mark Kushner: Um.

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Mark Kushner: And so and and you'll see that you know It's not just the expertise of engagement on

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Mark Kushner: space nuclear propulsion. We've got in space power generation, terrestrial micro reactors uh Pele, which is a Dod reactor to deployed to the battlefield. Uh all these different projects, all these different programs, some government. Some venture capital funded

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Mark Kushner: um, but all trying to engage and grow that industrial base. They're coming up with some very unique and new solutions that have never been tried before.

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Mark Kushner: So why is it a challenge? Well, the challenge is:

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Mark Kushner: Can I make a nuclear electric system work

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Mark Kushner: with Halu?

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Mark Kushner: It's not as higher performance as he. You I need more

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Mark Kushner: uranium total, more mass,

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Mark Kushner: because i'm making up for the fact that they're not as much fissile material

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Mark Kushner: which is fine. Um. I can probably live with that. Um, I mean nuclear power plans have much lower enrichment the things they're not Mass limited, you know. I can go out to a nuclear power plant. See the big cooling tower and everything. You know they're They're making gigawatts of electric power,

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Mark Kushner: but they're giant buildings and concrete structures, and those are things I can't fly in space. So that's the challenge. Can I make that halo work? Because if I can do that, I get to engage with that broad expertise I get to align with those other projects that are also using low enrichment. Um.

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Mark Kushner: Now we've done a lot of work on initial initial studies on on low enrich uranium.

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Mark Kushner: It looks promising. It looks like the mission will close with margin, so we think we can make it work. Um, These are space policy things. Um, Us. Policy. Basically. Um,

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Mark Kushner: we've used H for a long time because of the proliferation risk risk, and because of the political nature of nuclear in general. Um. The Government came out and said in Space Policy Directive Six.

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Mark Kushner: We want you to use low enriched uranium

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Mark Kushner: unless there's no other way to do the mission.

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Mark Kushner: We want you to use low, enriched uranium.

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Mark Kushner: So not only is it potentially really useful from an engagement or the workforce. It's very useful uh it. It It aligns with us. Uh: policy.

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Mark Kushner: Yeah, this is basically a linear relationship between like the original level. So it is a twenty percent low enriched uranium. I don't know four and a halfx less uh

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Mark Kushner: So the question is, if there's a linear relationship between the enrichment and the power output. Um! And the answer is not really so. Um, because you have, you have to have criticality.

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Mark Kushner: So you've got to make sure that the neutronics work out. So it turns out not to be linear um, and and that does seem to be something of a little bit of a problem. To some extent it's it's not. It's not very harmful either. Now,

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Mark Kushner: one of the things that that you can do as well. We are typically talking about moderated systems, and i'm not going to get into the nuclear engineering of that. Um. But you know you've got fast systems and moderated systems, and so their neutronics are different. So there are some some things you can do to

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Mark Kushner: not so much to take advantage of it, but but lesson the impact of the lower enrichment level.

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Mark Kushner: It's not perfect. You still have more mass, but it's not a one to one ratio.

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Mark Kushner: These are some of those projects I was talking about where that uh are trying to leverage halo. Um!

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Mark Kushner: Of course you got my project. The Space Nuclear propulsion project uh fission surface power, which you see here kind of a schematic one. One looks like you have the reactor, and then the pmad, and then you transmitted out here somewhere to where uh a habitat or astronauts might be on the surface of the moon. So that's tens of kilowatts

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Mark Kushner: uh darpa's draco, which is an ntp demonstrator in c. Lunar space

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Mark Kushner: um the Air force uh jetson uh project, which I hope they have the little noise when they when they run their rocket um, and that's a tens of Kilowatt Electric. Uh, proposed demonstrator for nuclear electric propulsion.

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Mark Kushner: Uh. And so what you're starting to see is that there are multiple agencies with kind of some overlapping interest. Now Draco and Jetson

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Mark Kushner: and the Nasa Marshal. Uh uh Nasa, Ntp and nap and fission surface hard work. They're different. They have different goals and they have different requirements, but there are overlaps and some of the technologies needed. And so at those points that's where it really is starting to make a lot of sense to look at,

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Mark Kushner: potentially partnering across the Government across different agencies, to try to bring some of these to fruition and even bring them to frozen faster.

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Mark Kushner: But in terrestrial use we I mentioned you got venture capital and the Department of Energy investing in these terrestrial micro reactors. And then, Pele, which is this deployable reactor which you put on a truck, move around, run it, supposed to be able to take it down in like a day or two, and put it on a truck and move it somewhere else, which sounds slightly crazy. Um,

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Mark Kushner: but you know, I I think I think it's got potential uh, But the nicer thing is that these reactors

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Mark Kushner: in terms of power levels output levels are kind of what I need for any P.

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Mark Kushner: So the reactor design part

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Mark Kushner: is kind of right in that sweet spot that i'm looking for for human Mars nuclear electric propulsion. So there's a lot I can leverage right from this area right here in terms of reactor design

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Mark Kushner: that's really great.

