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Nuclear Conversion for Starship
- Skunkleton 3y agoFirst I am reading about nuclear engines applied to Starship. I wonder if it would be more practical to launch the reactor, fuel, and propellant into orbit using conventional rockets. Later a mission could pick up this Nuclear rocket engine and use it as a sort of booster while not inside a strong gravitational field. Ofc that doesn’t sound like Starship at all.
- ianburrell 3y agoNuclear rockets are useless for launching things into orbit. They don't have the thrust-to-weight ratio to get off the ground. Nuclear rockets are useful because they have high specific impulse which means using less fuel for thrust.
- zare_st 3y agoExactly opposite of what the person above you is talking about.
- sonicanatidae 3y agoshhh...cage match.
- therein 3y agoOne of the core teachings of Kerbal Space Program.
- Kim_Bruning 3y agoHowever, in KSPI [1]: Consider the combination of a nuclear lightbulb with compressed air as the reaction mass: Surprisingly good midpoint qua TWR and ISP! If you install a compressor you can get some pretty interesting SSTOs out of it. Whether these would work IRL is a different question, of course. [2] Nuclear lightbulb is of course highly theoretical, but scientifically/engineeringly plausible at the least. [3] [1] https://forum.kerbalspaceprogram.com/topic/173818-181-1122-ksp-interstellar-extended-1295-release-thread/ https://forum.kerbalspaceprogram.com/topic/173818-181-1122-k... [2] https://xkcd.com/1244/ https://xkcd.com/1244/ [3] https://en.wikipedia.org/wiki/Nuclear_lightbulb https://en.wikipedia.org/wiki/Nuclear_lightbulb
- matheusmoreira 3y agoIt's that close flyby of the sun that always gets me.
- scythe 3y agoDid you read to the end? That's the idea he ends up with: only use nuclear propulsion for space-to-space travel where you don't care as much about shielding.
- Skunkleton 3y agoI make no claims about my reading comprehension. That last bit seemed too narrow to me. Once you have all the bits in orbit, shielding doesn’t seem too onerous. Is the claim that even space-space shielding + reactor is too heavy to be worth the advantage of the nuclear drive?
- marsokod 3y agoNo, they are saying that the nuclear drive shall be reserved to a shuttle that remains in space. At that point, it makes much more sense as you can really use the nuclear drive to its full capabilities. > If we need the full performance advantage of nuclear propulsion, we should design a spaceship that is intended for it from the get-go. It never lands, only going from orbit to orbit, so there is no need for heat shielding, flaps, high thrust engines, thick steel structure or aerodynamic shaping requirements.
- simonh 3y agoIn space if you’re careful you only need a plate of shielding between the drive and the crew/cargo section.
- Kim_Bruning 3y agoThat was (part of) the original plan, post Apollo program. Somehow it got stripped down to to just a space shuttle. :-( https://en.wikipedia.org/wiki/Space_Transportation_System https://en.wikipedia.org/wiki/Space_Transportation_System
- psunavy03 3y agoThe "we haven't solved all of our problems on Earth yet" crowd . . . as if we ever will.
- lifeisstillgood 3y agoHell we put humans on another planet, we can fix the stuff down here if we really want
- Kim_Bruning 3y agoIt's a different kind of problem, unfortunately.
- jerrysievert 3y agowhich other planet have humans been to? I can only remember humans making it to earth, which isn't that far of a journey ... from earth. we put humans on a moon, and we've put robots on another planet.
- matheusmoreira 3y agoThat's exactly what I do in Kerbal Space Program.
- datadrivenangel 3y agoThe summary of this methodical and enlightening article from an excellent source for mathematically backed science fiction / space travel is: No. Nuclear is not worth it for starship, as the added engine weight limits the additional delta V and the additional challenges of handling nuclear material.
- jdblair 3y agoThe no accompanies the short explanation of a nuclear planetary transfer vehicle that never lands on earth. A lot of conceptual work has been done on these designs, and Andy Weir’s The Martian features one. Nuclear powered space tugs is a particular rabbit hole I’ve spent too much time on. See, for example, this Boeing design: https://www.projectrho.com/public_html/rocket/spacetug.php#boeingnep1 https://www.projectrho.com/public_html/rocket/spacetug.php#b...
- chris_va 3y agoSince this is presumably for interplanetary, and not heavy lift, I'm not sure why you'd use this over just having thin-film solar + pulsed plasma thruster (which can do anything from 1km/s to 3000km/s exhaust velocity).
