Why Nuclear Rockets Are Going To Change Spaceflight

[@KevinBalch-dt8ot]

I originally wanted to be an aerospace engineer. But when the space program was cut back in the 1970s and the “energy crisis” was upon us, I switched to nuclear engineering hoping that nuclear rockets would come back. It never happened and I worked for 35 years in commercial nuclear power doing physics and safety analysis as well as writing software for real-time simulators. I guess I was born 30 years too early or 30 years too late. I remember one of our homework problems involved determining the startup rate for a nuclear rocket considering the reactor kinetics (just a simple point kinetics model). That was the closest I came to my childhood dream.

[@r3dp9]

The fun thing about this day and age is that much of what we learn and create will eventually spread to the next generation. No matter how big or small our contributions, they add up over time. That's how we got where we are in the first place.

[@enewhuis]

Well if you're bored we could always use more financial trading system automation systems builders. ;-)

[@KevinBalch-dt8ot]

@@enewhuis - No thank you. I prefer honest work that produces something useful.

[@snakevenom4954]

I'm going to be honest with you chief. I don't see nuclear engines being a reality. For starters, Hydrogen is known to be an extremely difficult element to work with. Let alone liquid hydrogen which has to be kept at 20 Kelvin. It also likes to just seep out of every miniscule hole too. I also don't see how this engine can be reusable. You're pushing the engine to bear some extreme temperatures since there isn't much, if any, cooling going through it. You can use ablative cooling but that only emphasizes the single use nature of the engine which is the opposite direction we are heading. Having a nuclear reactor inside the rocket to power your ion thrusters just makes more sense. Better efficiency and specific impulse there. Doesn't produce much thrust, sure. But you don't need much thrust when you're in the middle of space. Anything would accumulate greatly

[@mduckernz]

@@snakevenom4954I mean, we’ve used LH2 in space plenty. Stored it, even. It’s not too big of a problem. Its not easy, but nor is it horribly difficult

[@vensroofcat6415]

"Machined down uranium rods..." sounds like a great career path

[@babaksanaee1460]

I hope this is automated...

[@erikottema2620]

😂

[@benjaminhanke79]

I didn't realised for a long time that the production of fuel rods depends on machining nuclear material. What was the name of the US facility where a lathe with plutonium caught fire? Rocky flats?

[@boulder795]

"Machined down bomb-grade uranium rods" at that

[@nefarious_blue]

😂😂

[@NukeRocketScientist]

Hello Scott, I have been watching your videos for years, all the way back since the Interstellar Quest series on KSP! In that time, I have received a BSc in astronautical engineering and am now currently halfway though a MSc in nuclear engineering all because of you, KSP, and the goal to work in NTP. During my undergrad I was fortunate enough to work with professors on research in both solid core and liquid core NTP designs but the craziest part is that tomorrow at 9am I start a fellowship with the Center for Space Nuclear Research where I will be working on developing a gas core NTP engine design for the next 10 weeks. Your videos are always phenomenal and this video is no different. I can't thank you enough for all the years of youtube videos and the motivation to pursue NTP.

[@ttystikkrocks1042]

May the hopes and dreams for humanity's future rest gently on your shoulders. Well done!

[@snapshuttre]

and plasma core NTP is next? sorry just wandering, I'm sure you will do great there, go on

[@davidgunther8428]

Cool, I didn't know gas core designs were real!

[@davidgunther8428]

How hot can a gas core design operate at? Or, I guess the propellant temperature is what matters.

[@NukeRocketScientist]

@@snapshuttre A gas core design technically would be a plasma core since the uranium fuel would be better described as a plasma than a gas realistically.

[@Maadhawk]

14:57 When you are talking about Xenon poisoning of a nuclear core, I have actually seen that first hand. I saw in onboard the USS Salt Lake City while we were at power and sailing down the coast of California. We had been up north engaging in training exercises tracking ships transiting to and from Seattle. After we completed our training, we turned south to return to our homeport in San Diego. We had been traveling for an extended period of time at all ahead full. Reactor power was pretty much at 100% during this time. I was standing watch at the time as the Throttleman in Maneuvering, the room from which the reactor was overseen and controlled from. We got the order to come off the bell down to ahead 1/3. The captain wanted to tow the radio line so he could download the ships mail. While we were at this low power, because our reactor core was so old, the Xenon quickly began to build up from all the fission products we had been producing at high power. So long as we stayed at high power, the neutron flux was sufficient to burn it off as fast as it was made. But, now that wasn't the case. The neutron flux was too low. So the result was that the temperature in the reactor began to drop. As this continued, the Reactor Operator had to gradually pull the control rods out of the core to keep the temperature stable. Eventually he had pulled all the controls completely out and still the Xenon transient was continuing, dropping core temperature. At that point the Reactor Operator informed the Engineering Officer of the Watch, "Sir, unable to keep reactor temperature in the green band due to Xenon transient. Reactor rods fully withdrawn from the core. Recommend to Con to pull in the com wire and come up on the bell or else the reactor is going to shut itself off." Was both cool and funny to see such a large scale direct example of nuclear physics in action. The EOOW, the officer in charge, relayed the Reactor Operators recommendation to the Con. The Captain, then quickly ordered the line brought back in and decided he could finish reading and responding to the mail once we were back in port. About 5 minutes later I got the order to come back up to all ahead 2/3 then back to full shortly later. Temperature continued to drop for a short bit, but once back at power, quickly stabilized and returned to normal as the remaining excess Xenon was burned off. Eventually we arrived back in port, and aside from getting to watch physics in action, none the worse for the experience.

[@davidhess6593]

Interesting. Xenon has a similar effect on consciousness.

[@James-zp5po]

Nuclear reactors do not exist sry

[@X85283]

Surprised you're allowed to tell this story...