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Mark Kushner: So

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Mark Kushner: after you figure out that you can use low enriched uranium. Now, what okay number two the actual power system. How do I take

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Mark Kushner: that heat?

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Mark Kushner: Convert it to electricity

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Mark Kushner: and do it in a way that's mass efficient,

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Mark Kushner: all right. It can't way too much, or else my entire spacecraft will be power system, and I don't want that. I want to be able to actually carry something useful.

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Mark Kushner: So What do I have? I've got a lot of continuous operation couple of years worth of continuous up, continuous

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Mark Kushner: unattended

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Mark Kushner: operation, right? This is not like a nuclear power plant where I can shut down. Let everything cool off. Bring it A bunch of workers, you know, crane out some things Once this starts

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Mark Kushner: it's pretty much got to continue running the entire time, the missions going on

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Mark Kushner: so continuous operation for a long period of time

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Mark Kushner: the reactor.

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Mark Kushner: It's just a hot rock.

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Mark Kushner: Now,

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Mark Kushner: the difference between the terrestrial design and the uh in space design is, I want to run it hotter.

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Mark Kushner: I'll explain why that is in a minute not as hot as I need to run nuclear thermal propulsion by far, so i'm definitely more in the realm of the power reactors for the ground than I am for a nuclear thermal rocket which runs it

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Mark Kushner: three thousand degrees. K.

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Mark Kushner: It's really hot, these twelve to one thousand four hundred K.

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Mark Kushner: So I take that heat and what I do right. I put it into a power conversion system. It's a closed cycle. You see it one drawn here. You got a turbine and compressing the turbine turns. Both the compressor and a generator makes electricity. Uh, the heat comes in from the reactor. The cold side here goes out to

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Mark Kushner: the radiators right? Because it's a thermodynamic cycle. I need a hot side and a cold side.

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Mark Kushner: Um, and this is a a bright and six uh system you can imagine, uh K ranking, or a sterling power generation system, you know. But Brayton, for the power levels for megawatts of power. Um tends to be kind of the one that floats to the top is the most mass optimum.

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Mark Kushner: It's closed cycle, and I want a hot inlet. That kind of goes with the reactor. That's very hot.

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Mark Kushner: Here is the really big, interesting point.

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Mark Kushner: Normally, we want to maximize the efficiency on things right. That's what we do in aer of space. That's kind of how we work

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Mark Kushner: Turns out. You don't want to maximize the efficiency of the output here, little counterintuitively. Couple of you're staring at me like, What are you talking about? You always want to maximize the efficiency. Stick with me. I'll explain it.

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Mark Kushner: So the heat, rejection. The radiators are the last part. Right? That's the last part downstream. So you got power, generation, power, heat, creation, power, conversion, heat, rejection.

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Mark Kushner: So we got the radiators, which is the last part. That's the he goes out.

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Mark Kushner: But what's radiation? Well, it's. It follows this equation right? The radiation equation. You got the emissivity. Boltzmann's constant the area, and then this T to the force.

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Mark Kushner: Well,

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Mark Kushner: and then that t to the fourth is really important, right? So the radiators are hot,

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Mark Kushner: but they're not that hot things that glow right. They radiate really well, because they're really screaming hot.

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Mark Kushner: These radiators are not glowing there by, you know. Couple several hundred degrees, c. Right. They're warm,

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Mark Kushner: but they're not super hot, so they're not rating very well.

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Mark Kushner: So if my temperature is lowish, what does that mean? My area has to go up in order to reject enough power.

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Mark Kushner: This gets back to not wanting the highest possible efficiency. How does this tie in? So i'm not interested in the performance of any one of these things. I'm interested in the overall mass, because that's really what I have to launch into space. So how do I make the system lighter per unit power.

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Mark Kushner: I run the power conversion at a lower efficiency. What does that do it me? Well, First of all, I run my reactor hotter,

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Mark Kushner: I run my power conversion at a lower efficiency. So going into my heat rejection side, I'm. Hotter. What does that mean? That means my radiative temperature is higher. Well, if my temperature is higher, my area can be less

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Mark Kushner: so. Look at this graph, this chart here, so you've got two temperatures.

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Mark Kushner: This is a reactor temperature of one thousand two hundred K. This is one thousand four hundred K. Now this is broken out at a higher level of fidelity than I. I really need. But kind of start from this light blue line here and here, and add up everything above it here and everything above it here,

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Mark Kushner: and those are the radiator masses

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Mark Kushner: you can see for just a couple hundred degrees K. Difference on inlet temperature

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Mark Kushner: for optimized

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Mark Kushner: uh efficiency, not maximum, but optimum for mass.

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Mark Kushner: I can take a couple of uh, you know. Three to four. What is that kilowatt of specific power off? Okay, three to four kilograms for kilowatt

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Mark Kushner: Make that megawatts. That's what three thousand four thousand degree of uh kilograms

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Mark Kushner: that I don't have to watch.