- idlewords 3y agoBecause nuclear thermal is high thrust, and sometimes you need high thrust.
- politician 3y agoI think we'll see nuclear propulsion for Starship variants that receive fuel rods in orbit and are not designed for reentry. Interplanetary logistics between Earth/Moon/Mars orbits.
- idlewords 3y agoName me a country willing to give Elon Musk control of fissile material, however indirect.
- euroderf 3y agoNK, "if" he has enough cold hard cash.
- justrealist 3y agoNiger Central African Republic Cambodia Bolivia Palau Laos There are in fact a lot of countries that would be thrilled to give Elon fissile material in exchange for investment.
- idlewords 3y agoI'm going to go out on a limb and say Niger, CAR, Palau, etc don't have access to highly enriched uranium.
- 3y ago
- maxcan 3y agoAFAIK, the only nuclear rocket that makes sense is landing a reactor on an icy comet and using it to shoot super heated steam wherever you want thrust. #seveneves
- darknavi 3y agoJust don't let it leak. RIP New Caird
- idlewords 3y agoThe Project Orion design (shoot hundreds of fission bombs out the back and ride the shock wave on a reaction plate) is surprisingly practical, and probably our only way to get humans past Mars. It's just kind of terrifying.
- lostlogin 3y agoYup, it’s scary. “A moderate-sized nuclear device was estimated, at the time, to produce about 5 or 10 billion horsepower.” https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propu...
- idlewords 3y agoGeorge Dyson (Freeman's brother) wrote a book on it that is fantastic reading.
- whycome 3y ago> Freeman's brother Son. https://en.wikipedia.org/wiki/George_Dyson_(science_historian) https://en.wikipedia.org/wiki/George_Dyson_(science_historia... Relatives Sir George Dyson (grandfather) Freeman Dyson (father) Verena Huber-Dyson (mother)[1] Esther Dyson (sister)
- idlewords 3y agoMy bad; I should have checked. Thank you for the correction!
- ragnot 3y agoMight be a stupid question: would this result in radioactivity just flying through space as we try to propel spacecraft with it?
- tantony 3y agoThere's already plenty of it in space.
- idlewords 3y agoIt's not a stupid question. Space is already highly radioactive, with lots of protons and bigger nuclei from outside the solar system flying around in all directions, along with a ton of proton radiation from the Sun.
- marcosdumay 3y agoYes, but with very little long-lived decaying material that you could carry inside a survivable habitat.
- idlewords 3y agoMost nuclear spaceship designs have a long stick with the reactor at one end and the crew on the other, and some kind of shielding in between. Since you only need to shield a cone, it can be quite effective.
- marcosdumay 3y agoYes, but none of that changes the fact that when we talk about fission rockets, we have to think about nuclear safety on top of everything else. (All of your comment is thinking about nuclear safety.) And if we use them inside of a planet's magnetosphere, we have to think about environmental contamination too.
- devmor 3y agoYes, but space is already full of radioactivity. An incredibly large amount of it. The average range (outside of the upper Earth's atmosphere) would be equivalent to getting somewhere around 10 chest x-rays per day, every day.
- misterbishop 3y agoAren't SpaceX launch explosions big enough already?
- daveslash 3y agoI don't know why you're downvoted. I think it's a legitimate question. When I was in high school I asked "Why don't we just shoot our nuclear waste into the sun?". As an adult, Kerbal Space Program has taught me that it's incredibly difficult to lose the orbital velocity and get things into the Sun! But the answer my teachers told me was "Well, even if rockets have a 99.5% success rate and a 0.5% failure rate, and only 1 out of every 200 rockets explodes during launch... then eventually a rocket carrying nuclear waste is going to explode and spread it everywhere" As others have pointed out: Nuclear rockets don't have the thrust ratio necessary for take off, so presumably they'd be assembled and used in space. My question is: What level of risk does launching nuclear rocket parts/fuel into space pose?
- starbase 3y agoWe can store the fuel pellets in a crash can during transit. That way if the rocket blows up nothing hot gets dispersed. But even without a crash can, it's of less concern to public health than the radioisotopes in coal.
- rsynnott 3y ago> Nuclear rockets don't have the thrust ratio necessary for take off, so presumably they'd be assembled and used in space. Or just used as an upper stage! See https://en.wikipedia.org/wiki/Saturn_C-5N https://en.wikipedia.org/wiki/Saturn_C-5N, for instance, and a bunch of even more ridiculous Soviet designs. Amazingly, this project (nuclear third stage for Saturn V) was actually under serious development. This to be used on a rocket stack which had had two major incidents in 13 launches; it really was a very different safety culture back then.