[@notyetdeleted6319]

@@James-zp5powhat?

[@wally7856]

Why can't you run the reactor at a higher power rating (or even full power) while still at 1/3 ahead? Shouldn't there by some kind of bypass from before the turbines to just dump excess steam produced straight to the condensers?

[@RightOnTarget1]

My stepfather, Dr. Herbert T. Knight, who passed away in 2020, was the Project/Site Director for the NERVA project. I have sitting in front of me right now, his machined metal model of the engine. I have many photos and papers from the project, including photos of him touring John F. Kennedy around the facility.

[@dontebronaugh]

You have to donate those to a museum

[@Mumbamumba]

That's super cool!

[@westlydurkee6230]

Please document and publish this stuff to the internet. If you're not sure how or do not have the time, I'm sure many people would be willing to help.

[@flannelshirtdad]

Lol. "Engine-rich exhaust."

[@NHOrus]

Classic rocketman joke.

[@portalman95]

OMG i was going to comment about it too. so funny

[@SteveSiegelin]

As soon as I heard that I started laughing!

[@billmullins6833]

@flannelshirtdad You beat me to it! No fair!

[@queueeeee9000]

I heard him say that, but I'm dumb, what's the joke?

[@cynthiaklenk6313]

Scott, I saw this last night and wanted to personally THANK YOU. My uncle (deceased) was the chief on-site safety engineer for the NERVA/KIWI program, testing the KIWI's in Area 21, Nevada Test Site, Jackass Flats. My uncle took me out there after the program had shut down, and I saw the hot cells where they did disassembly of the reactor core, post test. I got to try out the remote manipulator arms-my uncle is at least partially responsible for my becoming an engineer, with physics deeply ingrained (Electrical Engineer). I was probably about 12 or 13. I had NEVER seen the films you show in this video, particularly with such clarity. THANK YOU. Uncle Jim was very proud of the NERVA program it was very successful, and not a waste of taxpayers money. I think the longest consecutive burn was 15 minutes continuous - the engine was still in fine shape, that was the length of the test. Later, I went to work as a young engineer, right out of college (graduated in 1974) at the site (NTS), working timing and firing for sub-surface and tunnel shots. I'm glad that the hard work of the NERVA team will finally come to fruition. Thanks again, this would have pleased my uncle. 💗

[@etbadaboum]

Never saw that heart emoji before!

[@paulelephant9521]

Your uncle has every right to be pleased, running a successful test program of such a complicated engineering project is a serious accomplishment. To be honest my mind boggles at the level of skill and ingenuity needed to create something as inttricate as a nuclear rocket, you've got crazy high temperatures, lots of force and movement, high levels of ionizing radiation, everything has to be as absolutely light as possible while still being very reliable, that's a next level challenge , even for a large well funded team of very clever people, bravo!

[@cynthiaklenk6313]

@@paulelephant9521 Indeed Paul, I am very proud of him and the accomplishments of the NERVA program, and I am very happy that the incredible work that they did, is going to come to fruition - And my uncle Jim encouraging me toward a career in science and engineering (so did my dad and mom). He was quite a wonderful person (and so was my aunt). I was and am, by nature a very curious monkey. By the way, a proof of concept of a nuclear powered aircraft was also done (not at the Nevada Test Site though) - It worked, but the shielding necessary to protect the crew made it infeasible. I think it was a liquid salt reactor. Have a wonderful day.

[@heyuhh422]

Cynthia - my dad worked for Aerojet on that project. He took me out there sometime in 1966. I was in 3rd grade in Vegas at the time. I remember ‘signing in’, wearing a dosimeter badge, and playing with the manipulator arms. Did you get to darken an ashtray or shot-glass through it? I may have met your uncle there. Do you remember the small village of Mercury before heading into the test facility? I was a total nerd and in hog-heaven for getting to see a reactor. It is sad that project was shut-down despite several successful tests. I was hoping to be an astronaut using that engine to Mars someday. Instead I became an engineer developing optical disc technologies. Thank you for writing your comments to Scott! It brought back some great memories… Sincerely, Brian in CA

[@skierpage]

​@@heyuhh422 get a room, Brian and Cynthia 💕! No, seriously, get a room. Earth needs more space nerd babies.

[@jeffreyschweitzer8289]

Only someone from Scotland would explain a nuclear reactor using golf analogies

[@Fortunes.Fool.]

Same thought, same comment 😂

[@daszieher]

and be so right about it 😂

[@SireBab]

And hilariously, this is the best analogy for it I've heard.

[@ThatOpalGuy]

he missed the most obvious moderator> grass.

[@riparianlife97701]

I'm reminded of the Robin Williams "invention of golf" bit: EIGHTEEN TIMES!!!

[@chrishughes7219]

'As the delta V requirements get bigger, eventually the tyranny of the rocket equation will win' - what an incredibly eloquent statement. I love watching your videos Scott

[@RazorsharpLT]

Unless... you have a Neutron Flux torch engine. That requires magnetic nozzles, though

[@idris4587]

​@@RazorsharpLT😂

[@AxionSmurf]

Life meme: The next big thing was already invented 50 years ago and a bureaucrat shut it down.

[@poindextertunes]

100%. i just commented something similar. oil money is very old and connected to Washington. its depressing lol

[@d3thkn1ghtmcgee74]

Same with thorium molten salt reactors. Big oil really didn't want to have that kind of competition and now the Chinese are using the technology with huge rewards

[@bricesuire5072]

@@d3thkn1ghtmcgee74there’s definitely other factors due to longevity of the reactor and byproduct management. But yes you are correct it has good qualities to it.

[@timtruett5184]

People who use government as a convenient scapegoat for a lack of progress are not thinking clearly. First, the research and development on advanced technology was probably either funded by a government agency or done by a government agency.