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Mark Kushner: I've just lightened up my system by several thousand kilograms, just by making my inlet temperature a little hotter.

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Mark Kushner: That's huge. That's a big lever you can toll. And so, you know, if I make this the highest possible efficiency. What have I done? I've made the temperature drop across my turbine bigger.

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Mark Kushner: I've made the temperature. I'm rejecting lower, I drive myself back to higher area.

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Mark Kushner: Now you can't go to zero efficiency right of obviously. So that's why there's this: There's this optimum in the middle. You don't want to maximize the efficiency. You want to optimize it for mass.

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Mark Kushner: So trying to figure out how to deal with that, how to put that whole system together in a way that optimally rejects that heat because the radiative heat rejection is really the choke point on this whole process.

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Mark Kushner: Um, both in terms of power throughput and in terms of the mass penalty, and imposes on the system,

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Mark Kushner: and a third one, So the electric propulsion system says the play. Oh, Yes, please, I was gonna ask what the readers are typically made out of.

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Mark Kushner: So uh, the question is what the radiators are made out of, and there's a lot. There are several different options uh carbon composites have been uh one. Uh you can imagine metal ones coded with uh various spray uh codings to give it hiring Missivity. Um Codings can be a little bit tricky, though, because while they may work really well at beginning of life,

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Mark Kushner: um, if they wear over time they may become less effective. So at the end of the day you may have a radiator that is just kind of down to its bare parent material, and it may not radiate nearly as well. So I need to really design for whatever that end of life conditions going to be, not the beginning of life condition. Yeah.

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Mark Kushner: To questions. The example was done at constant power about the mass reduction.

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Mark Kushner: Yes, it's a constant one month any cost to

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Mark Kushner: um, and then your brighter cycle. What's the working through it?

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Mark Kushner: So that fluid is a Helium Xenon uh mixture so you have two noble gases that are non-reactive, and they turn out that that's one that's been used kind of traditionally in this vein.

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Mark Kushner: Um, we've got a lot of experience with it. Basically The the helium carries uh the heat, and the Xenon uh carries the momentum for the stream.

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Mark Kushner: Alright. So the electric propulsion system. Uh, we are two types. I'm going to talk about here. So this is the part where we're getting the plasma

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Mark Kushner: uh one is the hall thruster. So those of you that are in the Pepper Lab are very familiar with this, and probably could tell me just as much as I could tell you. Um

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Mark Kushner: it both any P. System whatever. The Np. System, is It's got to run for a long time. It's kind of multi mega wants of power throughput for the human Mars Mission.

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Mark Kushner: We have no experience with anything above about ten kilowatts. Uh, we actually have less than that. Now we're going to have ten kilowatts with the Uh launch of the power propulsion element. Eventually

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Mark Kushner: the hall thruster. Xenon fed, you know, five kilowatt system, twelve and a half on the power and propulsion element. Um, there have been some gr brief ground tests at higher power uh up to about one hundred kilowatts on a couple of thrusters for short durations.

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Mark Kushner: Um, Now you see that there's there's a big difference between five kilowatts and multi- megawatts, and twelve and even one hundred for the ground and that's short duration. Not twenty to thirty thousand hours.

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Mark Kushner: Um, and they're relatively heavy, Right? You've got large magnetic circuit components and materials uh and finally

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Mark Kushner: it's. Xenon fed well. Xenon is hard to pump right these thrusters they have to run in vacuum uh in order to operate uh properly. If any of you have been to the the Pepper lab, you've seen the big vacuum chamber, and kind of what it takes to run those thrusters. And those are still kind of small thrusters in comparison to what we're talking about here where you start to put a lot of them together for megawatts of power.

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Mark Kushner: It's difficult to pump Xen on, and

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Mark Kushner: but you need to pump it. Well, in order to um effectively mimic the space conditions and get good data, get data that actually will match what it's going to do in space, but also get data. That shows you know how these things are going to interact with each other.

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Mark Kushner: So, and that's that's kind of one of the questions is, what do these things do?

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Mark Kushner: Uh when you run them? These are the challenges. These are the risks, if you will, that we're having to investigate for hall thrusters. You know. How do I run multiple thrusters together at high power in proximity to each other where

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Mark Kushner: they're operating at the same time off the same power system. But I don't want to do cross talk with each other, so I need them isolated. Um! They're gonna interact in the plume. They might interact with the spacecraft. They might interact with each other. They might interact with the facility.

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Mark Kushner: How do I test it? In a way where I believe the data,

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Mark Kushner: because typically these hall thrusters, you know, we've run it one hundred kilowatts. Let's say I can run it a couple of hundred kilowatts. I still need multiple ones together to even get to one megawatt, and even more to get to multi megawatts.

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Mark Kushner: The power processing that box, the expensive box, I said, that converts the flavor of power from the the spacecraft power to what the thruster wants to see,

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Mark Kushner: You know, developing that. What does that look like? Uh, How do we develop that system? Where do we get the components? What do we need to do to test them? Uh, that is a big challenge to it.