- _yb2s 3y agoThis article addresses that. They claim that, like you said, they are only used at very high altitude or in space, and the raw materials, before ignition are not dangerous. They say that the low enrichment uranium is even safe to touch with your bare hands.
- andrewla 3y agoI only skimmed the article; but as I understood it the liquid hydrogen here is being used strictly as ejecta. It is not being combusted, the way that it is used in the space shuttle boosters. If that is the case, liquid hydrogen seems like an awful substance -- hard to produce and transport, hard to store and the mass required to support keeping it is not insubstantialy, all for a mass density of ~70g/L. Why not just use water? Water is 1000g/L and can be stored without any real effort at all. If all you're doing is shooting it out the rear end of the rocket with as much energy as possible, it's mysterious why you would even consider liquid H2.
- CarVac 3y agoFor specific impulse. When you have unlimited power, you want the lightest possible molecular mass exhaust for the best total delta V.
- andrewla 3y agoI need to play Kerbel Space Program. I have absolutely no intuition about this sort of thing. Some intuition around orbital mechanics from my physics days but rocketry is a bit of a mystery.
- idlewords 3y agoFor me it helped to remember that the term that matters in the rocket equation is exhaust velocity, not momentum. You want to be shooting the lightest things you can out the back of the rocket, at the highest speed. Unfortunately with chemical rockets, the energy source and reaction mass are the same thing, so you're kind of stuck with whatever burning your fuel gives you. But when you can separate reaction mass from energy source (like in nuclear or electric rockets), hydrogen is always the best bet.
- Kim_Bruning 3y agoMostly true. However, there's tradeoffs qua thrust and specific impulse for different propellants. For pure vacuum work hydrogen is a good candidate. For operating in a gravity field (eg. the moon), you might be able to use a smaller nuclear engine with a denser propellant. Obviously you ARE trading in some range when doing this. But if the question is whether you can get off the ground in the first place, you may have less of a choice. It might also depend on what you can actually lay your hands on qua ISRU (if/when relevant)
- jhallenworld 3y agoThe design is not advanced enough, they should be thinking of https://en.wikipedia.org/wiki/Fission-fragment_rocket https://en.wikipedia.org/wiki/Fission-fragment_rocket So here is my science fiction theory: fusion will never be possible, but fission already is. So in the galactic civilization, rare uranium is the most valuable resource since it enables interstellar travel. Uranium is only produced in the collisions of neutron stars, so we are lucky to have any. We should not squander our uranium for power generation when we can use solar for that. It's like not using oil or gasoline for heating.. we need it for transportation.
- m463 3y ago> We should not squander our uranium for power generation. I think we might have enough. "He noted that fast breeder reactors, fueled by naturally-replenished uranium extracted from seawater, could supply energy at least as long as the sun's expected remaining lifespan of five billion years" https://en.wikipedia.org/wiki/Uranium_market#Available_supply https://en.wikipedia.org/wiki/Uranium_market#Available_suppl...
- Animats 3y agoThat's a useful analysis. Nuclear power gives you more energy, but you're still limited by how much reaction mass you can carry. The plans that work look like early 1960s NASA plans - build infrastructure in orbit, assemble nuclear power interplanetary craft in orbit, nuclear power is from planetary orbit to planetary orbit only. That was Wernher von Braun's "Man Will Conquer Space Soon" plan.[1] The Apollo program, at US$20 billion, was the economy version. To the moon and back, no space station, no permanent infrastructure in space. [1] https://www.youtube.com/watch?v=Sz7njI0wEIw https://www.youtube.com/watch?v=Sz7njI0wEIw
- asdff 3y agoIt makes you wonder though, should you set up such space based infrastructure, is it even worth publicizing lest you trigger an arms race?
- bobthespaceguy 3y agoI think advancing science sometimes comes with risks. I would welcome a friendly arms race for better access, but who knows what would actually happen.
- sandworm101 3y agoYou couldnt do it without publicizing. Space stuff is big and loud. Space itself is transparent. Doing big secret stuff in space is extrodinarily difficult.
- asdff 3y agoThere are spy satellites that we know nothing about in orbit, only until someone like Trump leaks an image on twitter. Who is to say where that line of development ended, if ever, given so little is spoken publicly of these efforts? Perhaps others could detect some of your efforts, but you hold them to secrecy like you do other state secrets among allies out of mutual benefit. I'd expect there to at least be a well worked out plan for such an infrastructure along these lines by now, if not implementation. It's one of those things where the losing move is not to engage with it, for fear someone else is and making strides.