[@timtruett5184]

Second, vested interests are the real obstacle that stifles development in particular directions even when overwhelming numbers of people want it.

[@aspzx]

"Uranium plasma"? Fly safe indeed.

[@SireBab]

You ain't seen nothing yet lol, watch Scott's video on the nuclear salt water rocket, that thing is an absolute nightmare.

[@eduarddoornbos2409]

What goes up will come down...

[@sanitarium017]

​@@eduarddoornbos2409come down where?

[@johndawson6057]

It could definitely fly. But only once.

[@mm-qq7bb]

​@@eduarddoornbos2409 Orbital mechanics say otherwise.

[@chopinbloc]

"Engine rich exhaust" is probably the funniest thing I'll hear today.

[@SuLokify]

Engineering euphemisms are my favorite inside joke

[@karenrobertsdottir4101]

My favourite is still "lithobraking" ;)

[@a64738]

One of our tractors had once a "engine rich exhaust" moment as it self destructed ....

[@Yaivenov]

​@@karenrobertsdottir4101there's a step up from that: lithostaging. Where you intentionally break pieces off with an impact as part of the normal operation and keep going afterwards.

[@markanderson1088]

Engine-rich exhaust is typically an indicator of a rapid unscheduled disassembly.

[@eliavrad2845]

The thing I love most about NERVA is how confidently it tries to lead up to a MINERVA engine.

[@moonasha]

I was always partial to the DUMBO. Can't beat that name.

[@NoNameAtAll2]

​@@moonasha DUMBOLDOR?

[@CathrineMacNiel]

What's the MINERVA engine?

[@caldodge]

Minerva is the tug. Wolfhound is the engine. It's effectively multifuel, using hydrolox when lots of thrust is needed quickly (close to the body being orbited), then switching to nuclear thermal when farther away from said body.

[@CptJistuce]

​@@NoNameAtAll2 Dumboldor the flying elephantldor.

[@JamieStuff]

My dad was part of the NERVA project. He made several trips out to Area 25, aka Jackass Flats, for the testing. The video here was from the later testing. The early tests had the engine exhaust pointing down, but they ran into some problems when the engine started pulling the pilings out of the ground...

[@markweikle5645]

I lived right near a testing facility and can just barely recall the red sky from the hydrogen plasma from the engines. My dad worked on these engines and also tested storage of the frozen hydrogen for long durations in vacuum as in flights to Mars.

[@meyersfarber]

did a little bit of work on NERVA as part of the SDI back in the 80s during grad school at MIT; it's great to see the technology being applied again

[@snowball7720]

no joke last night i was looking into nuclear thermal engines and i was quite disappointed to see scott didn't have a video on them, glad to see my prayers have been answered

[@Tjalve70]

He does have another video of nuclear engines. But that's of the nuclear engine where the fissile material is the exhaust. So not THIS kind of nuclear engine. I think I remember him saying that the exhaust is 2 Chernobyls per second.

[@OffGridInvestor]

I saw something YEARS ago that the soviets made multiple components for one for aircraft flight, but they never had a flying assembled and running engine, just multiple components that passed tests.

[@KnugLidi]

And we get all the way back to Clark's suggestion that Discovery and other ships like it would use ammonia rather than hydrogen as fuel. The man really was brilliant.

[@prdoyle]

I think he was a time traveller.

[@nicholashudson152]

A😅

[@drspangle13]

And Tsien taking the ISP hit on using water instead, due to availability..

[@chpsilva]

When he mentioned ammonia I immediately remembered the phrase "even in this part of the solar system, you cannot carry ammonia in buckets" from "2010"

[@IntrovertCorner480]

Your explanation of the difference between chemical and nuclear reactions was outstanding. I wish some would have explains that to me earlier.

[@Archgeek0]

A real fun NTR side-effect is that neutrons will get in places you don't expect, and bits of the structure will start to activate and transmute, and the hot structural members will start to do the same to other parts of the ship, resulting in the incredibly strange problem of parasitic _alchemy_ : "Fly far enough with your engines burning at full throttle, and your ship will turn slowly into gold, plus lithium, arsenic, chlorine, and a lot of other elements that were not aboard when you left."

[@htspencer9084]

Midas's Spaceship

[@-_.._._--_.-.-_-_-_-...-.-]

Eloquent moments in explaining some of this stuff. ...... this gentleman might be a genius! We'll never truly know the good, the inspiration, and the impact you have made with all these videos. The best to you! Great job!

[@slowercuber7767]

22:00 ROFL “…you get a very spectacular type of engine rich exhaust” thank you for that phrase.

[@patricks_music]

I love when Scott says “Right?” like I’m a subject matter expert. Great video Scott!

[@QuantumHistorian]

Personally, I find it kind of irritating. Not in a major way, but why is Scott asking me for confirmation? I want him to tell me what's right, not for me to judge his guesses. It also devalues what he's saying by making it seem like casual, general knowledge rather than precise, technical knowledge. Again, it's not a huge deal for me, but I do think his videos would be marginally better if he cut it out.

[@backseatgaming9087]

@@QuantumHistorian Maybe you aren't the intended audience for his videos?

[@QuantumHistorian]

@@backseatgaming9087 I expect I very much am lol. That doesn't mean I have to love every tiny aspect of the presentation, especially when it comes to what's little more than an unconscious verbal tick. Being able to like something without feeling the need to defend every tiny aspect of it is part of maturity.

[@erikziak1249]

6:09 Engine rich exhaust. LOL. That was great! 😀

[@yurialtunin9121]

First heard about Nerva around 1984 in rather sketchy article in Aviation Week and Space Technology magazine. Now you explained to me the details. And I am lucky. My knowledge about nuclear technology is much wider than 40 years ago so this explanation was well understood! Please go ahead with videos about nuclear tech in Space.