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Mark Kushner: Uh the lifetime itself of the various components. You did the cathode specifically. Um, you've got to draw hundreds of amps, sometimes lots more than hundreds of amps depending on the power level for thruster from the cathode. That's a

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Mark Kushner: that's this little component right here in the middle uh on the Michigan. Uh nested hall thruster there. Um! I use that one just for you guys. By the way, um

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Mark Kushner: you under hundreds of amps from this cathode while that cathode is being bombarded by particles over time and wearing away. Um. And so, you know, can that cathode

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Mark Kushner: deliver that current for that length of time without eroding away completely

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Mark Kushner: um

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Mark Kushner: the actual materials to build it. Um! Now this may be less of an issue now uh these channels. Uh you can see their white here. Um,

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Mark Kushner: uh, we're ceramic um, and getting ceramic stock that are that big is difficult. Um. Recently our colleagues at Jpl have shown that you might be able to do those channels with graphite

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Mark Kushner: uh, which is a lot easier to work with, and a lot easier to get large materials in stock, so that might be a solution to it. But even then you need to have large components to be able to put it all together. Um! And then this last part Xenon propellant storage. Um.

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Mark Kushner: So Xenon, Typically, when we flown hall thrusters, we store it as a gas super critical, so high density, high pressure

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Mark Kushner: uh who sort of the Nasa Don Mission,

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Mark Kushner: two people.

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Mark Kushner: So the aid on Mission went to vest in series with an iron thruster, but it was also the scene on Fed thruster um, and initially the flight tank and the flight spare tank failed.

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Mark Kushner: Uh, when they hydrostat tested it, we thought we understood how to do the tank better at high pressure than we did so to go back and redesign the whole thing, to make it be fear and heavier,

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Mark Kushner: and that was a small tent compared to what you need for a human Mars mission. So

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Mark Kushner: i'm very worried that you have very, very high pressure thousands of psi in very, very big tanks uh on my vehicle that also have all these nuclear components and astronauts.

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Mark Kushner: That's a hard problem

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Mark Kushner: for probably probably a very hard problem.

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Mark Kushner: But one of the ways you might be able to get around it is you might be able to store it as a cryogen that's something we've never done before,

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Mark Kushner: because it takes power. But I've got a nuclear power system on this thing, so I might have enough power to be able to do it here. Science missions are very power starved, but here I might be able to do it, so I might be able to store it as a cryogenic liquid at low pressure, but that's never been demonstrated. So I've got one way that we've done before small scale,

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Mark Kushner: but it have to scale it up really big or another way that's probably doable, but we've never done it before.

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Mark Kushner: So pick your voice.

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Mark Kushner: The Mpd. Thruster is the other option. So Npd is magneto plasma dynamic thruster again. The requirements are the same.

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Mark Kushner: Uh, no flight experience of any electric thruster at these power levels. Um! The Mpd thruster has no real operational flight experience. So the hall thruster has lots of operational flight experience, but it's all at really low power,

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Mark Kushner: so that's great. But as a system you haven't built anything at the size of the scale we're talking about.

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Mark Kushner: Uh, the Mpd. Has no operational flights uh experience. It has had ground, tested a lot higher power than the hall thruster. Uh, the Russians did five hundred kilowatts for five hundred hours, and in the uh,

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Mark Kushner: and and this minimal cathode erosion. So the cathode is this part you draw current through. It creates a self magnetic field which accelerates the plasma through A. J. Cross B. Lorenz Force. Um

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Mark Kushner: uh In typical Russian form. They were very quantitative in telling us that there was minimal cathode erosion.

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Mark Kushner: Very Russian. Um. So uh,

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Mark Kushner: but one of the things we want to do in our project is. Go back, build, you know. Take a thruster at this power level and even higher, and run it.

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Mark Kushner: Um!

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Mark Kushner: It is an inherently high power thruster, though. So a thruster typically can take

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Mark Kushner: like a megawatt, or maybe multi megawatts of power. If you can pull the heat out of the anode, so,

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Mark Kushner: whereas hall thrusters are typically have typically been run at lower power levels. You know, hundreds of kilowatts doesn't seem low, but when you talk about megawatts it still is. Um. The Mpd. Is kind of inherently high thrust density, high power device. Um,

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Mark Kushner: this is lithium fed

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Mark Kushner: lithium stores as a solid. You melt it. So it's very low pressure

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Mark Kushner: uh, but the nice other part about it is that I can put cold walls like water chilled walls in my vacuum chamber. And when my thruster fires, when that lithium vapor, when that lithium plasma hits the walls, it will condense out and basically flash freeze back onto the the panels, and so I can get very good trial Pumping, I say, cryo! It's cryo for the lithium um

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Mark Kushner: uh!

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Mark Kushner: Without too much effort, I still to take the heat out, but it's a lot easier to pump than the Xenon, So it's possible that this has a much better chance of being ground tested at scale than the Xenon thruster.