- paulsutter 3y ago>So will going Nuclear be worth it? >The short answer is no >If we need the full performance advantage of nuclear propulsion, we should design a spaceship that is intended for it from the get-go. It never lands, only going from orbit to orbit, so there is no need for heat shielding, flaps, high thrust engines, thick steel structure or aerodynamic shaping requirements.
- larrydag 3y agoWhat are the safety ramifications? Is there not a radiation fallout from the exhaust?
- moffkalast 3y agoThe ram-ifications of open cycle nuclear propulson are ill-advised. https://en.wikipedia.org/wiki/Project_Pluto https://en.wikipedia.org/wiki/Project_Pluto
- MrTortoise 3y agoyay radioactive shit falling from space again
- davedx 3y agoYes, there’s a lot of radioactive shit in space :P
- ben_w 3y agoThe sun is a giant fusion reactor known to cause cancer on a good day, and emit radiation bursts that can damage or disrupt power grids often enough that people can reasonably expect to read reports of them more than once in their lifetimes.
- flashback2199 3y ago> The sun is a giant fusion reactor And chernobyl was a giant fission reactor. What's your point?
- ben_w 3y agoThe comparison between the two is almost exactly the same as the comparison between a fart and a hurricane: 16 orders of magnitude, give or take. Space is really hostile.
- flashback2199 3y agoOk if it's not taking off or landing from earth then sure
- ben_w 3y agoEven then. The sun is always a big ball of dangerous radiation, even despite things like the ozone layer. A nuclear rocket taking off isn't something you want to be near, but even literal Chernobyl wasn't as deadly in total as skin cancer was just in the year the reactor exploded.
- bluescrn 3y agoNuclear doesn't work with Elon's approach to development. You can't blow up multiple nuclear rockets within the atmosphere just to learn what needs fixing for the next attempt. Then again, it's looking like the whole 'fail fast' approach is over anyway, with Starship grounded by red tape. A full-stack Starship failure is seemingly too big/dramatic/risky to get away with doing repeatedly, especially admidst the politics of Twitter/X.
- tim333 3y agoAssuming Elon gets Starship working reliably, which will probably happen, you could use it to lift a nuclear rocket to orbit. You could then fire the nuclear bit up away from the earth and use it to shuttle around the solar system.
- amluto 3y agoI assume some of this is that the many early Falcon failures merely blew up the test vehicles. The starship test kind of blew up the launch site.
- bunabhucan 3y agoYou can. You just can't legally do it in Texas. Maybe SpaceY will be based in North Korea or somewhere to escape the burdensome regulatory regime in the USA.
- nradov 3y agoCountries with less burdensome rules are subject to ITAR restrictions.
- smegger001 3y agoOr just launch from a barge in the middle of the ocean or some uninhabited atoll.
- bluescrn 3y agoHe could fund a new company elsewhere in the world and start from scratch, perhaps. But even if he was super-careful about ensuring that restricted information wasn't shared with the new company, I'm sure his political enemies would find ways to have him locked up if he tried that...
- kristianp 3y agoA loosely related article from a few days ago about Mars Cyclers will be of interest. https://news.ycombinator.com/item?id=38086518 https://news.ycombinator.com/item?id=38086518 https://planetocracy.substack.com/p/mars-cyclers https://planetocracy.substack.com/p/mars-cyclers
- INGSOCIALITE 3y agowhy aren't they just researching the creation of dilithium crystals?
- rockemsockem 3y agoInteresting thought experiment, not shocking at all that a craft not designed to use NTP wouldn't work well with it.
- credit_guy 3y agoThis is seriously underselling what US nuclear rocket program of the '60s [1], by calling everything that came after "modern". That program was the only one that built something, everything else was speculation on paper. The obstacles faced by the NERVA project were immense, and the iterations achieved spectacular improvements in record time. That project that lasted for less than one decade and was done on a shoestring budget is not quite the equal of the Manhattan project, but it's not much below it. It achieved the highest density of power generation by maybe a factor of 100 compared to any other reactor in history. All that stuff was pretty much lost. NASA is trying to revive this, but it will not have legs. We simply don't have the same pool of talent to recruit from. In the 60's there were lots of scientists and engineers that had first hand experience building nukes and nuclear reactors. Now this country has not built a reactor in 3 decades, with the exception of Vogtle. [1] https://en.wikipedia.org/wiki/NERVA https://en.wikipedia.org/wiki/NERVA