[@HitandRyan]

I once read about Project Pluto, a test program for a nuclear ramjet-propelled cruise missile that could fly at Mach 3 for days on end. Downside is the highly radioactive exhaust. I for one am glad to live on a planet with no flying Chernobyl disasters.

[@paulzuk1468]

For the purposes of an apocalypse weapon the radiation spewing exhaust was an UPside. But even cold war planners were not insane enough to put these into service. Which is a good thing.

[@onenote6619]

There were two versions. The first, safer version used a heat-exchanger, so no direct contact between atmosphere and core. But it was much heavier and less efficient, so option two was to say 'screw it' and have a reactor core open to the atmosphere.

[@MrHaggyy]

The exhaust of a nuclear missile would most likely be surprisingly harmless. You are always exposed to radiation, a bit more in the sunlight a bit less in the night. The problem with high radiation is that it damages cells faster than your body can tear them down and replace them. A sonic missile will mix it's exhaust with insane amount of air, and wind will diffuse it even more. Also exhaust has is extremely hot. At high temperature fission works faster. One huge problem of the 80's reactor was that the core had to be rather cold, because of the thermal/mechanical limits of steel. Modern reactors use ceramics or tungsten which allows them to burn their fuel more efficient.

[@moonasha]

now that you've tackled atomic rockets, you should do a video on near-future radiators! they're really cool and a lot of people don't know about them. NASA and co came up with a bunch of radiator designs where the ship would spew molten metal or metal dust out into space, then recollect it again after it cooled. There's a lot of really out there designs. Also a dive into the future of nuclear rockets (i.e., liquid core, gas core) would be cool

[@CathrineMacNiel]

Oh hey, its Sister Miriam Godwinson! How is Life on Alpha Centauri?

[@tal_os8148]

That sounds so metal! (hehe) where would I find info on that, is there a specifc project name nasa has for that?

[@krashd]

A cooling method in Elite Dangerous is to dump all of a ship's heat into a heatsink plate and jettison the plate, you can't retrieve them though as the cooling takes days.

[@p4inmaker]

That sounds cool, and would make for a very interesting video.

[@MrHaggyy]

It's really difficult to cool anything in space, as heat transfer does not work in a vacuum. Liquid metals would radiat some heat, but I would have quite a view questions on how this should work.

[@daleamon2547]

I've seen engine rich exhaust. A lovely green from the copper...

[@ttystikkrocks1042]

Each of these videos is a mini class on space technology and they really push me to think in new directions. As I get older, that is an ever rarer thing for which I thank you very much!

[@heyuhh422]

Hi Scott - fantastic job you did here! Brought back some great memories. My dad worked for Aerojet on that project. He took me out there for a test sometime in ‘66. It was the Kiwi-B reactor mounted inverted on a rail platform. Many of the details you talked about, my dad explained to me after test analysis. Engineers were optimistic that actual deep-space performance would cut a conventional powered manned trip to Mars to 1/3 the time! Plans were in the works for a manned Mars mission by 1985. I dreamed of being on that project. Thanks for the video - well done…

[@kburke1965]

Love to see more on “the tyranny of the rocket equation” specifically on the trade offs between specific impulse (propellant efficiency) and energy efficiency. And how different kinds of engine prioritise one or the other.

[@snapshuttre]

got the notification, read the title, instantly realised that it would be great, and now here watching.

[@pierrejones525]

Ditto!!

[@QuantumHistorian]

got the notification, read the title, instantly realised that it would be great, saw the top comment while the video loaded, got even more hyped, and now here typing this comment.

[@brandonbarr2784]

What you eating for lunch. lol. Too much

[@Virtueman1]

I pooped

[@brothergrimaldus3836]

Oh good. You got to the ammonia question. I remember reading in 2010 : The Year We Made Contact about their propulsion system. They used ammonia in the burn to Jupiter, but hydrogen for the return.

[@SebSN-y3f]

Admiral Rickover (the KOG or "kindly old gentleman"), the father of the US Navy's nuclear propulsion systems, worked on miniaturization and safe operation with nuclear fission, just like the Soviets. The research submarine NR1 (Nerwin) had a super small nuclear reactor on board. The story of how the masterful engineer was able to prevail against huge opposition and build the nuclear submarines (but there are also aircraft carriers with nuclear power, for example) and the research submarine is a real thriller. Thank you Scott! Your videos and explanations are always excellent.

[@sarah_757]

Rickover was a raging misanthrope. He bullied the navy into creating nuclear power and he went on to bully everyone. That bullying culture of casual cruelty lives on, and it made my time in the nuclear navy absolutely miserable. Thanks for the reminder on NR-1. That boat always looked so adorably small.

[@SebSN-y3f]

@@sarah_757 Everyone knows that he was not an easy-going person. But his achievements are undisputed. The US Navy's nuclear engines had no accidents, while the Soviets had at least 15. Anyone who tries to deny Rickover's achievements should do their research. By the way: the term containment also goes back to the admiral. The topic here was about small nuclear plants, which in some cases have to meet similar requirements for a vehicle (there were also experiments with airplanes). That is the only reason why this undoubtedly particularly talented engineer was referred to in this topic.

[@peterolsen9131]

moral of the story? that smr's were concieved, invented and built 50 years ago , using higher enriched uranium to minitureize the reactor in general

[@sarah_757]

@@SebSN-y3f But you specifically called him "kindly" and he was nothing of the sort. His disgusting attitudes to things like mental health and regular rest. I routinely stood RO on 4 hours or less of sleep and this was normal. The only reason we don't know about more accidents is they can hide behind classification. I was there, I know. This is Rickover's legacy. He was a good engineer but he was not kindly, or kind. My buddy came very close to self harm because of the nuclear navy. Captain said "until he hurts himself or others, we will do nothing". No therapy or counseling, nothing. And many nukes have self harmed for similar reasons. Rickover's legacy: we do nothing.