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Mark Kushner: What are the challenges?

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Mark Kushner: So

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Mark Kushner: So with the high infrastructure costs of creating these test facilities to do this testing at scale, have we looked at doing this scale testing in space?

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Mark Kushner: So we have. So here's the problem with doing the scale. Testing at space is

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Mark Kushner: you want to get it back to do post-test inspection, to be able to quantify the margins that's not easy to do in space. You might be able to bring it back, you might be able to do some kind of remote inspection. It won't be as good

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Mark Kushner: um, and he might spend as much to do it in space anyway, because I still need the power system to do it. I'm: basically building the entire thing just to do the test in space to show that it works,

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Mark Kushner: and if i'm going to put people on it,

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Mark Kushner: I'm going to have to do it on the ground. I don't think there's any way you get around it for any system, whether it's nuclear thermal nuclear electric. You know, Artemis, you know ours twenty-five chemical. You have to run it on the ground and be able to do that post-test inspection be able to quantify how much margin you really have left when you do tear down

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Mark Kushner: um.

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Mark Kushner: Now people have other opinions on that. That's my opinion. Uh. But you know I think it's It's a reasonable one, and I think it's one that at the end of the day when you start talking to like the human Space Flight Office, they'll insist upon

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Mark Kushner: um. So

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Mark Kushner: the cathode, the thing that had minimal erosion

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Mark Kushner: uh long duration cathode lifetime? Do we have enough lifetime in the cat, or does it have minimal erosion or not? What does it mean to be minimal? Um, the degradation of the annotes. So the flared part here on the outside, you know. Uh, does it get too hot? Does it start to melt in a road away.

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Mark Kushner: Can we avoid uh spot, mode or onset? Because this is a high current Discharge is an arc discharge, but it's diffuse right You spread it out, and that's how you can get away with it. But

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Mark Kushner: you can get into modes where it starts to arc almost like lightning strikes on different spots, and Now you're vaporizing parts of your cathode very destructively. You want to avoid that, So can we make sure we can do that

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Mark Kushner: uh the power processing unit that again that box. How do I convert the the power to from Ac input to the high power I need? We've kind of done something similar like this on a project back in the nineties for an arc jet at about twenty kilowatts, twenty to thirty.

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Mark Kushner: Now, i'm talking about megawatts. Do we still have that technology.

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Mark Kushner: And is it scalable? We think it is? But we certainly think we need to demonstrate before we say it's definitely scalable.

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Mark Kushner: Um

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Mark Kushner: at startup and shut down their big transients in the current. It goes up really fast. It comes down really fast. Uh, so it's startup and shut down. What are those look like, and let's face it, not just to the thruster, but to everything upstream. Am I blocking those transients, or is my pmad system? Is the the you know all the equipment

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Mark Kushner: in the astronaut quarters, seeing those transients and my frying electric circuits that would be not so good.

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Mark Kushner: Um! And there's a limited performance database There hasn't been a lot of thrusters run the Let me a lot of Mpd. Thrusters run. Most of them were pulse. They've been some run steady state. Even few were on lithium. So there's a very limited performance database. What we have is very promising,

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Mark Kushner: but we certainly want a lot more before we say that it's ready to go?

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Mark Kushner: I got a question from the the audience, all from the chat, and so Bingham and Ruben asks with lithium condensation on spacecraft surfaces, solar panels and radiators be a problem for um Solid prevalence. Yes, So the question is, if lithium condensation on the spacecraft will be a problem. And yes, it probably is an an issue. You definitely need to make sure that you're pointing your your thrusters, whether it's lithium or Xenon. Right? So the Xenon won't condense,

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Mark Kushner: but it will certainly interact if it impinges on uh other spacecraft surfaces and a road away. Surfaces uh lithium can uh interact with it could also code it. And so, yeah, you definitely have to be aware

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Mark Kushner: uh of that problem. Uh: So looking at it's another reason to run it at scale in a large enough facility, where you not only can quantify what the thruster is doing, but you can quantify what the plume is doing, because that plume some of it. Some of it does come back. Some of it does kind of find its way around,

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Mark Kushner: and you want to make sure that through, like you know, shadow shielding, or or kind of uh cones to kind of block it out. You kind of block the line of sight that you're keeping the the plume and the plasma away from all the vital areas of your spacecraft. So it's a little bit of design, a little bit of modeling,

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Mark Kushner: a little bit of luck uh you might be able to uh to get over that good, very good question, though.

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Mark Kushner: So

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Mark Kushner: this is it. This is the last slide final takeaways. So uh Nasa, we've been working with the our partners at the Department of Energy Um

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Mark Kushner: academia and industry uh to develop space nuclear propulsion technologies. I've spent upwards of two and a half years specifically looking at nuclear electric propulsion looking at the the watershed of technologies that are out there even technology is not developed

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Mark Kushner: for space nuclear propulsion that might be applicable to the problem. So our nap efforts we develop this maturation plan

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Mark Kushner: to take it from. We'll call it tierl low. I don't even care what it is right now. It's too low to be flown Right now. I need to advance it to a level where I can actually have confidence that I can go into a real design, and I understand the mass and the performance of, and the integration of that system.