[@SebSN-y3f]

@@sarah_757 Everything is understandable, but here it was about small nuclear units that fit into vehicles. And Rickover simply achieved something groundbreaking. And when you hear or read the reports of those who worked with him, they all say that they admire him far more than they had problems with his style. I have read and seen a lot of things about him out of interest. For example, the Rickover events at MIT and what Vice Admiral R. Y. "Yogi" Kaufman, USN (Ret.) wrote about this under the title: "SOB or KOG?". Everyone from the silent service appreciates Rickover's enormous knowledge and skills. This also included not only being well-versed in science, technology and the military, but also having a network in politics. All things that also play a major role in the space industry. I didn't come up with the nickname KOG. It probably had a certain undertone. But this time it was less about the person than about the smallest atomic units that fit into vehicles.

[@sixstringedthing]

I appreciate that Scott's personality and engineering mindset give him the confidence to publically state "at some point, if we want to go further, nuclear thermal propulsion will be the only viable option". It doesn't even matter if the statement turns out to be true or false. We are absolutely going to need the kind of people who think "right, current options can't get us to where we need to be, what do we have lying around here that can?", and this is a great example of that.

[@krashd]

He probably agrees with the 3 Body Problem TV show, they got all the smartest people on the planet in a room and all they could come up with to reach 1% of light speed was nuclear propulsion.

[@frankgulla2335]

Scott, what a great summary of the "Nuke" space engine. Thank you for the details, and animations. and films.

[@rallen7660]

I remember reading a book about nuclear rocket engines back in the 80's. It had photos of the engines on test stands at Marshall Space Flight Center, and talked about how good they were proving to be. The librarians pulled it from the shelves, and out of the card catalog. They "filtered" a lot of books like that.

[@ChessMasterNate]

I got a cool book about peaceful uses of nuclear bombs from a library sale. I had done quite a bit of thinking about the topic already, so it was nice to see what the real scientists had to say.

[@poindextertunes]

and now you can just google it 🤔

[@1sewalker]

Good stuff, Scott. This brought back many memories. From 1996 until 2003 I worked at the C-Plant, where we enriched Uranium. The plant was shut down several years ago after 61 years of operation. An amazing facility built in the early 50s. I would walk around in the plant and marvel at the craftsmanship and design that occurred long before we had computers. Yes, it is what you would expect from 50s technology but it still functioned until shut down in 2013. Brilliant people came up with the concept and design. Anyway, the terms used in this video remind me of the things I was trained for before I was allowed in the facility and used during my tenure. To my knowledge, the US no longer has a way to enrich uranium unless it is secret. They may still be working on a smaller scale at Oak Ridge.

[@cogoid]

URENCO has a US facility in Eunice, New Mexico, which uses centrifuges to enrich uranium.

[@1sewalker]

@@cogoid That is good to know. The facilities I worked in were owned by the DOE. I see the plant started producing after I left the industry in 2003. So my information ended in 2003. I didn't follow the industry after I left. I am happy we have the abilities in the US. It seemed short-sided to totally stop enriching here. The DOE plants tried running as a private operator, USEC, but Gassious Diffusion is very expensive because of the extreme amount of electricity needed. There were talks of centrifuges over the years (technology is not new) but nothing materialized except a test centrifuge in Portsmouth, OH. Thanks for the heads up.

[@vladimirdyuzhev]

@@cogoid So far AFAIK the output is tens of kilos (one load of 1GW reactor takes some 150 t). They promise to produce one tonne a year, AFAIR. With volumes like that the cost may be higher than the obtained with the diffusion method.

[@cogoid]

@@vladimirdyuzhev You are thinking about Centrus Energy, which is trying to restart their old centrifuge cascade. URENCO USA is producing around 500 tons each year.

[@TheBeomoose]

Ah, the nuclear lightbulb. When someone asks how hard you want the engineers to work and you just say "yes."

[@davisdf3064]

"Sir, at such temperatures, the core would vaporize itself, how a-" "Yes, that's intentional. Now, find a way to keep it contained."

[@oldfrend]

i mean, i have no idea how hot a fission vapor would be, but it has to be way way hotter than the melting point of any known material right?

[@davisdf3064]

@@oldfrend Yes, that's why there's two prominent designs to such approach, open cycle and closed cycle. But they both involve keeping the fissile gas within a gaseous vortex to keep it in place. The closed cycle one, does not allow the fissile material to exit the engine, thus it doesn't need to replenish the gaseous reactor. The open cycle allows fissile material to "leak" out, thus needing to replenish the reactor, however, this allows much higher temperatures to be reached, thus giving even higher ISP.

[@karenrobertsdottir4101]

I haven't followed the research on this in a while. Is there any solution to the fact that fused quartz blackens under neutron bombardment? Or is the blackening rate sufficiently low that it can be dealt with?

[@dantreadwell7421]

Ahh yes. Do you want that open or closed cycle. . .

[@lassefiedler3542]

"Engine rich exhaust" xD. I didn't know this concept existed, but it makes so much sense, while also sounding very funny

[@ShokkuKyushu]

One interesting fact is that these engine would be more convenient compared to hydrolox the higher the delta V requirement of the stage . The isp is around 9000 Ns/kg or twice the one of hydrolox. The advantage in mass ratio compared to a chemical rocket can be described as (e^(x/4500))/(e^(x/9000)) and it goes up as x( the delta v) goes up. Assuming a delta v of 5 km/s the ratio is 3 for chemical and 1.74 for ntr. For 10 km/s of delta v the ratio is 9.2 for chem and 3 for ntr.