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Mark Kushner: I am a big fan of multiple parallel development options, especially when we're at tierl low. Um that you know, this gets into something that we talk about more and more in the agency now. So we talk with T. Url, and we probably is familiar with technology readiness level

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Mark Kushner: Uh: we started using a new term which is eighty squared or advancement degree of difficulty. Some of you may have seen that, uh, but essentially it's the level of effort needed

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Mark Kushner: to go from one T. Url to the next, so you can be a low trl, but you can be pretty easy to advance. We're in a low url. It's still pretty hard to advance. There's a lot of steps that we need to do to show that we can move to that next step to that next step and have that confidence

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Mark Kushner: when you're at a high advancement degree of difficulty. You want to do multiple parallel efforts. Why? Because you don't know which one's going to pan out. And so you're kind of hedging your bets a little bit. So we're trying to do multiple parallel elements uh on maturing those key technologies.

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Mark Kushner: And when we're building test hardware, relevant conditions. I said this several times the the the scale, the power, the temperature. Uh we're looking, looking right now, doing one megawatt uh size, so demonstrating things at one megawatt. So if you think that your system needs Megawatts

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Mark Kushner: plural of power, we think it's easier to scale from one megawatt to megawatts. Uh that all the work is done from going from the ten kilowatts we have now up to the Megawatt going to Megawatts is probably a much easier lift once you've kind of gotten to that first megawatt of demonstration.

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Mark Kushner: Hi, Richard, or uh Halo the high assay low, enrich your aim, has opened the door to participation, uh, from industry and from from various partners. Um to increase that participation. Um, you know, both intellectually and in terms of the hardware that they've been able to build to apply to this problem.

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Mark Kushner: Um, we want to take advantage of uh various investments that are going on uh by Nasa, by other agencies like the Department of Energy, the Department of Defense uh, but also any kind of strategy that aligns with industry and what they're doing,

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Mark Kushner: and all that venture capital. I was talking about all the work that the Department of Energy is putting in there. Technology is not developed specifically for space nuclear applications. I put one here a couple here. The electric aircraft uh work. What are they doing? They're pushing around lots of power on an aircraft.

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Mark Kushner: It's a kind of a contained system, and the power levels are very similar to what we're talking about here. So probably a lot of synergy there between what they're trying to do and what we're going to need to do in terms of moving power around a spacecraft. Um,

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Mark Kushner: taking all the tools for modeling and design of ground-based reactors and applying them to the space problem. Uh, we've had a lot of luck and success with that so far, and I expect that to continue so. This is a very broad effort

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Mark Kushner: uh that we're trying to push. You know It's not just. You know it's not just space nuclear propulsions effort. It's not just uh nasa's effort. What I've talked about here, and what we're trying to push and what we're trying to develop is really meant to be the nation's efforts, because it does enable not just the missions I've talked about for human Mars, but kind of everything from here to that point. So all those intermediate missions where you don't need

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Mark Kushner: as much performance or as much power.

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Mark Kushner: You're still going to need at least some of those technologies to get there, and the idea is that as you do as you get wins, you're going to develop those technologies and make good steps forward to eventually getting to high power electric propulsion in space. With that i'm going to close, and I will take questions.

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Mark Kushner: All right. Let's go here first.

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Mark Kushner: Uh we give you a me spread what you have on slide Five You had all of uh yeah, two thousand and twenty two thousand and twenty-one with you.

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Mark Kushner: Those were written with malice of forethought. Basically, to say,

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Mark Kushner: we know that the technologies are not what

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Mark Kushner: the the advocates say there. We know they're not at the level that you say they are.

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Mark Kushner: We know that there's been money put into these efforts, but not a lot of progress is made in advancing those technology levels, technology readiness.

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Mark Kushner: And we're going to tell you that straight up we're in, Call you out on it,

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Mark Kushner: build a plan that actually advances technology readiness.

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Mark Kushner: Not just that, You know, funds a project because it's something that you like or funds something. And uh, you know, is a is a level where uh you claim you're going to be. You're a tier five and ready to go, and then you like um like uh uh uh James Webb right

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Mark Kushner: claimed it was ready to go. And here we were, you know, fifteen years later, and ten billion dollars later, finally launching it. Great pictures. It's a fantastic piece of engineering, but it took a lot longer to get there, because all of its readiness levels were overestimated when it was sold,

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Mark Kushner: trying to avoid that here, and that's what those things are really trying to call out is Don't. Start your program to do a human space flight until you're actually ready to do that.

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Mark Kushner: So I think there was a Yes. So that's the overall efficiency of your electric generation.

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Mark Kushner: So the questions that the more you need to generate one bigger.