[@thomasfholland]

This was great to watch, very informative as well. While I have spent many hours studying chemical propulsion systems this has peaked my interest. I really hope you will do a deeper dive in regards to nuclear propulsion. A huge thanks to you Scott for making this for us to watch. You’re the man !!!

[@Orion-CSAT]

I have always loved NTRs, they're super fascinating. There's also a concept for a bimodal system where power goes into NEP when high thrust isn't needed.

[@averiWonBTW]

NTR you say? 😳

[@Orion-CSAT]

@@averiWonBTW Yup

[@juniuwu]

Nuclear pulse propulsion is cool too :3

[@juniuwu]

(shame they arent politically viable though lol)

[@davisdf3064]

@@juniuwu If only humanity got their shit together and wasn't so sensitive about nuclear bombs

[@tartiflette6428]

My favorite rocket engine is the Nuclear Salt-Water Rocket. Take a solution of plutonium salts from its moderator-coated storage and pump it into a reaction chamber where it is free to go critical and you are effectively riding a continuous nuclear explosion!

[@lethargogpeterson4083]

Scott has an older video on the nuclear salt water rocket. I think he described it as an ongoing continuous Chernobyl.

[@PrebleStreetRecords]

A constant-duty Orion Drive. A NSWR with highly enriched uranium saltwater is basically the only thing we have on radar to be a proper interstellar torchship.

[@Flesh_Wizard]

Roses are red Gear and sprocket Thomas the Nuclear Saltwater Rocket

[@ASpaceOstrich]

This is a genuinely really great explanation of how a rocket works. I never knew the nozzle was hollow before.

[@Gloubi06]

Excellent explanation! Thank you for taking the time to explain all this. I have to admit that I had to go back on the video several times to understand some parts, but I prefer it over lengthy basic explanations. Exiting tech!

[@jeffk412]

"engine rich exhaust" Indeed!

[@andersjjensen]

"The tyranny of the rocket equation" is one of my favorite phrases.

[@phil4826]

Chemical rockets are just barely practical for climbing out of Earth's gravity well.

[@RCAvhstape]

There is an old sci fi short story out there called "The Cold Equations" in which a space traveler is faced with a very grim decision due to the rocket equation. Worth a read.

[@RCAvhstape]

@@chemplay866 Do what?

[@Chad.Commenter]

@@RCAvhstape I just read it, thanks for sharing

[@tarmaque]

Thank you Scott! I've always known the principal of a nuclear rocket, but never the details. This was fascinating.

[@ericcartman5722]

Always wondered what happened with nuclear rockets. Thanks, great video

[@Chad_Thundercock]

"engine rich exhaust.. " I love this low-key delivery.

[@dziban303]

this is how you get Space Godzilla

[@Pelicanzzz]

No, your crew turns into the fantastic four

[@johnladuke6475]

Why not both?

[@aelolul]

Gamera?

[@kingcosworth2643]

Well, someone's got to wake him up

[@frankchan4272]

Or those green guys from Kerbal. 😂

[@richardandersonmolinabetan1783]

Bro just dropped some.of the best videos about spaceships I've ever seen.

[@adamkerman475]

Comment for engagement. Love your videos Scott!

[@i-love-space390]

Your are a great explainer Scott. I had no idea the interesting details about atomic reactions. For some reason, I thought that a nuclear engine had higher temperature than a HydroLOX engine. Thanks for the PhD lecture sir. I also liked all the old animations and drawings. I especially liked the Skylab module, docked with Apollo CSM with the nuclear engine on the back. That must have been part of Von Braun's Apollo Applications version of the Mars program.

[@JamesByrne-vt8ns]

You provide here a thorough and complete review of the history and possible developments in nuclear rocket technology., for which the highest praise is due!

[@Sacto1654]

I think the biggest issue is protecting the reactor for a "safe" crash landing in case the launch rocket carrying the nuclear rocket into space explodes during the launch phase. That was an issue that kind of worried people if a rocket carrying a satellite with a radioisotope thermoelectric generator (RTG) exploded early in the launch cycle and a large amount of radioactive material is spread out.

[@Orion-CSAT]

RIFT was just planning on quenching the reactor and dropping it jnto the ocean, but that was a suborbital test IIRC.

[@cogoid]

Until the reactor is turned on and generates highly radioactive products, it is not too terrible. With a half-life of 703.8 million years, uranium 235 itself is not very radioactive. (About ten million times fewer decays per second per unit of mass, compared to plutonium-238 used in RTGs.)

[@JustBob-sw4rf]

@@cogoidAh yes, the radiation isn’t a problem. But the potential toxicity may very well be. From Wikipedia: “Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by uranium exposure, because uranium is a toxic metal.” The jury is still out on how bad this risk is. Some scientists think it should be a big concern, other’s not so much. Under those circumstances should rockets containing large amounts of such materials be launched close to highly populated areas? Until the issue is better resolved I would say, “Not in my neighborhood.”.

[@unvergebeneid]

​@@cogoidalthough it has to be said that fresh fuel rods are so relatively safe because nobody straps them on a giant bomb and turns them into fine dust. Uranium is a heavy metal and an alpha emitter, aka the kind of stuff you can safely touch but not safely breathe.

[@TimothyLipinski]

Great Comment ! Heard one story that a RTG was on one rocket that exploded and the RTG fell in the ocean ! The RTG was picked up from the ocean and dusted off and sent on a successful space mission ! tjl

[@alpani6805]

Not seeing what's so bad about those fishing products, delicious!

[@Tjalve70]

Knot awl fission pro-ducks our equal.

[@Ottee2]

As I'm watching this, I'm wondering what could possibly go wrong. The engineering challenges are considerable, and, even if mastered, the engine still seems dangerous, messy, and unpredictable. It's not enough that future space farers have to avoid being irradiated by the background radiation found in space, but they will also have to avoid being irradiated by their own rocket engine. In a word, NTRs lack eloquence. Thank you, Scott, for this detailed description.

[@shanent5793]

The last thing we need is a talking rocket engine.

[@arizonastrummer]

Well when you think about all the things that could go wrong with a purely chemical engine with exhaust temperatures hot enough to melt iron, we have always faced major engineering challenges and dangers.

[@taqresu5865]

The "Oops, looks like they just irradiated the crew," at 17:43 got me lol

[@BenJaMindReacts]

love the research that went into this. great work on the editing, too

[@alexandredevert4935]

Whoever wrote the book on uranium machining is an unsung hero. Uranium gas reactor, WTF

[@JohnCleaver-z8h]

Hi Scott, my Dad is Val (Arthur) Cleaver's cousin. Val was awarded an OBE for work on aircraft propellors (DeHaviland) and internal combustion engines (Rolls Royce) and, most importantly, chemical rocket engines for Blue Streak, the UK's nuclear deterrent rocket which was successfully tested in Australia but then cancelled by the government of the time. I remember after he died, as a small child visiting his sister, Auntie Bib, holding a small silver moon lander which I was told had a piece of moon rock inside. I never knew what connections allowed him to have such a thing until now. Thank you for this video, his family did not know he had been involved in developing nuclear rocket propulsion theory.

[@shiona]

"Engine rich exhaust" :DD

[@marlynwaege8084]

I’m listening to this a few more times so I can glean a decent percentage of this subject . Very information dense. Awesome content

[@dave2me]

Sounds awsome as always. You make it sound like I understand it all

[@averiWonBTW]

I like how the animation has the crew go to mars in a capsule. Very ksp like

[@kukuc96]

If I recall correctly, at the time they were thinking of high energy, low time transfers to Mars, that's why they needed something better than chemical rockets, but in exchange the mission time would have been down to under a year, from the 4 years if you used minimum energy Hohmann transfers. Even then just a capsule is rough. The shift in thinking to the low energy, long flight time approach (that is the basis for every proposal today too) happened in the 90s, when the Nuclear engine projects were long gone.

[@pekka_kakkinen]

I might have missed this, but wouldn’t a massive advantage also be that you don’t need to carry any heavy oxidizer mass into space?

[@sc1338]

I’d say, I wonder what the trade is

[@martinzihlmann822]

Absolutely! specific impulse is directly related to the speed at which you eject the particle out of your exhaust. for thermal engines this means its better the higher the temperature in the nozzle and the lighter the particle exhausted. In chemical engines you exhaust the combined molecule, H2O for LH2/LOX engines, so the oxidizer is not only adding dead weight to your rocket but actively reduces your specific impulse too. It's just a necessary nuisance to power chemical engines. LH2/LOX engines are actually often run fuel rich to get that extra bit higher specific impulse as now your exhausting some hydrogen alongside the H2O too (also oxidizer rich engines tend to burn engine rich over time) nuclear thermal engines can exhaust pure hydrogen maximizing that part of the equation. They are only beaten by ion engines as there the speed of the exhaust molecule follows completely different rules, as it's not a thermal engine.

[@davisdf3064]

Yes, the only really heavy part that you need to carry is the reactor engine itself and the shadow shield. This allows for much better use of payload mass and fuel mass, it's one of the reasons why Nuclear Tugs were studied for interplanetary travel

[@zbubby1202]

"very special type of engine rich exhaust" you madlad lol

[@riggo4457]

Scott, I'm a retired locomotive engineer and seeing that I've more life behind me now then ahead I find your videos satisfy my " what if I did" this or that instead of this or that 😎. thanks for your work. Be well and carry on.

[@Dpatel74]

Love all the information you give and the explanation on this topic

[@TheArklyte]

"And now we'll demonstrate the economics of it with Terra Invicta. You either pick up nuclear freighters or you die. Have fun with your RD-0410/NERVA engined Star-Raker!"

[@JosephHarner]

Good times. Sadly it does strain credulity when you start packing spacecraft with terawatt class gas core nuclear reactors into dense formations with one another. Though at that end of the tech tree I guess you do finally have the mass budget available for some radiation shielding.

[@TheArklyte]

@@JosephHarner how to protect crews from radiation for extended periods of time? Resistance - shielding. Exodus - shielding. Servants - alien shielding. Initiative - you condition is not service related. Protectorate - shielding. Humanity First - you're a martyr! Academy - shielding.

[@daszieher]

This has "interplanetary" written all over it...

[@SpandexMovie1]

I wonder at what point would it be more beneficial to use a nuclear powered ion engine rather than a straight nuclear thermal engine

[@thekinginyellow1744]

They already do that. They use RTGs instead of conventional reactors. As to when you want to switch from RTG to conventional reactor, it's probably going to to an issue of mass and cost. But as he said, because the thrust of ion thrusters is so low, you aren't really going to use it for manned space flight. But it might be sensible to use to push space station modules out to the asteroid belt.

[@gasdive]

No, much as they're loved by armchair engineers. When you run one you have to dump the waste heat. So you need radiators. But anywhere inside the orbit of Jupiter the size and weight of the radiators is higher than the size and weight of solar panels to make the same power, even before you include the weight of the reactor, coolant and shielding. Even outside the orbit of Jupiter it's marginal if you are willing to include a solar concentrator design using very thin and light Mylar mirrors to concentrate sunlight onto the panels.

[@kukuc96]

Then you are back at no thrust again. You can't hit the same power levels when you have to radiatively cool your reactor with huge radiators, as when you can ditch your hot "coolant" (that's actually propellant in this case).

[@Tuzszo]

​@@kukuc96Once you get out into the outer solar system the calculus of thrust vs. dV starts swinging heavily in favor of delta V as the biggest factor in flight time. The flight times are so long that even if it takes an ion/plasma drive months to build up velocity it will still beat a chemical or nuclear thermal rocket there. Still best to have a chemical stage to get you through the van Allen belts quickly though.