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Mark Kushner: Yeah. So the question is the overall efficiency. So we're looking at the the power generation. Efficiency is about. Um.

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Mark Kushner: So if you generate about is about twenty to twenty-five percent efficiency. So you figure about uh one megawatt gives you about two hundred kilowatts. One megawatt thermal gives you about two hundred Kilowatts Electric.

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Mark Kushner: So what is the weight of the U Two hundred and thirty-five?

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Mark Kushner: So it's not that much different really. And So I. I made some bigger to do about it. But really, you know, because you look at this thing,

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Mark Kushner: you know,

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Mark Kushner: you know. Here's the reactor down here. Now these are both halo two uh uh h you versus that. It might be a little lower. But you still got this whole massive radiator here that's much more than anything else in the system.

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Mark Kushner: It seems to me that that the you're not really using up that much. You don't need that much. You to thirty-five. Yeah, no, you're not burn up limited. You are not me even at that time level. You're not burn up limited. So you you are. You are really still um. You need to make sure you get the power,

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Mark Kushner: you know, to make sure you maintain criticality. But you're not burn up limited. I don't see any reason why you couldn't.

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Mark Kushner: Yeah, you should not.

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Mark Kushner: There's no reason why you should go to h you.

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Mark Kushner: We don't think so either, because the way this just seems to be. It's. It's just not that much different. I mean, people argue the weight issue, and and they're right. The reactor will weigh a little bit less that much you're talking about, but it's a whole system. It's a very large system, and the reactor is,

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Mark Kushner: you know,

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Mark Kushner: that little bit right there.

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Mark Kushner: Um, I had one here.

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Mark Kushner: Yeah. Um, In terms of developing kind of propulsion systems to utilize that much power. What are your thoughts on a raise of small? You kind of touched on, of the whole effect versus the Atv one. What your thoughts on an array of small thrusters using small nuts outreach with redundancy, complexity, and weight versus one large thruster with no redundancy, but to every less rate. So the question is about the power level of the thrusters and redundancy. If I use smaller thrusters.

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Mark Kushner: Um! So

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Mark Kushner: it gets to be a a very large sized array very quickly. Um! And so uh to to the level of being ridiculous. Um, really. But so each thruster has a sunk mass.

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Mark Kushner: The thrusters at this at the level i'm talking about are not, you know, overly burdened. So again it's like the H. You versus halo, you know, as as far as the overall vehicle goes, you know. Yes, Halls dusters are more are heavier than Mpd. Thrusters. Um, but from a vehicle's perspective they're not

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Mark Kushner: not that much more. Um! The bigger thing is um that that you've got to

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Mark Kushner: large number of them now they've got to manage. That's a lot of extra system Complexity um the other part which I do want to challenge a little bit. You can do a sparing strategy with the larger thrusters. You would have more of them, or you'd run them derrated, and maybe run them in higher power. If you had thrusters cock out. The Mbd. I think, is actually a little easier, because if you're if, if it's a thruster that does a megawatt, you can imagine flying,

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Mark Kushner: um,

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Mark Kushner: you know. So you need five megawatts. You fly like seven thrusters right? You run five, and then, if one cons out, you just switch on a new one, so you know, but it's light, right? So it's not a huge amount of sunk mass. So you know there are ways to do that, even with the larger thrusters, and you would want to have some spares. You definitely need a sparing strategy for your propulsion system, because you do want to make sure that if you have a problem with a thruster or two

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Mark Kushner: um, or however many it ends up being that that that the requirement is levied, that you are able to pick up that slack.

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Mark Kushner: Um! Right here.

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Mark Kushner: What are your thoughts on commercial nuclear electric propulsion, or even electric propulsion thrusters? Um! If you have any, if there are any so so like. For example,

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Mark Kushner: there's Neutron star with their proposed Mpd. Thruster uh

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Mark Kushner: I don't know what your thoughts are on. So the questions on proposed commercial electric propulsion thrusters. So

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Mark Kushner: so this is where it gets really fun for me.

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Mark Kushner: Um. So we've developed a technology maturation plan, and we did a survey basically of of industry and government and academia kind of looking for all the different technologies and trying to evaluate, you know, through various uh discussions with subject matter, Experts? Um!

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Mark Kushner: Which ones were the most likely candidates, and that's kind of what I've talked about here.

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Mark Kushner: I'm perfectly willing to be wrong, but

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Mark Kushner: when proposal calls go out eventually, eventually, you'll have funded work and funded research that goes out, and if somebody comes in and says, you know,

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Mark Kushner: you idiot! We're so much better than what you thought we were. And here's why, and here's how we're going to demonstrate to you that matches the same rigor that you're planning to, you know. Go with your your Government plan.