[@gavinlawhite8721]

Many details I never thought about great video 👍👍

[@doubledropmotors]

Fascinating deep dive, thanks Scott!

[@EvelynNdenial]

love the nuclear lightbulb, the peak of 60's insanity.

[@JacquesMartini]

Wait 60 years and see the nuclear space engine taking the same place.

[@SamFreeman-m2y]

​@@JacquesMartini No chance.

[@minorityofthought1306]

"Nukuler" ~ Homer Simpson.

[@bdetert82]

We should of had nuclear powered for intercontinental flights but the nuclear scare of the cold war made it unsavory.

[@scifirealism5943]

Yep

[@markwhittington5020]

Thank you. Another tremendously information packed video. You made this engineer's mind a little bigger today.

[@furnacebay5305]

My eyes opened….thank you. As a person who never studied this stuff, I was under many false impressions, but always suspected there were more issues with nuclear rocket engines than what I was encountering in the usual media.

[@michaelstora70]

This is how you get Reavers.

[@mattbland2380]

The nuclear Shuttle plans for the Mars missions after Apollo would have been great. I like that they included it in For All Mankind.

[@1112viggo]

That's embarrassing, it seems we've put the Uranium in the wrong end of our rockets...

[@davidgifford8112]

Nice to hear a shoutout for Val Cleaver and Les Shepard. Arthur C Clarke incorporated these BIS ideas into his “Interplanetary Flight” 1950 and his first published novel “The Sands of Mars” 1951. The first book sets out the theoretical aspects of the NTR as envisioned by Cleaver & Shepard, the novel is little more than an excuse to imagine the possible reality of manned spaceflight, however well worth a read for that alone, if not the greatest SF ever written.

[@replica1052]

for mars travel chemical rockets are plenty - when you can't make the solar panels bigger use reflectors (chemical rocket propellants are excellent batteries )

[@aglr1439]

2 times the Isp of a hydrolox IS a huge improvement

[@JacquesMartini]

Not in the context of space, not even in the solar system.

[@aglr1439]

@@JacquesMartini I'm not comparing it to the technology of a proper spacefaring civilization; I'm comparing it to the milestones we reached so far

[@JacquesMartini]

@@aglr1439 We havn't reached it yet, there is NO working nuclear engine in space, not even a prototype! But plenty of CGI! 😂

[@aglr1439]

@@JacquesMartini What's your point? Whether we reach it or not, 2 times the Isp of a hydrolox is a huge improvement.

[@JacquesMartini]

@@aglr1439 Double wrong. We have NO working engine, just ideas and CGI. Even if we have it, the "next big thing" of a mars trip would not profit from it as much as you might think. You get faster to mars, maybe in 45 days (6 weeks) instead of 30 weeks. But for the round trip you have to wait around 2 years. You have more time on mars to do, whatever you might want to, but the challenge of life support is the same.

[@WhatsleftofTom]

I’ve seen people saying they might enable Mars in 45 days. Isn’t that mind blowing!

[@paulmichaelfreedman8334]

I am assuming you are deaf and can lipread. Or did you actually HEAR them? And yes, nuclear rockets have a massive Isp on top of good thrust and can enable much shorter trip durations to Mars, and 45 days is definitely a possibility. Furthermore, Nuclear rockets have enough Isp AND thrust to make huge course corrections, should they be necessary. In other words, it can actually navigate the solar system instead of just an unpowered trajectory. Till now Ion thrusters are the best we have and they have a thrust of millinewtons.

[@Steven_Edwards]

​@@paulmichaelfreedman8334And none of this is actually going to get built until it is cost effective to get resources from space. That may be never but we can start right now by focusing on Lunar Resource Development. If we are able to make mining ANYTHING on the Moon cost effective (I have some ideas), then there will be market pressure to explore other resources.

[@NoNameAtAll2]

I'm terrified what will happen if the engine breaks while trying to brake...

[@Orion-CSAT]

​@@paulmichaelfreedman8334It's a figure of speech, and yeah. Maybe he did "see" someone say that. Articles exist, after all.

[@paulmichaelfreedman8334]

@@Orion-CSAT In that case, he would have READ it. Just nitpicking.

[@longcat]

Great closing sentence... nailed it x

[@BusstterNutt]

Thank you for all the hard work in making these excellent videos.

[@jimmy21584]

Most succinct description of it I’ve seen on KZbin.

[@Ikbeneengeit]

My two favorite SM topics in one video: nuclear and rockets!

[@cheaterman49]

Fantastic video Scott, congrats! I wonder if you could make a VASIMR update video at some point :-)

[@stevesellers-wilkinson7376]

As someone with a very good knowledge of nuclear physics, that was fascinating. And "engine-rich" exhaust made me smile!

[@tomcook5813]

Scott, Thank you for pronouncing “nuclear” correctly. Most news and many academics say “nucular”. Liked and subscribed

[@fredturk6447]

Nice explanation of nuclear fission rocket motors. Thanks

[@Wren6991]

That game you played at the start looks really cool, can't wait to see it completed :)

[@MrTurboTash]

double ISP looks great, but the penalty higher dry mass has on delta-v makes it less appealing than you might think, also lower thrust to weight means less benefit from the oberth effect. two things that dont get considered when your firing from a test stand.

[@GlideYNRG]

Thank you Scott. An amazing well presented topic. Fascinating stuff.

[@mrb.5610]

Great explanation video, Scott !

[@siimhrq]

That was a really cool video. Please do one for fusion reaction engine as well. I hear there is two competing ideas: using fusion energy to heat up a reaction mass or use the radiation from the reaction to propell.