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Mark Kushner: I'm perfectly willing to listen to that, You know. I'm certainly not going to rule anything out out of hand. Um,

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Mark Kushner: because there are things out there that I don't know. There are things out there that are not published that are kept proprietary or private, that only come out in a proposal opportunity, because that's where they can disclose it to us, you know, and and be assured that it will be kept, you know. Kind of very confidential. Very. See? That's not to say that we disclose public, you know private information,

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Mark Kushner: but that's kind of one of the safest environments for them to do it, and it's the one where they can actually make money while they're doing, because they can win a proposal.

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Mark Kushner: Um, that's where you get the real, the real secret sauce, if you will, the real knowledge on what's really been done, and what's really out there. I'm perfectly willing to be wrong. Um, I don't know that I am. Um, but it's certainly something that I don't dismiss out of hand.

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Uh, no, we're here.

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Mark Kushner: I'm. Curious how you see, like assembly of a system like this. So questions on assembly launches, and on what vehicles and

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Mark Kushner: a lot of previous studies have looked at trying to package them up kind of like kind of like James Webb. Actually, you fold them into a shroud as tightly packed as you can you launch them? And then you try to unfold bit by bit and expand it until you get to these large structures. But even then you have to do several launches and kind of put them all together.

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Mark Kushner: That's one way to do it. I don't think that's the best way to do it. So our colleagues over at Red Wire. Uh, we're part of one of these uh interchanges that we had we're talking about in Space Assembly. There was one of the specific topics we looked at, and they said, You can do it that way,

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Mark Kushner: Um, or you can actually do in Space Assembly, you but launch piece parts. Now, you wouldn't want the reactor piece parts. You'd launches one big unit, for example, but you could watch the radiators as a bunch of panels, because that's the really big thing.

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Mark Kushner: You launch the structures as pieces and assemble it in space.

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Mark Kushner: Now, what can I do now? I can build a system that's designed to do the mission

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Mark Kushner: not designed to be packaged origami style inside of a payload shroud,

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Mark Kushner: so I can optimize it for doing the actual job. I'm trying to do, not optimize for just trying to fit into a limited space and then deploy.

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Mark Kushner: Um! That's a lot harder problem. Now in Space Assembly has its own. You know it, basket of issues. But those are things we're developing. We're developing in space. Assembly techniques specifically for things like this. We'd be silly not to try to use them for it.

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Mark Kushner: And would it be done like robotically? Or would you have like the crew out there doing so? So? The questions of Who? Don't robotically, or with the crew? Um! It could be a combination of the two. I kind of see it as as mainly robotic, maybe with crew tended. So you know you may have somebody kind of they're watching over it as it as a robot

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Mark Kushner: uh is assembling it um

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Mark Kushner: again. Now I've got a robot involved right? So now I've got to have something up there that that can help me assemble it in space. So there's a whole new set of technologies.

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Mark Kushner: Hopefully, some other program is developing, and we do have. I am in Space Assembly and manufacturing um. It's a servicing assembly and manufacturing um

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Mark Kushner: which is developing those technologies. The idea is that those will be ready when we're ready to use them.

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Mark Kushner: One more question, and then Kurt will be absolutely. I sure I certainly will. Uh, John. Yeah. So I have to ask this one. But um. So at some point for Mars Um, it has to be a uh, you know. Pick one right nuclear electric propulsion or nuclear.

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Mark Kushner: Well, maybe um. Would you tell me what's the process? I guess I mean it's one going to be like um the risk reduction uh activity, and that is a prime. But also what is it? A fine? So

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Mark Kushner: So the the budgets are. So the question is nuclear electric versus nuclear thermal. And how do you go about picking one? Um.

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Mark Kushner: So

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Mark Kushner: right now we're talking in terms of and not? Or why are we doing that? Because several of those missions between here and the human Mars Mission

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Mark Kushner: are better suited for thermal nuclear thermal? Some are better suited for nuclear electric, and so we don't want to leave those behind.

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Mark Kushner: Um! Our adversaries are developing both, and there are niches for both.

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Mark Kushner: Um,

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Mark Kushner: Now, you said, This is one risk, reduction or not, you know. Would you develop one or the other? Now I don't know the answer to that off the you know immediately. Um. I know people, you know, advocates who say you has to be nuclear thermal because you can't do with nuclear electric,

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Mark Kushner: and we have people that say ask me nuclear electric, because nuclear thermal is never going to work. Um. So again,

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Mark Kushner: high eighty squared for both of them. Still, lot of lot of development to be done before you retire enough for the risk to make that decision. Um, it's what we're working on right now.

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Mark Kushner: But you know we've got kind of sketched in there if you get to like tier five. That's that's about when you would start a project,

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Mark Kushner: you know. Then you've got at least enough information where, if you had to down select to one,

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Mark Kushner: you could do it Um! In an informed way, you'd have enough data enough information available where you would be able to to make that decision uh and be smart about it. So we're not there yet, you know. I don't know what that decision looks like um.

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Mark Kushner: But right now, you know, we're trying to develop both of those sets of technologies because we can, and because there are going to be usefulness for each um, and different missions and different power levels, different thrust levels uh looking forward. I guess that's the last question. So thank you very much. Everybody.